Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. Panoramic views of a cloudscape
shows how its appearance changes according to the direction to the
Sun; on top you look away from the Sun, while on the bottom you
look more toward it.
Astronomy news for the week starting Friday, June 18, 2004.
This vacation version of Skylights covers the next three weeks.
The next Skylights will appear on Friday, July 16.
During this extended interval, the Moon waxes from first
quarter (which takes place on Friday, June 25, about Moonrise),
through gibbous to full on Friday, July
2 (about the time of Moonset). This full Moon falls just to the
east of the Winter Solstice in Sagittarius, and is the most southerly
of the year. The Moon then wanes through gibbous to third quarter,
which occurs just past midnight the night of Thursday, July 8, and
then through the morning crescent almost
to new again, allowing about three quarters of the lunar cycle to be admired. The period from Tuesday, July
13, to Thursday, July 15, is especially interesting, as the
crescent Moon plunges through and past northern Taurus, which has now cleared the
Sun. We also see the Moon swinging from perigee
(closest to the Earth) the day before full phase to apogee
(farthest) on Wednesday, July 14.
This three week period is filled with events. Venus is back with us, having popped
up in the morning sky. Look for it below the waning crescent Moon
around the beginning of dawn the morning of Tuesday, July 13th.
The following morning it will appear to the right of the even
thinner Moon. The brilliant planet will make a nice appearance in
Taurus around this time near the star Aldebaran and the Hyades cluster. Quickly climbing
the morning sky, Venus reaches greatest brilliance for this
apparition on Wednesday, July 14. It will then be with us the rest
of the year, not disappearing into twilight until after the
beginning of 2005.
Venus's brother planet Mercury then takes the stage. Though the
event will be difficult to see deep in evening twilight, Mercury will come into close conjunction
with Mars the evening
of Saturday, July 10, when the two will be but two-tenths of a
degree apart. Mars is so far away now that it will be
significantly fainter than Mercury. Binoculars will be needed.
While still dominating the early night sky, Jupiter now sets in mid
evening, leaving us with no planetary show at all until Venus comes
up.
Saturn is now completely gone, as it passes conjunction with
the Sun on Thursday, July 8.
Again, Earth makes news, as it passes its orbital aphelion, where
it is farthest from the Sun, on Monday, July 5, about the time of
sunrise in North America. At that time, it will stand 94.508
million miles from the Sun (152.095 million kilometers), 1.7
percent farther than average. That we are farthest from the Sun in
the middle of northern Summer clearly shows that distance has
little to do with the
seasons, which are caused entirely by the 23.4 degree tilt of
the Earth's axis against the perpendicular to the orbit.
The stars of Spring are now being shooed away by those of Summer.
Watch for the progression of a set of five marvelous northern
constellations that begins with Bootes, the Herdsman, which is well marked by the
luminary of the northern hemisphere, Arcturus. To the east of Bootes,
we see Corona Borealis (the
Northern Crown), then Hercules, Lyra with brilliant white Vega, and finally Cygnus (the Swan) topped at the north by Deneb. Far to the south, immediately
below Hercules, lies Scorpius (the
Scorpion), while to the east of Scorpius is Sagittarius (the Archer). When the Moon is out of the
way look from Cygnus on down through Aquila (the Eagle) and Scutum (the Shield) to admire the wonderful Summer Milky Way.
