Go Stargazing! December Edition

Jupiter is well placed for observing on December evenings. Face east at dusk and look for the brightest thing there—that’ll be Jupiter.

Venus has fully emerged from the Sun’s glare.

After Sunset (Moon & Venus & Jupiter)
Creative Commons License photo credit: scyllarides

Look for it low in the southwest at dusk. (Venus is slightly higher in the evening sky each night this month). We are still near the beginning of Venus’ apparition as evening star; it gets higher and easier to see for the rest of this year and is spectacular for about the first half of 2012.

Mars rises around midnight and is now high in the south at dawn. Although not nearly as bright as Venus or Jupiter, Mars has brightened enough to rival the brightest stars in the sky, and will keep brightening all winter as Earth approaches it.

Saturn remains in the morning sky this month.

Look low in the southeast at dawn, near the star Spica. (From the Big Dipper’s handle, arc to Arcturus and speed on to Spica).

The Summer Triangle sets in the west. Watch for the Great Square of Pegasus almost overhead at dusk now and in the west by Christmas. 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. In late autumn, as the Big Dipper hugs the horizon and actually sets for us in Houston, Cassiopeia is high in the north. Taurus, the Bull rises in the east. Look for the Pleiades star cluster above reddish Aldebaran. Dazzling Orion, the Hunter rises shortly after dusk (by month’s end, it is already up at dusk). As Orion enters the evening sky, we transition from the relatively dim evening skies of autumn to the brilliant stars of winter.

Orion nebula: M42
Creative Commons License photo credit: Alessandro S. Alba

Moon Phases in December 2011:
First Quarter December 2, 3:52 am
Full December 10, 8:37 am
Last Quarter December 17, 6:48 pm
New December 24, 12:07 pm

The Full Moon of Saturday morning, December 10, enters the Earth’s shadow, causing a total lunar eclipse.

Unlike last year’s event, however, this eclipse heavily favors western observers in North America; we miss most of it here in Houston. However, the Moon does nick the edge of Earth’s umbra at 6:46 am that morning, when it is a scant three degrees above our horizon in Houston. If you have a northwest horizon utterly clear of trees or buildings, you might try to observe the very beginning of the eclipse before moonset.

At 11:30 pm on Wednesday, December 21, the Sun is directly overhead as seen from the Tropic of Capricorn, the farthest point south where this is possible. That makes December 21 the winter solstice, the date when the noon Sun is lowest in the sky, and when we have the fewest daylight hours of the year. However, the earliest sunset of the year here in Houston is not on the solstice, but approximately on December 2! That’s because the Earth speeds up on its orbit as it approaches perihelion (closest approach to the Sun) next month. This acceleration shifts sunrise, local noon, and sunset slightly later each day this month and next. The effect is smaller that that of the Sun taking a lower path across the sky, which normally dominates in causing earlier sunsets and later sunrises. But the Sun’s apparent path varies very little near the solstice itself, allowing the secondary effect of the Earth approaching the Sun to predominate. For most people, then, (those who witness sunset but sleep through sunrise), days will seem to lengthen throughout December, although they don’t really begin lengthening until December 21.

We are making improvements to the main telescope at George Observatory! Visitors on Saturday, December 10 and December 17 will find the 36-inch Gueymard telescope closed for repairs. Our 14-inch east dome telescope and 18-inch west dome telescope will still be open to the public, however, so we hope you’ll join us anyway! Also, Christmas Eve and New Year’s Eve fall on Saturday this year; the observatory will be closed on December 24 and 31.

Visit www.hmns.org to see the Planetarium’s film Schedule.

On most clear Saturday nights at the George Observatory, you can hear me do live star tours on the observation deck with a green laser pointer. If you’re there, listen for my announcement.

Go Stargazing! February Edition

Jupiter!
Creative Commons License photo credit: Joshua Bury

Jupiter leaves the evening sky this month.  You can still see it during the next two weeks if you face southwest at dusk and look for the brightest point of light there. Jupiter sets by 7:30 as February opens, so you must look soon after dusk to see it.   However, Jupiter sets earlier and earlier and appears lower and lower to the horizon each February night, and soon disappears into the sun’s glare.  On Tuesday, Feb. 16, observers with a clear view of the horizon during twilight can try to see a very close conjunction of Jupiter and Venus, which is slowly moving out of the sun’s glare.  By the end of the month, Earth and Jupiter are on opposite sides of the Sun and Jupiter is therefore invisible to us.

