Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Asteroid 1998 JK, newly named
as "Asteroid 17581 Kaler," lies at the
center of the left hand
image. At the right are sequential overlayed images
that show the asteroid's motion over a three-hour
period. Since 17851 Kaler (a 5-10 km rock
at the inner edge of the main asteroid belt) is in these images
close to opposition, the motion is east to west, that is, left to
right. Images from the Near-Earth Asteroid Tracking Project,
Near-Earth Object Program.
Astronomy news for the week starting Friday, August 6, 2004.
The week begins with an almost
third quarter Moon, the phase reached on Saturday, August 7.
From that point on, our satellite wanes through
crescent toward new, which it passes next week. The end of the
week sees the slimming crescent moving through Taurus and Gemini as it visits both Venus
and Saturn
. The morning of Wednesday the 11th, the Moon will appear well
above brilliant Venus (which now rises shortly before 3 AM Daylight
Time), while the following morning the Moon will be to the left of
the planet. With luck, the morning of Friday the 13th will be
clear for us to see the Moon passing between Pollux in Gemini (to the left of the
Moon) and Saturn (to the right), the trio plus the other stars of
Gemini (and of course Venus!) making a fine sight. Of the bright
planets, in the evening we can really see only
Jupiter, which is getting more difficult observe in bright
western twilight. The ancient planets (those known since ancient
times) are in fact are all pretty much bundled in the direction of
the Sun, Saturn
and Venus to the west of it, Jupiter, Mars,
and
Mercury in a tight group to the east of it, the latter two
effectively invisible.
This is the week not for planets, however, but for the famed
Perseid meteor shower, which peaks on the morning of Thursday,
August 12. To our great advantage, the Moon will not be a factor
in lighting the sky, allowing the fainter meteors to be seen. The
shower, which may yield one or two meteors a minute, is caused by
debris from
Comet Swift-Tuttle, which orbits the Sun every 130 years on a
long looping path, and last passed into the inner Solar System only
a dozen years ago. The stream of little particles -- not much more
than grains of sand or small fragile rocks -- follows along the
cometary orbit. When our Earth plows through the swarm,
perspective makes the meteors (streaks of light caused by the
particles hitting our atmosphere tens of miles high and heating up)
appear to come out of the constellation Perseus, hence the name. The best place to look, from
the darkest site you can find, is however always straight up. The
Perseid shower is one of the best of the year, and one that you
don't need to wear a winter coat for.
Find Arcturus, the bright orange
star now to the west in the evening. Then look close to overhead
for an equally bright but white star, Vega. Draw a line from Arcturus to
Vega and find two classic northern constellations, first Corona Borealis, the Northern Crown,
and then Hercules, the
representation of the great Hero of ancient Greek times. At the
northern end of the latter a box of stars called the "Keystone,"
along the western line of which lies one of the great globular
clusters of the sky, Messier 13, which is
just visible to the naked eye.
