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Venus setting

Photo of the Week. Venus setting.

Astronomy news for the week starting Friday, August 2, 2013.

The Moon fades away this week in its waning crescent phase, each morning getting closer and closer to the eastern horizon until it passes new on Tuesday, August 6. It thereafter shifts itself past the Sun to be seen by the evening of Friday the 9th, perhaps even by the night before, as a waxing crescent. It passes apogee, where it is farthest from Earth, on Saturday the 3rd.

The narrowing Moon provides a good way to spot the three morning planets. The morning of Saturday, August 3, look down and to the left of the Moon for Jupiter, which will be obvious. The following morning, that of Sunday the 4th, the thinning crescent will be near-surrounded, with Jupiter above it, faint Mars up and to the left of it, bright Mercury down and to the left. The Moon will be nearly gone by the next morning, leaving the stack of planets behind. Jupiter rises shortly after 3 AM Daylight Time, about half an hour before Mars, and an hour before the beginning of twilight, which Mercury does not escape. Adding to the show are Gemini's Castor and Pollux, which appear farther to the left.

Then flip to the other side of the sky and the evening to find Venus, which sets just before twilight draws to a close and is making a particularly poor showing this orbital round as a result of the early evening ecliptic lying rather flat against the horizon. Every eight years, Venus and Earth occupy nearly the same orbital positions. In 2005, Venus's evening scene appeared as it does today; look to see it again in 2021.

Left out is the last of the ancient planets, Saturn. Well into the west as twilight ends, to the east of Spica, the ringed planet sets around 11:30 PM Daylight Time, so not that much time remains to view it. By the end of September, Saturn will have left the dark sky and for a while will be visible only in twilight.

The Moon's departure gives us a fine opportunity to see the glorious summer Milky Way. From a dark location, out in the country, you hardly need a guide, as the billions of stars in the disk of our Galaxy flood the sky in a broad avenue from north to south, culminating in the great Sagittarius star clouds near the Galactic center. Not at all uniform, the Milky Way is filled with dark lanes and patches that are the birthplaces of new stars. Together, they make the Great Rift that seems to divide the stream in two.
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