Astronomy news for the week starting Friday, June 17, 2011.
In its perpetual rounding of Earth, and having passed full phase
last week (when it survived yet another total
eclipse), the Moon spends the
early part of our week in the waning
gibbous phase, not going through its third quarter until the morning of
Thursday, June 23, when from North America you can see the near-
perfect quarter to the south at dawn. It then slips into the waning crescent phase. On the
evening of Monday the 20th, the Moon swings six degrees north of Neptune (the
rather large angle the result of the Moon's orbital tilt taking it
north of the ecliptic), while
during the night after third quarter it similarly takes on Uranus (both the
planet and the Moon near the Vernal
Equinox in Pisces). The
night of Thursday the 23rd the Moon finishes the week by going
through its apogee, where it
is farthest from the Earth.
Having passed the meridian well before
Saturn is now firmly into the southwest as the sky darkens, and
still to the northwest of Spica in
Virgo. Setting ever earlier, the
planet is now gone by 1:30 AM Daylight Time. Only half an hour
after Saturn's disappearance, though,
Jupiter makes its jump over the eastern horizon, the planet now
near the Pisces-Aries border.
The first in a line of three, Jupiter leads (and is pulling away
which now rises close to the Aries-Taurus boundary as dawn begins to light the sky.
Venus, moving oppositely to these two relative to the Sun, continues
to lose ground, not rising until mid-twilight.
The big event, though, involves
Earth, as at 12:16 PM Central Daylight Time on Tuesday the 21st
(1:16 EDT, 11:16 AM MDT, 10:16 PDT, etc.), the Sun passes across
the Summer Solstice (which is close
to the line that formally separates Gemini from Taurus),
marking the beginning of northern hemisphere astronomical summer.
On that day, the Sun (at its maximum angle of 23.4 degrees north of
the celestial equator) rises and sets
as far to the north of east and west possible, is up for the
maximum number of hours (giving us the year's two shortest nights),
is overhead at the Tropic of
Cancer (23.4 degrees north latitude), and is as high as
possible at noon for anyone to the north of that circle (and as
high as possible all day at the north pole).
For the next six months after, the Sun will be moving toward the
south and Winter Solstice passage
Look for Arcturus, the brightest
star of the northern hemisphere, high to the south as the sky
darkens. Then plunge far southward to see the stars of northern Centaurus, the classical
Centaur, as they glide above the southern horizon. From north of
50 degrees north latitude, they are lost, while from the Tropics
you can also see Centaurus's luminary, Alpha Cen, as well as the Southern Cross to the west of it, with bright Beta Cen in between.