Skylights featured three times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. The Moon rides above the shadow of the Earth (projected into
the atmosphere), the two setting in the west.
Astronomy news for the week starting Friday, June 18, 2004.
The Moon climbs the western evening sky this week as it waxes in
its crescent
phase, its nighttime side glowing with earthlight. As it moves each night
farther to the east, it takes on three planets. The night of
Friday the 18th, a very thin crescent will be visible in rather
bright twilight just to the right of Saturn, which is
becoming increasingly invisible. The following night, on Saturday
the 19th, the Moon will be nicely positioned just below a line that
connects the star Pollux in Gemini (to the right of the Moon)
and
Mars (to the left of the Moon).
By Tuesday the 22nd, the growing crescent will have entered western
Leo, and on the night of Wednesday
the 23rd, it will make an excellent sight just above bright Jupiter, which is about the
only "ancient" planet we have left to admire, all the others pretty
much gone. Venus
famously passed inferior conjunction with the Sun last June 8, when
it made a spectacular
transit across the solar disk, and on Friday the 18th, Mercury does
the opposite and goes through its superior conjunction, when it is
on the other side of the Sun. Venus is now preparing its morning
appearance in eastern dawn, while Mercury will in another month lay
weak claim to the low western evening sky.
But now it is us, the Earth, that makes the
news, as its rotation axis points to its maximum degree toward the
Sun and
astronomical summer begins in the northern hemisphere (winter
in the southern). On the Saturday, June 20, at 7:57 PM Central
Daylight Time (8:57 EDT, 6:57 MST, 5:57 PST, 3:57 Alaska-Hawaii),
the Sun will cross the Summer
Solstice in Gemini, as it reaches its greatest northerly extent
of 23.4 degrees north of the celestial equator. At that moment the
Sun will be overhead somewhere on the Tropic of Cancer (23.4
degrees north of the equator), will be as high at the Earth's North
Pole as possible, and will be circumpolar at the Arctic Circle
(66.6 degrees north latitude), bringing 24 hours of daylight to as
much of the Earth's surface as possible, and will just barely not
rise at the Antarctic Circle (66.6 degrees south). (Actually,
because of refraction by the Earth's atmosphere, which raises the
Sun upward, and the half-degree diameter of the Sun, the limits are
a bit south of both the Circles.)
It's time for Arcturus, the
zeroth magnitude star that is the brightest of the northern
hemisphere, one that can be seen quite well from the southern
hemisphere as well. Now on the meridian around 9 PM Daylight Time,
it anchors the large constellation of Bootes, the Herdsman, which spreads northward toward
the Big Dipper. To the west of
Arcturus is Tau Boo (just beyond
brighter Muphrid), which hosts a
Jupiter-like planet, while farther to the west is Coma Berenices, a nearby cluster of stars that with a couple
others makes its own constellation of the same name.
