Photo of the Week.. The fully eclipsed Moon of October 8,
2014, sets in early morning twilight. See a somewhat
later view with the Moon deeper into Earth's shadow.
Astronomy news for the week starting Friday, October 10, 2014.
After full Moon and the glorious total eclipse last Wednesday morning, the
Moon fades this week in its waning
gibbous phase, finally passing third
quarter on Wednesday, October 15, about the time of Moonset in
North America. Look for it in the morning sky when it is so close
to the actual quarter that you cannot tell the difference. We
thereafter see a little bit of the waning
crescent as our companion dives toward new Moon and a partial
eclipse of the Sun late next week.
In the third century B.C., 2300 years ago, Aristarchus of Samos
actually made an estimate of the ratio of the distance of the
Sun to that of the Moon by observing the angle between the Moon
and the Sun at the time of the quarters. If the Sun is
infinitely far away, the angle should be exactly 90?. The closer
the Sun, the smaller the angle. Aristarchus found an angle of
87? and announced that the Sun is 20 times farther from the Earth
than is the Moon. Unfortunately, his method is impossible to
apply with any accuracy because the Sun is so far away (20 times
more distant than he thought), and because the true angle is so
close to 90? that it cannot be discriminated from a right angle.
His result was produced by simple (and understandable)
observational error. Nevertheless, the idea is ingenious, and
even if his measurement was wrong, his conclusion of enormous
distance was correct. ("Astronomy!" HarperCollins 1994,
copyright J. B. Kaler)
Though Saturn is
effectively gone, lost to twilight, Mars drifts
along to the east against the background stars to the east of Antares between Scorpius and Sagittarius almost as far south of the celestial equator as the planet can
get (nearly 25 degrees) and not setting until an hour and a half
after the sky is fully dark. Then around 2 AM Daylight Time, Jupiter makes
its dazzling appearance popping up above the eastern horizon,
the giant planet on the border between Cancer and Leo to
the west of Leo's luminary, Regulus, and very obvious as the
sky lightens. On Thursday the 16th, Mercury
passes inferior conjunction with the Sun, the little planet more
or less between us and the Sun (though
not crossing it) and quite invisible.
By mid-evening, the Summer
Triangle of Deneb, Vega, and Altair (the Triangle's southern
anchor) is slipping to the west of the celestial meridian, while Pegasus, with its Great Square, lies to the
east of that north-south line. Not quite 30 degrees to the east
of Altair, find Enif, the bright
western leader of the celestial Horse. Just to the west of
Enif, in a dark sky you might spot the small ragged rectangle
that makes Equuleus, the "Little
Horse, which frisks just to the southeast of Delphinus, the Dolphin.
