[This is long, so I'll break it into two parts - part 1 will focus on the basic characteristics of telescopes in general, while part 2 will look at specific telescope designs and reasons why you might choose one over the other.]
So we enjoyed a few days of spring weather before winter returned with a vengeance, so now, short of pulling your skis back out of storage, there's not much to do but browse astronomy magazines pondering which telescope would look best next to your patio furniture. If you are indeed browsing telescopes in an astronomy magazine you're already well ahead of someone exploring the telescope aisle at "Buy'n'large" (if you don't know what I'm talking about, watch the movie Wall-E). The fact is, you should never, ever, buy a telescope from a department store. In a large city, you might be able to find a store (typically a camera store) that carries and is knowledgeable about quality telescope equipment, but otherwise, the internet is your best bet.
Let's consider what you should look for in a telescope. First, some telescope basics. In astronomy, there are two primary reasons to use a telescope:
1. Collect more light: A telescope is essentially a "light bucket". Most astronomical objects are fainter than the eye can see, so a telescope is used to collect more light and thereby allow us to see them. Just as when you want to collect more water, you need a bigger bucket, when you want to collect more light you need a bigger telescope. Telescope size is defined as the diameter of the largest mirror or lens (called the "primary" mirror or lens) in the telescope. In the same sense as animals that need to see in dark conditions (such as squid or owls) have giant eyes, telescopes with giant lenses or mirrors will allow you to see much fainter astronomical objects like nebulas and galaxies. Trust me, these are the things you want to see.
2. Resolve fine details: When you look at those amazing photos taken by the Hubble Space Telescope, one of the most awe inspiring characteristics (aside from the colors, and we'll talk about that in a bit) is the fine detail in the images. Being able to resolve fine detail allows you to pick out individual stars in a globular cluster, see small craters on the moon, and distinguish wisps of gas in a nebula. Having a telescope with good resolution is the difference between the cell phone camera you have today, and the one you had 10 years ago. The resolution of a telescope, like light-collecting power, depends on the size of the telescope, and again, bigger is better.
There are several misconceptions about telescopes, and these are often played up by department store telescopes in an attempt to attract the unwary customer. The first and most abused is magnification. Many people believe telescopes behave similarly to microscopes, in that they magnify images. There are two key differences between a telescope and a microscope - objects observed in a microscope are well illuminated, while telescope targets are faint, and objects observed in a microscope are very, very small, while telescope targets generally are not. As a matter of fact, most of the objects we would want to observe in a telescope appear relatively large in the night sky. A classic example is the Andromeda galaxy which is as large as the full moon in the sky, but hard to see because it's so faint. In contrast, the smallest objects in the night sky are stars, and they're not hard to see at all! The problem with magnification is that bigger is not always better, in fact, too much magnification can actually make an image much worse especially if you are viewing with a very small telescope - blowing up a faint, fuzzy image does not make it better! The other thing department store telescope ads fail to mention, is that you can change the magnification of a telescope by changing the eyepiece - an accessory that can be purchased after you've found the perfect telescope for you.
The second misconception is that when you look through a telescope you'll see colorful images just like the Hubble pictures. In general this will not be the case. Our eyes have two types of light detectors in them - cones, which detect color, and rods, which are sensitive to faint light. When viewing faint things, like objects in a telescope, only the rods are activated, allowing us to see the objects, but not their colors. This is also why you don't see colors in a dark room. In order to see color in astronomical objects, they must either be bright (like Jupiter or the double star Albireo) or you must take a long picture of them. Photographs pick up color because long exposures allow them to collect more light. And remember, the Hubble pictures are photographs too - often with much processing to enhance colors.
At this point you should have the idea that you want to buy the biggest telescope you can afford. This is mostly true, but you also want to make sure you get a good telescope and that you get the right telescope for you. We'll focus on the second point in part two, but I will include a list of reputable telescope brands below (note that this is not an all-inclusive list and I apologize if I leave out your favorite brand).
