Wednesday, 11 May 2022

Respect for all the brave people

(Originally posted on Wednesday, 11 May 2022; updated on 8 June 2022)

I respect all the brave people who say or do what they think is correct. They can be from a minority, like the old-time scientists who realised that Earth is not in the middle of the Solar System. Or they can be from a majority, like people who are not salves – like people who live in a democratic country and who can make their own decisions and have their own opinions. Unfortunately we live in a totally fucked-up times when people from a majority are often afraid to say what they really think! Even in democratic countries!

Respect for all these people:

To be precise:
Respect for the kneeling footballers for not being afraid to kneel.
Respect for the standing footballers for not being afraid to stand.
Respect for the people who prepared the poster for not being afraid to point out (in a hilarious way) that (any) sport shouldn't be mixed with politics.
Respect for ALL of them!

And respect for Elon Musk:

I agree with Elon Musk, but in the last 15 years I've actually moved more to the right side and now I stand smiling (exactly like the conservative on the picture), while looking at the madness of the extreme left side (of the “woke progressive”). And at the confusion of people who used to regard themselves as neutral center – their confusion is similar to Elon Musk's confusion.

And respect for Kevin Sorbo.

I agree with Kevin Sorbo, although I must admit that in some cases abortion technically is not a murder because it's legal. But I agree with him 100% when looking at it from a different perspective – thinking about what is done to a human being who is totally innocent. It's exactly like a murder. And it's pathetic that so many people in the 21st century don't understand their sexual drive! Just think about it – the sexual drive doesn't exist before a person becomes able to procreate. It's ALL about spawning new generations, for crying out loud!

In March 2022 I've become a father for the third time and it was one of the best things that happened to me and to my family as a whole. Everybody's happy! My wife, our children, our mothers (grandmothers of our children) and all our more distant relatives. I have to point out that we didn't plan having the third baby because we are relatively old – this year (2022) I will turn 44 and my wife will turn 42. Yet we didn't think about abortion even for a split of a second!

Respect for all the people who disagree with the tweets above.

I don't agree with people who disagree with the tweets above, but I still respect them. Why? Because they are not afraid to publicly speak about things that are totally different from the natural way of life. Because they are not afraid to publicly speak about such things totally ignoring science, like genetics and evolution. They are really brave in their own way.

For example from the point of view of genetics an unborn baby is a unique human being RIGHT FROM THE START of pregnancy! Yet, they claim that abortion is all about woman's wishes as if she were the ONLY person involved. Ridiculous, but I respect them for not being afraid to say ridiculous things. Even rape is not a “good enough” reason for abortion – there are many heterosexual pairs who are infertile and who would be happy to adopt such a baby.

And I can't believe that some people say that homosexual pairs are “normal in every way”. If all the people in the world turned into homosexuals then the human species would die out! From the point of view of a member of a human species such a thing (dying out of human species) couldn't be considered normal, by definition. So, from this point of view (dying out of human species) homosexuals pairs are not normal in this very way! But I respect anybody who is not afraid to speak about it differently.

Summing up:
I agree with Elon Musk and I agree with Kevin Sorbo, but I don’t want to take away the right for other people to say opposite things, no matter how stupid they may seem from the scientific point of view. On the other hand many people who disagree with me, or with Elon Musk, or with Kevin Sorbo, seem to prefer a total censorship, which is simply pathetic.



UPDATE:

Another great tweet from Sorbo:


Saturday, 2 April 2022

Easy astronomy for total amateurs

(Originally posted on Friday, 26 March 2021; updated most recently on 2 April 2022)

In the most recent update I made numerous changes and added LOTS of new content throughout the post. I did it because in the recent months I had gathered a lot of additional experience and I had also been very active on an astronomy Internet forum, writing many posts there, but neglecting this blog.

I am a total amateur as far as astronomy is concerned, but I am also a pure enthusiast who concentrates on positive things, instead of complaining about negative ones. This is why I truly enjoy watching the night sky through a small telescope from a balcony in a city with big light pollution. In fact I own two small telescopes – one refractor and one Dobson (a reflector), so I can compare them in a totally objective way.

At the time I finally bought my first telescope I was 43 years old and I have to say one thing: I wish I had done it earlier!


I. Urban astronomy and light pollution.

Some people claim it's pointless to buy a small relatively cheap telescope and/or watch the night-sky from a relatively large city, but this is simply NOT true! Even in a city with big light pollution you can see MUCH more stars even with the weakest binoculars! Actually it's a fantastic feeling when you look at the night-sky only with your own eyes and you see hardly any stars, then you look through binoculars or a small telescope and suddenly many more stars appear! Wow! And a small telescope can show you so much more than a pair of binoculars!

Light pollution is all about the night-sky being brighter near human settlements than at remote locations. The brighter the night-sky the less night-sky objects you can see, both with the naked eye and through any observing equipment. Nowadays it's a real problem to find a truly dark location that is relatively close to your home because even small cities produce significant amount of artificial light that “spills” over large areas around them.

Please notice that a modest amount of light pollution degrades diffuse objects such as comets, nebulas and galaxies far more than stars. On the other hand the Moon and the planets are generally IMMUNE to light pollution. Basically, there is always something interesting to look at even from a balcony, unless you have some unrealistic expectations.

Ib. Directions of observing.

My balcony faces south-southwest and the unobstructed view spans from south to south-west. I must admit that I am lucky, because the vast majority of interesting night-sky objects can be seen more or less to the south. Some of them can be seen at different times also to the east or west, but some other are visible only during summer and they are very low above the southern horizon.

A balcony facing north is clearly the worst case of urban astronomy, but you can always grab a small telescope, go out of your apartment building and find a place with an unobstructed view to the south.

Ic. Confusion about the Bortle scale.

I must admit that at first I got confused by the term “light pollution”, so I have to make it clear right at the start of my post. I shortened this part to make it more approachable for newcomers.

There is a scale describing different levels of light pollution as seen with the naked eye (it's called the Bortle scale, after the guy who created it), but there is LOTS of confusion about this scale. Some people use it in a totally indiscriminate way – they mix it up with bad transparency (bad clarity of the atmosphere) and/or bad seeing (big atmospheric turbulence) and/or artificial lights that makes your eye pupils constrict (for example street lamps).

Bortle himself wrote about light pollution in reference to SKY conditions as far as their DARKNESS is concerned. Unfortunately some people take out only particular sentences wrote by Bortle, ignoring all the other sentences.

Bortle wrote that his scale “would provide a consistent standard for comparing observations with light pollution”. You can’t achieve consistency in comparing light pollution when other important factors don’t remain equal. When seeing and/or transparency is poor then your observations will be obviously worse, but NOT because of light pollution! Please notice that transparency and/or seeing can be bad even at remote locations, where there is hardly any light pollution by definition.

The main problem with the Bortle scale that it is based on naked eye observations, so if you assess the sky conditions while being directly blinded by nearby street lamps you may misjudge what you could see through a telescope. An objective lens/mirror of a telescope doesn't constrict due to bright light, unlike the eye pupil does during naked-eye observations.

Please notice that every single street lamp that you can see (even in a distance) makes your eye pupil constrict. The same (but to lesser extent) happens because of every other source of artificial light that you can see (even in a distance), for example every single illuminated window in a nearby block of flats. It also happens because of light that is only REFLECTED, for example from a building that you can see (even in a distance) that is lit by street lamps, even when you can't see the street lamps themselves. Everything counts during naked eye observations!

Fortuantely you don't have to judge the Bortle class of your location yourself. On this site:
https://www.lightpollutionmap.info
with the overlay “World Atlas 2015” active, when you click at a particular place a description pops up, where you are given also the Bortle class of the chosen place. By the way, there are also different kinds of overlays, but it seems to me that the overlay “World Atlas 2015” is better at showing truly dark locations.

Id. Dark adaptation on a balcony.

The difference between looking at the night-sky while being directly blinded by nearby street lamps and looking at the same night-sky “from a covered place” is HUGE! The first time I tried to find the Hercules Globular Cluster (M13) from my balcony I couldn't see it in my 8x42 binoculars, but I was doing it while standing up, so the nearby street lamps were blinding me. The next time I looked at the M13 from my balcony I saw it even in my 8x42 binoculars, but I was doing it while half-lying on a portable reclining chair, so I was shielded from the nearby street lamps by a cover on my balcony guardrail. It proves that the street lamps make your eye pupils constrict in a significant way, which is totally independent from light pollution of the night-sky. Unfortunately you can't lie down when looking through a telescope.

