Skylights featured four times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. As spring comes on, Cassiopeia
and Perseus leave a reminder of fall and winter, the Milky
stretching between the two, the Double Cluster right in the middle.
Astronomy news for the short week starting Sunday, March
30, 2003.
The next Skylights will appear on Friday, April 4.
It is the week of the new
Moon, when the skies are dark all night, allowing us to see the
stars in all their glory, the phase taking place on Tuesday, April
1 (no April Fool here, it really does). Observational astronomers
divide themselves into two groups, one that requires "dark time"
between third and first quarter, and the "bright time" people,
whose work is not hampered by moonlight. First and third quarters
by themselves (and the couple days around them) are aptly referred
to as "grey time." Northern hemisphere Spring is the time that
dark time astronomers most emerge, as the Milky Way
lies on the horizon, allowing them a view perpendicular to the
Galaxy's dusty plane to see the realm of the galaxies, Virgo, Leo, Ursa Major, and Coma Berenices filled with them.
Two days after new, the Moon passes its apogee point, where it is
farthest from the Earth, a distinctly uneventful event. The waxing
crescent will become barely visible the night of Wednesday, April
2, when it will be just to the left of
Mercury, which is growing out of bright evening twilight. The
night of Thursday, the 3rd, the Moon will be far better visible,
with earthlight illuminating its
nighttime side.
Though Venus
is still with us as the "morning star," it is notably lower in the
southeast, now rising after the break of dawn. In the evening sky,
Saturn
goes to the other limit. Now well west of the meridian as the
sky grows dark, the planet sets around midnight. Two planets are
in the middle. Growing brighter in the morning southeast, Mars
rises around 2 AM, while
Jupiter, which quite dominates evening skies, is high in the
south at the end of twilight, and does not set until after Mars
rises.
April is time for Orion's
leaving, that icon of the winter sky now well to the west at
sunset. Now it is time to admire the icon of spring, the Big Dipper, which is high in the
northern sky by 10 PM. South of the Dipper lies Leo, while farther to the south
sprawls the longest constellation in the sky, Hydra, the sea serpent. On its back
ride three constellations, dim modern Sextans, the Sextant, also-
dim but ancient Crater, the Cup,
and quite prominent Corvus, the
Crow, its two upper stars pointing eastward to Spica in Virgo. Hydra spills from the northwest to the
southeast. At one time the 26,000 precessional wobble of the
Earth's axis had it resting close to the celestial equator.
