Photo of the Week. A flotilla of fair clouds floats
across the sky.
Astronomy news for the two weeks starting Friday, September 11,
2015.
The next skylights will appear September 25, 2015.
The Moon begins the fortnight very late in its waning crescent phase and, as we open the
show, is effectively invisible as it passes new on Saturday,
September 13, when it eclipses the Sun. But don't get too excited
about it, as the eclipse is partial and visible
only from southern Africa, Antarctica, and oceanic points between.
The Moon then emerges for us in western dusk as a narrow crescent the evening of Monday the
14th. The night of Friday the 18th finds the thickening crescent
passing just three degrees north of Saturn, while the following night the Moon glides above Antares in Scorpius with Saturn now to the west. The crescent
phase ends at first quarter the
morning of Monday the 21st shortly after moonset in North America,
after which it fattens in the waxing
gibbous. As the Moon passes full
the evening of Sunday the 27th (during our next session) we will
witness a spectacular total lunar eclipse that's visible throughout the
Americas with the Moon also near perigee, where
it is closest to Earth and appears largest in the sky (though not
by much). So prepare now for this most memorable Harvest Moon,
the one nearest the autumnal
equinox. (The Moon passes apogee, where it is farthest from
Earth, on Monday the 14th.)
Of equal interest, the Sun passes the
autumnal equinox (where the ecliptic intersects the
celestial equator, the Sun moving south) the morning of Wednesday
the 23rd at 3:21 AM CDT shortly before dawn. On that day (excluding the effects of
atmospheric refraction, solar diameter, and the exact timing of
equinoctial passage) the Sun will rise due east, set due west, be
up for 12 hours, and down for 12, hence the term "equinox." The
Sun will also formally set at the north pole
and rise at the south
pole, all in all quite the event as the northern hemisphere
moves from summer into fall.
Earth aside, the other planets are no less intriguing. Venus dominates the
morning sky. Rising well before dawn, our "sister planet" (not
much smaller than Earth) reaches greatest brilliancy on Monday the
21st just after the Moon passes third quarter.
Rising not long before the start of morning twilight, Mars lags behind Venus
and is not terribly bright, just second magnitude. The red planet
passes less than a degree north of Regulus in Leo on Thursday the 24th. Following these two, Jupiter rises as the morning sky lightens.
Back in the evening, Saturn, to the northwest of Antares, goes down by
10 PM Daylight Time, so look early and let the crescent Moon be
your guide (see above).
While the summer constellations
will be with us for some time, the stars of autumn are on their
way. Cygnus, the Swan, with
bright Deneb (the Swan's head) at
its northern end, rides high in early evening, the Milky Way running down the middle. It's
followed to the east by Pegasus (Perseus's
Flying Horse), which is recognizable by its Great Square. Off the northeastern corner run
the star streams that in part represent Andromeda, who was rescued by the great hero.