My dark adaptation is always very weak because when I look at the night-sky from my balcony there are several street lamps close by that are blinding me directly (more or less), even when I shield my eyes with my hands. Here’s a picture taken from my balcony:

I took the picture in the “night-mode” (the time of exposure was relatively long), so the planets Jupiter (on the left) and Saturn (above the Moon) would be visible (they were visible with the naked eye), but it made everything else (especially the street lamps and the blocks of flats) brighter that in reality.

As you can see there are lots of nearby street lamps, so “my balcony astronomical observatory” is simply terrible to the naked eye. When I look into a telescope eyepiece at particular angles (at some positions of my telescope) the street lights are especially annoying. I plan to buy some kind of movable cover, but so far I couldn't find anything that would suit me.

Ie. Good sides of balcony astronomy.

As I already wrote I am a pure enthusiast who concentrates on positive things, instead of complaining about negative things, so I enjoy looking at the night-sky even from my balcony. Obviously when you go out of a city to a place with significantly lower light pollution then you are stunned by how many stars you can see even with the naked eye. In such places you can see much more stars with any observing tool, but such voyages are quite rare. On the other hand when you look at the night sky from your own balcony you can do it much more often and together with your little children!

There are also some other HUGE advantages of using a telescope on a balcony – you can keep all the little things inside your home, you can put a normal (relatively heavy, but comfortable) chair next to your telescope AND you can always wash your hands in your bathroom when you accidentally touch a telescope element that is greased. You can't do such things “in the wild”.

Over time I noticed an additional advantage of balcony astronomy – easy access to a computer and very good online star maps. When I am star-hopping from an easy night-sky target to a more difficult one I usually go in and out of my apartment several times, checking my current “night-sky position” on the computer and planning the next “hop” one at a time.

If. Light pollution vs. the full Moon.

The full Moon (or close to the full Moon) has a similar effect to light pollution – it degrades diffuse objects such as comets, nebulas and galaxies far more than stars. It's true even at remote dark locations and some people don't go to such places when there is the full Moon (or close to the full Moon).

Some people add the effect of the full Moon to light pollution itself, but to me it's again incorrect. It would actually be totally silly to say something like this: “We're in the middle of a desert, very far from human settlements, but there is the full Moon, so the middle of the desert is full of light pollution.” To me light pollution is all about artificial lights produced by human settlements and the moonlight is not artificial. Moreover, the light pollution map I mentioned earlier does NOT change according to the phases of the Moon, so it treats light pollution as something totally independent from the Moon light, exactly like I do.

Anyway, when you look at the night sky from a place with a particular light pollution (for example a balcony in a particular city) and there is also the full Moon then the effect is simply terrible. The night-sky is even brighter and even less night-sky objects can be seen, both with the naked eye and through any observing equipment.


II. Binoculars vs. a telescope.

Obviously advanced astronomy is all about telescopes, but as far as amateur astronomy is concerned I have to give some credit to binoculars. The most impressive thing to me is the fact that I can see the brightest moons of Jupiter from my balcony even during the full Moon in just 8x42 binoculars!

I own three pairs of binoculars (all of them porro binoculars): 8x30, 8x42 and 12x60. The 8x30 binoculars are very light and my little son could use them already when he was 5 years old. On the other hand the 12x60 binoculars are so big and so heavy that my daughter was able to use them only for very short periods of time when she was 12 years old. I myself have trouble using them for longer periods of times, so I usually use the 8x42 binoculars. Here's a picture of all of my binoculars:

I compared different types of binoculars in detail here:
Most universal types of binoculars

IIb. When binoculars are clearly better than small telescopes.

From my own experience I have to say that bright binoculars (with the exit pupil of at least 5mm) are very fun for scanning the night-sky and looking at the most prominent open star clusters. The brightest stars are very “shiny” and some big star clusters look simply spectacular!

The filed of view (FOV) in binoculars is clearly larger than in telescopes, so you can see more of the night-sky at a particular moment. Some of the largest (as far as their angular size on the night sky is concerned) open star clusters can fit into the view ONLY in binoculars. However there are very few such star clusters.

Hand-held binoculars are much smaller and much more portable. Moreover you can use them instantly – the preparation time with a telescope, even a small one, is clearly longer.

Locating night-sky objects is MUCH quicker in binoculars than in a telescope. In a span of several seconds I can switch from the Orion's Sword (the area with the Orion Nebula in the middle) up to the Orion's Belt, then right to the star Aldebaran and the nearby open star cluster Hyades and then farther right to the open star cluster Pleiades. You can't do something like this in a telescope.

IIc. When small telescopes are clearly better than binoculars.

In a small telescope you can see the rings of Saturn (seen as one big ring) without any problems even in big light pollution and during the full Moon! I used the magnification 70x and it was more than enough to see them. It was clearly the best astronomy sight I have ever seen! To me seeing from my balcony the rings of Saturn, even as one big ring, was like a dream come true! As a bonus, in the same field of view (at the same magnification) I could also see the brightest moon of Saturn.

On the same night (from my balcony during the full Moon) I could see one (the darkest) belt of Jupiter (again at the magnification 70x). I have to point out that on the net I read that the belts of Jupiter (their size and their colours) change over time and sometimes they even disappear!

Additional thing that is clearly better in a small telescope is the fact that you can separate objects that are very close to each other on the night sky. For example you can see the brightest moons of Jupiter even in 8x42 binoculars, but only when they appear far enough from the planet (the moons circle the planet, so they hide behind the planet from time to time). In a small telescope you can see the moons also when they appear much closer to the planet.

The vast majority of open star clusters look better in a small telescope. For two different reasons. The first reason is similar to the moons of Jupiter – some of the open star clusters are relatively small (as far as their angular size on the night sky is concerned), so their stars appear too close to each other to be all visible in binoculars. In a small telescope you can see more stars separated from each other even at a small magnification (22x or 28x). The higher the magnification the more stars you can separate.

The second reason why the vast majority of open star clusters look better in a small telescope is the fact that the bigger magnification you use the weaker stars you can see. Generally magnification is more important than aperture (objective lens/mirror diameter) – more on that later (see the next point IId. Magnification vs. aperture).

The Moon also looks better in a small telescope – there is no comparison between the amount if detail that you can see in a telescope and in binoculars. Here's a picture I took with a smartphone by hand (without an adapter) at the magnification of 50x (the Moon is especially fun when only half of its disk is visible). Click to enlarge!

I used these manual settings of a smartphone camera app:
1. ISO-200.
2. Shutter-250 (1/250th of a second).
3. Focus – “Far”, but not at maximum (not focus at infinity – some smartphones/apps apparently allow focus “beyond infinity” and it messes things up).

As far as normal (daytime) pictures are concerned the standard Camera app in my smartphone works great, but it doesn't have manual focus (even in the “pro” mode), so I had to install another one. Well, I installed several free apps, but the one that worked for me was Lumio Cam. Here's a screenshot from a video I found on the net:

Generally you can see much more things and/or much more details in a small telescope, simply because you can use much bigger magnifications. You will NEVER see the rings of Saturn in hand-held binoculars.

I would say that if you can afford it then you should buy BOTH a pair of binoculars and a small telescope. They complement each other perfectly and I use them alternately. Moreover, a small telescope comes with a toy-like finder scope that is useless when looking from my balcony. Thanls to binoculars it’s easier to find crucial night-sky objects.

IId. Magnification vs. aperture.

Some people claim that telescopes are generally better than binoculars because the aperture (objective lens/mirror diameter) is bigger, ignoring the importance of magnification. There's an ever-going debate what is more important magnification or aperture, but the truth is that aperture on its own is meaningless – your equipment can't improve your own eyes. Looking through a telescope WITHOUT any magnification would be like looking through some kind of tube. The bigger the aperture the bigger the tube. Would that improve anything? Obviously not.

The naked eye “works at your maximum aperture”, but you can't see things like the rings of Saturn with the naked eye. Well, you can't see them even in binoculars, but they are obvious already in a small telescope (magnification 70x is more than enough to see them). So, to see more details you need magnification, no doubt about it. This fact alone decides that magnification is more important overall, BUT you have to increase aperture to PREVENT the view from getting too dark – bigger magnification => smaller exit pupil = darker view (more on that later – see the point VIId. Exit pupil).


