Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Evening falls quietly as we wait
for the stars.
Astronomy news for the week starting Friday, June 27, 2003.
The week begins almost at the new
Moon, as the phase occurs Sunday, June 29, just about noon in
North America. When the Sun is near its highest point in the sky,
the Moon will be just above (to the north of) it, and just missing
making a solar eclipse. By the evening of Monday the 30th, our
lunar companion will be visible low in the northwest at twilight.
The night of Wednesday, July 2 finds the growing crescent just to
the northeast of bright
Jupiter, the planet that still -- once the Moon is out of the
way -- dominates evening skies. Though not for long, as Jupiter is
now setting just at the end of evening twilight, and will be
getting ever-harder too see.
At midnight Central Standard Time the night of Thursday, July 3 (1
AM CDT the morning of Friday, July 4, 2 AM EDT, 0600 Greenwich Time,
11 PM CDT July 3), the Earth passes the aphelion of its orbit, where it is
farthest from the Sun, at a distance 1.7 percent farther than
average, 94.5 million miles, 152.1 million kilometers. That we are
farthest from the Sun in the middle of summer is a clear indication
that the
seasons are not caused by variation in solar distance, but
instead by the tilt of the Earth's axis relative to the orbital
perpendicular, allowing the Sun to shine high first in the northern
hemisphere (bringing spring and summer to the north) and then high
in the southern hemisphere (bringing spring and summer there,
autumn and winter in the north). Since we are farthest to the Sun
in southern hemisphere winter and nearest in southern summer
(reversed in the north), southern hemisphere seasons are -- all
things equal -- more extreme than those in the north, but the
effect is lost in that the southern hemisphere is dominated by
oceans, which moderate them.
Mars, on the other hand, has no liquid water. Its orbit is
eccentric, but otherwise the planet is configured much like Earth.
There the southern hemisphere seasons are notably more extreme than
the northern (the "snow," frost really, being dry ice rather than
water ice). That is something to ponder when watching the
brightening planet rise. Now about as bright as the sky's
brightest star, Sirius, and moving
through southern Aquarius, Mars
lofts itself above the southeastern horizon around midnight
Daylight Time, and thereafter dominates the morning (brighter Venus
rising less than an hour before the Sun and difficult to see).
Find bright reddish Antares of Scorpius beautifully visible low in the
south around 11 PM. Look upward to see two heroic figures, first
pentagon-shaped Ophiuchus, the
Serpent Bearer (wrapped with Serpens), and then Hercules, the strong man of ancient
times. Binoculars pointed to northern Hercules will reveal a fuzzy
patch, one of the great sights of the northern sky, the globular
star cluster M 13, which contains the order of a million stars.
