THE SOUTHWORTH PLANETARIUM
207-780-4249      www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
Julian date:  2457740.16

     "I demonstrate by means of philosophy that the earth is round, and is inhabited on all sides; that it is insignificantly small, and is borne through the stars."

                               -Johannes Kepler

THE DAILY ASTRONOMER

Tuesday, December 20, 2016

Christmas Star Astronomy

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"Astronomy of the Christmas Star"
The title of the next episode of "Radio Astronomy,"

airing on WMPG 90.9 FM  (www.wmpg,org) 

at 1:00 p.m. Friday, December 23.

Lutheran pastor Maria Anderson-Lippert is our

special guest as we delve into the astronomical

aspects of the Star of Bethlehem.

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The Christmas Star, better known as the "Star of Bethlehem," has intrigued many astronomers for centuries.   Many of them have developed theories attempting to explain the "star" that guided the three Zoroastrians to Bethlehem,  birthplace of Jesus.    If the star had actually been a naturally occurring celestial event -an issue that shall remain forever unresolved- what might it have been?  The matter is debated and discussed even today in the early 21st century, despite the protestations of some astronomers who not only consider the problem to be unsolvable, but also worry that these inquiries might offend certain religious sensibilities.      These understandable misgivings notwithstanding, we shall proceed to summarize and briefly discuss three of the most common theories.

Could the Magi have followed a comet?

​Comet McNaught during its 2006 visitation to the inner

solar system.

Comets are icy interlopers from the outer solar system.      During most of their journey toward and away from the Sun, they are dark and therefore invisible.    When a comet approaches the inner solar system, the Sun's heat melts some of the surface ice, creating a luminescent tail that can sometimes stretch over a million miles.     If the comet is sufficiently bright and large, it can produce quite a spectacle in the sky.    (One might think of the 1996 appearance of the massive long period Comet Hyakutake.)   Such a sight would certainly have attracted the attention of sky-admiring Zoroastrians.   A comet can also remain visible for weeks, providing the Magi with ample time to travel to the region toward which they were being guided.

However, the star was said to have announced a grand and joyous event.    Comets were generally regarded as malevolent harbingers: strange apparitions whose appearance portended disaster.     The sight of a comet occasioned dread, not hope.     Also, there is no record of a comet from the time period of Jesus' birth, a range extending from 3 BC. to 1 AD.  

Perhaps the Star of Bethlehem was a Supernova?

​"Supernova 1006'"  This digitally enhanced photo by Tunc Tezel  shows how the supernova might have appeared in Earth's sky in 1006

A supernova explosion occurs when a highly massive star explodes from the inside out.  These cataclysmic explosions literally destroy the star in a blaze of  glory.    A supernova can produce as much energy as a galaxy and, if close enough to Earth, will outshines all the stars and planets.  When Betelgeuse, Orion's eastern shoulder star,  goes supernova, it will be visible during the day and will cast a shadow on us at night!   A supernova could remain visible for a few months until it finally fades into invisibility: plenty of  time as to allow the Magi to make their pilgrimage to Bethlehem.

A principal objection to this theory is that we have no record of such an explosion having occurred between 3 BC and 1 AD or even within many years before or after.   Such a dramatic spectacle would have most assuredly come to the attention of some sky watchers around the globe.  

Maybe Venus and Jupiter?

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Venus and Jupiter experienced a rare close conjunction in 2 BC, within the time range of Jesus' birth.     Venus and Jupiter are the two brightest planets in our sky, with Venus being the far brighter of the two.      These two planets appeared to come so close to one another that Venus actually occulted Jupiter: an immensely rare event, indeed.       The combination of these two planets could have produced a "star like object" far brighter than any other single star!     

The problem with this notion is in the timing and region of visibility.   The Venus-Jupiter occultation was not visible in the Middle East.  (See graphic below.)    Such close planetary conjunctions, especially those involving a rapidly moving inferior planet such as Venus, don't last long.       Venus and Jupiter wouldn't have stayed together for long.    Also, even if they were close enough to appear as single star, the resultant light wouldn't have been as much of a spectacle as the previous paragraph implies.     Venus would have been more than seven times brighter than Jupiter and would have merely have appeared to "swallow" its giant planetary companion.

The Venus-Jupiter occultation was only visible within the colored region centered on South America.       While Venus and Jupiter would have appeared close together in Middle Eastern skies, the Magi would not have witnessed the occultation. 

Consider this article to have been a humble confession of ignorance.     We don't know what the star of Bethlehem might have been.    We don't even know if it were a natural, as opposed to a supernatural, phenomenon.    (More things in Heaven and Earth, Horatio...)    We do know that this mysterious star will continue to exercise a fascination over astronomers for many years to come, even though we all know that this persistent question might ever find an answer.