Skylights featured on Astronomy Picture of the Day

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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9 -- Full List Restored!

Canis Major

Photo of the Week. Cool off with winter's Sirius (to the upper right), the brightest star of the sky, and Canis Major, Orion's bigger Hunting Dog, which sprawls down and to the left. At the other end of first magnitude, Adhara lies at bottom center.

Astronomy news for the week starting Friday, July 19, 2013.

The week begins with the Moon waxing in a fat gibbous phase as it heads towards full on Monday the 22nd around mid-day and out of sight. The "grain Moon," the "green corn Moon," will therefore rise just shy of full (and sunset) the evening of Sunday the 21st and just past the phase and sunset on Monday. It then wanes in the gibbous phase for the rest of the week, not reaching third quarter until Monday the 29th. On the night of Wednesday the 24th, the Moon will glide six degrees north Neptune. More importantly, on Sunday the 21st, the Moon passes perigee, where it is closest to Earth on its modestly elliptical orbit (perigee some 5.5 percent closer than average). Perigee's nearness to full Moon will bring heavier tides than normal to the coasts.

Monday, July 22, is a remarkable day of events and coincidences. Not only do we have a full Moon (near noon and invisible), but have two close planetary passages, one in the east at dawn, the other in western evening twilight. In the morning, Mars and Jupiter rise just as dawn is beginning to break (around 4 AM) only 3/4 of a degree apart, Jupiter the brighter. Advancing twilight will make them difficult to see, however, so use binoculars. That evening Venus (which sets around 10 PM Daylight Time just before twilight ends) will hover just over a degree above the star Regulus in Leo, the star much fainter than the planet. Binoculars will help a lot. You'll need a good flat horizon for both. As the month proceeds and Jupiter rises ever earlier, its morning visibility will notably improve. So will that of Mercury , which rises in bright dawn.

That leaves us again with Saturn. Well into the southwest as the evening sky darkens, the planet sets just half an hour past midnight Daylight Time, giving us more than three hours with no bright planet. Having just entered direct easterly motion from westerly retrograde as seen against the stars, Saturn crawls with agonizing slowness, remaining a dozen degrees to the east of Spica.

When viewed at the same time on successive nights, the sky shifts a degree to the west as a result of the Earth orbiting the Sun and our facing in slightly different directions. By the time the sky is fully dark, Scorpius, with Ophiuchus and Serpens above, now straddles the southern celestial meridian. Bright orange Arcturus however will be seen now toward the west as the old spring stars slip away. Wait until around midnight to see Vega, just slightly fainter than Arcturus, nearly overhead as viewed from the middle latitudes of the northern hemisphere.
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