Find That Planet!   Teachers' Page  

Activity Profile:

  • Topics: Comets; Using star maps to find things in the sky; Celestial coordinates
  • Grade Levels: 6-12
  • Student Prerequisites: Able to read maps; Know what latitude and longitude are.
  • Time Requirements: Approximately 1 hour preparation time and 2 hours class time



  • Students meet a challenge that requires use of the Internet for acquiring information, images, or other media.
  • Students get the idea that computers are powerful tools not only for games, but for finding out about many subjects on the worldwide web.


  1. Students will learn to use star maps for finding a planet.
  2. Students will plot a planet path on star maps with coordinate grids.
  3. Students be able to find out when a planet is visible.

Materials Required For This Activity:

  1. Computer(s) connected to Internet
  2. Star Maps with coordinate grids
  3. Optional: Constellation Posters--(how to make them)


  1. Visit the JPL ephemeris web site and familiarize yourself with how it works.
  2. Decide if you can have students print out star maps during the activity, of if you should print them before hand and make photocopies for each student.
  3. You may find a map with the planet positions already plotted for the current month at the Sky & Telescope magazine website (http://www.skypub.com/) under "Monthly Sky Charts."
  4. Optional: You can recreate the night sky, at least the near-horizon part of it, with posters of the constellations that will be visible at each of the cardinal directions at the particular time that you would like students to practice finding the comet. This classroom "Horizon Planetarium" idea is from the GEMS guide Earth, Moon, and Stars from Lawrence Hall of Science

Classroom Strategies:

Be sure that students have a firm understanding of the concept of celestial coordinates and what an ephemeris is.

When students go to the JPL Ephemeris Generator, they will need to click on 4 buttons to provide

  1. Select New Body (Planet)
  2. Select New Location (observation postion on Earth--your town--you may need to find your Earth coordinates for this or just choose a nearby city that is on the preset listing)
  3. Set Time Span (Year/Month/Day/Hours/Minutes) and Interval between coordinate listings (days, hours or minutes)
  4. Select New Output Quantities -- here you should start simple: check only #2. Apparent RA and DEC (Right Ascension and Declination) and possibly # 29 Constellation ID. Later, if students really get into it, the following may be of interest:

      4. Apparent AZ and EL (Azimuth and Elevation angles)
      5. Rates; AZ and EL (Rate of change in Azimuth and Elevation Angles)
      9. Visual magnitude and surface brightness
      20. Observer range and range-rate (Distance to object and rate of change of distance to object)
      21. One-way light-time (another way to express distance to object)

If students need practice using star maps, try out the Activity (#5) from the GEMS guide Earth, Moon, and Stars in which the classroom is made into a "planetarium" with constellations posters hanging on the walls.

One tricky part is judging when a planet is visible at night. It is all well and good to pick a planet and a time that you want to see it, but the heavens do not always acquiesce to our wishes--the planet may be up only in the daytime in a particular time period. A few trials with the ephemeris generator may be necessary before successfully plotting a planet on a chart when the planet is really up when the sky is dark.

More Info for Teachers

Mail questions or comments: outreach@ssl.berkeley.edu
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