This is the Skywatch Line for Monday and Tuesday, January 7th and 8th.
The Sun sets at 4:37 PM; night falls at 6:19. Dawn begins at 5:44 AM and ends with the Sun rising at 7:25.
The only easily visible evening planet is Mars. Mars, in Pisces, is now brightest and largest for this year. This month it dims from 0.5 to 0.9 magnitude; it also thins from 7 to 6 arc-seconds in size. Mars appears about 87% illuminated and about 49º high at Civil Dusk. It sets at 11:13 PM.
Mars is sandwiched between two dimmer planets, each about 20º away. Neptune, in Aquarius, is a dim 8th magnitude and a tiny 2.2 arc-seconds in size. About 37º high at Dusk, it sets at 9:26 PM. Brighter Uranus shares Pisces with Mars, but at opposite sides of the constellation. Uranus is about 6th magnitude and a bit larger and 57º high when it is best observed at 6:33 PM; it sets at 1:16 AM.
The 2-day-old Moon, in Capricornus, appears about 3% lit and 9º high on Monday, setting at 6:14 PM. Tuesday it is brighter, about 7% lit and 16º high; it sets at 7:11 PM.
The Moon’s absence makes observing Comet Wirtanen easier. The comet is found in the faint constellation Lynx, midway between Auriga’s bright star Capella and the bowl stars of the Big Dipper, Megrez & Dubhe. It is up all night, shining with 5th magnitude.
Finder charts for Neptune, Uranus and comet Wirtanen are available from astronomical media.
The pre-dawn sky shows the brightest planet. Venus, in Libra, was at its greatest elongation from the Sun on Sunday. Rising at 3:45 AM, at Dawn, it is about 51% lit, blazes with minus 4th magnitude, 24 arc-seconds in size and stands 17º above the eastern horizon. Jupiter, in Ophiuchus, follows at 4:56 AM, shines with minus 1st magnitude and appears a large 32 arc-seconds in size. However, its 7º altitude makes observing the giant planet difficult. Note their 12º separation; later this month, they have a conjunction.
Mercury, in Sagittarius, is now ending its morning apparition; it rises at 6:40 AM. Mercury appears about 94% lit, glows with minus zero magnitude and appears about 5 arc-seconds in size. However, its low 2º altitude requires an unobstructed horizon for the observer to see this elusive planet.
Sunday, January 6th, was the Christian feast of the Epiphany, otherwise known as “Three Kings Day.” But, who were these “kings?” Most likely they were Magi from the eastern empire of Babylon. Babylonians were famous for their astronomical skill. By 2000 BC, they identified all five visible planets, the major constellations, the zodiac and the Saros cycle of eclipses. These priest-astrologers were very powerful and respected throughout the known world.
These dedicated sky watchers would certainly have noticed any new object or event in the night sky. While some think that a comet or supernova may have been the “Christmas Star.” The prevailing opinion is that it may have been an astrological event: the most likely being a triple conjunction between Saturn and Jupiter during the year 7 BC. During the course of the year, Jupiter appears to: chase Saturn, catch up with it, pass it, turn around and catch up with and pass Saturn again, and finally catch up with Saturn one more time before sailing eastward past it. This startling series of events took place in Pisces, a significant constellation. While we now know the planets to be worlds like our own Earth, to the ancients stars and planets were messengers from the gods. When two planets, associated with the most powerful gods, keep meeting, the Magi knew something significant was about to happen. These scholars were also familiar with their neighbors. A search of Jewish documents provided the inspiration to set off for that distant land and a possible meeting with a new god-king.