Photo of the Week.. Deepening twilight fills the
skies from 35,000 feet.
Astronomy news for the short week starting Sunday, October 27,
2002.
The Moon approaches its last quarter early in the week, reaching
the phase on the night of Monday the 28th, about midnight in the
Americas, just about the time of Moonrise. In the third century
BC, the great Greek astronomer Aristarchus of
Samos tried to measure the distance to the Sun (relative to the
Moon) by timing the exact moment of the quarter. The angle between
the two would be 90 degrees if the Sun were infinitely far away.
If it was not, then the angle would be less. From his estimated
angle of 87 degrees, Aristarchus found the Sun to be 20 times
farther than the Moon. The experiment is impossible, and the ratio
is actually 400. But Aristarchus was on the right track, clearly
locating the Sun much farther away than the Moon. The night of
Tuesday, the 29th, the Moon will have passed just to the north of
bright Jupiter
.
The time to see the two giants of the Solar
System, Jupiter and Saturn, is still early morning. At that
time, Saturn
lies to the south, just above Orion, while Jupiter is to the southeast, to the east
of the Beehive
Cluster in Cancer. In its
great majesty, Jupiter rolls around the heavens in a dozen years,
at the rate of one constellation of the Zodiac per year. Saturn
takes over twice as long.
On Sunday the 27th, little Mercury passes north of Spica in Virgo,
quite the impossible observation, while Venus passes invisibly
south of the Sun, going through its inferior conjunction with the
Sun on Thursday, the 31st. Because of the tilt of the orbit, the
passage is far to the south of the Sun. Look for this beautiful
planet, the brightest in the sky, in eastern morning twilight in
late November. Venus, the brilliant one, is the classic evening
and morning "star" that all cultures have noted and honored, the
Mayans even making it part of their calendar.
As the Moon departs the evening sky, watch now for the autumn
constellations. Aquarius, with its
"Y"-shaped "Water Jar" gives way to the
"Circlet" of Pisces, above which
lies the striking Great Square
of Pegasus, a centerpiece of fall. To the northeast is Andromeda, made of two graceful
strings of stars. Go a bit to the north of central Andromeda to
find the "Andromeda
Nebula," Messier 31, a "nearby" (all things relative) galaxy
much like ours some two million light years away, and the most
distant thing visible to the unaided eye. Such galaxies abound
into the distance, over a trillion of them potentially visible with
the most sophisticated telescopes. Near it in the constellation Triangulum (the eponymous Triangle) is
Messier 33,
another, though smaller, galaxy at about the same distance that is
also visible, though just barely, to the naked eye.
