A planisphere is your astronomy friend

Hands holding a flat, round blue and white object with constellations printed on part of it.
A planisphere will teach you what stars and constellations are overhead for any night of the year.

What is a planisphere?

If you want to learn the stars and constellations, then you need a planisphere. A planisphere is a rotating star locator. It shows you the view overhead any night of the year. All you have to do is to turn the wheel until you’ve aligned your date with the time of night you want to look. The stars and constellations on view on the wheel are the same as those above your head. Unlike most sky charts, a planisphere never goes out of date and always stays in step with the motions of the heavens.

Order your planisphere today!

Top tips and how to use one

    1. For best results, go to a dark-sky site. Locations away from light pollution allow many more stars to pop into view. 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. Use the wheel to 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. Notice the cardinal directions located on the planisphere. If you hold the planetarium upright with north at the bottom, stand and face north. Then when you lean back and tilt the planisphere over your head, the constellations of the planisphere should match up with those in the sky. The planisphere is essentially a view of the dome of the sky when held over your head. If you want to face south, you can turn the planisphere upside down so that south lines up with your horizon.
    4. To preserve your night vision, try using a small flashlight covered with red cellophane to read your planisphere. Or pick up a red light flashlight from the EarthSky store. Using a planisphere with a red light preserves your night vision more than using an app, which will limit how much you can see in the sky.
    5. Look for patterns – squares, semicircles, 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’re probably seeing a planet. The planets you can see with your unaided eye – Mercury, Venus, Mars, Jupiter, Saturn – are usually as bright or brighter than the brightest stars. Not sure if what you’re seeing is a planet? Check out EarthSky’s monthly planet guide.

Joining history

In learning to use a planisphere, you’re joining the august company of some of history’s most famous stargazers. Jakob 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.

Three people stand and stare at the Milky Way.
Learn what you’re looking at in the night sky with a planisphere. Image via Benjamin Davies/ Unsplash.

Bottom line: The first step to learning the night sky is being able to identify stars and constellations, and a planisphere is an easy-to-use tool that can help you do that.

March 21, 2013

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Bruce McClure

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