Almost everything that we know about the Universe comes from studying the light that is emitted or reflected by objects in space. Apart from a few exceptions, such as the collection of moon rocks, astronomers must rely on collecting and analyzing the faint light from distant objects in order to study the cosmos. This fact is even more remarkable when you consider the vastness of space. Light may travel for billions of years before reaching our telescopes. Astronomy is primarily a science where we cannot retrieve samples, study objects in a laboratory, or physically enter an environment for detailed study.
Fortunately, light carries a lot of information. By detecting and analyzing the light emitted by an object in space astronomers can learn about its distance, motion, temperature, density and chemical composition. Since the light from an object takes time to reach us, it also brings us information about the evolution and history of the Universe. When we receive light from an object in space, we are actually performing a type of archeology by studying the object's appearance as it was when the light was emitted. For example, when astronomers study a galaxy that is 200 million light-years away, they are examining that galaxy as it looked 200 million years ago. To see what it looks like today, we would have to wait another 200 million years.
It is natural to think of light as visible light - the light we see with our eyes. However, this is only one type of light. The entire range of light, which includes the rainbow of colors we normally see, is called the electromagnetic spectrum. The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. The only difference between these different types of radiation is their characteristic wavelength or frequency. Wavelength increases and frequency decreases from gamma rays to radio waves. All of these forms of radiation travel at the speed of light, which is about 186,000 miles per second (or 300 million meters per second).
Each type of radiation (or light) brings us unique information. To get a complete picture of the Universe we need to see it in all of its light, using each part of the electromagnetic spectrum! Technological developments over the past seventy years have led to electronic detectors capable of seeing light that is invisible to human eyes. In addition, we can now place telescopes on satellites and on high-flying airplanes and balloons which operate above the obscuring effects of Earth's atmosphere. This combination has led to a revolution in our understanding of the Universe, and to the discovery of yet more new mysteries.
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