Monday, June 29, 2009

Back atcha, Lemming

Last week I posted that the entire inner solar system was visible in the predawn sky. The reason for this is that Venus (and Mercury) were in between Earth and Mars. One of the reasons Mars (the dim red dot in the picture) was so dim is that it is on the opposite side of the inner solar system.

Figure 1. positions of the inner planets on June 19. Note that Mars, Venus, and Earth are co-linear.

Of course, any Martians looking back at Earth in the evening sky would see something very similar. Venus and Earth would be close together in the evening sky, with Mercury low on the horizon. Figure 2 shows a simulation.

Figure 2. What Venus and Earth would look like as seen from Mars.

This may seem like a silly thing to wonder about, since there is obviously nobody up on Mars looking back at us. But here’s the catch: even though there are no people on Mars, there are several robots controlled by people. And those robots have cameras.

Figure 3. Spirit rover picture of Venus and Earth in the Martian twilight.
Picture from here.

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