Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
.
Photo of the Week.. Not a rainbow, but the "22-
degree halo" around the Sun (hidden in the trees below) caused by
refraction through floating ice crystals. The "upper tangential
arc" is barely visible at the top of the halo.
Astronomy news for the week starting Friday, February 28, 2003.
So ends our shortest month, which next year will be extended to 29
days to give us 366 days in the year and which averages out over
the short term to 366.25, very close to the 365.2422...days that
actually are in the year. Dropping 3 leap
years every 400 years (as we do in century years not divisible
by 400) gives us a long term average of 365.2425 calendar days,
almost perfect.
This week "sees" the "dark of the Moon," the poetic name for the
new Moon, which takes place on Sunday, March 2. We will see the
last glimmering of the waning crescent
the mornings of Friday, February 28, and Saturday, March 1, and
then pick up the first sight of the waxing crescent
in the evening of Monday, March 3, although that will be a
difficult sighting to make. By the night of Tuesday the 4th,
however, the growing crescent will be obvious. "Darkness"
referring to the Moon is filled with misconception. "The Dark Side
of the Moon" commonly refers to the "far
side," which we cannot see, as the Moon keeps one face pointed
at us. In truth, the far side gets as much sunlight as the near
side. While at new Moon the near side is in night, the far side in
full daylight, as it faces the Sun. "Dark" in this context means
"hidden." We now have a full picture of the far side, which is
heavily cratered but lacks the large, dark, lava-filled basins that
make the "man in the Moon."
Venus
is brilliant as always, but rides lower now in the southeastern
morning sky, though still rising a bit before dawn. Venus, Mars, and
Antares in Scorpius make a long line stretching to the west.
Venus's inner companion Mercury
, now not visible, makes two passages, one with the Moon on
Saturday the first, the other with Uranus
on Tuesday, the 4th. The evening sky captivates, with Saturn
high to the south, not quite overhead, during the middle of evening
twilight and Jupiter
well up in the east, the giant planet crossing the meridian to
the south about 10 PM.
As the Earth orbits the Sun, the constellations slip one degree per
night (when seen at the same time) to the west. Orion stands tall to the south
around 7 PM, but in two weeks, he will glide past the meridian an
hour earlier. Look below him to see Lepus the Hare, and then below that to find the pretty
triangle that makes Columba, the
Dove. Columba makes a good reference with which to find a much
more obscure modern constellation, Caelum, the Engraving Tool, which consists of a small
string of faint stars to the west and southwest of Columba. In the
other direction, below Sirius (the
brilliant star down to the left of Orion), if you are far enough
south you can spot the second brightest star of the sky, Canopus in Carina, the Hull of the great ship Argo. You must be south of 37 degrees north latitude,
however, before Canopus can be seen to swing above the southern
horizon.
