Date: April 16, 2012
Title: Encore : Introduction to Practical Astronomy
Podcasters: Justin Clayden
Organization: The Skeptheist- http://www.skeptheist.com
This podcast originally aired on April 10, 2010
http://365daysofastronomy.org/2010/04/10/april-10th-introduction-to-practical-astronomy/
Description: If you’re just getting into Astronomy, you may be slightly bewildered by the choice of instrumentation- you know, telescopes and stuff. This episode of 365 Days of Astronomy is designed to give you a framework; a nice overview of the important things to consider when purchasing sensory augmentation- you know, telescopes and stuff.
Bio: Justin is a software engineer from New South Wales, Australia. He earned a Masters of Philosophy from the University of Sydney; his thesis was “A Framework for Representing Virtual Worlds”. This might explain why this episode has a framework. Justin enjoys astronomy in his backyard, recreational computer programming and microelectronics, and doing his best to make science more approachable, popular and fun. Animation and music are another two of his favourite ways of trying to achieve this goal. He also runs a skeptical podcast called “The Skeptheist”.
Sponsor: This episode of “365 days of Astronomy” is sponsored by — NO ONE. Please consider sponsoring a day or two in 2012 so we can continue to bring you daily “infotainment”
Transcript:
Welcome to this April 10th edition of the ‘365 Days of Astronomy’ podcast. My name‘s Justy, and I produce ‘The Skeptheist’; a tube-cast available at www.skeptheist.com.
I’m an amateur astronomer and I got my start when I made a simple reflecting telescope from a shaving mirror. These days I have a Celestron 4in. refracting telescope on an equatorial mount.
If you’re just getting Astronomy now yourself, I hope this talk will be of some use to you in helping you go through a thought process that will assist you in choosing the best instrumentation. I’ll talk about what you can see in the sky, what will affect the quality of your viewing experience, what instrumentation you can use to see it, and a little bit on budgetary considerations.
In order to make up your mind about what you want to see in the sky, you first have to know what you can see in the sky; so I’ve broken this into three categories- things that orbit the Earth, things that orbit the Sun, and.. everything else.
Let’s dive right in to things that orbit the Earth. The most obvious of course is our Moon. It’s best seen when it’s in its crescent phase, when its highly cratered surface is in good, sharp relief. Then there are artificial satellites.. and of course, space stations. Personally I subscribe to the Twitter feed for the International Space Station, and this tells me where it will be at night so I can go out with my telescope and track it.
Now let’s talk about things that orbit the Sun. The other planets in the solar system make fine viewing, as do their moons. Asteroids, or small planetary bodies are other objects that orbit the Sun, and they can be tracked with telescopes. Comets are also an interesting type of object that orbit the Sun. They have a distinctive tail that is the result of the Sun’s radiation blowing off their icy structure. The tails of Comets always point away from the Sun.
Now we come to ‘everything else’. At night time there are hundreds to thousands of stars visible with the naked eye. Our own Sun of course is an example of a Star, but it should go without saying that it should never be observed with the naked eye. There are filters that you can obtain that cut out 99.999% or more of the Sun’s rays. These should always be used when observing the Sun.
We can look up in the sky, and with the right sort of instrumentation, see galaxies, which are collections of billions and billions of stars that lie far, far away. Another interesting thing to observe in the sky are nebulae. A nebula is a large body of gas. Nebulae are often referred to as ‘stellar nurseries’, because it is believed that new stars are formed within their gaseous confines.
When a star explodes, it’s called a ‘nova’. An extremely energetic version of this is known as a ‘supernova’. When a star goes supernova it might briefly outshine an entire galaxy, only to fade away over the subsequent weeks and months.
So once you’ve learned what you can see in the sky, you can make a good decision about what you want to see in the sky. Determining what you want to see in the sky is a good first step in determining the instrumentation you want to buy.
