Skylights featured five times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
, 5
Photo of the Week.. Trees stand before the glory of
the rising Sun...
Astronomy news for the two week period starting Friday,
June 24, 2005.
Skylights will next appear on Friday, July 8.
During this fortnight, the Moon glides through its waning phases,
beginning with the
waning gibbous, passing through third quarter on
Tuesday, June 28th, then continuing with the waning crescent.
On Friday the 24th, our companion passes five degrees south of Neptune (in Capricornus)
and then on Sunday the 26th, three degrees to the south of Uranus (in Aquarius).
The morning of Wednesday the 29th will be
Mars's turn, the Moon passing a couple degrees to the north of
the red planet.
The grand event, one of the fine ones of the year, is a tight
gathering of planets that will appear low in the west-southwest in
the evening twilight sky (the low altitude and brightness of the
sky making it rather difficult to view). The best time is around
the nights of Friday the 24th and Saturday the 25th, when you will
see (from left to right) Saturn
, Venus
, and
Mercury all in a row only a couple degrees long, Venus by far
the brightest. Farther to the right will be Gemini's Pollux and Castor. The motions of the planets
will be easily visible from night to night. On Saturday the 25th,
Venus will pass 1.3 degrees to the north of Saturn, while on Monday
the 27th, Venus will have switched places with Mercury and will
pass a mere tenth of a degree north of the smaller planet, making
one of the closest planetary couplings anyone is likely to see.
The two will hang together for a few days, while Saturn sinks ever
farther into twilight. Find a clear horizon, and take binoculars.
The low altitudes of these planets then leaves the evening
nighttime sky to Jupiter. As twilight
ends, the giant planet will lie well to the southwest, moving
slowly eastward against the stars back towards Spica in Virgo. Around Saturday the 26th, Jupiter does a sort
of "crossover" with Mars, the former setting near local midnight (1
AM Daylight Time) as the latter, now in Pisces, rises.
The last passage the period involves our own planet, which goes
through aphelion, our farthest point from the Sun, about midnight the
night of Monday, July 4, coincidentally to the sight and sound of
fireworks in the US. At that time, the Earth will be
94,512,036 miles (152,102,378 kilometers) from the Sun, about 1.7
percent farther than average. Obviously, given that greatest
distance corresponds to the hottest time of the year, the solar
distance has nothing to do with the
seasons, which are caused exclusively by the tilt of the
Earth's rotation axis relative to its orbital axis and the varying
altitude of the Sun during the day (which affects the heating of
the ground).
Two of the most famed figures of the sky oddly lie at about the
same separation from their respective celestial poles. In the
south, Crux, the Southern Cross,
is just 30 degrees from the South
Celestial Pole, while in the north, The Big Dipper of Ursa
Major lies between 30 and 40 degrees from the North Celestial
Pole (and Polaris in Ursa Minor). Residents a bit south of
30 degrees south latitude then see the Cross as circumpolar (never
setting), while those north of about 40 degrees north latitude see
the Dipper as circumpolar. An even better match is between Crux
and the "W" of Cassiopeia, which is
closer (only 30 degrees from) the North Celestial Pole and is
circumpolar for those only a bit north of 30 degrees north
latitude.
