Glorious End to 2020
There remains much beauty to be seen in 2020. Looking away from earth after sunset, you can witness a quiet spectacle unfolding in the twilight. As the planets Jupiter and Saturn gradually close the gap between each other, they collectively glide toward the southwest. On December 21, 2020, they seem nearly to touch, passing each other by a mere tenth of a degree.
Jupiter overtakes Saturn every twenty years, so a conjunction is not rare. However, this year the planetary encounter is closer than most. Jeff Hunt describes the circumstances and notes that the last time they were this close was 1632, when the telescope was just emerging. However, the close pair was not easily visible that year in the twilight.
For details and animations, see Patrick Hartigan's article at https://sparky.rice.edu/~hartigan/public-night/jupsat2.html. Hartigan notes the pair of planets were visible and closer in 1226 at 2.1 minutes of separation, compared to 1623 (5' separation) and 2020 (6' separation).
Going into autumn, toward the south after sunset the two planets are separated by about eight degrees, less than a fist held at arm's length. Jupiter is the bright one to the right with fainter Saturn on the left. Follow the pair just after sunset through December.
Both are gas giant planets. Being closer to earth, Jupiter is brighter at magnitude= -2.0; distant Saturn is magnitude= 0.6. The moon glides underneath the pair December 16-17.
The conjunction's occurring on the same day as the December solstice is merely a coincidence with the calendar. [As an aside, the solstice is a good time to mount or to recover a solargraph.]
On December 21 just after sunset, well left of the planetary pair is the crescent moon, and that far again is reddish Mars at magnitude= -0.5. Mars is on the decline in brightness, having opened the autumn at a stunning magnitude= -2.3. Though Neptune is shown in the diagram, it is too faint to be seen in the twilight.
Around conjunction on December 21, Jupiter is visible in the twilight immediately after sunset. Saturn will require several more minutes until it emerges from the light background. At 6 minutes (6') of separation, the planets should be resolvable to the human eye if your vision is at least 20/100, per a tweet by Neil deGrasse Tyson. However, as the planets sink into the atmospheric muck near the horizon, observing them will be a challenge.
To close out the year 2020, the giants Jupiter and Saturn continue to separate before disappearing into the evening twilight. Exhale.
While most people will notice the alignment unfolding in December with their naked eyes, the conjunction offers a special treat for observers with telescopes. On December 21, both planets appear in the same field of view of a modest telescope with magnification of 40x-50x. At that magnification, you may see the four Galiean moons and dark belts of Jupiter, and Saturn will be non-circular with a moon or two visible, as illustrated below.
All in the same field of view! Now that is a glorious end to 2020.
Added Dec. 18, 2020