Sunday, December 27, 2009

The Star of Bethlehem Explained?

One of the greatest mysteries of the Bible and astronomy is the Star of Bethlehem, which guided the Magi on their journey to the baby Jesus. The description of the star in the Bible leaves a lot of questions, and just as many possible answers to its true identity.

One problem, by far the biggest, must be confronted right before we can even start to narrow down the possible identities of the star: no one knows exactly when Jesus was born. Our current calendar is based on the birth of Christ. Unfortunately, this is wrong. It is now thought that Christ was actually born in the span of 8 to 4 B.C. In the Bible, the Holy Family fled into Egypt to avoid the wrath of King Herod, who died in 4 B.C. Thus, that year is the last possible year in which Jesus could have been born.

Now that our time frame has been narrowed down, we can start looking to the sky. There are two schools of thought about the Star of Bethlehem: it was either astronomical or astrological.
Astronomical possibilities include supernova, planets, comets, and conjunctions. In the year 7 B.C., there was a conjunction of Jupiter and Saturn. However, this is very unlikely as the planets were about a degree (little finger at arm's length) apart. Unless the Magi had very poor eyesight, there is no way that two planets this far apart could be mistaken for a single object. Comets have been suggested, especially since they were often described as “hanging” in the sky. This is exactly as the Star was described in the Bible. A last possible interpretation is a supernova. A bright object was seen for about 70 days in 5 B.C. By Chinese and Korean astronomers. This may just be it, but there's a problem: the star was described as moving, which leads into the other school of thought: astrology.

People at this time were almost universal believers in astrology. A notable exception here were the Jews, who were forbidden to practice astrology at numerous spots in the Old Testament. As far as everyone else was concerned, heavenly bodies had special meaning.

One thing we know was that the Magi came from the East. Considering the geographical location of Judea, “East” almost certainly meant Persia. In Persian language, the word “magi” referred to Zoroastrian priests, who practiced medicine and magic (“magic” comes from “magi”), which could also include astrology, at which the Persians were very sophisticated.

One particular passage in Matthew can greatly narrow down possible candidates for the true Star of Bethlehem. According to the Gospel, “the star which they had seen in the East went before them till it came and stood over where the young Child was.” If this is to be believed, the Star was a planet. Over the course of months, a star's position will change as it rises about four minutes earlier each night. Stars don't stand still, but planets do.

Observe a planet over the course of a year, noting where it is in the constellations. For most of the time, it moves forward. However, there are times where it stops, reverses course, stops again, then continues forward. This apparent change in direction called retrograde motion is an optical illusion caused by the Earth passing the slower planet as both orbit the Sun. A comparison can be made to passing cars on the highway. As you pass, the slower car seems to travel backwards. The same is true of planets.

Besides retrograde motion, there is more. Planets and constellations had different significances. Jupiter was widely considered to be associated with kingship. The constellation of Aires the ram was often associated with Israel/Judea. Putting this information together with the knowledge that the Star of Bethlehem was almost certainly a planet allows one to start putting the puzzle together.

In 6 B.C., an astronomical/astrological event that fits the bill very nicely occurred. In that year, the planet Jupiter (planet of kingship) moved into the constellation of Aires (the constellation for Israel/Judea). Thus, this could be interpreted as a sign that a new king of Israel was born. To add even more weight to the hypothesis, Jupiter first appeared as a morning object in the East. At this time, the Sun was also in Aires (Jupiter was rising just ahead of the Sun). In astrology, any constellation is at its most influential when the Sun is in it. Also, it was believed at the time that planets were at their most powerful as they emerged in the East after a period of invisibility in the Sun's glare.

As it would have taken the Magi months to reach Bethlehem from Persia, this also explains the motion of the Star. As time progressed, the Magi could have observed Jupiter slow down and stop before going into retrograde motion. The stoppage could have coincided with the arrival of the Magi in Bethlehem after stopping in Jerusalem and being told of the prophecy predicting the Messiah's birth there.

This is by no means more than a hypothesis. The Star of Bethlehem will probably never be conclusively explained. Either way, merry belated Christmas if you celebrated on the 25th, or merry Christmas if you celebrate on January 7.

Tuesday, December 15, 2009

Vega setting, Vega rising

On the last post explaining what was going on in the sky in the month of December, I set a unique challenge: in this season of long nights, try and observe (or even better, photograph) the same star on the set and on the rise. It is possible now and will be possible even into February. Above are my efforts from three years ago with my old HP Photosmart 945, so get out and give it a try. Click on the top picture and that cross shaped constellation (pointing straight down) is Cygnus the swan.



Wednesday, December 2, 2009

December Skies: What's Up This Month

The months of December through February are the cloudiestof the year, averaging only about 30% of possible sun, and star light. Needless to say, clear nights in December should be cherished, especially considering the sights to be seen and the fact that December brings the longest nights of the year, which allows for some unique fun. Only at this time of year is it possible to observe something twice on the same night: once on the set in the evening and again on the rise in the morning. Vega and Deneb, two bright stars of the Summer Triangle, make great targets for this once a year opportunity. I've done it, you should, too. On to constellations, December allows for observation of the sky for three quarters of the year. Take a last look at the fall constellations as the sun sets, probe the winter constellations in the dead of night, and race the light to behold the spring constellations as dawn nears. There's way too much to be seen for going into detail here, so grab your sky atlas and some warm clothing to prepare for an all night observing session that will take you through the majority of the year. As two last planetary notes, keep an eye on Mars, it will nearly double in brightness by the end of the month. Want to see Neptune? Look near Jupiter. This is the way Galileo saw it 400 years ago.

December Visual Observing Highlights

Early December: Jupiter emerges due South at twilight, no better time for telescopic observation. Also be sure to catch Venus at dawn low, extremely low, on the Southeastern horizon.
December 1: The full moon splits the sky between the Pleiades and Hyades
December 5: The waning gibbeous moon, Pollux, and Castor line up.
December 6: The moon is within 5 degrees of the Beehive Cluster. Use binoculars.
December 7: Cosmic triangle: Regulus, moon, Mars. Grab the camera. Earliest sunset of the year.
December 13/14: Geminid Meteors peak. Keep an eye to the sky about a week either side of this date.
December 18: The moon meets Mercury low in the Southwest. Test your horizon.
December 21: Winter Solstice, the longest night of the year.
December 28: The waxing gibbeous moon scrapes the Pleiades
December 31: Blue moon (second full moon of a month)
All month: Morning planets: Mars in Leo and Saturn in Virgo