Photo of the Week. Continuous lightning over the sea
furiously backlights the clouds that created it. (Second in a
series of three. See number 1.)
Astronomy news for the week starting Friday, September 1, 2006.
With a couple of good exceptions, this seems to be a week for the
outer planets, which might then be appreciated even if unseen.
First, though, comes the Moon, which
spends most of the week waxing through its
gibbous phase, fattening to full, which is passed on Thursday,
September 7 (yes, it is September, time to think about fall, which
begins this year in North America on September 22). On Tuesday the
5th, the Moon passes a few degrees to the south of Neptune (still in far-eastern Capricornus), and then on Thursday the
7th much closer to the south of Uranus (in Aquarius,
10 degrees southeast of the "Water
Jar"). The planet is actually occulted by the Moon as seen
from Australia.
Then the Moon takes on the Earth's shadow, at full phase clipping
it for a partial eclipse. Unfortunately it takes place in
early afternoon for North America with the full Moon out of sight.
Europeans and Africans, however, will get a fine view of it. Not
that it will be very impressive, as only a tiny northern section
actually gets into full shadow.
Uranus is now at its best, passing opposition with the Sun on
Tuesday the 5th, when it rises at sunset, crosses the meridian at
midnight, and sets at sunrise. Just shy of fifth magnitude, the
planet is visible to the naked eye in a dark sky, and is an easy
object in binoculars: providing you can position it on an atlas
among the stars. By odd coincidence, at almost the same hour Pluto ceases
retrograde (westerly) motion, the planet (which can stray far
from the ecliptic) close to
the juncture where Serpens
Cauda, Ophiuchus, and Sagittarius all come together.
Planet or not? Traditionally called a planet
(since its 1930 discovery by Clyde Tombaugh), Pluto is the leading member
of the Kuiper
Belt, a broad region of planetary debris that extends far
beyond Neptune. Though barely second largest after "Xena" (2003
UB313) it is much closer, a small portion of its orbit dipping
inside Neptune's. The International
Astronomical Union has just dropped Pluto from its status as
official "planet." In many minds and hearts, however, it will
unofficially remain in its own unique category as "honorary
planet."
With the naked eye, you still have Venus to
admire. The bright planet rises in early morning twilight around
5:30 AM, with much dimmer Saturn to the west of it. While a
quarter as bright as Venus, Jupiter
stands out the better, as it is so nicely visible in the early
evening (in Libra, just northwest
of Zubenelgenubi) in a dark
southwestern sky. Setting ever earlier, however, it is now down
and out of sight by 10 PM, leaving the sky devoid of any of the
classical ancient planets.
This is a fine time of year to admire the vastness of Ophiuchus, the Serpent Bearer
(wrapped with Serpens itself).
The constellation looms like a huge distorted pentagon between Scorpius to the south and Hercules to the north. Dominated by
second magnitude Rasalhague
(Alpha Ophiuchi), the eastern portion of it is host to the western
branch of the Milky Way. To
the northeast in the giant constellation is a small, pretty vee-
shaped asterism called "Poniatowski's
Bull," which at one time was considered a constellation in its own right.
