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;
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.