Sunrise and Sunset Times for December 2008

DAYLIGHT
The earth’s orbit reaches perihelion (closest point to the sun) on January 4. That doesn’t mean warmer days, because the northern hemisphere is still tilted away from the sun. It does increase the earth’s speed as it travels along its pathway towards the spring equinox. That means the period of daylight lengthens, but don’t expect earlier sunrises. The first three weeks of January show only a four minute advance in the time of sunrise—a 12 minute difference for the entire month. The longer days result from a later sunset--about one minute per day, 32 minutes total by the end of the month. Fortunately, twilight extends the period of daylight. Astronomical twilight brightens the horizon one and one-half hours before sunrise when the sun is still 18 degrees below the horizon. Nautical twilight begins one hour before sunrise when the sun is 12 degrees below the horizon. Civil twilight begins one-half hour before sunrise when the sun is six degrees below the horizon. The reverse progression occurs with sunset. Actual time of sunrise and sunset for a specific location depends upon the landscape.

MOON HAPPENINGS
January begins with a large waxing crescent moon high in the evening sky.  The moon becomes full on January 10 at 8:27pm.  Watch it rise at 4:56pm.  On January 14 a waning gibbous moon and Saturn rise within minutes of one another around 10:00pm.  The new moon occurs on January 26 at 12:55am.  A very thin crescent reappears low in the southwestern sky on January 28.  On January 29 the waxing crescent moon appears below Venus; on January 30 it has moved past Venus and appears above it.  Times may vary depending upon the landscape.

STAR COLOR
The cold, dry skies of winter provide excellent conditions for viewing variation in star color.  High in the night sky search for the blueish stars of the Pleiades.  Directly below this star cluster, look for the orange light of Aldebaran in Taurus.  Then find the three stars of Orion's belt.  The orange star Betelgeuse is above the belt and to the east.  The blue star Rigel is below the belt to the west.  Southeast of Orion is blue Sirius, the brightest of all stars (magnitude -1.4).  Above it is white Procyon.    Higher in the sky is the constellation Gemini highlighted by its twin stars.  Castor appears white, while Pollux appears slightly orange.  Back to the west is Capella (in Auriga).  It shines a yellow-white, very much like our own Sun would appear. 

Star color is an indication of the star's surface temperature.  Blue stars are hottest, cooling down to white, yellow, orange, then red.  Hot, blue stars tend to be massive and have short life spans of a few hundred million years.  White and yellow stars tend to be moderate in mass (like our sun) with life spans measured in billions of years.  Orange and red stars are at the end of their life cycle with swollen surfaces that result from the depletion of hydrogen fuel for their nuclear furnaces. 

METEOR EVENTS
A first quarter moon sets soon after midnight on January 3-4, which favors the peak of the Quadrantid Meteor Shower. Its radiant is low on the horizon, east of the Big Dipper and north of the orangeish star Arcturus. It has been known to produce 10-60 faint, blue meteors per hour. From January 15 to 18 watch the eastern sky between 10:00pm and midnight for occasional meteors from the Delta Cancrid and Coma Berenicid Meteor Showers.

Note: Hold your hand at arm’s length to measure apparent distances in the sky. Adjust for the size of your hand. The width of the little finger approximates 1.5 degrees. Middle, ring, and little finger touching represent about 5 degrees. The width of a fist is about 10 degrees. The hand stretched from thumb to little finger equals 20 degrees. The diameter of both the full moon and the sun spans only 0.5 degree.


VISIBLE PLANETS
Jupiter - Still outshines everything in the night sky except Venus and the moon. It appears lower on the southwestern horizon each evening. By midmonth it sets so soon after the sun that we no longer see it. Shines at magnitude -1.9 in Sagittarius

Mercury - Always difficult to see, but look for it during the first few days of the month hovering above Jupiter. Mercury rises a littler higher each evening as Jupiter sinks below the horizon. Continue to look, from a high viewpoint, for Mercury, shining below Venus at magnitude -0.7 in Capricornus. Best seen about 40 minutes after sunset.

Saturn - Visible in the morning sky throughout the month, but also appears in the evening sky before midnight. By month’s end, it appears around 9:00pm each evening. Shines at magnitude +0.9 in Leo. }

Uranus - On a moonless night (try January 22-23), look for a blue-green point of light east of Venus. With good eyesight and dark skies it is barely visible at magnitude +5.9 in Aquarius.

Venus - Sunset reveals Venus higher in the sky each night, separating itself from Mercury and Jupiter below. It increases in brightness throughout the month, reaching its brightest magnitude of -4.7 by month’s end.

Note: Apparent magnitude values range from -4 to +6 for most planets and visible stars. The lower the value the brighter the object. A decrease of 1.0 magnitude is 2.5 times brighter.

Primary Sources: USGS, U.S. Naval Observatory, http://www.fourmilab.ch/yoursky/