Saturday: The
earliest sunsets of the year occur all this week – 4:13 p.m. That seems
counterintuitive because the shortest day of the year in the Northern
Hemisphere isn’t until December 21. Since the Earth’s orbit is elliptical, the
Sun does not appear to move across the sky at the same rate from day to day
throughout the year. That means some parts of the year the Sun is “fast” and
sometimes “slow”. Today, the Sun reaches the noontime position of due south at
11:52 a.m. meaning it will also reach the setting position a few minutes
earlier than the expected time. For more information on this, go to http://goo.gl/kjnHP. Or just go watch the
sunset. But don’t stare at the Sun.
Monday: Okay
boys and girls. Let’s follow along with the moon this week as it tours the
bright objects in the southeastern sky. At 6:30 a.m., the bright star Spica is
less than a half a fist above the moon. Spica is believed to be the star that
provided the ancient astronomer Hipparchus with the data to show that the Earth
precesses like a spinning, wobbling top.
Tuesday:
On these cold mornings, it is difficult to get going. You just want to plop
into a chair and sit still. But, are you really sitting still? You’re moving at
about 700 miles per hour due to the rotation of the Earth on its axis and
66,000 miles per hour due to the revolution of the Earth around the Sun. If
that’s not enough, the entire solar system is orbiting the center of the galaxy
at a whopping 480,000 miles per hour! So while you may be sitting still with
respect to your living room (and all of the over achievers in your house), you
are NOT sitting still with respect to the center of the galaxy. For more
information about this concept, go to http://goo.gl/lPVPS.
Before you barf from all of that motion, go outside at 6:30 a.m. and observe
Saturn, less than a fist above the moon in the southeast sky. Because of
Saturn’s rapid rotation, only 10.5 hours, it appears visible flattened.
Tuesday: At
6:30 this morning, the moon marks the right angle corner of a right triangle
with the very bright Venus above it and Mercury to its lower left.
Wednesday:
Just like during last month’s new moon, people are humming the astronomy
version of 1981 Blondie hit The Tide is High: “The tide is high ‘cause
the moon is new. Higher still when the moon’s close, too.” Tonight's moon is
new. The new moon is the phase where the Moon is directly between the Earth and
the Sun. That means the moon and Sun are both stretching the Earth in the same
direction causing the ocean water in line with the Sun and moon to be pulled upward.
In addition, the moon is at perigee so this is the day of the month when the
moon is closest to the Earth. This accentuates the upward pull on the water and
makes the tides really high.
Thursday: The
Geminid meteor shower peaks late tonight and early tomorrow morning. Meteor
showers are named after the constellation from which the meteors appear to
originate. These meteors appear to come from a point in Gemini the twins. This
point is about three fists held upright and at arm’s length above the east-northeast
horizon at 9 p.m. tonight. You can follow this point throughout the night, as
it will remain near the bright star Castor, the right hand star of the “twin”
stars Pollux and Castor. This shower is typically one of the best ones of the
year producing bright, medium speed meteors with up to 80 meteors per hour near
the peak. This year, the moon will be new during the peak night ensuring dark
skies.
Most
meteor showers occur when the Earth passes through the orbital trail of a
comet. The broken off comet fragments collide with the earth and burn up in the
atmosphere. Astronomers had searched for a comet source for this shower since
1862 when the shower was first observed. Finally, in 1983, astronomers
discovered the object that created the fragments that cause the meteor shower.
To their surprise, it was a dark, rock that looked like an asteroid, not a
shiny icy comet. Astronomers named this object Asteroid 3200 Phaethon. But,
they still don’t know if it an asteroid or if it is a comet with all of its ice
sublimated away by many close passes by the Sun. For more information about
3200 Phaethon, go to http://goo.gl/LuwGW.
Friday: Mars
is less than a fist to the left of the thin crescent moon, low in the southwest
sky.
The
positional information in this column about stars and planets is typically
accurate for the entire week.
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