Astronomy news for the week starting Friday, January 8, 1999.
We begin the week with the Moon just entering its last quarter, the
phase actually reached the morning of Saturday the 9th around 8 AM
while the Moon is still brightly visible in the western morning
daytime sky. At that time you will see that the Moon is exactly 90
degrees to the west of the Sun. Note that if you bisect the
"terminator" (the day-night division on the Moon, which always
faces away from the Sun), the line will pass through the Sun, as of
course the Sun is the Moon's illuminator.
On the morning of Saturday the 9th, the Moon will also be just to
the west of Mars, while on the morning of Sunday the 10th it will
be to the east of the red planet. Mars must therefore be close to
"quadrature," when it too is 90 degrees from the Sun as viewed from
Earth. Mars is becoming ever more visible, and will soon encroach
on evening hours. Its mythological opposite, Venus, is now
becoming visible as well, glowing brightly in western evening
twilight. The two will never really get together this year,
however, as by the time Mars is setting in the early evening, Venus
will be gone, their closest approach to be in late summer. In
between the two planets, of course, is brilliant Jupiter and
fainter Saturn, both now to the southwest in mid-evening.
As the new year now proceeds, sunrise is finally coming earlier.
Because of the elliptical shape of the Earth's orbit and the tilt
of the terrestrial axis, earliest sunset and latest sunrise do not
take place at the time of the solstice when daylight hours are
least; earliest sunset is in early December, while latest sunrise
was last week.
While admiring the planets, don't forget to look at the winter
stars, and then focus in on Sirius, the brightest star in the sky,
down and to the left of Orion's belt. All stars twinkle as a
result of variable refraction -- bending -- of light in the Earth's
atmosphere. As the brightest star, and also because it is fairly
far south and for most northern observers low in the sky, Sirius is
also the champion twinkler, the star beautifully jumping and
flashing with variations in color, so much so that it is often
taken as a "UFO." It is, however, just a star, though an
interesting one a bit over twice as massive as the Sun with a
"white dwarf" companion that is only the size of Earth!