Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Saturn shows off its beautiful
rings and banded cloudy surface, which is made of ammonia crystals.
The rings consist of countless small icy rocks. The gap in the
ring system, the "Cassini Division," is caused by gravitaional
effects of orbiting satellites. The picture, as it appears through
the telescope, is upside-down. Photo by Mark Killion.
Astronomy news for the week starting Friday, April 30, 2004.
The Moon passes through its full phase
this week on Tuesday, May 4, rather well before moonrise in North America. As a
result it will rise shortly after sunset in darkening twilight. It
will also undergo total eclipse on that date, but since full (a
requirement for lunar eclipse) takes place in the North American
afternoon, the event will not be seen there. Europe and Africa, on
the other hand, will get a fine view.
Venus
tops the planetary list this week as it reaches its greatest
brilliancy (for this orbital evening vista) on Sunday, May 2, when
it hits "apparent magnitude" -4.5. (The magnitude scale is such
that each division corresponds to a factor of 2.5 in brightness;
the smaller the number, the brighter the object. The faintest
stars visible without a telescope are magnitude 6) At that
time Venus will be over eight times brighter than
Jupiter (which will have a magnitude of -2.2), 16 times
brighter than the brightest star, Sirius (magnitude -1.46), and a
remarkable 275 times brighter than
Mars, which has fallen to second magnitude and which
attractively will lie up and to the left of Venus. On May second
Venus will also lie very close to the star Elnath, Beta Tauri, the whole affair
making the western evening sky quite busy. Adding to the show, Saturn, which now sets around midnight,
lies between Venus and Jupiter.
Venus is brightest as seen from Earth when it is in a fairly thin
crescent phase. (Since it is preparing to
come between us and the Sun, we see only a part of its daytime
side). Its closeness, however, offsets the phase effect. Still
setting quite late in the evening (around 11:30 PM Daylight Time),
Venus will now quickly descend toward the evening horizon. On June
8 it will pass in front of the Sun for a very rare transit, the last one seen in 1882. It will then pop up in
the morning sky.
Jupiter, high to the south as evening descends, takes second place
in planetary news, as it ceases its retrograde motion on Wednesday the 5th, and starts its normal
easterly trek against the stars and heads from Leo toward Virgo.
The most familiar figure of northern skies is probably the Big Dipper of Ursa Major, the Greater Bear. Though the Dipper is
obvious, with an active imagination even the outline of the Bear
can be seen, the bowl of the Dipper making its hind quarters, the
handle the tail (never mind that real bears have short tails). To
the south and southwest of the Dipper are three attractive pairs of
stars (which are physically unrelated) that make three of the
Bear's paws. Different cultures see things differently, however.
In old Arabia, the paws (from east to west) were the three "leaps"
of the gazelle, which one might picture bounding along leaving its
tracks behind.
