Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Two ancient ruins: the Moon
glows faintly over the corner of the Parthenon in Athens.
Astronomy news for the week starting Friday, October 17, 2003.
The Moon begins the week just shy of its third quarter, the
phase actually reached on Saturday, October 18, just about the time
of sunrise in North America, allowing us to see very close to the
"perfect third" when it is high to the south, rather well above the
ecliptic, and glorious in the growing dawn. Having passed Saturn
the morning of the 17th, the Moon will appear at its third quarter
to the northeast of the ringed planet. Continuing its perpetual
course through its waning crescent phase, the Moon passes Jupiter
the evening of Tuesday the 21st. The morning of the 21st thus sees
the Moon to the west of Jupiter, while the following morning the
thinning crescent shines prettily to the east of it.
While
Venus climbs ever so slowly to the west-southwest in bright
evening twilight (and is still quite difficult to see), and Mars
continues its bright and obvious easterly procession in southern Aquarius (the red planet so very
nicely visible to the south in the evening), Saturn now begins to
make an impact on the nightly sky, rising about 10:30 PM Daylight
Time. Situated high along the ecliptic in central Gemini, Saturn rises almost exactly
the same time as Betelgeuse in
Orion, the Hunter seen nicely
just past the meridian to the south as dawn brightens the sky. At
the same time note brilliant Sirius lower to the south. About
half an hour after Mars sets (around 3 AM Daylight Time), bright
Jupiter rises, and later dominates growing morning twilight. Lost
among the bright planets are much dimmer
Uranus (in Aquarius) and
Neptune (in Capricornus).
Neptune, the most distant of the large planets, 30 times the
distance of Earth from the Sun, finally ceases its
retrograde motion on Wednesday, the 22nd, and begins to move
westerly against the stars. Uranus will follow in November. Since
it was discovered in 1846 as a result of its gravitational effect
on Uranus, Neptune has yet to make a complete orbit around the Sun
(the whole circuit taking 164 years).
As Earth circles the
Sun, we face in a
different direction (if observing at the same clock time) each
night, so the stars and constellations constantly shift to the
west. Given 365 days in a year and 360 degrees in a circle (no
coincidence), for the same clock time, the stars move westerly by
a degree per night, seven degrees for each of Skylights' week. So
this week, summer Cygnus and its
Northern Cross lie seven degrees farther westerly than they did
last week. The summer stars thus glide away, while the autumn
constellations -- Pegasus, Andromeda, Cassiopeia -- take their places, and the winter stars -
- in Orion, Canis Major, Gemini
-- shift across the morning sky waiting patiently to take the place
of the autumn stars, and so it has gone from time immemorial and
will go into the infinity of the future.
