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Figure 2.9.26
On Jupiter’s (Mars) Luminosity
When Earth and Jupiter (Mars) are relatively close to each other in their respective orbits (see position 6),
Jupiter (Mars) appears brighter.
When they are farther apart (see position 1),
Jupiter seems dimmer. Our Line of Sight
The apparent motion of Jupiter, as seen from Earth, is shown in the red curve.
Jupiter appears to loop back and forth in retrograde motion because our line of sight (in light blue) from Earth to Jupiter changes as the two planets orbit the Sun. They are always at an angle, except when in spot 6 when Earth and Mars’s orbits are closely aligned.
26 Chaisson, McMillan. Astronomy Today. 7th Edition. 39. •33•
