Photo of the Week. Blowing clouds enhance a blue
sky.
Astronomy news for the two weeks starting Friday, July 31,
2015.
The next skylights will appear August 14, 2015.
We have before us a beautifully symmetric lunar fortnight that
begins with the full Moon the morning
of Friday, July 31, and ending with new Moon on Friday, August 14.
After full, the Moon goes through its waning
gibbous phase, hitting third
quarter on Thursday the 6th shortly before moonrise, then
fading through the waning crescent until
it finally hits new. The last viewing of the skinny crescent will be in eastern dawn
the morning of Thursday the 13th (but much easier the previous
morning). Though the Moon passes Neptune on Sunday the 2nd, Uranus on Wednesday the 5th, and Mars on
Wednesday the 12th, we can forget about seeing any of the events.
Uranus and Neptune are too faint for the naked eye and Mars is
still caught in morning twilight. The thinning crescent Moon will
lie west of Aldebaran in Taurus the morning of Saturday the
8th, to the east of the star the following morning. The Moon
passes perigee, where
it is closest to Earth, on Sunday the 2nd.
The planets go through their dance in bright twilight and mostly
out of sight. Though
Venus and
Jupiter are again in conjunction as we open our period
(Jupiter 6 degrees to the north), the two set shortly after sunset
and will be hard to see. We'll miss brilliant Venus, which has
graced the evening sky since the last mid-winter. But take heart,
as by month's end it will have cleared morning twilight. Jupiter,
speeding up in direct motion to the east against the stars, goes
less than half a degree north of Regulus in Leo on Monday the 10th, but again their proximity is
pretty much blotted out by evening twilight. The same can be said
for the conjunction between Mercury and Venus on Wednesday the
5th and between Mercury and Jupiter the following night, Mercury
close to invisible. The Ace of the planetary sky is now
Saturn. In the southwestern sky to the northwest of reddish
Antares in Scorpius, Saturn does not set until shortly after
midnight Daylight Time. The ringed planet ceases retrograde and begins
its normal easterly motion against the stars on Sunday the 2nd.
Back in the morning, Mars begins to rise in darkness about as our
period closes.
The annual Perseid meteor shower will be at its best the
night of Wednesday, August 12, after midnight (the morning of the
13th before just before dawn is prime), but is active for a few
days both before and after. The Perseids, which appear to emanate
from the constellation Perseus,
arise from the debris flaked off periodic comet Swift-Tuttle,
which takes 130 years to orbit the Sun and last came by in 1992.
The Perseids typically give us a meteor a minute, often more, and
with the Moon late in its waning crescent phase, the sky will be
especially dark. It's best to look overhead . You do, however,
need a location far away from town lights. That the meteors seem
to come from Perseus is a perspective effect caused by the
relative motions of the Earth and comet. The little meteoroids
are no more than tiny rocks on parallel tracks that burn up in the
Earth's atmosphere. None ever hits the ground.
North of Scorpius, which really
does resemble a giant scorpion with the red supergiant Antares at
its heart, look for the giant distorted pentagon that makes the
great figure of Ophiuchus, the
Serpent Bearer, which is wrapped with equally giant Serpens (which comes in two parts,
Serpens Caput, the Head, and Serpens Cauda, the Tail). To the
north of them find Hercules, the
great mythological Hero, best known for the four star Keystone.
