Telescopes were invented by accident in 1608 when Hans Lippershey, an eyeglass maker in Holland, looked at a church steeple through two lenses. The discovery, now called the science of optics, caught on immediately and, by 1610, Galileo was tracking the moons of Jupiter, giving birth to modern astronomy.
Today, sophisticated professional telescopes search the farthest reaches of the universe, but amateur astronomers can have great fun and enjoy the beauty of outer space and the Earth using very inexpensive equipment. Here is some information to help you understand the basic technologies so you can choose the telescope that will work best for you.
There are two basic types--refracting telescopes and reflecting telescopes. Both have strengths and weaknesses, but both are great if used for the right applications. Before you buy, understanding how each type works can help you get the most from your scope.
The refractor is Lippershey's original telescope model. Simply, it is two or more lenses that focus light, making objects appear closer than they are. Refractors use two types of lenses: Convex lenses (like the lens in the human eye) curve outward, making images appear larger. Unlike the eye, they also make objects unclear. Concave lenses curve inward, making images clearer, but also smaller. Refracting telescopes use a combination of convex and concave lenses to make images larger and clearer. Refractors have one basic limitation--they bend light through glass, and since different colors bend differently, there can be some distortion.
The reflector was invented by Sir Isaac Newton in 1668; it uses mirrors to collect and magnify light. One large, bowl-shaped mirror gathers light like a bucket fills with water then a second mirror reflects it into the eyepiece, much the same way curves in a pipeline change the direction of flowing water. Since reflecting telescopes don't bend light, color isn't distorted. However, the inner and outer edges of the mirror may have slightly different focal points, so pushing all the light to the same point sometimes causes 'coma,' a little halo around objects at the edge of the viewing area.
Hand-held telescopes are now called monoculars (more correct but not nearly as much fun as calling it a 'spyglass') to distinguish them from larger, tripod mounted models. Binoculars are simply two telescopes tied together--one for each eye. Because these are usually designed for hand-held use, they are generally smaller than other telescopes. Night vision scopes are monoculars or binoculars with special low-light features that allow you to see in near total darkness. Great for seeing nocturnal creatures in their natural habitat.
The big lens or mirror is called the objective lens or objective mirror, and it determines how much light is gathered. This is more important than magnification, since magnifying something a million times does no good if you can't see any details. The wider the objective, the more light enters the scope.
When buying any telescope, get the biggest package offered, meaning, the most accessories included in the price: instructional videos, a pre-assembled tripod, software, finderscopes, etc.
Since the Earth rotates under the heavens, special motors are used so the telescope moves exactly opposite the Earth's rotation, keeping the objects you're viewing stationary. Obviously, these are necessary only for night viewing. Some telescope packages include these motor mounts; they are optional with others. Decide before you buy whether you'll be day-viewing or night-viewing and buy accordingly.
This motor system is called the equatorial mount; it can be equipped with a computer control preprogrammed with the 'declination' (rise above the equator) and the 'right ascension' (the object's position relative to other stars). Once these are set, the telescope can automatically track almost any celestial object.
Many larger telescopes have a small scope piggy-backed on the side, used to 'spot' a scope to the general area you are trying to view. These useful additions are called finderscopes or spotting scopes.
Store your telescope is a cool, dry place. A well-padded case or footlocker is a great idea, especially if you have a lot of optional paraphernalia. When you take it out, let the equipment adjust to the temperature of the air before using it. Clean the dust off regularly, but carefully. Telescopes are not do-it-yourself items; service and repair shouldn't be needed often but, when it is, take it to a trained technician. You can probably find one at your local hobbies & toys store.
Modern telescopes measure in millimeters, with size listed as two numbers: 500x100, for example. The first is the focal length (distance between the objective lens or objective mirror and the eyepiece); the second is the aperture (diameter of the objective lens or objective mirror). Aperture determines how much light is gathered. To avoid a lot of unnecessary math, the easy rule is 'the bigger, the better.' This vast stream of light going into the eye has to be compressed to fit through the pupil, down to about 0.5mm in diameter, so a 100mm aperture will magnify images roughly 200 times.
For photographers, focal ratio is also important. Divide the aperture into the focal length (100mm/500mm) for a focal length of f/5, the minimum considered 'fast' enough for good photos.
There are three common types of reflectors: A Newtonian telescope has one light-gathering mirror that reflects light onto a mirror that reflects it into the eyepiece on the side of the tube. The Schmidt-Cassegrain telescope (or SCT) has mirrors at each end of the tube. The objective mirror has a small hole in the center, through which light passes to the eyepiece. These two mirrors make the telescope smaller, lighter and easier to handle. The Nasmyth telescope mixes both designs; instead of a hole in the objective mirror, it uses a third mirror to reflect the image to the eyepiece.
Which telescope is right for me?
If you're a beginner with limited resources, a Newtonian is probably the best starter model. They can be very small and give good viewing at a low price. Refractors are generally considered better for Earth-based observations (such as bird watching) while reflectors are considered better for celestial observation, since they can be built with larger objectives to gather more light. Schmidt-Cassegrain models are preferred by astro-photographers.
Can I take pictures through my telescope?
Absolutely, camera lenses are built using the same principles as a refractor, especially telephoto lenses. (You can find those in our electronics store.) Many telescopes have optional camera mounts available.
The farther you get from the light pollution of cities, the better your view of the heavens. If you really want to see nature, you need to get out into the wild places. Take a good look at our camping & outdoors equipment, pick up a few backpacks, then take the family on an expedition. Tents and sleeping bags are a must, a good set of camp cookware can make you feel at home and, if you're planning to get lost, our navigation aids can derail those plans very effectively (especially the GPS navigators in our electronics store). Also, check out our entertainment store for books and DVDs on telescopes, astronomy, nature, etc.
If you want to inspire the family before you head out, take a peek at the official NASA website . You'll find images from NASA planetary missions, spectacular photos from the Hubble Space Telescope and loads of other aids to amateur astronomers. (Might also help the kids with their science homework!)
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