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Gidday Gals, Guys & Gurus,
Welcome to the first thread on amateur astronomy. I have always been interested in the night sky but until recently did not have access to an astronomical telescope. That all changed around the time of my last birthday when my wife and I were visiting a local optical equipment supplier to obtain a couple of polarizing filters for an experiment I was trying to do with Schlieren Photography. It was actually on Melbourne Cup day and the shop was totally devoid of customers so we ended up having a fairly lengthy chat with the store owner who it turns out had spent time working in Papua New Guinea like my wife and myself. The conversation inevitably came round to the sort of telescope that was suitable for my needs and I literally fell off my seat when my wife piped up with, "Ok we'll have one of those, now what sort of accessories are needed to go with it."
They did not have any of the model in question in stock so I had to wait for a few weeks for it to arrive but I was basically thrust from having an interest to being an amateur astronomer in a couple of weeks. As a result I am learning everything from scratch so I thought it was the perfect opportunity to introduce others by passing on what I learnt.
Astronomy is fairly unique among the sciences as the work of amateurs is not only accepted by professional astronomers but actively encouraged. The night sky is a mind overwhelmingly complex and vast place that unlike the belief of ancient scholars, is highly dynamic. To have any chance of noticing something new or interesting requires an absolute army of observers and this is where the amateurs come in. By monitoring the more obscure objects the amateurs allow the professional astronomers to use their incredibly large and horrendously expensive telescopes to concentrate on what really matters. This is how things like new comets, planetoids, asteroids, supernovae etcetera are often first spotted.
At this point I would just like to note that not all amateur astronomy is limited to the optical spectrum and there is now a not insignificant contribution to the science of astronomy being made by dedicated radio astronomers. However, while this is still astronomy it is a completely different game and requires totally different equipment, skills and techniques. From time to time this blog will touch on the subject of radio astronomy but in general it will be constrained to amateur astronomy in the optical spectrum.
There is considerable debate over who invented the telescope and was the first to point it at the night sky. In 385 BC Democritus describe the milky as being composed of a vast magnitude of stars. Since you can't discriminate many of the individual stars of the Milky Way with the naked eye some therefore claim that he must have had access to a telescope and would therefore be the fist astronomer to use one. There were certainly lenses available at the time and it is technically possible but it is unlikely that we will ever know for sure if this was the case. Regardless of the debate over who was the first astronomer to use a telescope the telescope has become a critical tool for astronomers both amateur and professional. The modern problems of light and atmospheric pollution also mean that to even see the sky in as much detail as a couple of centuries ago requires the use of some sort of vision enhancing device.
There are two completely separate phenomena used in the construction of telescopes: refraction and reflection which leads to telescopes falling under three main categories.
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Refracting Telescopes: These are telescopes which use transparent lenses that refract light. This was the type of telescope used by Galileo Galilei. There are several variations on the theme of refracting telescopes but the main limiting factor is the mass of the glass involved in the lenses. This severely limits the diameter of the telescope to somewhere around 1,000 mm in diameter.
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Reflecting Telescope: This type of telescope utilizes curved mirrors that reflect the light rather than lenses which bend it. This can greatly reduce the mass of the glass required to produce an image and allows for the construction of considerably larger telescopes. Niccolò Zucchi was credited with the invention of this telescope in 1616 but was unable to produce a working telescope and gave up on the concept. Sir Isaac Newton took up where Niccolò Zucchi and eventually solved the problems in 1668 and is credited with constructing the first practical version of this telescope.
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Catadioptric Telescope: This type of telescope utilizes a combination of both reflective and refractive elements. It also combines the best features of both the refractive and reflective telescopes and has several advantages over the other designs.
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They normally employ the use of spherical components which are easier and cheaper to manufacture than parabolic or elliptic elements. The distortions that the spherical elements create do, however, limit the diameter of these telescopes to around 400 mm (16 inches).
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By virtually folding the telescope you can produce considerably longer focal lengths than can be achieved with other designs.
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They are more rugged than other designs and therefore more suitable for use by amateurs where maintenance and setting up can be a limiting constraint.