Mars has become an evening object.  It is now already up in the east-northeast by dusk.  Mars already outshines all stars in the night sky except the very brightest (Sirius), and will continue to brighten throughout February.  On Jan. 29, Mars came to opposition as Earth passed between Mars and the sun, putting Mars in our sky all night long.  Earth now starts to pull ahead of Mars on its faster orbit.  As a result, Mars is slightly dimmer each night for the rest of 2010.  However, during February, Mars remains about as bright as the brightest stars, and thus remains easy to see.

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

Joseph Nollekens (1737 - 1823) Castor and Pollux front (V&A 2007)
Castor and Pollux
Creative Commons License photo credit: ketrin1407

Dazzling Orion is high in the south, 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.  On February and March evenings, look below Sirius and a bit to its right for Canopus, the second brightest star we ever see at night. This star is in the keel (bottom) of the legendary ship Argo.  Canopus is so far south that most Americans never get to see it.  We, however, are far enough to the south that it barely rises for us, remaining low on the southern horizon.

Moon Phases in February 2010:

Last Quarter                  February 5, 5:50 pm
New Moon                      February 13, 8:52 pm
1st Quarter                     February 21, 6:42 pm 
Full Moon                       February 28, 10:37 am

The new moon of Feb. 13 is the second new moon after the winter solstice.  Accordingly, it marks the Chinese New Year, beginning the Year of the Tiger.  (Correct for the time zone difference, and you’ll see that the date is February 14 in China).

Chinese New Year - Dragon
Creative Commons License photo credit: ajagendorf25

The Shadow Knows

Who knows how much longer the winter will last?

The Shadow knows.

Okay, so that’s not exactly how those old radio serials used to begin.  However, the idea of all-knowing shadows brings to mind a strange weather forecast that will take place in a few weeks.

Wuchak
Creative Commons License photo credit: Furryscaly

Early next month, a large rodent will emerge and look at the ground. If he sees his shadow, he scurries back into his winter den, and it is said that winter will continue for six more weeks. If there is no shadow, he stays out, and an early spring is in the offing. But, how does the groundhog’s shadow let us know how long the winter will be?

Understanding this forecast begins with knowing the cycle of the seasons.  The Earth orbits the sun with its axis tilted by about 23.5 degrees.  On about June 21 each year, the North Pole is tilted as much as possible towards the sun and the sun takes its highest path across our sky.  This is the summer solstice for us and the winter solstice for the Southern Hemisphere.  Six months later, the South Pole is tilted as much as possible towards the sun and the sun takes its lowest path across our sky.  Dec. 21 is our winter solstice and the summer solstice below the equator.  Halfway between these dates, on about March 20 and September 22, the sun is overhead at the equator and both poles are on the day-night terminator.  As everyone then has the same amount of daylight and nighttime, these dates are the equinoxes.  We can think of the solstices and equinoxes as ‘quarter days.’

We have come to define our seasons as beginning at the solstices and equinoxes.  Northern European pagans, however, paid equal if not more attention to dates about halfway between the solstices and equinoxes, called the ‘cross-quarter days.’  For them, seasons began at the cross-quarter days, while the solstices and equinoxes were the midpoints of the seasons.  A while ago, I blogged about the cross-quarter day between the fall equinox and the winter solstice, Samhain, and explained how its traditions influenced our Halloween celebrations.  Now, as January ends and February begins, we are approaching the halfway point between the winter solstice and the spring equinox–another cross-quarter day.

For the Celts, this was Imbolc (pronounced as if there were no ‘b’), sacred to Brigid, goddess of fine craftsmanship, healing, poetry and generally anything involving the higher faculties of mankind, as the Celts understood them.  Among the traditions associated with Imbolc was the belief that Brigid’s snake would emerge from its winter resting place and test the weather.  Germans used a hedgehog to forecast the weather.  If the animal in question scurried back into its burrow, it was a sign that much more winter was ahead.

