How do astronomers use telescopes to take pictures of stars and planets? Can this be done at home on a smaller scale?
Most astrophotography is done using CCD cameras.
The only information that we are able to gather about the universe outside of our solar system comes to us in the form of light. Astrophotography, therefore, needs to provide a significant amount of information about the light that is gathered to create images. The majority of astrophotography uses CCD (charge couple device) cameras.
A CCD camera consists of a grid of photon receptors which count how many photons go into creating each pixel in an image. This counting process relies on the photoelectric effect, where each photon knocks an electron into a corresponding receptor. Knowing how much light has been received is handy for calculating things like luminosity.
CCD cameras are especially useful for imaging dim objects, and limitations on the hardware actually make it difficult to take pictures of things that are too bright. Astronomers typically use other forms of digital cameras for imaging the moon, sun, or even nearby planets.
Regardless of which device is used, the camera is typically mounted in place of the eyepiece on the telescope, effectively using the telescope as a large zoom lens. There are lots of CCD cameras on the market that can be attached to personal telescopes, as well as adapters for attaching other types of cameras to telescopes. Astrophotography is a common hobby for amateur astronomers.