Skylights featured on Astronomy Picture of the Day

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V Hya and R Crt

Photo of the Week. Two very red stars. R Crateris, a dying cool red giant lurks just to the left of Alkes, Alpha Crateris (up and to the left of center), while the cool carbon star V Hydrae lies just below center. Both are dying advanced giant stars that have dead carbon-oxygen cores; V Hydrae has actually brought some of the carbon to its surface. Both are unstable variables, will shortly expel their outer envelopes, and finish as white dwarfs. Much of the carbon in the Universe comes from stars like V Hydrae.

Astronomy news for the week starting Friday, July 4, 2008.

Happy Birthday USA, 'tis (was) the Fourth of July. The Earth helps to celebrate the day this year by going through aphelion, where it is farthest from the Sun, at a distance of 94,513,144 miles (152,104,160 km), 1.7 percent farther than average. We don't, however, notice the changing solar distance; the seasons are created by the tilt of the Earth's axis relative to the orbital axis.

The Moon gets into the act by starting the week in a slim waxing crescent phase (nicely visible in western evening twilight) as it heads to first quarter the night of Wednesday the 9th, thereafter going into its waxing gibbous phase. That the Moon is at new phase near aphelion actually makes the Earth even farther from the Sun as the Earth is also on the far side of the center of mass of the Earth-Moon system. The night of Saturday the 5th, the Moon will be seen to the west of the Regulus-Mars-Saturn trio (in order from west to east, all in Leo), whereas the following night it will lie to the southeast of the three.

And speaking of this assembly, they are making a very nice showing in the west in early evening, with Mars spending most of the week moving from west to east in between Regulus and Saturn, as it prepares to pass south of Saturn the night of Thursday the 10th, when the two will be only 0.7 degrees apart, a bit more than the angular diameter of the Moon. It's a great opportunity to watch the movement of a planet as it and our own Earth swing about the Sun. First magnitude Saturn is the brightest of the three, 1.7 times brighter than Regulus, and twice as bright as Mars (which, with increasing distance from Earth, is fading).

That leaves us with Jupiter. On the other side of the sky in Sagittarius to the northeast of the Little Milk Dipper, the giant planet makes its own mark by passing opposition to the Sun the night of Tuesday the 8th, when it rises at sunset, crosses the meridian to the south near local midnight (1 AM Daylight), and sets at sunrise, thereby becoming more of an evening planet than a morning one.

Look to the far southwest in evening to find box-like Corvus the Crow or Raven, which rides on the back of Hydra, the Water Serpent, which is also slithering away to the west. Corvus is also quite the sign post. The Bird's top two stars point eastward to Virgo's Spica, while the western two point downward to Beta Hydrae and the bottom two eastward to Gamma Hydrae.
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