The Sun Sets on Venus in the East

As we've seen, Mercury's peculiar rotational pattern can be explained by its proximity to the sun. But no such gravitational explanation is available for the peculiar behavior of Venus. If at 59 days, Mercury rotates on its axis slowly, Venus is even more sluggish, consuming 243 Earth days to accomplish a single spin.

What's more, it spins backwards! That is, viewed from a perspective above the earth's North Pole, all of the planets (terrestrial and jovian) spin counterclockwise—except for Venus, which spins clockwise.

Nobody knows why for sure, but we can guess that the rotational peculiarities of Venus were caused by some random event that occurred during the formation of the solar system—a collision or close encounter with another planetesimal, perhaps. A violent collision, like the one that formed the earth's moon, might have started Venus on its slow backward spin.

Star Words

Calderas are craters produced not by meteoroid impact, but by volcanic activity. Coronae are another effect of volcanic activity: large upwellings in the mantle, which take the form of concentric fissures, or stretch marks in the planet's surface.

Star Words

Calderas are craters produced not by meteoroid impact, but by volcanic activity. Coronae are another effect of volcanic activity: large upwellings in the mantle, which take the form of concentric fissures, or stretch marks in the planet's surface.

Close Encounter

Except for the moon, Venus is the brightest object in the night sky and is, therefore, quite easy to find. Just look for a bright, steadily shining (not twinkling) object in the western sky at or before sunset, or in the eastern sky at or before sunrise. It is so bright, in fact, that training your telescope on it during a very dark night might prove disappointing. If you make your observations in the evening, before full darkness, or in the early morning twilight, you stand a better chance of making out some atmospheric features. Unfortunately, you can't see any surface features because of the planet's thick atmosphere. The most interesting phenomena to observe are the phases, which resemble those of the moon. As with Mercury, the planet appears largest during its crescent phase (when it is backlit by the sun, and closest to the earth). When Galileo saw the variations in the size of the disk of Venus, he realized that it confirmed that the planets moved around the sun, and not around the earth.

Don't totally give up on Venus in a dark sky. If you observe the planet in its thinnest crescent phase, you may (as with observations of the crescent moon) see the rest of the shadowed disk.

Often, Venus can also be observed during the daytime, even at low magnification. As with observing Mercury in daylight, be very careful to avoid pointing your telescope or binoculars at the sun. To do so, even for a moment, will cause permanent damage to your eyesight.

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