Astronomy news for short week starting Friday, April 18, 2003.
The Moon passes its last (third)
quarter the morning of Wednesday, the 23rd, just about the time
of sunrise in North America, when the Moon is seen nearly due south
and low in between the classic figures of Sagittarius and Capricornus. About midnight on the night of Tuesday,
the 22nd (just as Tuesday goes to Wednesday), our Moon will pass
about three degrees to the south of Mars, which
(now well to the east of the Little Milk Dipper in Sagittarius) is
heading toward Capricornus itself. The juxtaposition will help in
locating the red planet, which has now brightened to "zeroth"
magnitude, which places it in the realm of the very brightest stars
and comparable to Betelgeuse
in Orion, the star now well to
the southwest at the end of twilight.
The "magnitude" system goes back to ancient Greek times, when Hipparchus divided the stars into six brightness
groups, first magnitude the brightest. The "first magnitude"
stars, however, span a very large range, and in modern times the
brightest had to be put into magnitude zero, even -1.
Venus, still visible low in the east in morning twilight, is
now at -4, and is the brightest object in the sky other than the
Sun and Moon, and at its brightest (now well past) is visible in
The outer planets,
Uranus (respectively in central Capricornus and western
Aquarius) are now well clear of the Sun. The Moon will pass five
degrees to the south of Neptune about midnight the night of
Wednesday, the 23rd, the planet visible in a small telescope.
Since these planets are both close to the ecliptic plane, note that
the Moon at this point in its orbit is well to the south of the
ecliptic, the result of the 5-degree tilt of its path
(relative to the ecliptic) around the
Earth. Better to admire the giant planets Jupiter and Saturn. Jupiter is glorious very high to the
south at the end of evening twilight, while Saturn hovers in the
west just to the right of Zeta
Tauri (which makes the southern horn of Taurus).
Almost immediately to the south of Jupiter (now in central Cancer near the Beehive cluster) you can find a
distorted circlet of stars that makes the head of Hydra, the great "Water Serpent,"
which winds to the southeast past its luminary, the lonely Alphard, then down to the bright
star Spica, in Virgo, Hydra the longest
constellation in the sky. On its back ride fairly obvious Corvus, the Crow, an elongated box,
the top two stars of which point east to Spica, and Crater, the Cup, a figure so dim that
one wonders why the ancients made a constellation of it. Jupiter,
Hydra's head, and Procyon in Canis Minor (to the west of Hydra)
form nearly a right triangle, making the "beast" easy to find.