SKYLIGHTS
Astronomy news for the week starting Friday, January 28, 2000.
The Moon begins our week in its third quarter and then spends the
rest of the week waning in its crescent phase toward new, becoming
lower and lower in the early morning sky. The morning of
Wednesday, February 2, it will pass very close to Venus, the two
making a wonderful classic sight in the southeastern morning
twilight, one worth getting up to see. At 9 AM Central Time, the
crescent Moon will lie only 1.5 degrees north of the brilliant
planet, so that in twilight it will be only a bit farther to the
northwest. By all means try to take a look. The morning of Friday
February 4 the Moon presents a somewhat unusual challange, as in
North America it will be only about 24 hours from new. The minimum
is commonly taken as 19 or 20 hours, giving us a chance to see an
extraodinarily thin Moon close to the horizon. The Moon also says
goodbye to January by passing its apogee, when it is farthest from
the Earth, on the last day of the month.
The moonless evening, now beautifully dark for observing the stars,
is still dominated by Jupiter, high to the southwest at nightfall,
and by Saturn, just a bit to the east of Jupiter. "Nightfall,"
however, though commmonly used, is a poor choice of word. Look
after sunset to the east and you can see Earth casting its shadow
onto the atmosphere, the shadow appearing as a dark band on the
horizon. As the Sun sets, the shadow rises higher and higher until
it sweeps overhead and the sky becomes dark. Night does not fall;
it rises.
The end of January is prime Orion time, the Hunter due south at 9
PM. Mintaka, the right hand star of the three-star belt (the
Arab's "String of Pearls"), closely marks the celestial equator,
the circle that lies above the equator of the Earth and that
divides the sky into its northern and southern hemispheres. Only
18 minutes of arc (0.3 degree) south of the equator, Mintaka is
closer to the equator than Polaris is to the pole! Then look to
the three-star "sword" that drops down directly below the belt.
Even the simplest binoculars will show that the center star is
fuzzy. It marks the position of the great Orion Nebula, a
spectacular sight in even a small telescope. Some 1300 light years
away, this vast cloud of interstellar gas, lit by a hot massive
star in the center (Theta-1 Orionis C), is 25 light years across --
6 times the distance between the Sun and the nearest star, Alpha
Centauri. It is filled with new stars and lies at the front of a
vast cloud of dark dusty interstellar matter that fills most of the
constellation and that is an immense factory for the birthing of
yet more stars. Go admire this grand sight of winter.
