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The Jupiter Mission

Activity 3B: Finding Jupiter's Moons


To calculate and predict the location of Jupiter's 4 large moons

Ask students how the earth's moon moves. Then ask how a satellite moves. (Both are in orbit around the earth.) Ask how long it takes for the moon to circle the earth (27.3 days). Ask how long it takes for the Shuttle to circle the earth (90 minutes). Assist students in concluding that objects nearer the earth orbit at a faster speed and with a shorter period.

Explain that Jupiter has four large moons that will be visible to the KAO infrared detector even in the daytime (though Io may be tough to find!). However, the tracker telescope, using visible light, may not be able to see the moons during the day--only Jupiter.

Materials activity 3B bound into a Mission Logbook

Procedure Study the diagrams of Jupiter's moons in orbit around the planet. Explain that the "squashed" image represents exactly the same scene as the overhead view. When we observe Jupiter from earth, we have an edge-on view of the moons. By comparing image (i) and (ii), students can see how much each moon moves in 16 hours. To figure out where Jupiter's moons will be at the time of the KAO observations, move each moon half as far again as it moved between image (i) and image (ii). Mark the position of each moon with a black circle on image (iii). Then carry those positions down to the edge-on view.

math symbol

Ask students to draw Jupiter with the moons correctly shown for the time of the observation. Use 16:00 hrs Eastern as the baseline, and adapt the spacing accordingly. Then ask students to estimate the orbital period for each moon in earth days. (Io: 1.7 days, Europa: 3.6 days, Ganymede: 7.2 days, Callisto: 16.7 days)

Interdisciplinary Connectionmath symbol

All the planets of our solar system also have different speeds in their orbits around the sun. The table below lists the period for each planet in terms of earth years. Ask students if the orbital periods change in the same way for the planets as they do for the moons of Jupiter. For older students, you can introduce Kepler's Third Law of Planetary Motion.
Mercury 0.24 earth years
Venus 0.61 earth years
Earth 1.0 earth year
Mars 1.9 earth years
Jupiter 11.9 earth years
Saturn 29.4 earth years
Uranus 83.8 earth years
Neptune 163.7 earth years
Pluto 248.0 earth years

KAO Connection

Ask students to describe how to find each of the moons once the telescope has located Jupiter.


Myra Cohn Livingston

Space blazes with jewels,
a shimmering ice
of billions of diamonds
the Milky Way:
Jupiter, a giant agate,
Uranus, a ball of jade,
Pluto, a luminescent pearl,
Saturn, a halo of rings,
A slice
of moon, a crescent brooch.
Bright rubies splay
in this

From Space Songs, by (Holiday House, New York) (c) 1988 by Myra Cohn Livingston. Used by permission of Marian Reiner for the author.

When I Heard the Learn'd Astronomer

Walt Whitman (1819-1892)

When I heard the learn'd astronomer,
When the proofs, the figures, were ranged in columns
When I was shown the charts and diagrams, to add, divide,
and measure them,
When I sitting heard the astronomer where he lectured
with much applause in the lecture-room,
How soon unaccountable I became tired and sick,
Till rising and gliding out I wander'd off by myself,
In the mystical moist night air, and from time to time,
Look'd up in perfect silence at the stars.


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