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.

The Unconquered Sun: Winter Solstice Today!

At 11:47 am Central Time on Monday, December 21, the sun is overhead at the Tropic of Capricorn. This is the farthest point south at which the sun can be overhead, indicating that the North Pole is tilted as far away from the sun as possible. At the Tropic of Capricorn and elsewhere in the Southern Hemisphere, the high sun results in the longest day of the year and the beginning of summer.  Up here in the Northern Hemisphere, however, the sun is as low as possible in the sky, and we have our shortest day of the year.  This is the winter solstice for us.

Ancient peoples across America, Europe and Asia noticed that the sun got lower and lower and the daylight shorter and shorter throughout autumn.  When the sun reached its lowest point, this meant that it had stopped going away and would return–a cause for celebration.  One of the many pagan winter solstice festivals was Yule, celebrated in northern Europe.  Another was the festival of Sol Invictus (the Unconquered Sun) celebrated in Rome on Dec. 25.  Keep in mind that in antiquity the 25 was the date of the solstice itself–the sun which had stopped going away and begun to return was ‘unconquered.’  Due to the imprecision of the Julian calendar, the solstice had shifted to Dec. 21 by the year 325 A.D., when the Nicene Council convened. Since Pope Gregory’s reform was calculated to restore the equinoxes and solstices as of the Nicene Council, the winter solstice is now on Dec. 21 (occasionally Dec. 22).

No one in antiquity knew what date Jesus was born.  For one thing, many of the early Christians rejected all birthday celebrations of any kind as a pagan ritual.  Even had folks wanted to observe Jesus’ birth, the lunar calendar used in Israel at the time would complicate the choice of date.  The Chronology of 354 is the oldest document to list Christmas as a festival.  When the church selected Dec. 25 for this festival, it was probably because late December was already a festive time across the Roman Empire.

Sunset over Chicago
Creative Commons License photo credit: kevindooley

Although today is the shortest day of the year, you may have already noticed that sunset is a few minutes later now than at the beginning of the month.  In June, the North Pole was tilted towards the sun as much as possible.  Since then, the North Pole has tilted a little more away from the sun each day.  Days have been getting shorter because each day the sun has taken a slightly lower path across the sky.  Sunrises have been getting earlier and sunsets have been getting later.  By late November the sun had already gotten about as low as it is now.  As the day to day difference in the sun’s height gets smaller, another effect begins to dominate.

Earth’s orbit is not a circle; it is an ellipse.  The orbit is almost a circle, however; the eccentricity (out-of-roundness) is just 0.016, where 0 is a perfect circle and 1 a parabola.  This is enough of a difference to bring Earth slightly closer to the sun in early January and take it slightly farther away in early July.  Therefore, Earth is now beginning to make its closest approach to the sun (called perihelion).  As a result, Earth is speeding up on its orbit.  This causes sunrise, local noon, and sunset to occur just a little later each day.  By the 21, sunset will occur at 5:27 pm, as opposed to 5:22 pm on Dec. 2 (the actual date of the earliest sunset).  Sunrise, however, will have shifted from 7:00 am to 7:13 am.  Thus, that days are still getting shorter even though the sunsets are a little later.

Many people assume that the winter solstice should be the coldest day, but this is usually not true. January is usually colder.  Although days get a little bit longer and the sun a little bit higher beginning Monday, it takes quite awhile for this to add up to an appreciable difference in the Sun’s height in the sky and in the amount of light and heat reaching the arctic.  Frigid air masses continue to form in the arctic and move across the Northern Hemisphere throughout January, February, and often March.  Although the sun is higher in those months than in December, the air can be just as cold if not colder.

Equinox 2

Hopefully, we are getting all of our cloudy, gloomy weather over with , and the solstice will be sunnier. If so, you can join us on the museum sundial at noon on Monday, Dec. 21 to observe the sun!  This is one of the Fun Hundred events celebrating our 100 anniversary here at the Museum.   On top of the gnomon on our sundial is a silver ball with three sets of holes, which allows the sun to shine through pairs of lenses near each solstice or equinox.  To account for cloudy weather, our gnomon’s holes are big enough that the sun aligns with them for a few days before and after the exact equinox or solstice date.  The holes aligned with the winter solstice are so big that you can still project the sun’s image through them deep into January!  If the weather does not cooperate Monday, you can come and observe the sun on our sundial near noon on any day in the next few weeks.