III. Types of telescopes.

There are basically two kinds of telescopes: refractors and reflectors. Before I will show you some simplified examples how they work I have to point out one very important thing – any observing equipment works in a very counter-intuitive way. Here's an example for binoculars, but any telescope generates image in a similar way:

Totally mind-blowing! Please notice that every point at the exit pupil contains light rays coming from ALL the objects in view! You can verify this fact by looking through any kind of binoculars while covering half of the objective lenses – you will still see the whole view (NOT half of it), but the whole view will be half as bright. Here is a fascinating discussion on this topic:
https://www.cloudynights.com/topic/603397-a-basic-exit-pupil-question/

This quote is awesome: “And on your part, I want to thank you for your honest and concerted effort to understand this confusing issue. I can tell you in the Astromart thread I referenced earlier, members whose names are well known here gave Alan French quite a battle before they finally grasped the concept. At the time, I was merely a bystander...”

Below there are some examples for different types of telescopes, but they are greatly simplified and may be misleading unless you remember the example above.

IIIb. Refractors.

A refracting telescope uses a lens as its objective to form an image:

The objective lens is mounted in a fixed way, so it doesn't need any adjustments later. This is why a refractor is totally unproblematic as far as maintenance is concerned. It's very similar to binoculars in this regard – just take it out and watch the night-sky.

Please notice that the mirror on the other end of a refractor is theoretically not needed, but it helps to look at the night sky at a more convenient angle. If there were no mirror diagonal then you would have to literally lie under the telescope when it would be pointing straight up. By the way: the mirror in the diagonal is mounted in a fixed way too (it's more than big enough).

IIIc. Reflectors.

A reflecting telescope uses one or more curved mirrors to form an image:


The first reflector above (the simple one) is called a Newtonian telescope (or simply a Newton), just because it was invented by Newton (the famous scientist) himself. By the way: a Dobsonian telescope (called also a Dobson) is a Newtonian telescope with a simplified mechanical design – perfect for newcomers (exactly like a small refractor).

As you can see the secondary mirror is “obstructing the view”, but it only makes the view a little darker (as I pointed out above) and sometimes it causes diffraction spikes (more on that in the next point).

IIId. Practical differences between refractors and reflectors.

Reflectors are generally brighter (better as far as light gathering is concerned) even though a secondary mirror is “obstructing the view”. How is that possible? The objective mirrors in reflectors are less expensive to produce than the objective lenses in refractors, so the reflectors have bigger aperture (bigger objective lens/mirror diameter) at the same cost.

The loss of brightness due to the central obstruction (due to the secondary mirror) is only several percent. For example if the central obstruction is 25% of aperture then the AREA of the central obstruction is only 6.25% (A = aperture; I omitted some elements from the formula for the area because they get reduced anyway):
(0.25*A)^2 / (A)^2 = (0.25)^2 / 1^2 = 0.0625 = 6.25%

There is one main downside of the central obstruction – the diffraction spikes. The secondary mirror has to be held in place somehow, so there are some tiny spider vanes that make very bright stars appear not quite realistic (not as points). ONLY the brightest stars – the vast majority of stars appear in a normal way (as points). Some purist may be annoyed by the diffraction spikes, but I like them myself. They are very rare and they make a single bright star look very interesting.

Pleas notice that there are different types of spider vanes, but in small Newtonian telescopes the typical type is the “cross” – second to last on this picture:

A reflecting telescope takes longer to cool down, which is important when there is a significant difference in temperatures between indoors and outdoors. On the net I found this quote:

“In general, small refractors cool quickly. Unless the temperature differential is large, a refractor is ready for use within a few minutes after it is set up. A 6” to 10” Newtonian reflector (such as a Dob) may require 30–60 minutes to cool down, depending on the temperature differential, and less if fans are used to expedite cooling.”

For some reason(s) mirrors in a reflecting telescope are NOT mounted in a fixed way. It doesn't matter why, it matters that they are mounted in an adjustable way and from time to time you need to align the mirrors again. This process is called collimation.

For a total newcomer collimation may look like a very troublesome thing. Well, in some cases it is a very troublesome thing – there are LOTS of topics on various astronomy forums where people tell some “hair-raising stories” about collimation. HOWEVER it turns out that collimating a “slow” (see the point IV. Telescopes numbers) Newtonian telescope is much easier than collimating a “fast” (see the point IV. Telescopes numbers) one, just because the room for error is much bigger. Moreover collimating a secondary mirror (the hardest part of the full collimation) is usually NOT important as far as visual astronomy is concerned, unless you can't see the whole primary mirror while looking at the secondary mirror (it would cause a loss of light, so a loss of brightness).

I had wanted to keep everything as easy as possible, so I avoided collimation issues by buying a refractor. HOWEVER after just one year I learned the crucial info about collimating a “slow” (see the point IV. Telescopes numbers) reflector and I instantly bought such a telescope myself.

Another difference is that in my reflector the view is upside down, while in my refractor the view is mirrored (left is on the right and right is on the left). As far as astronomy is concerned the view upside-down is actually better! Why? Because when I look at a star map all I have to do is to turn my head upside down and I see what I can see in the telescope. In the mirrored view I can't use any “trick”, but I have to use my imagination.

IIIe. Practical differences between a Dobson and a telescope on a tripod (either a refractor or a Newton).

I can place my Dobson right next to my balcony guardrail, so I am able to look almost straight up. With a refractor I couldn't do it because the legs of the tripod “pushed” the refractor away from the guardrail.

On the other hand I had to buy some kind of platform to raise my (little) Dobson off the ground. The main reason was that I wanted to be able to look into an eyepiece while sitting on a normal chair and the second one was that I wanted to aim my telescope more horizontally, above my balcony guardrail.



I had had one folding step in my apartment already, so I had to buy only two more. This solution woks perfectly well for me – I can look into the eyepiece while sitting on a normal chair, no matter which direction my telescope is pointing at.

By the way: the balcony guardrail still forces me to discard all the night-sky objects that are rather low above the horizon (less then 20 degrees), so I save some time and avoid possible disappointments.


IV. Telescopes numbers.

You can describe a particular telescope in several different ways, so it's important to understand some basic terms.

Aperture – objective lens/mirror diameter

It describes in a simplified way the light gathering abilities of a telescope (or binoculars), HOWEVER what really matters is the AREA of aperture (or rather the area of exit pupil that is calculated from aperture – more on that later (see the point VIId. Exit pupil).

Focal length – distance from the objective lens/mirror to a place where all light rays come together

In a refractor or in a Newton it's basically the length of the telescope.


I prefer to describe my telescopes as “Aperture/Focal length” given in millimeters, for example 70/700 or 114/900. Unfortunately many astronomers describe their telescopes using Aperture and Focal ratio. What's worse some of them, especially in the US, give the Aperture in inches instead of millimeters. Even worse, the focal ratio is always given in an “inverted way”, which make it even more confusing.

Focal ratio = focal length / aperture

Please notice that it's all about proportions – for example two different telescopes (70/700 and 100/1000) have the same focal ratio of 10 (700/70 = 1000/100), which is written as “f/10”. I hate this “inverted focal ratio notation” with all my passion.

Another thing connected with the focal ratio that annoys me very much is the fact that it is common to describe some telescopes as “slow” (f/8 and “above”, so f/9, f10 and so on) or “fast” (f/5 and “below”, so f/4, f/3 and so on).

Here's a description that I found on the net:

“The terms fast and slow in reference to focal length come from photography and make more intuitive sense when applied to telescopes used for astrophotography. To take an image of the night sky, your DSLR or CCD collects photons of light. The trick to good astrophotography is to catch as many photons as you can as quickly as possible. Speed is important because longer exposures increase the risk of noise in the image sensor and your telescope drifting off target.”

I don't really care about the reference to photography and from my point of view the focal ratio basically tells me if the telescope looks “fat” (f/5) or “lean” (f/10). The only thing I have found really useful about the focal ratio is the fact that collimating a “slow/lean” (f/8) Newtonian telescope is much easier than collimating a “fast/fat” (f/5) one.

These are all the numbers that describe a telescope alone. Please notice that things like magnification, exit pupil and field of view don't come from a telescope alone, but from a combination of a telescope and an eyepiece. More on that later (see the point VII. Eyepieces and all the following sub-points).


V. Mount of a telescope.

There are basically two kinds of mounts of a telescope: alt-azimuth (altitude-azimuth) mount and equatorial (or parallactic) mount. The alt-azimuth mount is light and easy to assemble and operate – there are independent movements up-down and left-right that don't require complex mechanisms or any geographical alignments.

On the other hand, the equatorial mount allows you to move your telescope according to the movements of the night-sky objects, but it's definitely more difficult to assemble and operate. Moreover the mechanism is much heavier because there has to be a counterweight attached.

