December 2020 Jupiter-Saturn conjunction
By Jeff H.
➢ The 21st of December marks a very special celestial event. The
conjunction, or close passing, of Jupiter just south of Saturn in the sky. The
last time this close of a conjunction had occurred was in 1623 with a
separation of only 5 arc minutes. The Moon averages 30 arc minutes in
apparent size. The next one as close as this one won’t occur again until
March of 2080 with a separation of 6 arc minutes…slightly less than the one
this month which will be just over 6 arc minutes of separation. The night
before the two will be about 7 arc minutes apart.
➢ Closest separation occurs at 6am on the 21st but the two planets don’t
rise until 9:52am so the best time will be in the evening of the 21stsome
time between 5 and 6 pm since the Sun sets at 4:21pm and the two planets
will be setting by 6:45pm in the SW.
➢ At the time of the observing, Jupiter’s moon Ganymede (the largest
moon in our solar system at 3,270 mi. dia.) will be transiting the disk of
Jupiter starting at 4:02pm. It’s transit ends after Jupiter sets at 6:45pm.
Through a telescope with south facing up, Jupiter’s moon Europa will be to
the left of Jupiter. To the right of Jupiter will first be Io then Callisto. For
Saturn, it’s largest moon Titan (the second largest moon in our solar system
at 3,200 mi. dia.) will be visible to its lower left. Both planets will be located
in western Capricornus with a first quarter Moon to their east in Pisces and
Mars just east of the Moon also in Pisces.
➢ Mars will be crossing the Meridian at 7:32pm still bright orange with a
magnitude of -0.5. It’s distance increases as Earth continues to pull further
ahead of Mars but it’s still possible, with good skies, to make out light and
dark regions on its surface. (albedo) There is still a threat for dust storms on
Mars since its southern summer solstice occurred early September and its
Perihelion in August. The next time Earth passes Mars (opposition) will be
in December 7, 2022.
Good luck…and clear skies, at least for the conjunction. Stay safe!