Sometimes we get those quiet weeks in which not much goes on, which
allows us just to go back to enjoy the peaceful sky. This is one
of them. The ever-present Moon<
/a> of course continues its monthly round, this week beginning in
its waning
gibbous phase, then going through its third quarter (the
name from the quartering of the orbit since "new") on the night of
Tuesday the 15th. The last of the week sees it waning as a fat crescent in the
morning sky far to the north of the celestial equator in the
neighborhood of the classical figures of Taurus and Auriga.
Interestingly, the third quarter is not as bright as the first
quarter, the result of the concentration of dark maria on the
"third-quarter side." These dark areas, easily visible to the
naked eye, are ancient lava flows, many of which fill huge,
circular impact basins (hence the "man in the Moon" and other
fanciful figures).
The planetary evening is still dominated by bright
Jupiter, which is obvious in the southwest as the sky darkens.
Look at it even with binoculars to see its largest moons. To the
west of it, find the bright star Spica in Virgo, to the east Antares in Scorpius. Setting ever earlier, the planet is now down
by 11:30 PM Daylight Time. The morning sky is similarly dominated
-- as it has been nearly all year -- by brilliant
Venus, which still lies above much fainter
Mercury. Venus now begins its slow slide into morning dawn, as
it will rise ever later after the start of morning twilight until
it finally disappears as fall begins. Take heart, however, as it
will pop up in the evening sky at years' end.
Perhaps you will see a few of the
Perseids, meteors that come out of the constellation Perseus, which are best this year the
morning of Sunday the 13th. Unfortunately, the bright Moon will
get in the way, limiting us to only the brightest of them. But if
you are out at 4 AM, at least look overhead to see the debris
flaked off Comet Swift-
Tuttle, which with its 130 year period last passed near the
Earth in 1992, bringing more Perseids with it and to a peak of some
200 per minute.
We are in the midst of "Milky
Way" season. At 9 PM, Vega
shines nearly overhead in mid-northern latitudes. Look for Deneb in Cygnus to the east of it. From Cygnus, the Milky Way -
- the combined light of the billions of stars in the disk of our
Galaxy -- flows down through Auriga past Altair
(completing the Summer
Triangle), then plunges in two streams through Scorpius and Sagittarius, the latter holding the center of the Galaxy. From a dark
sky, the view is glorious
indeed, with bright stars set into the flowing milky circle.
