Go Stargazing! January Edition

The full moon of Jan. 15 partially blocks the sun, causing an eclipse visible in Africa and Asia. Because it is close to apogee, the moon is too small in the sky to ever block the sun completely, and no total eclipse occurs. Instead, folks on a path stretching from Uganda and Kenya across the Indian Ocean to Sri Lanka, Burma, and China see an annular eclipse. The moon will appear to be completely inside the sun’s disk with a ring of sun around it.

Eclipsed? Not totally.
Creative Commons License photo credit: James Jordan

At about 6 p.m. on Saturday, Jan. 2, the Earth came to perihelion. This means it was as close to the sun as possible—about 147 million km away (Earth is about 152 million km from the sun in July). This is not enough of a difference to influence our weather. Earth’s 23.5 degree tilt is much more important. Our North Pole is still tilted very much away from the sun and the sun still takes a very low path across our sky. Therefore, in spite of being as close to the sun as we’ll be all year, we’re going to be quite cold in Houston this week.

The latest sunrise of the year (at Houston’s latitude) occurs on Jan. 10. Earth is now just past perihelion, and has sped up a little in its orbit since it is a little closer to the sun. As a result, sunrise, local noon, and sunset have been happening a little later each day since early December. The noon sun is ever so slightly higher at noon each day since the solstice on Dec. 21, but as of today, the sun is still very close to its solstice height. Beginning Jan. 11, the noon sun’s greater height in the sky again becomes the dominant effect (as it is for most of the year). From then until June, sunsets are getting later while sunrises are getting earlier.

Jupiter is the brightest thing in the evening sky this month, except for the moon. You can easily see it by looking to the southwest.  Jupiter appears lower and lower to the horizon each January night.  By the end of the month, Jupiter sets just after 7 p.m.  At the end of February, Earth and Jupiter will be on opposite sides of the sun and Jupiter will therefore be invisible to us.

Mars has become an evening object.  It now rises in the east about 8 p.m. and will rise by dusk at the end of the month.  Mars already outshines all stars in the night sky except the very brightest (Sirius), and will continue to brighten throughout January.  On Jan. 29, Earth will pass between Mars and the sun, putting Mars in our sky all night long (this alignment is called opposition).

Saturn
Creative Commons License photo credit: Elsie esq.

Saturn is currently high in the south at dawn.  Although not as bright as Mars this month, Saturn  is also brightening as it approaches its own opposition in March.

Venus is behind the sun (at superior conjunction) on Jan. 11 and is therefore not visible this month.

The Great Square of Pegasus is in the west at dusk.  The star in its upper left hand corner is also the head of Andromeda.  Facing north, you’ll see five stars in a distinct ‘M’ like shape—this is Cassiopeia, the Queen.  Her stars are about as bright as those in the Big Dipper, and she is directly across the North Star from that Dipper.  Since the Dipper is low and out of sight at dusk this month, Cassiopeia rides high.

Dazzling Orion is high in the southeast, reminding us that winter is here.  His belt points up to Aldebaran, the eye of Taurus, the Bull.  The Dog Stars Sirius and Procyon are below Orion in the east.  Sirius is the brightest star we ever see at night.  Gemini, the Twins, are to Orion’s left as he rises (and to his upper left once they appear to the south).  Look for two stars of equal brightness less than 5 degrees (three fingers at arms’ length) apart.  These are Castor and Pollux, marking the twins’ heads.  High in the northeast is Capella, the sixth brightest star ever seen at night.

Moon Phases in January 2010:

Last quarter moon                 January 7, 4:41 am
New moon                                January 15, 1:12 am
First quarter moon                January 23, 4:53 am 
Full moon                                 January 30, 12:18 am

Go Stargazing! December Edition

The ‘main event’ of December evenings occurs in the southwest at dusk, where you can watch Venus pull away from Jupiter.  Look southwest right as night falls for the two brightest things there except for the Moon.  The brighter one low in the southwest is Venus, which outshines everything else in the night sky.  Jupiter is the dimmer of the two, although it still outshines all the stars we ever see at night.  Venus and Jupiter begin the month about 2 degrees apart (your finger at arms length blocks about 1 degree.)  However, Venus will extend that gap quite noticeably each night, until it appears high above Jupiter on December 31. 

Mercury emerges from the Sun’s glare in time to form a nice pair with Jupiter on New Year’s Eve.  As you prepare to ring in 2009, take a moment to look at Mercury just to Jupiter’s left in late twilight.  That same night, the Moon will be near Venus. Saturn can be found high in the south at dawn.  Mars is lost in the Sun’s glare this month, and will remain out of sight into 2009.  It is directly behind the Sun (in conjunction with the Sun) on December 5.

Orion no céu
Creative Commons License photo credit: giumaiolini

The enormous Summer Triangle, consisting of the stars Deneb, Vega, and Altair, sets in the west.  The Great Square of Pegasus is overhead at dusk.  The star in its upper left hand corner is also the head of Andromeda.  Facing north, you’ll see five stars in a distinct ‘M’ like shape—this is Cassiopeia, the Queen.  Her stars are about as bright as those in the Big Dipper, and she is directly across the North Star from the Dipper.  In fall and early winter, while the Dipper is low and out of sight, Cassiopeia rides high.

Dazzling Orion rises in the east, reminding us that winter is on the way.  His belt points up to Aldebaran, the eye of Taurus the Bull.  By 9 pm tonight (7 pm by New Year’s Eve), the Dog Stars Sirius and Procyon will have risen below Orion in the east.  Sirius is the brightest star we ever see at night. 

Moon Phases in December 2008:

1st Quarter         December 5, 3:25 pm
Full                     December 12, 10:38 am
Last Quarter        December 19, 4:30 am
New                    December 27, 6:22 am

At 6:04 am on Sunday, December 21, the Sun is directly overhead at the Tropic of Capricorn, meaning that the North Pole is tilted as much as possible away from the Sun.  This is the winter solstice.  For people in the Northern Hemisphere, December 21 has less daylight and more night than any other day of the year. 

Sunset at Appalachian Trail
Creative Commons License photo credit: Pardesi*

However, the earliest sunsets occur on December 1 and 2.  We are already close enough to the solstice that the Sun’s apparent path across the sky on December 21 is only slightly lower than on any other day this month.  Meanwhile, Earth is about to make its nearest approach to the Sun, called perihelion, in January.  As a result, the Earth is speeding up.  The effect isn’t much (Earth’s orbit is nearly circular), but it’s enough to make both sunrise and sunset a little later each day this month and next.  With the Sun’s apparent height in the sky not changing that much in December and January, the small effect of Earth’s acceleration near perihelion dominates.  Since most of us sleep through sunrise and witness sunset, the days seem be slightly lengthening between the beginning of the month and the 21st, although they are actually getting slightly shorter.