Paper Plate Education
"Serving the Universe on a Paper Plate"

Activity: The Photographic Plate

This and several other activities from the Paper Plate Astronomy videotape and DVD are now available online as
free streaming video!

Star trails are long duration photographs in which the stars appear smeared from the earth rotating underneath them. In this activity you will predict the appearance of a long duration exposure of circumpolar stars, for any given date and time and for any given exposure.

Please refer to The Platisphere for instructions on making a starfield plate. (As detailed in The Platisphere, to mass produce starfield plates, place one plate with a circumpolar star chart on top of an unopened package of plates. Then drill through each star on the top plate and through the stack below as well.)

Subdivide and label a larger 10-inch white plate into 24 hours, with one hour equal to 15 degrees (360 degrees divided by 24 hours).

Secure a 9-inch starfield plate on top of a larger white plate with a paper fastener in the center. Position the upper starfield plate, which has holes drilled out to denote the circumpolar stars, so it corresponds to the current night sky.

In our sample star trails prediction we will mark three hours in the "starwise" direction.

Place a pen tip in one star hole and rotate the top plate an angular amount that corresponds to the time of a long duration camera exposure.

For example, to simulate the three-hour photograph of the north circumpolar stars, rotate the top plate counterclockwise 45 degrees while sweeping out the arc with the pen.

Return the plate to the starting position and repeat for each of the remaining star holes.

Remove the top plate to view the predicted star trails of your long duration exposure.

Again, please refer to The Platisphere for instructions on making the top horizon plate.

(For south circumpolar stars, rotate in the opposite direction, or clockwise.)

See the Gemini's Signature activity for extensions on predicting star trails.

See http://pages.prodigy.net/pam.orman/JoeTrails.html for star trail photographs.

Contributed by Chuck Bueter.

GLPA Proceedings, 2000, pp. 67-68.

[Note: This activity is included in the Paper Plate Astronomy video/DVD/streaming video.]

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