Tuesday, January 29, 2008

Build your own Planisphere (Star Finder)!

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One of the Astronomer badge requirements is to use a seasonal star chart. One of the most compact and useful star charts is called a Planisphere, Star Finder, or Star Wheel.

Tonight we will send home star finders with our Cubs. Our planisphere came from the National Research Council of Canada web site as a downloadable template you can make yourself, here. For best results print the template on stiff card stock.

The NRC also an online star chart and information on constellations and other astronomy, here. In fact, you could get most of what you need to earn your Astronomers badge from this site alone.

Using a planisphere is simplicity itself, you just dial the disk until the time of day lines up with the current date. Hold it above your head as you look to the sky (otherwise east and west are reversed).

You should adjust for Daylight Savings Time, by subtracting one hour when it is in effect. You don't need to adjust for leap years as the day to day change in the position of the stars is much less than an hour of the Earth's rotation.

Planispheres are actually designed for observers at specific distances from the equator (latitudes). A planisphere disk for Canada and the US, doesn't work well above the Arctic circle or close to the equator. Entirely different planisphere frames and disks are required in the southern hemisphere as the directions reverse.

Some other star finders templates:
  • The State of New Jersey publishes one, here. It's not too much different than the NRC one.
  • The Royal Astronomical Society of Canada has one, here. And other resources, here.
  • A southern hemisphere template can be found, here.
  • A northern and southern hemisphere templates can be found, here.
  • A Lakota star chart that may be usable in a planisphere frame can be found, here, with more information, here.
High quality planispheres can be purchased from local astronomy stores or online. One innovative design reduces edge distortion using a two sided approach, here.

1 comment:

Spud said...


Thanks for sharing this detailed info on where to find and how to make a planisphere... we're planning to make these with our Cubs this week.

Check out our blog to see how we get on... 4thglasgowcubs.blogspot.com

Yours in Scouting,
Cub Scout Leader
4th Glasgow (Scotland)