Let's Find the Constellations with a Planisphere


My good old planisphere!
It's almost time for the night sky to darken early enough for stargazing again. Soon, I will go back to writing articles about locating constellations in the night sky. First, I want to tell you about a device that helps stargazers find constellations. It is called a planisphere (play-nĭ-sfear), which is also known by other names including a star finder wheel or night sky finder. It's a very handy map of the night sky that will tell you when and where to find the constellations.

Click here to see a larger photo of my trusty old planisphere. It will open in a different window so you can refer to it as you read the first part of this article. (View the photo in full screen or it will look all scrunched up.) As you can see, it has been used a lot!


Parts of a Planisphere and What They Tell You

My planisphere is made up of three circles. Most planispheres are made of two circles, but they all work the same way. Here are the parts and what they show:

  1. The edge of the bottom circle is the outermost ring showing the twelve months of the year. Numbers representing every other day of the month are also on this circle inside the month ring.

  2. The next circle is blue (the one with the chunk missing). It lists the hours of the day and night. The dots represent ten minute intervals between the hours. Therefore, if you start at the 8 pm dot, the next dot represents 8:10, the next one represents 8:20, then 8:30, then 8:40, then 8:50, and finally you reach 9:00pm.

  3. Next is the top circle that contains a clear plastic area that looks egg-shaped with a bump on top. The white part is actually part of the bottom circle showing through the window of clear plastic. The dots and lines that you see are the constellations. Around the edge of egg-shaped window with the bump on top, you will see the directions. Starting from the bottom and working around toward the right - Southern Horizon, SW, Western Horizon, NW, Northern Horizon, NE, Eastern Horizon, SE, and back to where we started.

How Do We Use This Contraption? Line Up the Circles!

If I wanted to know what constellations will be visible in the western sky on August 14th at 9:00 PM, I would move the time circle so that the 9:00 pm is lined up with the 14 in the August section on the bottom circle. Keeping those lined up, I would then turn the entire planisphere so that the "Western Horizon" is at the bottom.

The copyright of the article Let's Find the Constellations with a Planisphere in Kids' Amateur Astronomy is owned by Christina Coruth. Permission to republish Let's Find the Constellations with a Planisphere in print or online must be granted by the author in writing.

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