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Heliocentric Plotting

(This page under revision. Check back later for updates.) - 5/25/16)

This is an activity that could precede a visit to the planetarium in which current planet positions are shown, and planetary motions are demonstrated. The students plot the positions of the zodiac constellations and planet positions, answer questions, and make predictions.

Offered by Gary Sampson (retired)
Grade level: 10-12, ages 16-18



1. Using ESSCO S511 graph paper*, plot the location of the zodiac constellations around the periphery. The heliocentric coordinates of the constellations are listed in the appendix of most college-level astronomy texts.

2. Using heliocentric coordinates from The Astronomical Almanac or any upper-level computer astronomy planetarium program, plot the planets for the time specified:

a. Mercury -- twice per month for the present four-month period.

b. Venus -- twice per month for the present nine-month period.

c. Earth -- once per month for the current year.

d. Mars -- once per month for a two-year period.

3. Answer the following questions:

a. List the apparent locations against the background zodiac for
Mercury, Venus and Mars for the first of the month for their respective
plotted time sequences.

b. When was (is) Mars at opposition to the Earth?

c. When was (is) Mars at conjunction to the Earth?

d. During what period was Mars in retrograde?

e. When was (is) Mercury at inferior conjunction? to the Earth?
at superior conjunction?

f. (If it applies) When was (is) Venus at inferior conjunction?
or When was (is) Venus at superior conjunction?

Follow up: Using the planetarium, compare the above predicted results
to their actual relationships.


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