Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Mars passes north of the waning
gibbous Moon on July 17, 2003, amidst the stars of Aquarius.
Astronomy news for the short week starting Sunday, August 24,
2003.
Skylights will resume its normal schedule on Friday, August 29.
The Moon
passes its new phase this week on Wednesday, August 27, and is
effectively out of sight for this short period except for dedicated
viewers who might see it as a thinning waning crescent the morning of
Monday the 25th, or as an equally thin waxing crescent in twilight the
night of Thursday the 28th. That evening the Moon will be in
conjunction with Mercury,
passing well to the north of the nearly invisible planet.
Two planetary oppositions (to the Sun) occur this week, the first
one belonging to
Uranus (on Sunday, the 24th), rendering the planet about as
bright as it gets (at magnitude 5.7) as it moves
retrograde within southern Aquarius. The event is overwhelmed, however, as is
about everything else, with the
favorable opposition of
Mars, which will take place on Thursday, August 28th, at around
noon in the Americas, not that one or two days makes much
difference, as Mars slowly moves into this position and slowly
moves away from it as it too retrogrades through southern Aquarius.
For the few days bracketing opposition, Mars will rise at close to
sunset, set around sunrise, and cross the meridian to the south
around midnight, 1 AM Daylight Time. (The opposition is actually
not exact, as Mars is seven degrees south of the ecliptic, so in
the Northern Hemisphere, it will actually rise after sunset.) The
planet's orbit is among the more elliptical of the planets. Its
"synodic period," that between successive oppositions, is 2.14
years. When the opposition is at Martian aphelion (farthest from
the Sun), the planet is about twice as far away as when it is at
Martian perihelion (closest to the Sun), when the opposition is
called "favorable." Such favorable oppositions occur on a 15-year
cycle. This particular opposition is nearly perfect, and is the
closest in over 50,000 years (34,646,418 miles, 55,758,006
kilometers), though the difference with past favorable oppositions
is rather marginal (Mars only about one percent closer than it was
at the fine 1971 favorable opposition). Because of the
eccentricity of the orbit, the closest approach actually occurs a
day and a third earlier than the actual opposition, on the morning
of Wednesday, the 27th, when the planet will be as bright as it can
get as seen from Earth. The angular size of the Martian disk will
also be as large as possible, 25.1 seconds of arc across, just
under half a minute of arc, which is still unresolvable to the
naked eye (that is, Mars will appear as a yellowish to reddish
point, depending on your color vision). The telescope will show
dark markings and a polar cap. If you stay up late to admire the
"red planet" be sure to find Saturn, which rises, beautifully set in Gemini, around 2 AM Daylight
Time.
While waiting for Mars to climb above the trees and houses, be sure
also to admire Scorpius low in the
southwest, Ophiuchus above it,
and Sagittarius to the left.