No contest – the alt-azimuth mount is MUCH better for a total amateur, BUT please remember that the equatorial mount with proper setup allows also the alt-azimuth type of movements.


VI. Size of a telescope vs. expectations.

In case of professional refractors the rule is obvious: the bigger the better, but for an amateur it's NOT the case! First of all a telescope for an amateur can't be too heavy! The heavier the telescope the heavier (more stable) tripod/base it requires. What’s worse, practically all relatively heavy refractors have the equatorial mount, which requires additional counterweight, which makes the whole set even more heavy. Definitely NOT good for an amateur!

I own a 70/700 refractor and a 114/900 Dobson and they are both light enough to be moved together with a tripod/base without ANY problems. Moreover they are both simple to use and definitely more powerful than my 12x60 binoculars. What more could you want?

Well, some people have some unrealistic expectations about small telescopes because some Internet sites, including online astronomy shops, state that you can see many Messier objects (object from the Messier Catalogue) even in small telescopes. It's true, HOWEVER please remember that the word “see” in this context should be understood as “I see that I can see something”, which is better than “I can’t see the object at all”.

What’s worse some Internet sites give you “examples” of what you can see by showing pictures taken with BIG (professional) telescopes, which is is extremely misleading for total amateurs! On the picture below there is a comparison how the M13 (Hercules Globular Cluster) looks in binoculars (the very first example) and several different telescopes.


Please notice that the most famous catalogue of astronomical objects – the Messier Catalogue was created only because these objects were blurry and could be mistaken for a comet! Moreover there was hardly any light pollution in those times (18th century), so they were blurry under very dark skies!

A small telescope is great for looking at very bright large objects like the Moon, Jupiter or Saturn and all point-like objects like stars (especially in open star clusters) or the brightest moons of Jupiter and Saturn. Non-point-like objects like globular clusters, nebulas and galaxies can be seen only as “faint fuzzies” – they look like a cloud of light – something clearly different from the stars that are simply dots. Unfortunately many of such non-point objects can't be seen in a small telescope from a city with significant light pollution at all.

It isn't important how well you can see deep-sky objects, but what it means that you can see them at all. Open star clusters are typically thousands of light-years away. Globular star clusters are typically tens of thousand of light-years away. Galaxies are typically millions of light-years away. The Andromeda Galaxy is so bright that you can see it in a small telescope without any problems even from a city. Just think about it – you can see with your own eyes light that travelled for millions of years!

Please notice that when you look at a picture of a galaxy you can see only light reflected from the picture, so light that travelled for no more than several minutes (the distance from the sun is exactly 8.317 light-minutes). It's not the same as looking through a telescope!


VII. Eyepieces.

An eyepiece looks like a small tube with a lens (in fact there are more than one lenses inside) that you insert into the part of a telescope that is called focuser or focus tube.

A particular telescope can be used with many different eyepieces, which means that you can achieve many different results. A particular eyepieces combined with a telescope is responsible for magnification, which influences both the field of view and the exit pupil. These three things should be ALWAYS analysed together!

A quote comes to my mind: “It was my understanding that there would be no math”.



VIIb. Magnification

Magnification = focal length of the telescope / focal length of the eyepieces

The shorter the eyepiece the bigger the magnification. For example my 70/700 refractor came with two different eyepieces:
1) a 25mm eyepiece gives the magnification 28x (700/25),
2) a 10mm eyepiece gives the magnification 70x (700/10).

The same eyepieces give different magnifications with a different telescope. For example my 114/900 Dobson came with the same eyepieces:
1) a 25mm eyepiece gives the magnification 36x (900/25),
2) a 10mm eyepiece gives the magnification 90x (900/10).

The “longer” the telescope the bigger the magnifications with the same eyepieces. And the bigger the magnification the more details you can see, unless the object/view is too dim.

Fun fact: magnification is almost exactly like shortening the distance to a particular object. For example when distance is shortened by 50% then the angle is twice as big. It works the other way round too: when the angle is twice as big then the distance must be shorter by 50%.

With small angles (true in astronomy) the changes are almost perfectly proportional. You can verify this fact with the tangent function:

One value is constant (the size of the object – “Opposite”) and the other is reduced (the distance – “Adjacent”). So, the bigger the angle (magnification) the higher value of the tangent function and the smaller the distance. You can toy with this calculator:
https://www.rapidtables.com/calc/math/Tan_Calculator.html
so you can see that the changes are proportional with small angles (true in astronomy) – tripling an angle triples the tangent value, which means that the distance is three times shorter.

I’ve made calculation for a thought experiment (about getting closer to a flashlight, but it’s not important now) and I realised that even moderate magnification “brings us” VERY close to a star (or any other night-sky object):
Magnification 2x => distance is reduced by 50% (1 – 1/2)
Magnification 4x => distance is reduced by 75% (1 – 1/4)
Magnification 10x => distance is reduced by 90% (1 – 1/10)
Magnification 20x => distance is reduced by 95% (1 – 1/20)
Magnification 40x => distance is reduced by 97.5% (1 – 1/40)
Magnification 50x => distance is reduced by 98% (1 – 1/50)
Magnification 100x => distance is reduced by 99% (1 – 1/100)
Magnification 200x => distance is reduced by 99.5% (1 – 1/200)
Magnification 500x => distance is reduced by 99.8% (1 – 1/500)
Magnification 1000x => distance is reduced by 99.9% (1 – 1/1000)

Precise calculation should look like this:
Magnification 2x => distance is reduced by 50% ((1/2 – 1)/1 = -1/2 = -50%)
but they would be less “readable” then.

On a side note:
Obviously when we increase the magnification from 100x to 200x then we reduce the relative distance by 50%:
(1/200 – 1/100)/(1/100) = (1/200 – 2/200)/(1/100) = (-1/200)/(1/100) = (-100/200) = -1/2 = -0.5 = -50%

VIIc. Field of view (FOV)

Field of view (FOV) = apparent field of view of the eyepiece (AFOV) / magnification

Both my small telescopes use 1.25-inch eyepieces and standard such eyepieces have the AFOV of around 50 degrees:
1) magnification 28x gives the FOV of 1.79 degree (50/28),
2) magnification 36x gives the FOV of 1.39 degree (50/36),
3) magnification 70x gives the FOV of 0.71 degree (50/70),
4) magnification 90x gives the FOV of 0.56 degree (50/90).

Obviously the bigger the magnification the smaller the field of view. It's actually quite natural – when you use bigger magnification you see a smaller part of the whole picture, so you look through a narrower path, hence narrower field of view. As simple as that. This general rule can be slightly “bent” by using wide-view eyepieces (eyepieces with bigger apparent field of view).

Interestingly it's easier to understand and explain narrow-view optics, so wide-view optics are simply a “reversed” case. A relatively good 32mm 1.25-inch eyepiece has the AFOV of 52 degrees, but a relatively good 40mm eyepiece (from the same producer) has the AFOV of only 43 degrees. In my 70/700 refractor these eyepieces give the magnifications 21.875x and 17.5x:
1) the 32mm eyepiece (magnification 21.875x) gives the FOV of 2.38 degree (52/21.875),
2) the 40mm eyepiece (magnification 17.5x) gives the FOV of 2.46 degree (43/17.5).

So, in the 40mm eyepiece the field of view is only MARGINALLY wider than in the 32mm eyepiece, while the magnification is clearly smaller. This surprising result made me read about wide-view optics again and I finally grasped the concept!

Narrow-view optics can be combined with bigger or smaller magnification. Wide-view optics can be also combined with bigger or smaller magnification, so there are MANY different combinations! I will show some examples that in my opinion are crucial.

I used this awesome site:
https://www.stelvision.com/en/telescope-simulator/
to simulate what can be seen in my 70/700 telescope. The second picture in the first example is only theoretical because there is no narrow-view 25mm eyepiece available, but it greatly helps to explain the concept.

Please, remember that you can open all the pictures in different tabs and switch between the tabs to see the differences better.

1. The same magnification, but different optics.

Normal-view (52 degrees) 25mm eyepiece (magnification: 28x)

NARROW-view (43 degrees) 25mm eyepiece (magnification: 28x)

It's like looking at the same picture, but in the narrow-view you are looking through some kind of tube/tunnel. This “looking through a tunnel” effect is annoying to some people, so total amateurs should rather avoid it.

When the idea is reversed the second picture could be considered as the normal-view and the first picture could be considered as the wide-view. So, a wide-view is like looking through a shorter tube/tunnel.

