A planisphere is a rotating star locator. It’s a virtually indispensable tool for beginning stargazers. Want to learn the stars and constellations? A planisphere is a great place to start. All you have to do is to wheel it around until the time and date match up. Presto! At the drop of a hat, the stars and constellations on the planisphere instantly match those in the real sky. Unlike most sky charts, the wizardly planisphere never goes out of date, and always stays in step with the motions of the heavens. Need tips on using it? See below.
Who uses a planisphere? Nearly every stargazer we know has used one at one time or another.
Top tips on using a planisphere
1. For best results, go to a dark place, a place where many stars pop into view, to use your planisphere. If you want to observe from your yard, where fewer stars are visible, notice that the brighter stars are portrayed as larger dots on the planisphere.
2. Set the time you are viewing and the day’s date.
3. Be sure you’re holding the planisphere correctly with respect to the real sky. For example, when you look northward, hold the planisphere upright, with north at the bottom. When you’re looking southward, hold the planisphere upright, with south at the bottom … and so on. If aligned correctly, the bottom half of the planisphere represents the half of the sky that you’re looking at. The top half represents the portion of sky behind your head.
4. To preserve your night vision, try using a small flashlight covered with red cellophane to read your planisphere.
5. Look for patterns – squares, half-circles, dippers and so on – among the stars. Remember, constellations rarely look like their namesakes. Don’t worry about seeing Canis Minor as a dog, or Andromeda as a princess.
6. Learn each constellation in relation to its neighbors. Use each one as a stepping stone to the next.
7. If you find a bright star out of place somewhere along the ecliptic – or path of the sun and moon across the sky – you are probably seeing a planet. The planets – Mercury, Venus, Mars, Jupiter, Saturn – are usually as bright or brighter than the brightest stars. Not sure what you’re seeing is a planet? Check out EarthSky’s monthly planet guide.
In learning to use a planisphere, you’re joining the august company of some of history’s most famous stargazers. Jacob Bartsch – son-in-law of Johannes Kepler, discoverer of Kepler’s laws of planetary motion – made the first star chart to bear the name planisphere in 1624.
Bottom line: Many beginning stargazers start out learning the heavens with a planisphere. Here’s all you need to know about using one, some history, top tips for using your planisphere and a place to order one. Have fun!
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.