Skylights featured five times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
, 5
Photo of the Week.. The waxing crescent Moon (Earthlight on the nighttime side
faintly visible) made a fine passage above Venus the night of July
TK, 2005. Mercury is faintly visible down and to the left of
Venus. Mercury was seen better earlier
in the week.
Astronomy news for the week starting Friday, August 5, 2005.
The Moon, having passed its new phase on Thursday, August 4,
completely spans the week in its waxing crescent phase (see the
photo of the week above), the first
quarter not reached until Friday the 12th about the time the
sky darkens. While it is technically possible to see the slim
crescent in western twilight the evening of Friday the 5th, first
visibility is not really reached until the evening of Saturday the
6th. As the crescent grow over successive nights and the Moon
climbs higher in the darkening evening sky we first begin to see
the Earthlight on the lunar
nighttime side and then watch it fade away.
The waxing crescent will provide a pair of treats as it passes the
two brightest planets. On the evening of Sunday the 7th, watch in
bright western twilight for a classic and spectacular pairing of
the crescent with brilliant
Venus, the Moon immediately to the right of the planet. As
seen from Alaska and northwestern Canada, the Moon actually
occults, or passes over, Venus. The following night you will see
the Moon between Venus and Jupiter, which in twilight lies in the southwest and
much higher than Venus. Then the evening of Tuesday the 9th,
the fattening crescent takes on
Jupiter, the planet seen above and to the left of the northern
lunar horn. Note the nice triangle with Porrima, Gamma Virginis, the star
lying up and to the right of the Moon. Again, the Moon will occult
the planet, but as seen only from the southern Indian Ocean and
parts of Antarctica. (Such
occultations are not seen all over the globe because of the
lunar "parallax." The Moon is so close to us, just over a quarter
million miles away, that its position against the more distant sky
depends on the location on Earth: as you move in one direction, the
Moon appears to move in the other, much as an outstretched finger
shifts when seen with one eye and then the other.)
Venus sets in twilight, and Jupiter (still to the west of Spica) goes down around 10:30 PM
Daylight Time, while Mars does the
reverse, and rises brightly an hour later south of the classic
figure of Aries. Additional
planetary news involves opposing events. On Monday the 8th,
Neptune, in Capricornus, passes
opposition with the Sun, while on Friday the
5th,
Mercury passes inferior conjunction with the Sun, when it is
more or less between us and the Sun and thereafter becomes a
morning object.
August is "meteor month," when we celebrate the famed Perseid meteor
shower, which will be at its best for North America the
mornings of Friday the 12th and Saturday the 13th. The shower
results from the shed debris of Comet
Swift-Tuttle hitting the Earth's upper atmosphere. With the Moon out
of the way, under a dark sky we should have a nice show, the
meteors tyically coming at a rate of about one a minute.
If you want to see the newly discovered "tenth
planet," which seems to be slightly larger than
Pluto, you will need a good-sized telescope, as at nearly
magnitude 19 it is over 90,000 times fainter than the human eye can
see. At a current distance of 96.6 AU,
2003 UB313 (no proper name yet) is the most distant Solar
System object ever observed. Near its aphelion point, the body has
an orbital period of 557 years, averages 67.7 AU from the Sun, and
on its looping, eccentric orbit, comes as close as 37.7 AU, closer
than Pluto. Like Pluto, it seems to be a large "Kuiper
Belt" object (part of a debris ring outside the orbit of
Neptune) that was kicked into its big and highly inclined orbit (it
is now in central Cetus, well off
the ecliptic) by Neptune in the early days of the Solar System.
Pluto, and
Triton, the large moon of Neptune, are similar.
The season features the southern sky, with Scorpius riding the meridian to the south as the sky
darkens, and Sagittarius with its
brilliant (at least in a dark sky) Milky Way
transiting the meridian a bit later. Look for the red supergiant
Antares, which lies at the
Scorpion's heart, for the trio of stars up and to the right of it
that marks the beast's head, and then the graceful curve of stars
that (for northerners) descends to the horizon and mark the body.
