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The Venusian clouds kept astronomers from seeing the planet's surface. Without visible landmarks, they could not measure how fast Venus turns on its axis. It took cloud-penetrating radar, first aimed at Venus in the early 1960s, for scientists to discover that Venus rotates backward as compared to the other planets in the solar system. This means that the Sun rises in the west and sets in the east. And Venus' rotation is extremely slow, so a "day" on Venus is longer than a year.

Ongoing Explorations

January 12
NASA’s New Horizons mission is scheduled to begin scanning Pluto and its entourage of moons. It will fly past Pluto later in the year.
MESSENGER will conclude four years of orbiting Mercury this month. The date will be dictated by spacecraft fuel supplies and other factors.
July 14


In mythology, Virgo was associated with the harvest. It represented a harvest goddess or the daughter of a goddess. The constellation's brightest star, Spica, was a stalk of wheat held in her hand. Virgo was associated with the harvest because the Sun passed across the constellation during late summer or early autumn, when farmers were reaping the crops they had planted months earlier.


Aquarius, one of the 12 constellations of the zodiac, is best viewed during the evening skies of late summer and early autumn, when it scoots across the south and is in view all night. It is one of 48 ancient constellations listed by the Greek astronomer Ptolemy almost 2,000 years ago. It's the tenth-largest of the 88 modern constellations.

Cancer, the Crab

It is a small constellation of faint stars, so it is difficult to find in the sky.

In mythology, it forms part of the story of Hercules. According to one version of the tale, while Hercules was tackling the multi-headed monster Hydra, the goddess Hera sent a giant crab to distract the strongman. Unfortunately for the big crustacean, though, it wasn't much of a challenge. Hercules crushed it, then quickly returned to his monster killing. Hera placed the remains of the crab in the sky, but gave it only faint stars because of its failure.

Libra, the Scales

Libra's brightest stars, however, are named for the next constellation over, Scorpius.

The stars are Zubenelgenubi and Zubeneschamali, which are Arabic names that mean the southern and northern claws, respectively. In ancient times, the stars represented the scorpion's claws. By thousands of years ago, however, the claws had been snipped off and assigned to Libra instead. The timing of the split is unclear, although it dates at least to the days of ancient Rome.

Pisces, the Fish

Several thousand years ago, when the zodiac was first drawn, the Sun stood inside Aries at the time of the equinox. And today, the March equinox is still known as the "first point of Aries." Yet the Sun has moved from Aries into Pisces because of an effect known as precession. It is a wobble in Earth's rotation caused by the gravitational pull of the Sun and Moon. As a result of this wobble, the point of the equinox moves all the way around the sky.

Aries, the Ram

Aries is famous not because of its brilliance, though, but because of its location: It is one of the 12 constellations of the zodiac. These constellations straddle the Sun's path across the sky, known as the ecliptic. In ancient times, that gave these regions of the sky extra significance.

The Solar System: Home Sweet Home

In the winter of 1504, astronomer Nicolaus Copernicus watched as the planets Mars, Jupiter, and Saturn grouped close together in the evening sky. As he tracked them from night to night, he was troubled, because the planets bunched closest to each other about 10 days later than predicted by reference tables of planetary motions.