Skylights featured four times on Earth Science
Picture of the Day: 1
, 2
, 3
, 4
.
Photo of the Week.. In memory of the past winter, Orion and his hunting dog Canis Major stalk the skies beyond
leafless trees.
Astronomy news for short week starting Friday, April 4, 2003.
Skylights now resumes its normal schedule. The Moon passes through
its first
quarter this week, the night of Wednesday the 9th just about
the time of sunset in North America, giving us a splendid view of
this phase set on the meridian to the south. In the third century
BC, the great ancient Greek astronomer Aristarchus tried to determine the distance of
the Sun relative to the Moon by measuring the exact angle between
them when the Moon came just to first quarter. It would be a right
angle if the Sun were infinitely far away, less if it were not.
From his estimate of 87 degrees, he said the Sun was 20 times the
lunar distance. Though the true value is 400, Aristarchus' method
was ingenious, and the result was correct in that he found the Sun
notably farther than the Moon. The actual value (which was still
off some) was not known until the 17th century.
As the Moon heads toward first quarter in eastern Gemini, it passes northeast of Saturn
the night of Monday the 7th, and then after the quarter it swings
four degrees north of Jupiter
the night Thursday, the 10th. Both these outer planets, which
share so much in their physical natures, are now in direct motion
to the east against the background stars. Saturn, in eastern Taurus, now sets around midnight,
while Jupiter, in eastern Cancer
(one of the dimmer constellations of the Zodiac), is high to the
sky to the south as twilight ends.
The morning sky sees Venus
getting ever closer to the horizon, as the planet now rises shortly
after twilight begins. Nevertheless, it is glorious in the morning
southeastern sky. Rather far to the west of Venus rides reddish Mars just
to the northeast of the "Little Milk Dipper" in Sagittarius.
Within the set of "modern" constellations, invented between 1600
and 1800, are a variety of navigational tools: Sextans (the Sextant), Octans (the
Octant), and Quadrans (the Quadrant). Octans surrounds the South
Celestial Pole, while Quadrans, no longer recognized as a formal
constellation, lies near the Big
Dipper (and is the "source" of the Quadrantid meteor shower, which hits on January 4th).
Sextans, still viable, lies just to the south of Leo the Lion. Simply go south of Regulus (the Alpha Star in Leo) to
find a triangle of faint stars, Alpha and Beta Sextantis
lying on a line almost exactly parallel to the celestial
equator.
