StarDate, Volume 41, Number 1, January/February 2013 Page: 6
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T he cold February evenings offer some of the
brightest stars in the entire night sky. Sirius,
the brightest of all, climbs across the south, trail-
ing below and behind beautiful Orion. Taurus,
the bull, looks down on them. From the southern
United States the second-brightest star, Canopus,
huddles below Sirius. And brilliant Capella lords
over them all from high overhead. Among the
planets, only dazzling Jupiter puts in a good
showing this month, although Mercury just peeks
into view in the west for a few evenings around
mid-month.1 Spica, the brightest star of Virgo, stands to the left of the Moon
at first light.
2 Spica is to the right or upper right of the Moon at first light, with
the brighter planet Saturn farther to the left or upper left of the Moon.
3 The golden planet Saturn stands above the Moon at dawn.
5 Antares, the brightest star of Scorpius, huddles to the lower right
of the Moon at first light. The star shows a distinctly orange hue.
17 Mercury, the closest planet to the Sun, puts in a brief appear-
ance in the evening sky. It is low in the west shortly after sunset.
Although it looks like a fairly bright star, it can be tough to spot
through the glare of twilight.
17/ 18 Jupiter, which looks like a brilliant cream-colored star, is
to the upper left of the Moon at nightfall on the 17th, and to the
upper right of the Moon on the 18th. Orange Aldebaran, the "eye" of
Taurus, looks on from a little lower in the sky.
24 Regulus, the brightest star of Leo, is to the left of the Moon
at nightfall.
FEATURED EVENT
28 Spica huddles quite close to the Moon as they climb into good
view by late evening.Su M
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T W Th F Sa
Spinning Through the Stars
You don't need big telescopes or electronic instru-
ments to learn about the universe. Sometimes,
you can learn a great deal with little more than your
eyes alone.
In 127 BC, for example, the Greek astronomer Hip-
parchus learned that the stars shift position relative to
the Sun from year to year. He did so by measuring the
position of Spica, the brightest star of the constella-
tion Virgo. It stages a dazzlingly close encounter with
the Moon on the night of February 28, as the Moon
passes just a fraction of a degree from the bright star.
During a lunar eclipse, Hipparchus measured the
angle from Spica to the middle of the Moon, which in
turn allowed him to calculate Spica's position relative
to the Sun. By comparing that position with records
of another eclipse about 150 years earlier, he deter-
mined that the star had moved about two degrees,
which is roughly the width of a finger held at arm's
length, over that period. Hipparchus realized that
the entire celestial sphere - the background of fixed
stars - rotated with respect to the Sun.
That rotation is known as the precession of the
equinoxes. It's caused not by the stars, though, but
by Earth. Our planet "wobbles" on its axis like a spin-
ning gyroscope that's running down. As it does so,
the stars appear to shift position relative to the Sun. It
takes about 26,000 years to complete one full wobble
and have the stars return to their starting positions.
Precession was an important discovery because
it showed that the heavens can change, setting the
intellectual stage for future discoveries about the uni-
verse and our place in it.6 JANUARY/FEBRUARY 2013
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McDonald Observatory. StarDate, Volume 41, Number 1, January/February 2013, periodical, February 2013; Austin, Texas. (https://texashistory.unt.edu/ark:/67531/metapth639232/m1/6/: accessed August 15, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.