Circumpolar: Stars Above the Horizon (page 2)

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Author: Janice VanCleave

Try New Approaches

Model the motion of stars at lower latitudes. lift the sheet of plastic from the model. Randomly add 40 or more dots to the outer region of the paper circle. Remove the brad and the paper circle. With the compass point, make a hole in the poster board about 1 inch (2.5 cm) below the existing hole. Center the paper circle on the new hole and secure with the paper brad, then lower the plastic (see Figure 24.2). Turn the paper circle counterclockwise and observe the movement of the dots. Turn the paper clockwise and observe again. Determine which stars are circumpolar. Also note how many of the stars that were circumpolar at latitude 90° are no longer circumpolar at the lower latitude represented by this experiment.

Design Your Own Experiment

Polaris, represented by the brad, is so near the north celestial pole (north end of the celestial sphere's axis) that it appears stationary to observers in Earth's Northern Hemisphere. Design an experiment to find out how the altitude of Polaris relates to the latitude of observers on Earth. Measure the altitude of Polaris at the latitude where you live and at other latitudes when you travel. Ask friends at different latitudes to make measurements for additional data. Record the data in a table. What conclusions can you draw from your data?

Circumpolar: Stars above the Horizon

Get the Facts

Declination is the angular distance of a celestial body in degrees north or south of the celestial equator (0° declination). Declination on the celestial sphere aligns with the latitude lines of Earth. How can declination predict the visibility of a star at a given latitude? For information, see Janice VanCleave's Constellations for Every Kid (New York: Wiley, 1997), pp.46–48.

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