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The addition of what is referred to as a corrector plate means the telescope is sealed from the environment. This is a critical factor for amateurs as it protects the delicate mirror surfaces that are open to the elements in straight reflecting telescopes.
Before we go any further we need to look at several important parameters that govern the performance of a telescope:
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Diameter: D-xxx The pupil in your eye is actually an aperture or hole which can have its diameter controlled by the iris. There is an involuntary reflex that keeps the amount of light falling on the retina by continually adjusting the diameter of the pupil. It is, however, limited to a range of diameters between about 1.5 – 8.0 mm or 1.77 mm2 to 50 mm2. Similarly the diameter of the primary element in a telescope governs the amount of light that can be gathered and therefore allows you to see things that have an intensity which is not detectable by the naked eye. A telescope with a diameter of 100 mm will collect around 150 times the light of the naked eye while the larger telescopes used by professional astronomers collects something like 400,000 time the light.
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Focal Length: F-xxx The focal length of a telescope is important as it plays a big part in the magnification that can be achieved. Basically the magnification that is governed by the focal length of the main elements divided by the focal length of the eyepiece. For example a 1,900 mm focal length telescope with a 15 mm focal length eyepiece will give you a magnification of around 127 times. This is important when trying to view objects like the Moon, planets, asteroids and comets. The overall magnification is, however, limited to a certain extent by the diameter as the greater the magnification the more light is required and a telescope of a given diameter will have a limitation to the magnification that can be achieved.
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f-Number: f/xxx This is a combination of the focal length and diameter and gives you an overall measurement of the performance of the telescope. The smaller the value the more sensitive the telescope will be and the dimmer the detectable objects The f/# or f-number is calculated as follows.
So, what sort of telescope do I have? There are several factors that governed the selection of my telescope:
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Size: As I do not have the luxury of a dedicated structure to house my telescope the size was restricted to something that I could lift and set up on my own.
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Location: Since I live in Sydney, Australia and am less than 700 m from the Pacific Ocean the environment throws in a few constraints.
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Light Pollution: There would be no point having a really large telescope as the background light from houses, street lights, cars etcetera can easily swamp the dim light from distant stars. Being near the coast is an advantage on this front as only half the sky has lights beneath it but it does introduce other problems.
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Airborne Salt: The proximity to the ocean means that there is often a significant amount of suspended salt water in the air that can easily damage the mirrored surfaces in an open telescope. This limits me to using one of the catadioptric telescopes that are sealed and thus offer greater protection for the delicate mirrored surfaces.
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Finances: Like most people I do not have access to a bottomless pit of money so the amount of money available severely limits what can be purchased. The most important factor here is quality or value for money. You can often find larger cheaper telescopes but when you try and use them they do not offer anything like the image quality of smaller higher quality telescopes. A smaller higher quality telescope will often produce a much clearer and higher quality image so I would always suggest at going for the highest quality you can afford even if it does mean selecting a smaller less powerful telescope.
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Warranty & Repair: You can often find what would appear to be bargains on the internet but keep in mind if you ever need to have it repaired or it has problems with warranty you will more than likely be on your own and need to send the telescope back to the manufacturer. This can be an extremely costly exercise that can rapidly cost several times more than you save and leave you without a telescope for lengthy periods of time. I would therefore always recommend that you deal with an authorized local distributor that is capable of handling warranty and ordinary repairs. I had considerable problems with my first telescope, but as it was purchased from a Sydney based agent it was a simple matter of taking the telescope back to them rather than shipping it back to the USA.
This all adds up to a Makustov-Cassegrain f/15.2 F-1900 D-125 telescope on a computerized mount. It is capable of detecting objects down to about magnitude 15 and achieving a magnification of around 290 times.
In subsequent threads we will look at types and methods of mounting a telescope as well as accessories and a whole plethora of goodies that will fill up your birthday present wish list for decades to come.
As usual there is a wealth of material available on this subject and you can easily get whisked away on a tangent by the many interesting discussions and debates contained in the following links.
So, next time there is a clear calm night, turn off all the lights, sit down outside, turn your gaze skywards and start to wonder about those sparkling gems you see suspended above you.
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Re: MaSu on Meteors: Telescopes
