Chapter 2: Multi-Wavelength Telescopes
All telescopes perform basically the same function. They gather as much light as possible from a faint astronomical object, and focus the light onto a detector. Historically, the gathering of light was done by a lens or concave mirror, and the detector was a photographic plate, or simply the astronomer's eye. to study the invisible universe, the mirrors and the detectors in a particular telescope need to be highly specialized to detect the part of the electromagnetic spectrum they are designed to study. Four such telescopes follow.
Figure 2 shows the Hubble Space Telescope. Hubble is designed to detect visible light, but its electronic detectors are also sensitive to infrared and ultraviolet. Hubble orbits the Earth 575 kilometers (360 miles) above the ground, putting it above our turbulent, hazy atmosphere that would blur and distort incoming starlight. It has a cylindrical body as big as a school bus. Follow the ray of starlight (an intermittent line) as it enters the telescope from the left (at ten o'clock and moves towards four o'clock). The ray reflects off a large primary mirror to a second smaller mirror, then back through a hole in the primary mirror and into the detector (a grid texture). The detector stores the image, which is then transmitted back to Earth.
Figure 3 shows the Spitzer Space telescope. Spitzer is in orbit above the Earth's atmosphere because the atmosphere blocks the infrared light that Spitzer is trying to detect. Follow the ray of infrared light entering the Spitzer Space Telescope at 11 o'clock, moving towards five o'clock. Like Hubble, there is a larger primary mirror, which reflects the light to a secondary mirror and then down through a hole in the primary and into a detector. Because all but images at different times and at different wavelengths. A vertical dotted line separates two images on the same page. Special texture codes are located below the images.