Star charts and star maps are used by astronomers and other sky watchers to identify constellations, individual stars and objects of interest such as galaxies in the sky.
Most people first become interested in astronomy because of their wonder and amazement at the spectacle of the stars on a dark, clear night. Just like the ancient people in the time before telescopes, they first learn about naked eye sky watching by identifying constellations - groups of stars which resemble the shape of animals, humans, mythical figures, or other objects.
This is where star charts become useful: they help in learning the names and shapes of the constellations which are visible to you, and how the constellations which are visible change from month to month.
Star charts usually come in two forms:
1. Maps of the whole northern or southern hemisphere stars, to give an overall view of the constellations and the Milky Way.
2. Individual charts of the constellations.
The overall hemisphere star charts will also generally show the ecliptic, the path of the sun through the sky, and the place where planets will be spotted.
The individual constellation star charts will also show the arbitrary lines which connect the stars in a constellation, illustrating the shape it represents. Whole some constellations such as Scorpio or Libra or Crux have a faint resemblance to the object the name suggests (in these cases, a scorpion, a set of scales and a cross) others really have little connection.
The individual charts will also identify the individual stars within the constellations, by name.
While the brighter stars have common names, many stars will only be identified by their abbreviated constellation name and Greek letter. Normally on the charts the brightest star is given the first Greek letter, alpha. For example, the brightest star in the constellation Taurus, the Bull, is called Aldebaran, or Alpha Tauri. The second brightest star is Beta Tauri and so on. On star charts the Greek letter alone will often be used to identify the star, within the constellation lines.
As an illustration, the bright stars in the constellation Orion are well known as Rigel and Betelgeuse, but the less bright stars of Orion's belt are referred to on star maps as ζ Ori (Zeta Orionis), ε Ori (Epsilon Orionis), and δ Ori (Delta Orionis).
Though this system may seem puzzling to those new to astronomy and star maps, it is an effective and well established way of identifying individual stars.
While some people never get beyond their first glance at a star map, a little study of them will enhance your enjoyment of the night sky tremendously.
