Learn about astronomy from the Web and the sky itself.

Astronomy is the scientific study of the universe. Almost everything known about the the universe, beyond planet Earth, is learned by making observations of electromagnetic waves that were produced by very distant objects or have been reflected off the surface of distant objects, or absorbed by them Except for gravity, electromagnetic waves are the only phenomena that can travel over light years of distance bearing evidence of the nature outer
space.

Astronomers have developed instruments to detect electromagnetic radiation over a wide range of wavelengths and also a wide range of cameras that can form images of the heavens. Telescopes are cameras with the ability to collect
and concentrate electromagnetic radiation and to make images from it. Though we often think of telescopes as using visible light to form these images, there are very useful telescopes that are sensitive to very long wavelengths ( radio ) waves and infrared waves and telescopes that are sensitive to very short wavelengths; ultraviolet and X-rays.

From what is known about the ways that each wavelength of electromagnetic radiation can be formed, reflected, refracted ( bent ) and absorbed by various kinds of matter, a great deal can be learned about the distant universe by observing these rays. Astronomy is very tightly tied to physics and chemistry.

About Telescopes
When we think about telescopes, we usually think about an instrument with lenses and or mirrors that we can look through to see things bigger. Some telescopes are exactly that. They have been around, in one form or another, since Galileo and Newton.

Telescopes have come a long way since those days. Some have no lenses and no mirrors at all. Scientists began to realize that light waves make up only a small part of a huge range of electromagnetic radiation and that many other kinds of electromagnetic radiation find there way to Earth from the rest of the cosmos. What if, they thought, we could study those other kinds of radiation in addition to light? What if we could make images ( pictures, no less ) from the patterns of those kinds of radiation just like we have been doing with optical telescopes? And so they did.

Telescopes, on earth, in orbits around it and on spacecraft very far from earth, now provide images made from many wavelengths of elecromagnetic radiation. Here are some of them,
beginning with the shortest wavelengths:

Gamma Rays : These are very, very short wavelengths that come from some of the most energetic, violent places in the universe.

X-Rays : X-rays have wavelengths a bit longer than gamma rays. The distinction is a matter of human definition. Like all the other kinds of waves astronomers regularly observe, names have been given based on wavelength.

Ultraviolet : Ultraviolet ( UV ) waves are longer than X-rays and shorter than the waves ( light ) that we can see with our eyes. Images can be made based on ultraviolet, just as they can with visible light.

Visible light: This is a range of electromagnetic waves that our human eyes can detect. This is the only type of radiation the telescopes of Galileo and Newton were able to help us with. Many modern telescopes make images, either on film, electronic cameras and sometimes directly on the retinas of our eyes. Patterns of visible light that tell us a lot about objects, both on earth and in the rest of the cosmos.

Visible light comes in various wavelengths. Our eyes respond differently to the differing wavelengths. They see the longest ones as "Red" and the shortest ones as "Violet". The other colors our eyes detect have wavelengths between Red and Violet. It should be no surprise that the first telescopes dealt with visible light.

Telescopes do two things with visible light. They collect a whole lot of it so we can see it or make photographs of it. Consider that your eye has an opening for light ( the pupil ) only about the size of this " O ". It can only collect the light from anywhere in the universe that happens to fall inside this little circle. A telescope may have an opening many feet in diameter and it can collect all that light and concentrate it in a very small picture that is
thousands of times brighter than the light from just that little " O " sized collector we were born with. The most important thing telescopes do is concentrate very dim light into much brighter images.

The second thing telescopes do is make images of very small areas of the sky larger than the images on the retina of your eye and larger that on the film of a regular camera. Actually, telescopes ARE cameras. They are cameras with a very large lens or mirror and a very long focal length. So the images of, say Saturn and its moons is bigger and brighter than the one formed by you eye or your camera.

It turns out that there is one more important thing telescopes do for images. They make them more detailed. This is difficult to explain here, but it turns out that bigger lenses ( or mirrors ) make images with more detail in them than small ones. This is not just because they make them bigger. In fact, if you have a small lens that makes an image of a planet that is , say 1/4 of an inch in diameter, and you have a really big lens that makes an image the same size, the image from the large lens will show much more detail than the image from the small one, even though they are the same size. This is a very important reason. It is easy to make a very big image from a very small lens, but it will not be as clear as one of the same size made by a big lens.

Infrared There a large amounts of energy that comes to us from space in the form of waves longer than our eyes can detect. The actual length of the waves in both the visible and the infrared tells us a lot about the temperature of the place from which they came. The shorter the wave, the higher the temperature.

Microwaves Longer than infrared, is a range of waves called microwaves. You may be wondering just how long we are talking about. Microwaves are roughly in the range of a few millimeters to a few centimeters. These are considered to be very short radio waves. They are in the range used by our radars, our microwave ovens, and and short range communication on earth. They come in from space, too. Huge telescopes that collect microwaves from the cosmos are sometimes used to search for intelligent life, far from Earth because intelligent being there would probably be generating microwaves for their communications and other purposes.

Waves longer than microwaves, we usually call radio waves. Because it requires immense antennas or telescopes to collect enough energy from these waves to make an image and show any detail, they are not much explored as a source of information about distant objects.