Now let’s talk about things you can use to see. The first of course, are your own eyeballs. Whether you’re going to gaze up at the sky with just your eyes or through a telescope, you’ll want to get your eyes ‘dark adapted’. This means taking the time away from bright light sources to let your pupils dilate. One wonderful advantage of eyeballs of course is their portability, but it wouldn’t be fair to give a talk about astronomy without mentioning the fact that it’s possible for sight challenged people to use braille to see the sky. One great example of this is a book by Norene Grice called ‘Touch the Invisible Sky’.
From eyeballs and fingertips, we move into augmented instrumentation. Yes, I’m talking about binoculars and telescopes.
So binoculars are a great, portable, cheap and stereoscopic means of looking at the sky. I first saw the moons of Jupiter and the rings of Saturn with a pair of binoculars. When you use a pair of binoculars, you’re feeding your brain two images. The visual processing aspect of your brain is very good indeed at making the most of these two feeds of information. In this case, the whole really is greater than the sum of its parts. Another advantage of binoculars is that they’re highly portable.
Now we move to telescopes, and the things that we put them on, also known as mounts. There are two types of telescopes that I’ll discuss today. The first is the ‘refractor’. This was the first type of telescope that was invented. Galileo used a telescope such as this. The basic design is a primary objective lens, and its eyepiece. The light takes one path through the objective, and makes its way through the eyepiece to your eye. A refractor uses a convex lens to magnify the image.
In a reflecting telescope, not surprisingly the light is reflected by a magnifying mirror onto another mirror, and then out into an eyepiece. This basic design is referred to as a ‘Newtonian Reflector’. A ‘Schmidt-Cassegrain’ telescope has the advantage of being shorter than a regular Newtonian Reflector.
Some important factors to consider when evaluating telescopes are: The diameter of the objective component, the weight of the instrument, and the length of the instrument.
Consider a moment what’s required to make the objective components of both of these telescopes. The difference here relates to volume versus area. As the diameter of the objective lens of a refracting telescope increases, so too does the volume of that lens.
Contrast this with a reflecting telescope where the area increases as the diameter of the objective increases. What this means straight away is that more ‘stuff’ is required to make a refracting telescope’s objective component. This is the reason that the largest telescopes in the world are reflectors. One disadvantage of reflecting telescopes however, especially in the Schmidt-Cassegrain design, is that the light must travel back through the objective mirror, thus reducing the overall light gathering ability (for comparable diameters of objective lenses). However, because reflecting telescope objective mirrors may be made much larger than lenses, this limitation is generally overcome.
Let’s talk now about mounts. Binoculars are fine to hold in your hands, but telescopes certainly aren’t. A telescope needs to be placed on a stable, reliable, bump-free mount. There are two major kinds of telescopic mount that I’ll discuss today. Both kinds of mount rely on two controls to determine where the telescope will point in the sky.
The first kind of mount I’ll discuss is known as an ‘equatorial mount’. When correctly configured, an equatorial mount only needs to have one control changed to correctly compensate for the Earth’s rotation. This is very useful in astrophotography, where the idea is to leave the shutter of your camera open for as long as possible to gather as much light onto the image as you can. Needless to say, if the telescope deviates from its target even just a bit, the image that you capture will be blurry and not of a high quality.
The other kind of mount to discuss is the ‘alt/azimuth mount’. Its primary disadvantage is that it can’t compensate for the Earth’s rotation in the way that the equatorial mount can. But its advantage is that it can be built very simply, and support large telescopes. You’ll commonly find alt/azimuth mounts in computer controlled ‘scopes as well. A computer controlled ‘scope is cool, because you can simply say “I want to look at object X”, and if it’s in the database, it’ll track where it is, and center it for you.
In the best possible situation, a telescopic mount will be fixed to a highly stable surface, such as concrete or steel. Obviously this has a large bearing on the portability of the instrument.
So now you’ve decided what you want to look at, you’ve decided what kind of instrument you’re going to use. Now let’s look at what affects the quality of your viewing experience.