2. Different magnifications, but the same optics.

Normal-view (52 degrees) 25mm eyepiece (magnification: 28x)

Normal-view (52 degrees) 32mm eyepiece (magnification: 22x)

It's like looking at similar pictures, but taken with different zooms – on the picture taken with less zoom everything is smaller, but you can also see some additional things on the sides of the picture. Pretty natural concept, right?

3. Different magnifications and different optics + wider FOV.

Normal-view (52 degrees) 25mm eyepiece (magnification: 28x)

NARROW-view (43 degrees) 40mm eyepiece (magnification: 17.5x)

It's like looking at similar pictures, but taken with different zooms AND in the narrow-view you are looking through some kind of tube/tunnel. In THIS combination you can still see some additional things on the sides of the picture. On the picture taken with less zoom everything is smaller.

4. Different magnifications and different optics + the same FOV (more or less).

Normal-view (52 degrees) 32mm eyepiece (magnification: 22x)

NARROW-view (43 degrees) 40mm eyepiece (magnification: 17.5x)

Again it's like looking at similar pictures, but taken with different zooms AND in the narrow-view you are looking through some kind of tube/tunnel. However in THIS combination it's almost like looking at the same picture (the field of view is almost equal) but the in narrow-view the picture is held farther away from your eyes, so the picture and everything on the picture looks smaller. Strange, isn't it?

So, what's the point of using the narrow-view 40mm eyepiece instead of normal 32mm eyepiece? The different lies in the exit pupil – in the narrow-view 40mm eyepiece the exit pupil is bigger (the view is brighter) because the magnification is smaller. However, the usefulness of this “move” is very limited because, as I already described, magnification is generally more important, so increasing only the exit pupil is usually “doubtful”.

VIId. Exit pupil.

Exit pupil = aperture / magnification

Exit pupil can be compared to a small hole that you look through. When the hole is “big enough” it doesn't matter at all. When the hole gets smaller and smaller it's harder and harder to see things on the other side of the hole. In order to see big diffuse (non-point-like) objects the hole has to be relatively big, for small diffuse objects the hole can be “medium” and for point-like objects the hole can be relatively small.

When magnification gets bigger exit pupil gets smaller: In case of my 70/700 refractor:
1) a 25mm eyepiece (magnification 28x) gives the exit pupil of 2.5mm (70/28),
2) a 10mm eyepiece (magnification 70x) gives the exit pupil of 1.0mm (70/70).

In case of my 114/900 Dobson:
1) a 25mm eyepiece (magnification 36x) gives the exit pupil of 3.2mm (114/36),
2) a 10mm eyepiece (magnification 90x) gives the exit pupil of 1.3mm (114/90).

Generally a telescope with bigger aperture produces bigger exit pupils with the same eyepieces, although they may be some exceptions.

The bigger the exit pupil the brighter the view, HOWEVER comparing “raw values” of different exit pupils may be misleading because these values are “one-dimentional”. To compare brightness you have to compare exit pupil AREAS. For example the exit pupil of 3mm is NINE times brighter than the exit pupil of 1mm (I omitted some elements from the formula for the area because they get reduced anyway):
(3mm)^2 / (1mm)^2 = 9

Now let's compare the brightness of the exit pupils 5mm and 2mm:
(5mm)^2 / (2mm)^2 = 25/4 = 6.25

In the second example the “simple” difference between the exit pupils is bigger (3mm instead of 2mm), BUT the difference in brightness is actually smaller! Counter-intuitive, isn't it? Well, it's not quite counter-intuitive when you notice the different proportions: 3mm/1mm is bigger than 5mm/2mm.

This way of comparing brightness is awkward because you have to first calculate exit pupils and then compare the areas of the exit pupils. Moreover in the final step (while comparing the exit pupils areas) you may forget about different magnifications, so you may forget about their importance. The same exit pupils at magnifications 22x and 90x will NOT give the same number of details! Much better way of comparing brightness is using my formula (see the next point VIIe. The easiest way to precisely compare brightness of equipment).

Please, notice that brightness/exit pupil is important also when looking at stars (point-like objects), but only when the exit pupil (the hole) becomes very small. Some people say that “stars don't dim” due to high magnification, but from my own experience I can say that it's NOT true for bright stars! To me, when exit pupil is around 1mm (or less) bright stars appear definitely less “shiny”, so they get dimmer.

Interestingly, there is a paradox – at the same time (when increasing the magnification) some weak stars start being visible (they become brighter) while some bright stars become less “shiny” (they become dimmer). I think it's connected with the fact that bright stars appear larger just because they are bright. Here are some quotes I found on the net:

“Bright stars tend to "saturate the detector", so their brightness tends to spill over making them appear larger than the point sources they are. That brightness also allows some of the aberrations of the eye to become a lot more noticeable, further enlarging the spot of light which the eye sees.”

“At all but the highest magnifications, the human eye is by far the dominant factor. It's much the same reason that bright stars appear bigger in film photos.”

“Example: the crescent moon appears to have a larger diameter than the earthlit part visible immediately adjacent.
The reason: The brain sees brighter as larger.
Reduce the brightness by using a telescope (which reduces the exit pupil and the unit area brightness) and the diameter difference goes away.”

“It's been demonstrated in experiments wherein two identically-sized squares, side-by-side, are differentially illuminated. The brain sees the brighter square as larger.”

From my own experience I have to add that exit pupil of around 2mm is big enough to be “neutral” for bright stars – they are still “shiny” then.

VIIe. The easiest way to precisely compare brightness of equipment.

EBC – equipment brightness comparison
M – magnification
A – aperture

EBC(M1xA1; M2xA2) = (M2/M1)^2 * (A1/A2)^2

I used the notation MxA just like it is used in binoculars (for example 12x60). My formula works also for telescopes because it’s just a different (greatly simplified) way of comparing exit pupil areas. I described it in detail here:
Binoculars and spotting scopes brightness comparison

When you compare only eyepieces combined with the same telescope the aperture stays the same, so you have to calculate only the (M2/M1)^2 part. For example let's compare the eyepieces 25mm and 10mm combined with a 114/900 Dobson (magnifications 36x and 90x respectively):
EBC(36x114; 90x114) = (90/36)^2 * (114/114)^2 = (2.5)^2 * 1^2 = 6.25

Please notice that I ignored the central obstruction of the Dobson simply because it stays the same.

When you compare only eyepieces combined with the same telescope it's actually better to compare them “in reverse”:
EBC(90x114; 36x114) = (36/90)^2 * (114/114)^2 = (0.4)^2 * 1^2 = 0.16
EBC(90x114; 36x114) = 1/EBC(36x114; 90x114) = 1/6.25 = 0.16

The value 0.16 means that at the magnification 90x the brightness is only 16% of the brightness at the magnification 36x. It also means that the drop in brightness caused by the change in the magnification form 36x to 90x is 84%!

My formula excels at comparing different kinds of equipment/telescopes. For example let's compare a 114/900 Dobson combined with a 10mm eyepiece ( magnifications 90x) with a 70/700 refractor combined with a 25mm eyepiece (magnifications 28x). This time we have to take into account the central obstruction of the Dobson (it's around 25% of aperture, so the AREA of the central obstruction is only 6.25%, as we calculated earlier):
EBC(90x114; 28x70) = (28/90)^2 * (114/70)^2 * (1 – 0.0625) = 0.24067

If the comparison were made “in reverse” then the central obstruction would have to be taken into account in a different way:
EBC(28x70; 90x114) = (90/28)^2 * (70/114)^2 * (1/(1 – 0.0625)) = 4.1551
EBC(28x70; 90x114) = 1/EBC(90x114; 28x70) = 1/0.24067 = 4.1551

It may be surprising that the view in a 114/900 Dobson is dimmer than in a 70/700 refractor, but it is the “fault” of the much bigger magnification. To see the “light power” of the Dobson you have to compare the telescopes either at the same magnification (the brightness will be different) or at the same brightness (magnifications will be different).

At the same magnification (any magnification) a 114/900 Dobson is two and a half times as bright:
EBC(36x114; 36x70) = (36/36)^2 * (114/70)^2 * (1 – 0.0625) = 2.4865

The views in a 114 Dobson and a 70/700 refractor are almost equally bright when the magnifications are 56x and 36x respectively: EBC(56x114; 36x70) = (36/56)^2 * (114/70)^2 * (1 – 0.0625) = 1.0276

The difference between the magnifications (with the same brightness) is significant, so the Dobson is clearly better.

