A planetary conjunction occurs when two or more planets appear to be very close together in the night sky as seen from Earth. Conjunctions between Venus and Jupiter are fairly common, occurring as often as three times a year. But on the morning of November 5th, just before dawn, Venus and Jupiter will be less than one degree apart in the sky in the constellation of Virgo the Maiden. A degree is about the width of one finger held at arms distance. The pair will be at their closest at 1:58 UTC on the 5th, when they are 33 arc-minutes apart, or about 0.42 degrees.
This year’s conjunction is rare for two reasons. First, the two planets are less than one degree apart; and second, they are more than fifteen degrees from the sun. Large number conjunctions, such as the one that occurred in 1995, are less than fifteen degrees from the sun and therefore lost in the sun’s glare. The conjunction on November 5th is also special because it is the last close conjunction between Venus and Jupiter until September 1st 2005.
A conjunction very much like the one occurring on the 5th occurred in August of the year 3 B.C. This historic conjunction occurred on August 12th at 03:00 UTC and was widely visible from the Middle East. That year Venus and Jupiter were only 10 arc-minutes or 0.16 degrees apart in the constellation of Leo the Lion. With such a narrow separation, light reflected from the two would seem to merge into one as seen with the unaided eye.
Some scholars have speculated that this close conjunction may have been interpreted as a sign by a group known as the Magi. The Magi, or wise men, were priests of an ancient religion known as Zoroastrianism. Could this close conjunction have been what sent the wise men traveling to a far of city known as Bethlehem? Unfortunately we can’t draw any definitive conclusions. There are no known written records that tell exactly what the Magi saw, or how they interpreted it.
Regardless of what the Magi saw, modern computer software confirms that there was a very close conjunction between Venus and Jupiter in the year 3 B.C. The conjunction of 2004, while not as close, should be no less spectacular sight in the sky. Telescope or binocular users should have no difficulty fitting both planets into one field of view. This conjunction is also an excellent opportunity for aspiring (or seasoned) astro-photographers.
Exposures of from 1/15s to 1/60s are good for those using SLR’s with standard 50mm lenses. A zoom lens of 180mm can reduce the required shutter speed to a range of 1/60s to 1/250s depending on conditions. But as with any kind of astro-photography, the key is multiple exposures at various shutter speeds and apertures.
A planetary conjunction is a rare and beautiful sight. Because Venus and Jupiter are both so bright in the sky, the Venus-Jupiter conjunction of 2004 should not be missed. With a little imagination we can transport ourselves back in time to the Middle Eastern Skies before the Common Era, when a bright conjunction dominated the pre-dawn skies.
Rod Kennedy is a technician and education outreach coordinator at the Casper Planetarium, Wyoming’s first planetarium. He received his Chemistry degree from the University of Northern Colorado, and has been interested in astronomy for 10 years.