Generally reliable telescope brands (in no particular order, but the top 3 cater more to first-time buyers):
Meade
Celestron
Orion
Losmandy
Levenhuk
Astro-physics
Takahashi
So we enjoyed a few days of spring weather before winter returned with a vengeance, so now, short of pulling your skis back out of storage, there's not much to do but browse astronomy magazines pondering which telescope would look best next to your patio furniture. If you are indeed browsing telescopes in an astronomy magazine you're already well ahead of someone exploring the telescope aisle at "Buy'n'large" (if you don't know what I'm talking about, watch the movie Wall-E). The fact is, you should never, ever, buy a telescope from a department store. In a large city, you might be able to find a store (typically a camera store) that carries and is knowledgeable about quality telescope equipment, but otherwise, the internet is your best bet.
Let's consider what you should look for in a telescope. First, some telescope basics. In astronomy, there are two primary reasons to use a telescope:
1. Collect more light: A telescope is essentially a "light bucket". Most astronomical objects are fainter than the eye can see, so a telescope is used to collect more light and thereby allow us to see them. Just as when you want to collect more water, you need a bigger bucket, when you want to collect more light you need a bigger telescope. Telescope size is defined as the diameter of the largest mirror or lens (called the "primary" mirror or lens) in the telescope. In the same sense as animals that need to see in dark conditions (such as squid or owls) have giant eyes, telescopes with giant lenses or mirrors will allow you to see much fainter astronomical objects like nebulas and galaxies. Trust me, these are the things you want to see.
 |
| Andromeda galaxy viewed through a smaller telescope (a), and a bigger telescope (b). The view through the bigger telescope allows the faint spiral arms to be seen. |
2. Resolve fine details: When you look at those amazing photos taken by the Hubble Space Telescope, one of the most awe inspiring characteristics (aside from the colors, and we'll talk about that in a bit) is the fine detail in the images. Being able to resolve fine detail allows you to pick out individual stars in a globular cluster, see small craters on the moon, and distinguish wisps of gas in a nebula. Having a telescope with good resolution is the difference between the cell phone camera you have today, and the one you had 10 years ago. The resolution of a telescope, like light-collecting power, depends on the size of the telescope, and again, bigger is better.
 |
| Andromeda galaxy viewed with increasing resolution (a - d). The view through a larger telescope (d) allows finer detail to be resolved. |
There are several misconceptions about telescopes, and these are often played up by department store telescopes in an attempt to attract the unwary customer. The first and most abused is magnification. Many people believe telescopes behave similarly to microscopes, in that they magnify images. There are two key differences between a telescope and a microscope - objects observed in a microscope are well illuminated, while telescope targets are faint, and objects observed in a microscope are very, very small, while telescope targets generally are not. As a matter of fact, most of the objects we would want to observe in a telescope appear relatively large in the night sky. A classic example is the Andromeda galaxy which is as large as the full moon in the sky, but hard to see because it's so faint. In contrast, the smallest objects in the night sky are stars, and they're not hard to see at all! The problem with magnification is that bigger is not always better, in fact, too much magnification can actually make an image much worse especially if you are viewing with a very small telescope - blowing up a faint, fuzzy image does not make it better! The other thing department store telescope ads fail to mention, is that you can change the magnification of a telescope by changing the eyepiece - an accessory that can be purchased after you've found the perfect telescope for you.
 |
| A little magnification is good, but too much magnification may make your image worse. |
At this point you should have the idea that you want to buy the biggest telescope you can afford. This is mostly true, but you also want to make sure you get a good telescope and that you get the right telescope for you. We'll focus on the second point in part two, but I will include a list of reputable telescope brands below (note that this is not an all-inclusive list and I apologize if I leave out your favorite brand).
Generally reliable telescope brands (in no particular order, but the top 3 cater more to first-time buyers):
Meade
Celestron
Orion
Losmandy
Levenhuk
Astro-physics
Takahashi
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