An astronomy chart is a chart which maps out an area of the universe. People often use this term to refer specifically to charts showing various views of the heavens from Earth, although it is theoretically possible to make astronomy charts which show the view from other planets or points in the universe. Astronomy charts are used in a number of different settings, from amateur star gazing to astrology.
A typical astronomy chart shows a section of the night sky with stars drawn out on it. The chart may outline constellations, point out visible planets, and provide other information which people may find interesting. It also uses coordinates so that people can orient themselves in relation to the map. Also known as a star chart or star map, an astronomy chart can provide a wealth of data.
As many people have noted, the stars visible from Earth vary, depending on where on the planet one is and what time of year it is. Astronomy charts are tailored to particular areas and seasons. Several websites for stargazers can create custom maps on the basis of a zip code or set of coordinates, showing exactly which stars should be visible in that area at a given point in time. People can use star charts to track stars or constellations of interest as they move around the sky, both over the course of the evening and over the course of the year.
Printed books of astronomy charts are readily available. Stargazers can use these as references when they are looking at the stars at night, and they also have other purposes. For example, people trying to identify supernovae use such charts to see if a star has been mapped before. Likewise, astronomers use these charts to find information about the location of stars and other phenomena. Astrologers may use astronomy charts backdated to the time and place of someone's birth when preparing an astrology chart, in the belief that the position of the stars may influence someone's destiny.
Reading an astronomy chart of the basic type is usually pretty easy. It usually points out stars which can be used as reference points, and people can use these stars to identify other objects of interest in the night sky. The astronomy chart may also include information about how to adjust the chart as the Earth rotates during the night so that observers can follow the moving stars around the sky.