Photo of the Week. Cool off with winter's Sirius (to the upper right), the brightest star of the sky, and Canis Major, Orion's bigger Hunting Dog, which sprawls down and to
the left. At the other end of first magnitude, Adhara lies at bottom center.
Astronomy news for the week starting Friday, July 19, 2013.
The week begins with the Moon waxing in a fat gibbous phase as it heads towards full on Monday the 22nd around mid-day and
out of sight. The "grain Moon," the "green corn Moon," will
therefore rise just shy of full (and sunset) the evening of Sunday
the 21st and just past the phase and sunset on Monday. It then wanes in the gibbous phase for the rest of
the week, not reaching third quarter until
Monday the 29th. On the night of Wednesday the 24th, the Moon will
glide six degrees north Neptune. More
importantly, on Sunday the 21st, the Moon passes perigee, where
it is closest to Earth on its modestly elliptical orbit (perigee
some 5.5 percent closer than average). Perigee's nearness to full
Moon will bring heavier tides than normal
to the coasts.
Monday, July 22, is a remarkable day of events and coincidences.
Not only do we have a full Moon (near noon and invisible), but have
two close planetary passages, one in the east at dawn, the other in
western evening twilight. In the morning, Mars and Jupiter rise just as dawn is beginning to
break (around 4 AM) only 3/4 of a degree apart, Jupiter the
brighter. Advancing twilight will make them difficult to see,
however, so use binoculars. That evening Venus (which sets around 10 PM Daylight Time
just before twilight ends) will hover just over a degree above the
star Regulus in Leo, the star much fainter than the
planet. Binoculars will help a lot. You'll need a good flat
horizon for both. As the month proceeds and Jupiter rises ever
earlier, its morning visibility will notably improve. So will that
of Mercury
, which rises in bright dawn.
That leaves us again with Saturn. Well into the
southwest as the evening sky darkens, the planet sets just half an
hour past midnight Daylight Time, giving us more than three hours
with no bright planet. Having just entered direct easterly motion
from westerly
retrograde as seen against the stars, Saturn crawls with
agonizing slowness, remaining a dozen degrees to the east of Spica.
When viewed at the same time on successive nights, the sky shifts a degree to
the west as a result of the Earth orbiting the Sun and our
facing in slightly different directions. By the time the
sky is fully dark, Scorpius, with
Ophiuchus and Serpens above, now
straddles the southern celestial
meridian. Bright orange Arcturus however will be seen now
toward the west as the old spring stars slip away. Wait until
around midnight to see Vega, just
slightly fainter than Arcturus, nearly overhead as viewed from the
middle latitudes of the northern hemisphere.
