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!


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Astronomy news for the two weeks starting Friday, September 25, 2015.

The next skylights will appear October 9, 2015.

Sometimes everything seems to happen all at once. The Moon begins our fortnight late in its waxing gibbous phase and then hits full on Sunday, September 27, when it goes through the Earth's shadow to present us with a marvelous early evening total lunar eclipse that's visible throughout the Americas. The partial phase, wherein the Moon first encounters the full shadow of the Earth, begins at 8:07 PM Central Daylight Time. Total eclipse, with the Moon fully immersed in umbral shadow, starts at 9:11 PM, with mid-eclipse taking place at 9:48 PM, when the Moon is just to the south of the central part of the shadow. The Moon starts to leave full shadow at 10:23 PM and the partial portion is over at 11:27. Add an hour for EDT, subtract one for MDT, two for PDT. In the far west, the Moon will rise during the partial portion before totality, while in Alaska the eclipse will be even farther along. The penumbral phases, during which some direct sunlight falls on the Moon, are here ignored. Even during totality, the Moon will be visible as a dull reddish orb as a result of sunlight scattered and refracted into the Earth's shadow. The brightness of the totally eclipsed Moon depends on atmospheric transparency, most critically on prior terrestrial volcanic activity. Since the eclipse is not exactly central, at mid-eclipse the northern part of the Moon will be darker than the southern.

More remarkably, the Moon passes perigee, where it is closest to Earth, and therefore of maximum angular size, just an hour before maximum eclipse. Even without the eclipse, this full Moon is famed as the "harvest Moon." It's not just a name. This time of year the evening ecliptic (the solar path that the Moon closely follows) lies at a shallow angle to the horizon. As a result, near full phase, the delay in moonrise from one night to the next is minimized, giving us lots of moonlight in the early evening to help bring in the harvest. This eclipse also ends a "tetrad" of four total eclipses in a row, each separated by about half a year. It can't better than this, except of course for having clear skies. The display during totality is beautiful and quite colorful as seen through binoculars or a telescope.

After the eclipse, the Moon passes through the waning gibbous phase, which ends at third quarter on Sunday, October 4, following which it wanes as a crescent. A day after the eclipse, the fat gibbous passes just south of Uranus. The night of Thursday the 1st, the fading gibbous Moon will be seen west of Aldebaran in Taurus, while the following night it will fall to the east of the star with the Pleiades floating north of them both. The Moon actually occults the star during the day in North America. The thinning crescent will then present us with more delightful sights. The morning of Thursday the 8th, it will lie just above Venus, while the following morning it will be between Venus and Jupiter with Mars to the left, all to the south of the rising classical figure of Leo. As seen above, the morning planets present us with quite a line- up, with Venus, Mars, and Jupiter falling in a ragged line toward the pre-dawn horizon, the configuration of the trio continuously changing. Venus far outshines them all, Jupiter next, Mars relatively faint. Early in our period Mars will lie just to the north of somewhat brighter Regulus, while by the end of the fortnight, it will be Venus's turn, the brilliant planet now passing to the south of the Leo's luminary.

The night of Thursday the 8th and the morning of Friday the 9th be on the lookout for the Draconid meteor shower, the product of short-period comet (6.6 years) Giacobini-Zinner, whose leavings appear to come out of the northern constellation Draco. While it usually does not amount to much, in 1933 and 1946 the Draconids put on spectacular displays.

With the Moon fading away as a crescent, or even during the total part of the eclipse, if in a dark location take time to admire the evening Milky Way as it comes out of Cassiopeia in the northeast, then passes through two celestial birds, first Cygnus (the Swan) with bright Deneb, then across the celestial equator through Aquila (the Eagle) with first magnitude Altair. To the northeast of Aquila and south of Deneb, look for Delphinus, the Dolphin, which looks like small hand with a finger pointing to the southwest.

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