Choosing and Using a Telescope
Year of Astronomy Coin
Choosing a Telescope
What telescope you choose depends on what it will be used for, and what you expect to get out of it. There are many types of telescopes, and the choice of what is best may change over time as you become more or less involved in astronomy. Amateurs often start with a curiosity, which can be served by a telescope that is not suitable to a professional astronomer. Yet, they can provide some entertaining evenings.
Different telescopes have different purposes.
Intro Image: Perth Mint
2010 Was The International Year of Astronomy
The image used for this lens depicts the Perth Mint's coin for the International Year of Astronomy. The telescope represents Galileo's telescope.
The first telescopes were undoubtedly refractor telescopes. In a refractor telescope, converging lenses are used to magnify distant objects. They work much like long magnifying glasses. Light from distant stars and galaxies is gathered and magnified using converging lenses. The observer looks through a lens at the light, and sees distant objects magnified.
Refractor telescopes often have aberration problems. Colors bend as slightly different angles when entering and leaving a lens. This causes a minor separation of colors, which often results in colors showing at the edges of objects. This can be corrected with additional lenses, but every time light goes into a lens, and more so when it exits a lens, light is lost due to a reflection. Additionally, light reflecting twice in a lens will exit in the wrong place, so there will still be a minor problem.
The lens at the front of the telescope reverses the image, so up is down and right is left. Again, an additional lens can correct this, but will cause the same problems as mentioned above.
Reflector telescopes are able to gather to light, and focus the light on a mirror.. The mirrors are curved, and cause no aberrations. The problem is the mirrors must be exactly placed. Mirrors do not add to the aberrations if curved properly, and can even provide a truer image. Magnifying power is greater for a reflector telescope than for a same size lens refractor telescope. This makes smaller and more easily handled reflectors abke to magnify as much as a much larger refractor.
Astronomy for Dummies
These are relatively short telescopes that can gather light from a wider field. They are made as combinations of refractor and reflector telescopes. They give a wider field of view, which can be significant to amateur astronomers.
Eyepieces can either be mounted directly in line or at right angles with the telescope. At right angles it would probably have a prism reflecting the light, since less light would be lost.
The Earth is rotating. As it rotates, objects in the sky appear to move. If you wish to keep the object in the field of view for any amount of time, use a tracking motor. It you really need the object to appear to be stationary, as you would for photography, use a tracking motor. Light from stars is so faint, especially if the light is magnified, that time exposure is required for good photography.
Where Should You Go with Your Telescope?
First, get away from all street lights. Stray light from street lights can be scattered so as to make the background too bright. You need to be in the dark.
To avoid strange things like twinkling of stars, get above as much of the atmosphere as possible. Did you ever see wavy images when you look through a heated air column, like air rising from a chimney. The atmosphere has the same effect. Imagine how much air you are looking through from the surface of the Earth. Reduce it for better results. Many of the large research telescopes are located on mountains.