8981 - St Petersburg - Hermitage - Gaius Julius Caesar
Creative Commons License photo credit: thisisbossi

In the time before the Celts encountered the solar calendar established by Julius Caesar, the actual date of Imbolc varied from year to year.  With the adoption of the Romans’ calendar, Imbolc came to be observed on Feb. 1 (just as observations of Samhain moved to Nov. 1 and the eve of that day).  The actual midpoint between the winter solstice and the vernal equinox is Feb. 3.

Feb. 2 is Candlemas Day, the 40th day of Christmas (with Christmas as day 1).  Christians observe this as the presentation of the baby Jesus at the temple.  As has often occurred when Christian observances nearly coincide with pagan ones, folklore from one became attached to the other.  Thus, as northern Europeans began to migrate to America, they had a weather forecast descended from Imbolc associated with Feb. 2.  Upon arriving here, they replaced the hedgehog (not native to America) with a uniquely American animal, the groundhog.

Light and Dark
Creative Commons License photo credit: ZeroOne

Let’s look more closely at the rules for the Groundhog Day forecast.  If we don’t want the groundhog to see his shadow on Feb. 2, then we must not want sunshine that day.  Good weather (bright and sunny) is a bad omen, while bad weather is a good omen.  This page quotes some sayings from Europe and America which make this explicit.  To appreciate this apparent reverse psychology, let’s consider another day on which bad weather is welcome: Christmas.

Think back to early last month, when Houston experienced a snowfall on Dec. 4 (it had never snowed that early in the winter here in Houston).  Think back even further to our Christmas Eve snowfall in 2004 (our first white Christmas ever).  Such unusual weather (for us) reminded many of favorite holiday songs such as ‘Let it Snow’ or ‘White Christmas.’  “Now this feels like Christmas,” many told themselves.  Now recall the bitter cold a few weeks ago this January.  Did anyone break into song?  Was anyone saying, “At least this feels more like January?”  Why the double standard?  Why is the type of weather we welcome at Christmas just bad weather when it happens in January?

It seems that people who made their living off the land and thus depended on regular seasonal changes constantly looked for reassurance that the natural cycles were functioning properly.  A winter that was truly wintry was therefore a good omen.  If winter happened when it should, then perhaps spring, summer, and the harvest would occur in their proper times, and everything was in balance.  If winter were warm and sunny, however, then something was wrong.  If winter was not happening in its season, then other seasons might also fail to appear.  In particular, people feared that failing to have a true winter at the proper time would require ‘remedial’ winter during springtime.

In time, the winter solstice and the cross-quarter day, Imbolc (later Christmas and Candlemas Day) came to stand in for the whole winter.  Thus, wintry weather on Christmas and on Feb. 2 is a good omen, while bright, sunny weather on these days is a bad omen.  And so, the sight of his shadow frightens the groundhog back into his burrow.

Into the sun
Creative Commons License photo credit: James Jordan

The winter of 2009-2010 has been more severe than usual, not just in Houston but across much of the Northern Hemisphere.  Thus, many can sympathize with those who are looking for any possible sign of spring.  As it turns out, there is a sign of approaching spring that becomes noticeable as February begins–the greater height of the sun.

Ever since the winter solstice, we have seen the sun take a slightly higher path across our skies each day.  However, the difference in height is difficult to notice until February.  This is because the height of the sun during the year varies like a sine wave.  There is little variation near the maximum and minimum; most of the change occurs midway between these points.  During February, March and April, the sun’s higher path is more apparent than in January. All shadows, including those of groundhogs, get noticeably shorter each week.  If you can’t measure shadows during the day, try observing the same change in the position of sunset.  From the same vantage point, notice where the sun sets once each week during February, March and April.  You’ll notice a distinct shift towards the north (towards the right as you face sunset in the west) with each observation.  Since this happens every year as winter turns to spring, you now have reliable assurance that spring is on the way.  No need to be afraid of shadows.

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