Reasons for the Seasons

If you have been outside lately, you may have noticed a slight increase in sweaty people around you, and potentially an increased amount of personal perspiration. You may long for the chill of the lukewarm Decembers Mother Nature promises you as a Houstonian. I have found myself, on occasion, cursing the sun and its inexorable inferno. “Why, WHY can’t we all live in Southern California???”

 …But why curse the weather and your resulting ridiculous air conditioning bills when you can have WAY more fun trying to understand the heat source! The seasons, or the regular change of weather, happen because of the planet’s orientation to the sun. There is a common misconception that they occur because of the earth’s elliptical (like an oval) orbit, making it closer to and further from the center of our solar system at different times throughout our year. However, the ellipse that the earth follows is very nearly a circle, so this theory just doesn’t hold water.

GlowGlobe
Creative Commons License photo credit: etohaholic

 The real reason for the seasons is explained by the earth’s axis! Our planet is tilted at an angle of about 23.5 degrees with the perpendicular to Earth’s orbit around the sun. This means that the world is leaning slightly to one side at all times. Also, this would be a good time to note that this tilt stays the same throughout the orbit; it doesn’t swirl and swivel around as it moves along. So, the Northern Hemisphere leans slightly away from the sun in our winter, making the sun’s rays hit the earth at an oblique angle, which, in turn, makes its heat more diffuse over a large area, which equals cooler weather! The seasons are opposite in the Southern Hemisphere for the same reasons; when the North is tilted away from the sun, the South is tilted towards it, and vice versa. This alternating cycle of direct and obtuse solar rays effects other facets of life on earth; it is the reason for the changing lengths of days and the reason why some people get so sunburned in more tropical areas (which are closer to the equator, go figure.)

mars-06-crop
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 We all have first hand knowledge of what the seasons bring to the blue planet, but what about some of the others? Mercury rotates 3 times in 2 of its years and it has some of the most extreme temperature variations in the solar system, with a range of about -297 to 800 degrees F! On Mars, seasons change every 7 months and are much more severe than those on Earth. And although seasons on a gas giant don’t mean what they do on a terrestrial planet, on Jupiter, a change occurs only every seven years! Facts like these make me extremely glad to be an Earthling.

So, instead of pondering what to wear now that heather gray is out of the question, or heading out to buy new bead covers for your flesh-searing vinyl car seats, come to the Houston Museum of Natural Science and explore science in the cool, climate controlled heart of the Museum District.

A Trick or a Treat?

In less than a week, people all over the country, including right here at our museum, will be celebrating Halloween. Perhaps your workplaces and schools are already festooned with ghosts, skeletons, graveyards, and the like.  If you stop and think about it, you may wonder just how it is that we came to celebrate by trying to disguise ourselves or by trying to frighten people.  Is this a trick or a treat?

Picket fence and yellow trees
Creative Commons License photo credit: joiseyshowaa

The short answer as to why we celebrate this time of year with images of death is that we are in the middle of autumn, the season when nature itself is dying.  To fully understand why we celebrate Halloween when we do, we must fully understand the seasons.

Earth orbits the Sun with its axis pointed at the North Star, Polaris. As a result, its axis is tilted by about 23.5 degrees with respect to its orbital plane.  This tilt, combined with Earth’s revolution around the Sun, causes the seasons.  If the North Pole leans towards the Sun, the Sun is higher in our sky and we get more direct sunlight.  Also, daytime is longer than nighttime.  As the North Pole begins to tilt away fron the Sun, the Sun appears lower and lower across the sky, and daytime gets shorter and shorter.  Eventually, the slanted-in solar rays and short days bring about winter.  Very cold air masses form in the darkened Arctic and begin to move south, some of which can even reach Houston.

Keep in mind that the Earth’s axis does not tilt back and forth; it points at Polaris the whole time.  In June, the North Pole is leaning towards the Sun, but by December, the Earth’s motion has carried it to the other side of the Sun.  The North Pole, still tilting the same way, now leans away from the Sun.

