A Greener View

Question: With the recent sightings of the aurora borealis in our area and the space station becoming a reality, my kids want a telescope. My husband wants a telescope to look at the eagle's nest across the lake at our summer vacation spot. Can one telescope work for both applications? What should I look for in buying one for them?

Answer: Telescopes are fun tools that can help us learn about many things on and off our planet. The choice of a telescope design is decided by the primary use and of course your budget. The first step in the decision making process is to determine what the primary use will be. What will you look at most of the time?

Some telescopes work better for daytime use and are usually called spotting scopes. They are used to magnify the appearance of things close by, while still having a wide enough field of view area around the object to follow it if it moves. Because of the way they are made, you will see the object right side up. Some of them are set to magnify at only one constant power, while others can zoom in closer. They work great for bird watchers, because some birds are out on lakes or nest in difficult places to access.

Astronomical objects like the moon, sun and planets are a little farther out, but are still relatively close by. Comets often come close as well. Things like double stars, nebulae and galaxies are much farther away and produce a much fainter light. Some spotting scopes will work okay for close and big objects like the moon, Jupiter and Saturn.

When looking at distant, faint objects you must remember that no matter what you see, it will not look like the photos in a book, since they use long time-lapse photography that lets the colors accumulate on the film. Astrophotography is a very rewarding hobby and can be relatively easy, but does take some practice. On the other hand, photography with a spotting scope is just like using a very powerful telephoto camera lens.

There are three main styles of telescope design. Each design has it's own advantages and all will work, if well made. They are all trying to do the same thing; collect enough light so that it can be magnified and focused.

The most important thing a telescope must do is gather light coming from the object. They do this with a lens or a mirror. Just like the pupil of your eye opening larger in the dark to gather more light, the larger this piece of glass is, the more light it gathers. This size of the piece of glass is called the aperture. It is the diameter of the lens or mirror as measured in millimeters. The farther away the object is, the less light you get and so the bigger the aperture of the telescope must be. The minimum aperture on spotting scopes should be around 50mm and it should be at least one hundred or more for astronomical telescopes.

The typical idea most people have of a telescope, is of a long tube with a lens at each end. This style is known as the refractor, because it bends (refracts) the light into a focus point for your eye. They are easy to use and maintain. They are good for terrestrial viewing and excellent for close astronomical viewing of the moon and planets (the sun requires special filters to protect your eyes). Refracting telescopes often have a poor reputation because of many toy quality ones on the market. They are longer, heavier and bulkier than the following two styles for the same sized aperture. Most spotting scopes are short versions of refractors to make them easier to carry around.

The next style is known as the reflector. It lets light in the front end unobstructed. It then bounces the light off the curved mirror in the back to a small slanted mirror near the front. This mirror bounces the light out a hole in the side of the telescope into the eyepiece. This style has a lower cost for the same size aperture because mirrors are easier to make than lenses. Because the light bounces through the scope twice, it can be made shorter. They are good for deep space work, but less good for looking at the moon and the planets. They have an open-ended tube and are sensitive to dust contamination.

The next style is a combination of the other two. The light is gathered by a lens at the front, bounced off a curved mirror in the back to another mirror on the back of the front lens and then out a hole in the curved mirror and into the eyepiece. It sounds complicated, but it actually combines the best of the lenses and mirrors while canceling out many of the disadvantages. Depending on the size, it can be used for terrestrial and both close and far astronomical viewing.

In both of the previous telescopes, the object in the view is usually upside down and flipped left to right, unless a special lens is added. Extra lenses reduce the amount of light you can get out of the eyepiece; so dim objects are often better viewed upside down.

In general, the longer the light path in the telescope, the more power it has, the larger the image will be and the smaller the field of view. When buying a telescope, power is not the most important thing to look for, aperture is. More power reduces the amount of light, makes atmospheric distortions worse, and makes it harder to find objects. No matter what the power is, stars are always going to be dots of light. Looking at bigger dots is not as good as looking at clearer dots that can be distinguished from the background. For the best results, fifty is the highest power that should be used for most astronomical and spotting scopes.

Telescopes may not have changed a great deal since Galileo built one 400 years ago, but we have learned a few things since then. We can use binoculars (two short telescopes) and telescopes to see the stars and we can use star maps, books and videos to learn more about them. These accessories and many others, like tripods, are necessary for a good understanding of what you are seeing.

One problem you might have is that in many areas, the reflected light from man made sources screens from view all but the brightest stars and satellites. Going out into the darker countryside helps make an amazing number of stars visible. Local astronomy clubs that often use local junior college or high school planetariums are good sources of information. One of the best books for beginners is ‘Night Watch' by Terence Dickerson. It gives detailed information on purchasing telescopes and it has many photos and easy to use charts on how when to see the planets and stars.

Telescopes are fun tools to use and can start the kids off on an enjoyable life long hobby. The least expensive good ones will cost at least three to five hundred dollars, so it is an investment that will probably not be made quickly.