Zodiac Band: Background for the Ecliptic (page 2)

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Author: Janice VanCleave

Try New Approaches

Earth moves around the Sun; the Sun does not move around Earth. To show the relationship of Earth and the Sun to the zodiac constellations, cut a new strip of poster board 5 inches (7.5 cm) long. Punch and attach the constellation wheel as you did before. Label the brad "Sun." Draw the Earth at the short end of the strip. Draw a straight line from Earth through the Sun and past the brad to the other end of the strip. Draw an arrowhead that points to a constellation (see Figure 23.2). Rotate the strip as before, noting the constellation at the end of the arrow with each 30° movement of Earth. You might want to label the first strip you made "How It Seems to Be" and the second strip "How It Really Is."

Zodiac Band: Background for the Ecliptic

Design Your Own Experiment

  1. As the planets appear to move across the sky, they follow paths very near the ecliptic, so the zodiac constellations also provide a backdrop for them. The planets visible with the naked eye are Mercury, Venus, Mars, Jupiter, and Saturn. When Venus and Mercury are west of the Sun, they are called morning stars. They rise before the Sun in the morning. When these planets are east of the Sun, they are called evening stars. They appear after the Sun sets in the evening. On the first and fifteenth of each month for 3 or more months, determine whether Venus is a morning or evening star. Do this by following these steps:
    • Determine the Sun's position in a constellation for a specific date. For example, on January 15, 2003, the Sun enters the region of Capricornus. (The year affects the location of a planet on a certain day, but not the Sun.)
    • Using a Planetary Longitudes table for the year in question, find the location of Venus and Mercury on that day. (For purposes of example, a portion of a planetary longitudes table is shown in Table 23.2.) On January 15, 2003, Venus is at longitude 248°. For planetary longitude tables for other years, see the National Audubon Society Field Guide to the Night Sky (New York: Knopf, use most current publication).
    • On January 15, 2003, the Sun enters Capricornus, which is between 300° to 330° longitude. From the Constellation longitudes chart shown in Figure 23.3, the longitude of the Sun entering Capricornus is 300°. Venus is at longitude 248° on January 15, 2003, and 248° is to the west of the Sun. So, on January 15, 2003, Venus will be a morning star.
  2. Use the procedure from the previous experiment to predict the locations of Mercury, Mars, Jupiter, and Saturn. Observe the sky to test your predictions.

Zodiac Band: Background for the Ecliptic

Get the Facts

  1. Most diagrams and descriptions of the zodiac show only 12 constellations, but the Sun actually passes through a thirteenth zodiac constellation each year. This constellation is called Ophiuchus. Where is Ophiuchus in relation to the other zodiac constellations? When does the Sun enter it? For information, see Janice VanCleave's Constellations for Every Kid (New York: Wiley, 1997), pp. 123–124.
  2. You may have noticed that the dates associated with the constellations of the zodiac do not correspond with the dates in astrological horoscopes found in many daily newspapers. Why are these dates different? Why is astrology called a pseudoscience? For information, see Janice VanCleave's Constellations, pp. 102–105.
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