The first of course is weather. Many an astronomical occasion has been ruined by clouds rolling in. Another factor is light pollution. Light pollution occurs generally near town and city centers, where a lot of artificial light will tend to wash out the sky, and reduce the number of objects you can see. Related to this is atmospheric pollution. One thing to think about is if you look up into the sky, you have approximately one kilometer of atmosphere between space and your eyeball. If you look out towards the horizon, on the other hand, you have a great deal more atmosphere between space and your eyeball.
One thing to mention here is that if you’re interested in planetary astronomy, planets tend to lie in the plane of the ecliptic, which generally speaking lies near the horizon. One way we get away from light and atmospheric pollution, is to go far away from these town centers, and this of course raises the issue of portability. One tradeoff you can imagine is having a highly expensive well mounted telescope near a city center, versus taking a cheap pair of binoculars out camping with you where such pollution levels are much lower.
Now let’s get to budgetary considerations. One thing I’ll mention here is that if your budget is limited, you might even consider not spending any money on instrumentation but rather make use of the high quality observatories in your area. One good piece of advice I received is until you can afford to buy a decent quality ‘scope, resist the temptation to buy a cheap one. The level of quality will frustrate you, ultimately. It’s better just to save that money until you can afford a decent one.
It’s hard to give you a hard and fast idea of what constitutes a high quality telescope, but needless to say, if the lenses aren’t glass.. forget it! Another aspect of these cheap telescopes is that the mounts that they have are flimsy to say the least.
Save your money, and while you’re doing that, do some research bout what kind of telescope and mount is right for you.
Other factors that affect the cost of your purchase include: computer control (which obviously adds to the cost), the quality of the mount (and generally speaking equatorial mounts are more expensive), and the quality of the optics. Larger ‘scopes tend to be less portable and more expensive. Therefore, you might consider the tradeoff between the cost of transport to get away from your light polluted area versus the portability of the instrument.
Another aspect of telescopes worth mentioning is the inclusion of a ‘finder scope’. A finder ‘scope is a low magnification telescope that sits on your telescope and helps you find the objects you’re looking for. Telescopes have a very narrow field of view, which is to be expected. This though makes it very difficult to track the object you’re interested in. So, what a finder scope lets you do, is to look through it, find the object in the finder ‘scope, and it should correspond to the object in the middle of the larger telescope.
Hopefully now you have all of these elements in place, you can make an informed decision about what sort of gear to buy. I’ll run you through two scenarios quickly as an example of this thought process.
The first was my own. Luckily, I live in a fairly un-light polluted area, and I’m interested in planetary astronomy, and astrophotography. The choice for me therefore, was a refracting telescope on an equatorial mount. Why a refractor? Simply because I was interested in the quality of the optics, and the length of the telescope really didn’t affect me all that much.
I chose an equatorial mount because I was able to compensate for the Earth’s rotation, and get some high quality astrophotography.
Let’s go through another scenario. Let’s just say you’re interested in stellar astronomy, and you live in the city. Well, the first thing you’re going to want to do is to get out of the city, so you need a telescope that’s portable. A reflecting telescope such as a Schmidt-Cassegrain is ideally portable for this purpose. The mount of choice for this situation is an alt/azimuth mount with computer control. One thing about stellar astronomy is that there are far more stars in the sky that are visible with most telescopes, than any kind of object. Therefore the cataloguing of these objects is of paramount importance. Plus, the size of the instrument makes it portable enough to get away from the major city centers to where the skies are clearer and the light pollution is less.
I hope you’ve enjoyed this short introduction to practical astronomy and the kind of thought process you’ll need to go through when choosing an instrument. My last piece of advice is to do as much research as you possibly can before buying your instrument.
This has been Justy from The Skeptheist tubecast signing off, and remember:
“Keep watching the skies!”
End of podcast:
365 Days of Astronomy
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