A common misconception is that the Earth is closer to the Sun in summer and more distant in winter, and that is what causes our seasons.  In fact, Earth’s perihelion (closest approach to the Sun) occurs just after the new year (January 1-4), while aphelion (greatest distance from the Sun) occurs around the 4th of July.  Earth’s orbit is an ellipse, but the Earth-Sun distance does not change by enough to affect our seasons.

where are you?
Creative Commons License photo credit: shioshvili

In the cycle of seasons, there are four points of note.  At the March equinox, neither pole is tilted toward the Sun and the Sun is directly overhead at the equator.  The is the vernal (spring) equinox for us and the autumnal (fall) equinox for folks south of the equator.  At the June solstice, the North Pole is tilted as much as possible towards the Sun, and the Sun is overhead at 23.5 degrees North (the Tropic of Cancer).  This is the summer solstice for us and the winter solstice in the Southern Hemisphere.  At the September equinox, once again neither pole tilts toward the Sun, and the Sun is again overhead at the equator.  This is our fall equinox and their spring equinox.  At the December solstice, the North Pole is tilted as much as possible away from the Sun, and the Sun is overhead at 23.5 degrees South (the Tropic of Capricorn).  This is the winter solstice for us and the summer solstice below the equator. 

We generally think of these points as the beginning of spring, summer, fall, and winter, but it doesn’t have to be that way.  After all, nothing magically happens with our weather on these dates.  We could just as well consider these points the midpoints of each season.  In that case, the seasons would begin and end at points roughly halfway between the equinoxes and solstices, in early February, May, August, and November.  If the equinoxes and solstices are ‘quarter days,’ the points halfway between them become the ‘cross-quarter days.’

The ancient Celts of Europe appear to have divided their year in precisely that way.  Gauls living in what is now France used a calendar of twelve lunar months with a 13th month added every 2.5 years (similar to the Hebrew calendar today).  Their two most significant months were Gamonios (lunar month corresponding to April/May ), which began the summer half of the year, and Samonios (lunar month corresponding to October/November) which began the winter half of the year.  Julius Caesar noted that daytime followed nighttime in Celtic days.  By extension, the dark (winter) half of the Celtic year preceded the light (summer) half, making Samonios the start of their new year.

The Celts in the British Isles (Irish and Scots) also had festivals aligned with the cross-quarter days.  In early February was Imbolc (or St. Brigid’s day).  Weather predicting traditions of this day are preserved in our current Groundhog Day.  Traditional May Day celebrations are similar to those of the Celtic BeltaneLughnasadh, in early August, marked the start of the harvest. 

'' The Sentiment of Light''
Creative Commons License photo credit: jdl_deleon

The most important, though, was Samhain (pronounced ’sah win’, not ‘Sam Hane’, due to rules of Gaelic spelling), in early November.  This three-day festival marked the beginning of the winter half of the year and the start of the whole year, like Gaulish Samonios.  It was the close of the harvest opened at Lughnasagh, and the time for culling excess livestock.  At this time, the veil between the living and the world of the dead was considered thinner than usual, and people looked forward to meeting and communing with ancestors and relatives who had died.  A ‘dumb supper‘ was set aside for departed relatives.  To scare away unwanted spirits, people dressed in frightening garb.  Note that these spirits were considered unpredictable and possibly mischievous because they were not the familiar ancestors–not because they were particularly evil.  Divination was also practiced at this time, as people sought to predict whom they would marry or how many children they would have. 

Doing the math, you’ve probably figured out that Halloween is not quite halfway from the equinox (September 22) to the solstice (December 21).  But remember, the Celts used a lunar calendar.  They celebrated their festivals on a certain phase of the Moon, possibly full moon, occurring nearest the cross-quarter day.  Upon the adoption of the Julian calendar, which was not strictly lunar, the festivals were moved to the beginning of February, May, August, and November, although this meant they were no longer exactly on the cross-quarter days. 

Saint
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The Wandering Angel

In the eighth century AD, Pope Gregory III moved the church’s commemoration of the souls in heaven (All Saints’ Day) from May 13 to November 1.  Another name for All Saints’ Day is All Hallows Day.  (’Hallow’ is an older term for ’sanctify’ or ‘make holy.’  Think of ‘…hallowed be thy name’ from the Lord’s Prayer).  The next day became All Souls’ Day.  The day before All Hallows Day or All Saints’ Day is All Hallows Eve, or Halloween.  The traditions of Samhain, with its similar focus on honoring the dearly departed, were a natural fit for All Hallows Day and All Hallows Eve.

Halloween, then, is ultimately just one expression of the human need to come to terms with death as a natural occurence and to honor those who have gone before.  In the season of the fall of the leaf, with the Sun taking a slightly lower path across the sky each day, the natural world is going through its own ‘death,’ providing a perfect context for our own activities.  We can therefore think of Halloween itself as a treat, not a trick.

I wish everyone a Happy Halloween, with many more treats than tricks.