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Venus, our eccentric sister

Radar data from the Magellan spacecraft scientists to penetrate Venus' thick clouds and create simulated views of its surface. Photo: NASA

On Saturday, January 8, Venus will reach its greatest elongation — that is, its greatest distance from the sun in our sky. At the end of December, Venus began to appear ever lower in the sky, and will continue to “descend” until the end of June. And then it will disappear entirely from view as it moves behind the sun. Now visible in the morning, when it reappears in August, it will be the evening star.

The planet’s seven-month descent — particularly when paired with the waning crescent moon — is said to be the inspiration for one of history’s oldest myths. Although Venus is named for the Roman goddess of love and beauty, the Sumerian myths about the goddess Inanna are probably the first to describe the planet’s transition from morning star to evening star.

1. Our lone goddess

Clay tablets from 2000 B.C. tell the story of Inanna, the Sumerian queen of heaven and earth, and her descent into the underworld. On her way to visit her elder sister Ereshkigal, ruler of the underworld, the goddess passes through seven gates. Ereshkigal, suspicious of Inanna, gives the gatekeepers special instructions for her entry.

At the first gate, Inanna is forced to remove her crown. At each successive gate, she gives up ornamental jewels, her scepter and finally her robe, entering the underworld completely naked. The seven gates are thought to symbolize the seven conjunctions Venus makes with the waning moon. During this time, the planet goes into a gibbous phase but appears to shrink in diameter.

Ereshkigal, not much of a hostess, kills Inanna upon her arrival, symbolizing the invisibility of the planet Venus. Inanna is eventually resurrected and returns to find her husband, Dumuzi, carrying on as if nothing unusual had happened. Unhappy with this cold welcome, she sends him to take her place in the underworld.

2. Star of morning and evening

Because of Venus’ two roles as the morning and evening star, the ancient Greeks and Egyptians thought the planet was two separate heavenly bodies. While Pythagoras (570 to 495 B.C.) is thought to have realized Venus was one object, the Babylonians were recording Venus cycles as early as 1646 B.C.

3. A little black dot on the sun

The June 8, 2004, transit of Venus as seen from NASA's sun-observing TRACE spacecraft. Photo: NASA

We are in the middle of the two most significant Venus events of the century — the twin transits of Venus. Like the moon during a solar eclipse, Venus passes between Earth and the sun, appearing as a small black dot on the fiery star. Venus transits happen in pairs in a pattern that repeats every 243 years. The last transit occurred in 2004, and the next is June 6, 2012. We’ll miss the next pair, as they won’t occur until 2117 and 2125.

4. The phases of Venus

Pre-Renaissance astronomers thought that Venus orbited Earth. But Copernicus predicted that Venus would undergo a full range of phases like the moon as it traveled around the sun. In 1610, Galileo, with the help of a telescope, was the first to see the phases of Venus. That discovery helped to dislodge the geocentric model of the universe.

5. As the only goddess, she goes her own way

Venus orbits the sun in the same direction as the other planets, but it spins on its axis in the opposite direction. Scientists think a moon or other large body may have spiraled into the planet and changed its rotation.

(Bonus) Hottest and brightest

While Mercury is closer to the sun than Venus, it doesn’t have an atmosphere that can trap heat. Venus is the hottest planet, with an average surface temperature of 465 degrees C.

Venus is the brightest planet both because it is the closest to Earth and because its cloud cover reflects light back at us. The clouds aren’t made of water, they’re sulphuric acid. Venus’ atmosphere is very thick — at about 96.5 percent carbon dioxide, it’s an example of a full-blown greenhouse effect.