Astronomy news for the week starting Friday, June 29, 2012.
We start our week with the Moon in the waxing gibbous phase as it approaches full on Tuesday, July 3, during daylight
hours so that it will rise that night just barely past the phase.
It thereafter gibbously wanes until it
reaches third quarter next week. Just
before full phase, the Moon goes barely south of Pluto, passing
in front of the distant planet as seen from Antarctica, not
that anyone will actually SEE it happen. Consistently, on Friday,
June 29, Pluto is also opposite the Sun, almost lost among the
myriad stars of northern ]sag-p.html">Sagittarius. Then, only
two days before full, on Sunday the 1st, the Moon goes through perigee, where
it is closest to Earth, the proximity in time helping to raise
larger tides
on the coasts.
Earth, on the
other hand, does just the opposite, as on the night of Wednesday,
the fourth of July, it passes aphelion, its farthest distance from
the Sun on
its elliptical orbit, 94.5 million miles (152.1 million
kilometers), about 1.7 percent farther than average. Obviously,
given July's heat, distance from the Sun has little to do with the
seasons, which are caused
almost entirely by the tilt
of the Earth's rotation axis of 23.4 degrees relative to the
orbital perpendicular.
Other planetary action is vastly better than that involving poor
Pluto. Both rising around the beginning of morning twilight, Jupiter and
brighter Venus again make
a fine pairing, giving us something of a repeat of their marvelous
evening conjunction last March. Not so close as before, Jupiter
will stand above Venus for some time, the two gradually drawing
apart. Look the morning of Sunday the first to see (from bottom to
top) Aldebaran and the Hyades of Taurus, Venus, Jupiter, and above them all, the Pleiades.
On the other side of the sky, Mercury goes
through greatest eastern elongation relative to the Sun on
Saturday, June 30, the little planet setting just before the end of
evening twilight. Transiting the meridian before sunset, Saturn is in the
western celestial hemisphere when it becomes visible still to the
north of Virgo's Spica, the two making a most notable
pair. Farther over to the west, Mars, in western Virgo, falls to the southeast of Regulus, between it and Spica-
Saturn, the red planet setting around midnight, Saturn going down an hour later.
The Moon interferes with our admiration of the constellations. But once it is out of
the way, look far below the Saturn-Spica pair to find the bright
stars of sprawling Centaurus,
which blend in smoothly with those of Lupus (the Wolf) to the east, which in turn howls to
the southwest of striking Scorpius.
