SKYLIGHTS
Astronomy news for the week starting Friday, October 15, 1999.
Next week's Skylights will be sent out on Saturday, October 23.
The Moon begins the week having just passed north of Mars and then
passes through its first quarter on Sunday, the 17th in western
Capricornus. The same night, it passes Neptune, the following
night Uranus (which is actually hidden, or occulted, around
midnight). The remainder of the week sees the Moon growing and
brightening through gibbous as it heads toward full.
Jupiter is now becoming glorious in the early evening sky, rising
shortly after sunset, more distant and dimmer Saturn following soon
thereafter. Shining at minus third magnitude, this giant of the
Solar System, a tenth the diameter of the Sun and a thousandth its
mass, dominates the nighttime sky until Venus makes its appearance
in the east well before the arrival of dawn. By then Jupiter has
moved far to the west. Though Venus has passed its point of
greatest brilliancy, it has dimmed very little and is still moving
farther in angle from the Sun. Not yet having reached its greatest
elongation, or angular solar separation, the planet is still in a
crescent phase, that is, we see less than half its illuminated
face. Galileo's observations of the Venusian phases was powerful
evidence that Copernicus was right, that the Earth really did orbit
the Sun and not the other way around.
The sky is now putting on a grand autumn show, the constellations
of the Perseus myth climbing in the east. Look to the northeast to
see the "W" of Cassiopeia, and toward east to find the diamond-like
Great Square of Pegasus, Andromeda coming off the northeastern star
like a giant string of pearls that ends in Perseus at famed Algol,
the "Demon Star," which represents the head of the slain Medusa.
Algol is the sky's brightest eclipsing double. When every 2.87
days the larger of the pair gets in front of the smaller, blocking
its light, Algol's brightness sinks to a third normal. Below
rising Andromeda find the thin triangle of stars that makes the
ancient constellation Triangulum and below that the flatter
triangle of Aries. Andromeda and Triangulum are not only paired in
space, but also by what they contain. A small fuzzy patch in
central Andromeda, easily visible to the naked eye, is revealed by
the telescope to be a massive Galaxy similar to our own. Two
million light years away, the Andromeda Galaxy, M 31, is the
farthest thing you can easily see without a telescope. Triangulum
contains another, though smaller, somewhat more distant Galaxy, M
33, under ideal conditions also visible to the naked eye.
