Ever since the first humans looked up at the night sky they’ve wondered what the heavens are made of. It would be a long time before the technology to investigate the heavens was available. When the first telescope was created is a matter some debate. Some scientists believe it was over 3,000 years ago, while others claim that it wasn't until the late 16th or early 17th century. However, there is no argument that the telescope has played a vital role in the human quest for knowledge about the stars and the universe.
Looking up to the night sky is something that we have all done at one point, or another during our lifetime. In doing this, we are using our eyes as tools to detect and separate light into its many different wavelengths, or colors. In fact, this is the way we see all things, not just at night. Despite the sophistication of our built in tools, we are still unable to detect with the naked eye, so much of the electromagnetic spectrum. To do this job, scientists use some of the most sophisticated telescopes. These tools function in much of the same way as our eyes, by separating light into different wavelengths of the electromagnetic spectrum. Electromagnetic radiation in this range of the spectrum is called visible light or simply light. Human eyes can only detect what is know as the visible, or optical spectrum where white light is comprised of different wavelengths.
Just like our eyes, telescopes let us observe distant stellar objects by detecting various wavelengths of the electromagnetic spectrum, such as infrared, ultraviolet, radio, gamma rays, x-rays, or the visual spectrum, the wavelengths that human eyes have evolved to see, commonly known as light. There are three categories of optical telescopes that are used to magnify light. Refracting telescopes use lenses to focus and bend light into an eyepiece lens. Reflecting telescopes use mirrors to focus and bend light to an eyepiece. Catadioptric telescopes use both mirrors and lenses to bend and focus the light. Despite engineering differences, all three types work on the same principle. Parallel light rays from very distant stars enter the telescope and are brought into a focus at a focal point, where they are observed through an eyepiece, or, more commonly, sent to an instrument with a detector. Modern research telescopes commonly use CCD detectors similar to those in digital cameras but cooled with liquid nitrogen to reduce electronic noise in low-intensity exposures.