As a complement to my formula above I would like to share another formula that I “discovered” while pondering about brightness. It’s a formula for the “brightness sweet spot” between two eyepieces – it points at another (third) eyepiece which guarantees that the percentage drops in brightness (the percentage drops in the exit pupil area) between the sequent eyepieces are exactly the same. Obviously the more eyepieces you own the better, but if you can't afford them all my formula might be helpful.

BSS – “brightness sweet spot”
e1 – length of eyepiece #1 (the shorter eyepiece)
e2 – length of eyepiece #2

BSS(e1; e2)= square root(e2/e1) * e1

Example:
BSS(10mm; 32mm) = square root(32mm/10mm) * 10mm = square root(3.2) * 10mm = 1.789 * 10mm = 17.89mm = 18mm (after rounding)

Verification for a …/900 telescope (the aperture is not important because it’s constant for a given telescope):
M1 = 900mm/10mm = 90x
M2 = 900mm/32mm = 28.125x
M3 (for the BSS) = 900mm/18mm = 50x

EBC(90xA; 28.125xA) = (28.125/90)^2 * (A/A)^2 = 0.0977
It’s a 90.23% (1 – 0.0977 = 0.9023) drop in brightness (a drop in exit pupil area) between the eyepieces 32mm and 10mm (between the original pair of eyepieces).

EBC(50xA; 28.125xA) = (28.125/50)^2 * (A/A)^2 = 0.31641
It’s a 68.359% (1 – 0.31641 = 0.68359) drop in brightness between the eyepieces 32mm and 18mm.

EBC(90xA; 50xA) = (50/90)^2 * (A/A)^2 = 0.30864
It’s a 69.136% (1 – 0.30864 = 0.69136) drop in brightness between the eyepieces 18mm and 10mm.

Verification “in steps”:
EBC(50xA; 28.125xA) * EBC(90xA; 50xA) = 0.31641 * 0.30864 = 0.977

Verification with common sense calculations:
The total DROP in brightness = drop from 32mm to 18mm + remaining brightness * drop from 18mm to 10mm = 0.68359 + 0.31641 * 0.69136 = 0.9023

Such calculations helped me choose which new eyepiece to buy myself. I had a 32mm eyepiece that was bright, but produced low magnification and I also had a 10mm eyepiece that produced big magnification, but was very dark. I wanted something in between as far as brightness was concerned. Please notice that I ignored my 25mm eyepiece that had come with my telescope because I wasn't using it at all (the 32mm eyepiece that I bought later was clearly better because it had a bigger field of view).

VIIf. Eye relief.

Eye relief is the distance from the eyepiece to the position where you can see the whole field of view. If your eye is too far (farther than the eye relief) then you can't see the whole FOV.


The pictures above show a person wearing glasses and eye relief is usually described in this context, HOWEVER when the eye relief is very short (in very short eyepieces) it's a problem even for people without glasses. General rule is that shorter eyepieces have shorter eye relief.

I myself strongly dislike standard 10mm eyepieces that came with my telescopes because of the short eye relief. I had thought it was all about the narrow field of view (AFOV/big magnification), but it turns out that the “true field of view” is even smaller just because I am not able to see the whole FOV at the same time and it's not even close. I realised this fact after taking some pictures of the Moon through the 10mm eyepiece (combined with a yellow #12 filter), while pressing my smartphone against the rubber cup of the eyepiece. Here's one of my pictures:

As you can see even at such a short distance (smartphone was pressed against the rubber cup of the eyepiece) the picture was far from what I expected – theoretically the whole lunar disk should be visible. When I looked with my own eye through the same eyepiece it wasn't as bad, but I still couldn't see the whole lunar disk at the same time and it was not even close.

Short eye relief may be annoying, but the overall number of details of the Moon is fantastic even in a small telescope. The 10mm eyepiece is also very good when looking at the planets, especially at Saturn (you can see its rings) and Jupiter (you can see its belts). The extremely narrow “true field of view” is not a problem then because the planets are much smaller than the Moon.

VIIg. Filters.

The most important goal of using a filter is too make the view dimmer without changing magnification (gray filters) OR to block some light wavelengths (color filters). On the net I found a picture of the Moon taken with an orange filter I instantly fell in love with the view. To me the Moon looked a little like Mars and the view was much more interesting than the typical gray view of the Moon.

Out of curiosity I bought these 4 inexpensive filters:
1. Gray (neutral density 0.6) – light transmission 25%.
2. Orange (#21) filter – light transmission 46%.
3. Green/light green (#56) filter – light transmission 53%.
4. Yellow (#12) filter – light transmission 74%.

I discarded the blue (#80A) filter (it usually gets good opinions) just because I prefer warm colors.

I compared my filters while looking at the full Moon. Some people say that they look at the full Moon without any filter and it's not bothering them, but to me the filtered view was much more comfortable and relaxing than the unfiltered one.

All the pictures below were taken with a smartphone by hand (without an adapter) with these manual settings of the camera:
1. ISO-200.
2. Shutter-250 (1/250th of a second).
3. Focus – “Far”, but not at maximum (not focus at infinity – some smartphones/apps apparently allow focus “beyond infinity” and it messes things up).

First four pictures below (all except the yellow filter) were taken through a 25mm eyepiece (magnification 36x; exit pupil 3.2mm).

1. No filter (the base for comparison):

Quite realistic picture.

2. Gray (ND 0.6) filter (loss of light 75%):

Clearly better view than the unfiltered one.

3. Green/light green (#56) filter (loss of light 47%):

Surprisingly good picture. In reality the view was slightly yellow to me, but barely.

4. Orange (#21) filter (loss of light 54%):

Totally unrealistic view – my smartphone couldn't handle the colors at all and the picture lacks some details. Through the eyepiece the view was truly orange and it was at least as good as the green one. Probably better.

5. Yellow (#12) filter + LONGER (32mm) eyepiece (GAIN of light 21%):

Click to enlarge (or open all pictures in new tabs, so you can switch between the tabs back and forth) => the yellow Moon is smaller than the rest because the magnification is smaller..

The view in the longer eyepiece with a yellow filter is truly brighter than the unfiltered view through the shorter eyepiece. The yellow (#12) filter is very bright on its own (good light transmission), so it's not really useful on the full Moon. With this picture I decided to show you the effect of a bigger exit pupil. Or in reverse = when you want dimmer view then you should simply use a shorter eyepiece. The problem lies in what you can frame into the view – when you want to see the whole lunar disk you can't use too short an eyepiece.

The new exit pupil was 4.05mm (previously it was 3.17mm), so the relative difference between areas of the exit pupil was 1.63 = (4.05mm/3.17mm)^2 (the exit pupil area was 63% bigger), but the light transmission was 74%, so the overall difference (gain) in brightness was 21% (1.63 * 0.74 = 1.2062).

VIIh. Barlow lens.

Just for the sake of completeness I have to mention Barlow lens. I don't like it. When I looked at the Moon at the 140x magnification with a Barlow lens (the 70x “normal” magnification combined with a 2x Barlow lens) the view wasn't as interesting. Yes, the moon was definitely bigger (I could see only a small part of it), but the details were “less detailed” simply because they were “stretched”. That ended my thirst for using the Barlow lens for some time.

The next time I used a Barlow lens I was looking at the rings of Saturn. First I was looking at the magnification 70x and I had to move my telescope a little to the side from time to time (the Earth is rotating, so “the sky is moving” and the Saturn “slides” outside the field of view after some time), but it was acceptable. After I added the Barlow lens and the magnification was 140x I had to move my telescope twice as often and it was already annoying! This is actually a good reason for a total amateur not to use “too big” magnifications even without a Barlow lens. I think the maximum limit for a total amateur is the magnification 100x.


VIII. Forget about a toy finder scope!

Seriously, you should forget about a toy finder scope that comes with a small telescope. I attached it to each of my telescopes once and I will never do it again. It is simply too weak when looking from my balcony, with all those street lights blinding me. All that matters to me is the telescope itself.

As my finder scope I use my 8x42 binoculars, but the truth is that ANY binoculars should be good enough. If you don't have any binoculars then you should rely only on the stars that are visible with the naked eye. You have to rely on them even while using binoculars because you have to use some kind of reference point anyway.

The problem is that it's very hard to point a telescope in exactly the same direction as binoculars just a moment ago. The angles are totally different unless you sit down with your butt on the ground and aim binoculars along the tube of the telescope. It's relatively easy to do with a refractor and much more difficult with a Dobson. Either way, a total amateur needs a long eyepiece that gives the maximum (or almost maximum) field of view. I think that a 32mm eyepiece is a must buy.

