In some cases, astronomers can't travel to the observatory at all. Of course, astronomers using the Hubble Space Telescope and other orbiting spacecraft to make observations must rely completely on remote control from the ground. (Only astronauts occasionally visit the HST to make repairs or install new equipment. Astronomers are wisely not allowed near it.) In such cases, specially trained engineers and technicians translate each astronomer's desire to look at specific celestial objects with specific equipment into computer commands that are radioed up to the spacecraft. The astronomers can be present at the ground station at the time their observations are being made (as long as they promise not to touch anything) or just stay home and receive their data in the mail or via computer link for later analysis.
There are certain basic instruments in the astronomer's "tool kit." One of the most common is a camera. Photography was first introduced into astronomy in the mid-1800s. The development was exciting because, for the first time, it allowed astronomers to objectively record what their telescopes were pointed at rather than relying on subjective sketches done by hand, which could vary significantly from one astronomer to another. For many years, the main limitation of film's use in astronomy was its relative insensitivity to light, especially given the faintness of most astronomical objects. As time went by, film increased in sensitivity and a variety of techniques were developed by astronomers to help it along, from baking the film in an oven before its use to chilling it down. While some astronomical images exist in color, most images taken for the purposes of doing astronomical research are recorded in black and white.
In recent years, an electronic alternative to film has swept astronomy. It is known as the CCD, or charge-coupled device, and you can find one in your home camcorder. The device consists of a square or rectangular array of tens of thousands to millions of very tiny electronic light-sensitive cells known as pixels that build up an electronic charge when exposed to light. By electronically reading the charge on each pixel, a computer can reconstruct the pattern of light and dark (the image) that fell on the CCD to make a picture that can then be displayed on a monitor or printed out as a hard copy. The advantage of the CCD over photographic film is that CCDs are typically much more sensitive to light and, whereas film can only be used once, the same CCD can be used over and over again. In addition, once the CCD's image is stored in a computer it can be electronically manipulated, just like any other digital image, to change its contrast, bring out hidden detail, and so forth. CCDs and other clever technical advances now allow today's astronomers to wring hundreds of times more data out of every hour of telescope time than their predecessors could only a few decades ago.
CCDs are typically used to take images onboard spacecraft. If a conventional photograph is taken in an observatory, it can be easily developed in a convenient darkroom. But when it comes to spacecraft, its not as easy to run up and change the film. So modern spacecraft use CCDs and similar cameras to take images electronically. The images are stored onboard the spacecraft in a computer or on magnetic tape in the form of a series of numbers that are then transmitted back to Earth via radio and reconstructed back into an image by a computer on the ground.