Skylights featured five times on Earth Science
Picture of the Day: 1
Photo of the Week.. Venus (at right) and Mercury
visit each other during the first week of July, 2005.
Astronomy news for the week starting Friday, July 22, 2005.
Our Moon spends most of the week in its
waning gibbous phase, rising later and later after sundown, and
finally passes its
third quarter on the night of Wednesday, July 27, when it rises
around midnight Daylight Time, after which it goes into the first
stages of the waning crescent. On the night of Saturday the 23rd,
the Moon passes to the south of Uranus, and during the day of Wednesday the 27th
a few degrees to the north of Mars. The night of Tuesday the 26th, the Moon will
therefore be to the west of the red planet, while on the night of
Wednesday the 27th it will be to the east of it.
Venus shines ever more brightly in the western
evening twilight sky. Watch as it passes just above the star Regulus in Leo the night of Friday the 22nd. Saturn,
however, is now truly gone from view, as it passes conjunction with
the Sun on Saturday
the 23rd, when it is on the other side of the Sun and far away, at
a distance of just over 10 times that between the Sun and the
Earth. Conjunctions of the outer planets with the Sun mark their
passage from the evening sky to the morning sky. Within a few
weeks you will see the ringed planet rising in dawn as it slowly
leaves Gemini for the next Zodiacal constellation to the
east, Cancer, the Crab. The
passage, and the setting of Venus, leaves the evening sky to giant
Jupiter alone. Now fully
an evening object, Jupiter, in the southwest at nightfall, sets
around 11:30 PM. For a brief time, the sky is then empty of
ancient planets (those known since ancient times), after which we
see the rising of Mars at midnight, the red planet moving rather
quickly to the east against the stars of Pisces.
Mars has an orbital period around the Sun of close to
double that of the Earth (1.88 years). Unlike Jupiter and Saturn,
whose orbital periods are much longer (12 and nearly 30 years), it
takes the Earth a long time to catch up with Mars and to pass it.
As a result, Mars only slowly moves into the evening sky. It will
not come into opposition with the Sun, when it is up all night,
until early November.
For early evening observers, this is the prime season for Ursa Minor, as at twilight its Little
Dipper stands nearly vertically on its handle, its end marked by
the North Star, Polaris. Above
the Dipper lies a great curve that marks the center section of Draco the Dragon. High in the
northwest find the Big Dipper of
Ursa Major, while low in the
northeast Cassiopeia rises upward,
reminding us that the cool nights of autumn are not that far off.