In the last point I showed you how to search for some objects with the naked eye even in big light pollution.


IX. Use a chair!

Generally it's a very good idea to place a normal (relatively heavy, but comfortable) chair next to your telescope. To me it was like a God-sent idea because I tried it out when I was looking at the rings of Saturn for the first time. The view was simply hypnotizing and I spent LOTS of time in the same position! And right after that I switched to watching Jupiter and its moons from the exact same spot! It was in 2021, so the planets appeared quite close to each other on the night-sky. What a night! Unforgettable!


X. Differences in temperatures.

1. Cold air + warm telescope.

The cold air that “touches” the warm telescope gets warmer (making the telescope colder), but this warmer air instantly mixes up with the cold air that is farther away from the telescope, so the air close to the telescope is constantly “moving”, similarly to the air over a very hot object during summer. So, it's important to cool down the telescope as a whole.

2. Warm air + cool telescope.

If you wear glasses then you know that when it's cold outside and you go into a warm building the glasses will instantly fog up. If you don't wear glasses then fill an empty glass with ice water – on the outside side of the glass small drops of water will appear. It's all about water condensation. Please, read the long answer on this site:
https://www.reddit.com/r/Astronomy/comments/9c94nu/why_does_my_telescope_get_so_much_condensation/

Please remember that you should AVOID wiping the dew off your eyepieces! You don't want to scratch the eyepieces by accident – there can be some dust or grit on the eyepiece besides the dew that you won't be able to see in the darkness.


XI. Observing conditions are not only about the light pollution!

One night I used my telescope and even though there were no clouds the observing conditions were much worse than previously! I couldn't even clearly see the Orion's Belt with the naked eye! To be honest I had never thought that there could be such a big difference independent from the light pollution. On the net I found the info that “Bad transparency is caused by pollutants in the air, either artificial, natural, or (most often) both.” and “Bad seeing is caused by turbulence combined with temperature differences in the atmosphere”. On this site:
https://www.cloudynights.com/topic/487715-why-does-poor-seeing-happen-or-is-it-poor-transparency/
there is an interesting discussion on this topic.

I found a great site with a complex astronomy forecast:
https://clearoutside.com

This site is great for another reason – you can check at what time starts and ends the astronomical darkness AND you can also see a picture for the whole year! Just click the button “Annual Darkness”.

Los Angeles:

Seattle:

My home city:

Please notice that in my home city during the summer months there are “astronomical white nights” when the night-sky is never fully dark because the Sun is too little below the horizon and the astronomical twilight never ends.

A site that is even better for checking the exact times for twilight end, nautical twilight end and astronomical twilight end is this:
https://sunrise-sunset.org

XIb. How much are your “astronomy hours” skewed?

Have you ever wondered what does the word midnight mean? The word midnight means literally the middle of a night. Unfortunately in the vast majority of cases the true (astronomical) middle of a night is not at midnight local time. And I am not even talking about daylight saving time!

“Astronomy hours” at some places are simply ridiculous. At some places they are ridiculous only during the DST (daylight saving time – summer time), but in some other places, like the western China, they are ridiculous all year long. On the other hand there are some places where the astronomy hours are perfect all year long.

Here's a very interesting solar noon map that I found on the net (click to enlarge):

The picture is for standard/winter time, but when the DST starts many places go “more red”. In the western Spain during the DST the Sun is highest above the horizon around 2:30PM, so the middle of the astronomical night is around 2:30AM. Interestingly the Great Britain lies at the same longitudes as Spain, but it is in a different time zone, which is much more reasonable.

In China there is no DST, but there is one whole big time zone, so in the western China the Sun is highest above the horizon around 3:00PM, so the middle of the astronomical night is around 3:00AM. Oh, man.

On the site sunrise-sunset.org (link given above) there is info also about solar noon, so you can calculate the true (astronomical) middle of the night right away (+12hours from the solar noon).


XII. Apparent magnitude and limiting magnitude.

Apparent magnitude is a number that shows how bright a particular object appears from a particular place. The lower the number the brighter the object. Here are examples of apparent magnitude as seen from the Earth at maximum brightness:
– full Moon -12.9
– planet Venus -4.92
– planet Jupiter -2.94
– planet Mars -2.94
– star system Sirius -1.47
– star Canopus -0.72
– planet Saturn -0.55

All the night-sky objects above are extremely bright and can be easily seen with the naked eye even in the worst light pollution. From my own experience I can say that in a small telescope even stars of magnitude around 0.5 still look literally like diamonds in the sky and stars of magnitude around 2 still look relatively bright. Unfortunately weaker stars (magnitude 3 and above) are more and more negatively influenced by light pollution.

The magnitude of the weakest stars that can be seen with the naked eye depends on light pollution and it varies greatly. Without any light pollution the maximum magnitude is 7 or 8 and in the worst light pollution it's less than 4. Interestingly, even in significant light pollution a small telescope will show you stars of magnitude at least 9 – more than you could ever see with the naked eye even in darkest locations on Earth! The catch is that the field of view in any telescope is extremely small when compared to the field of view of the naked eye, so the “WOW effect” is greatly diminished. But it's cool anyway!

The maximum magnitude of stars that can bee seen in a telescope is called limiting magnitude and it depends on many different things, not only light pollution. A fantastic telescope limiting magnitude calculator can be found on this site:
https://www.cruxis.com/scope/limitingmagnitude.htm

It's worth to notice that in big light pollution it's better to increase magnification than aperture. Just set the value Naked Eye Limiting Magnitude near the Zenith to 4 (which means big light pollution), then set a particular aperture and a particular magnification and press “Calculate”. Remember the result then double the magnification, press “Calculate” and see the new result (much bigger). Reverse to the original magnification, press “Calculate” to see the original result again, then double the aperture, press “Calculate” and see the newest result (hardly any change in reference to the original result = much LOWER result than the result with doubled magnification).

Please notice that when you increase magnification very much (use a 10mm eyepiece) then the view gets very dark and the “new stars” are barely visible. To me it's not enjoyable at all. When I want to see more stars I change from my longest (32mm) eyepiece to my 18mm eyepiece that gives magnification 39x (in my 70/700 refractor) or 50x (in my 114/900 Dobson).

There is one additional thing to remember – the apparent magnitude of a galaxy, a nebula or a star cluster is NOT the same as the magnitude of a single star (a point-like object)! On the net I found these quotes (a question and an answer):

“Is it possible, that I can see apparent magnitude stars of 10 or 11 in my ten inch dob, and not be able to see AM 8 and 9 DSOs.”

“Yes it is extremely possible that you could see mag 10 stars and not make out mag8-9 DSO. Galaxies for example tend to be diffuse, with the brightness increasing gradually as you move towards the core. This makes them harder to tease out of the background sky than a star, which is a pinpoint of light.”

Fun fact: the yellow (#12) filter (light transmission 74%) with my 32mm eyepiece doesn't really change the limiting magnitude of stars (when compared to the unfiltered view through the same eyepiece). There must be a slight drop in the limiting magnitude by definition but it is so small that I can't really notice it.


XIII. Maps of the night sky.

Thankfully we live in modern times a we can use sites like this:
https://stellarium-web.org

This awesome site allows you to search for a particular night-sky object without learning anything about star constellations! You can also change date and time to see where a particular object was (in the past) or where it will be (in the future). AWESOME!

A good method is to change the time minute by minute until a particular object is exactly in the direction you want it to be. It's quite useful on a balcony where you have some parts of the sky obstructed by nearby blocks of flats.

Please notice that you can simulate the night-sky seen with the naked eye in big light pollution by setting the time to an early hour, but it's not quite realistic. Most examples in the next point are made this way.

I have also installed the free program Stellarium from this site:
https://stellarium.org/
The program is not perfect but it's still very good:
1) the program has much more options and is much more configurable,
2) the program is much less burdening for the computer.

Please notice that I still regularly use the website, especially when I want quick results, better visuals or deeper star field.

I described the program Stellarium in detail here:
Stellarium program vs. Stellarium website

There is also a free astronomy Android app – Stellarium Mobile (153MB in total) that I installed on my smartphone. It shows only stars of magnitude below 8, but at least it seems consistent, unlike another free Android app that I installed (I will not name it).


XIV. More astronomy fun.

You can find plenty of interesting things about astronomy on the net and I HAVE to point at two fantastic things – a great Youtube video and a beautiful free Android app.


XIVb. Great timelapse of a night sky.

I enjoy timelapses of the night sky and this Youtube video is by far the best I have ever seen! It's best to watch it at full-screen!


What’s especially good:
1. There are numerous timelapses from the same place and almost from the same time (all were recorded in a span of 10 days), but aiming at different parts of the (same) night-sky.
2. It’s the southern sky, which is mostly alien for a person from the central Europe like me.
3. All the timelapses are at least very good and some of them are simply fantastic.
4. Some night-sky objects are named and there are also some other comments.
5. The timelapses are not too fast, but not too slow – simply perfect.
6. The music is beautiful on its own and fits the timelapses perfectly.
7. You can see that night-sky objects move in a very curious way, especially when you look in a relatively narrow field of view – “from right to left” when looking in one direction and “from left to right” when looking in another direction. The catch is that the night-sky objects always set (hide behind the horizon) going in the same direction – “from right to left” on the southern hemisphere and “from left to right” on the northern hemisphere.

XIVc. Beautiful free Android app with cool travel through space, even to other stars.

Solar System Scope is a free Android app with cool travel through space, even to other stars! It's not perfect – for example the positions of some Messier objects seem to be incorrect, but I don't care about it because there is no “visit” option to travel to them anyway.

It's very hard to describe this beautiful app with words, so I made a video focusing on the travel aspect:


It's 14 minutes long, so it's easy to miss some things if you randomly jump through the movie, so I made some screenshots (you still have to watch the video to see the actual travel):










XV. Examples of how to find night-sky objects.

In most of the pictures below I used the site stellarium.org to simulated the night-sky seen with the naked eye in big light pollution by setting the time to an early hour, so most of the stars are NOT visible.

1. Orion's Sword with the Orion Nebula (M42) in the middle.

It's a little below the Orion's Belt. To be honest I didn't notice the Orion Nebula in a small telescope the first time I looked at it, probably because my expectations were too big after I had seen some pictures of the nebula on the net. The nebula can be seen even in binoculars, but only as a little glow (that actually looks cool).

1b. Trapezium.

The Trapezium is a tight open star cluster in the heart of the Orion Nebula. In a small telescope you can see it's main 4 stars even at the magnification 50x, but this asterism (a pattern of stars on the night sky) is very small then. At the magnification 70x or 90x it's much easier to see.


2. Pleiades (M45).

The easiest way to locate them is to find the bright star Aldebaran to the right and a little above of the line of the Orion's Belt and then look 50% farther to the right, roughly in the same direction, but a little lower. The Pleiades are quite spectacular even in binoculars.

3. Hyades (Aldebaran region).

Hyades are right next to the star Aldebaran. Not as spectacular as the Pleiades, but in bigger magnification you can see many more stars.

4. Lambda-Lambda asterism.

The name of this asterism comes from the fact that its shape resembles the letter lambda, and its central star is Lambda Orionis (Meissa) – the “head” of the Orion constellation.
By the way, this asterism is a great way to verify what is the current range of your observing tool. When you buy a telescope you are given its theoretical range, but in the middle of a city with big light pollution you will never see such weak stars. Thanks to this asterism (or rather its main part) you can judge the current range yourself. It works also for binoculars that are NOT given theoretical range at all.

When I was playing around on the site stellarium-web.org I noticed that when very few stars are visible this asterism looks like a mirrored letter L. What's more important the brightest stars appear almost one by one, which is very important to my idea. Here's the crucial part of the asterism seen with a very deep range.
I noted the magnitudes of most the stars in the crucial part of the asterism AND I numbered the 11 brightest ones.
In my 70/700 refractor with the magnification 28x I could see clearly more than 11 stars, so the then range of my telescope was definitely over 9.


5. Andromeda Galaxy (M31) – my first “faint fuzzy”.

In this post:
Binoculars and spotting scopes brightness comparison
I described how to find the Andromeda Galaxy in detail, but you need a big part of the night sky to do it that way. Please notice that I made that post in a totally different time of year, so now this part of the night-sky looks almost upside-down, like this:
Instead, you can visit the site stellarium-web.org and search for the constellation Cassiopeia and find the crucial triangle of stars right away. Then you have to extend the “bottom” line of this triangle to the “right” by a little more than 100% and a little “below” this line there is the Andromeda Galaxy. Please remember that the concepts “bottom”, “right” and “below” change CONSTANTLY, so you have to be careful. In this case the “bottom” can be defined as the side of the triangle with 4 stars.

6. Alpha Persei Cluster (Mirphak region).

The star Mirphak is bright enough to be visible to the naked eye. The first time I have ever looked in that direction in my small telescope the observing conditions were very weak, but the view was interesting anyway.

7. NGC 869 (h Persei) and NGC884 (chi Persei).

Outside a city, under relatively dark skies and through binoculars the Double Cluster looks very good, but it's very small. From my balcony I can't see it with binoculars at all.


8. M34.

From my balcony I can't see this open star cluster with binoculars at all. To me M34 looks like a flying bird with a long neck.



9. M35.

From my balcony I can't see this open star cluster with binoculars at all. M35 is high “above” the constellation of Orion. Seeing M35 gave me a true WOW effect. Even in my wildest dreams I would never imagine that an open star cluster can look so good from my balcony. The best descriptions that comes to my mind is “rich in stars”.

10. Praesepe (M44).

There is a very easy way to find Praesepe. First of all you should go to the site stellarium-web.org and search for the constellation Gemini (Twins). In big light pollution you won’t be able to see most of its stars, but when you know in what direction to look then you can find the 2 crucial stars – the heads of the twins.



Imagine a line between these two stars and extend this line by around 300% to the left and a little above this line there is Praesepe.


This open star cluster is quite interesting, but the stars are not as bright as in the Pleiades. I found Praesepe with my 12x60 binoculars (magnification x12 and FOV of 5.3 degree), but the view was shaky. This open star cluster is even better to verify what is the current range of your observing tool than the Lambda-Lambda asterism.


11. Coma Berenices Star Cluster (Melotte 111).

This star cluster is rarely mentioned on the Internet, but in the binoculars it's SPECTACULAR! When I saw it in my 12x60 binoculars for the first time I was stunned! I was not prepared for what I saw – it was totally a WOW effect!

Go to the site stellarium-web.org and search for the constellation Leo. In big light pollution you won’t be able to see most of its stars, but when you know in what direction to look then you should be able to find the 4 crucial stars.



Imagine a line between the two top stars and extend this line by around 130% to the left and a little above this line there is the Coma Berenices Star Cluster.


Please notice that the star Gamma Comae Berenices (“15 Comae Berenices”), which is a part of the star constellation Coma Berenices, is on the edge of the Coma Berenices Star Cluster. The best part of this cluster is a little BELOW this star!


In my 12x60 binoculars I could see the whole area above, but in a telescope the FOV is smaller, so you won't be able to see everything at once.


12. Coathanger asterism (Collinder 399)

This asterism really looks like a coathanger! It's relatively easy to find even from my balcony. Go to the site stellarium-web.org and search for the stars Vega and Altair. These stars are one of the brightest stars in the sky, so they are easily visible even from my balcony. The Coathanger asterism is between them, closer to the star Altair, as shown below. There is also a third relatively bright star (marked with yellow circle) that can be helpful, if you can see it.


The third star (marked with yellow circle) is called Albireo and it's actually a double star with a striking colour contrast between the brighter yellow star and its fainter blue companion. Unfortunately I haven't looked at it yet myself.


13. Hercules Globular Cluster (M13) – another “faint fuzzy”.

The M13 is the first night sky object that I found after simulating light pollution for a particular hour of observations thanks to the free program Stellarium. Previously, when I was using the website stellarium-web.org, I was simulating light pollution by setting the time to an early hour, but the star constellations were tilted then.

To find the M13 you have to start with the stars Vega and Altair.

The yellow circle marks a crucial star that is “the point of an arrow”. The arrow is very easy to locate in 8x42 binoculars because the field of view is “almost big enough” then. A little below to the left there is the M13.

14. Bright stars.

Even if there is a time of year when you can't see “anything interesting” from you balcony, you can simply look at bright stars. Some of them look literally like diamonds in the sky and some other show some strong colors (blue, yellow, orange or almost red). They all look cool in a small telescope.


15. Scan the night-sky in a totally random way.

You can scan the night-sky in a totally random way and still have fun! Well, there are so many interesting night sky objects, including relatively bright stars that I hardly ever do it, but sometimes when I try to locate a specific target I find a cool small unnamed asterism by sheer accident and I say to myself: “Wow, it looks cool!”