Special: Jupiter and Saturn Get Together on December 21st!

 For this article, I'm turning our subject from instruments to look at the sky, to the sky itself, for a very special event. More specifically, to the planets Jupiter and Saturn.
On December 21,202O, about forty-five minutes after sunset, the two planets will stand about 14 degrees above the southwestern horizon and will appear to be much less than 1 degree apart in the sky! Your pinkie-finger, held up against the sky at arm's length, is 1 degree, and the span between your pinkie-finger and your pointer (index finger) is roughly 15 degrees, again with your outstretched arm held against the sky That's not far above the horizon, so you might want to find a spot with a clear view of the horizon (around Michiana, Lake Michigan would be an ideal spot, weather permitting).
This celestial event is known as a conjunction (more precisely a non-solar conjunction, since neither of the objects is the sun). Two non-solar objects are in conjunction if they have the same Right Ascension. Right Ascension corresponds to longitude on earth, but instead is reckoned on the celestial sphere. Another term for locating objects in the sky is Declination, which corresponds to latitude on the earth.
Through a telescope at moderate magnification, both Jupiter and Saturn (and their brighter moons) will fit into your eyepiece's view.
According to one Steve Albers, the last conjunction of these two planets that was closer and readily observable occurred in the year 1226, (nearly 800 years ago). Of course, though they appear so close together in the sky, they are, in fact, about 4O3 million miles apart. Jupiter orbits the sun at an average distance of 484 million miles and takes about twelve years to go around the sun once, and Saturn averages 887 million miles from the sun and its orbit around the sun takes about 29 1/2 years.
So, though they are physically separated in space by nearly a half- billion miles, they still line up in the sky visually "every once in in a blue moon" (oops, the Moon's not involved!).

Happy Holidays!!

George Drake, M.D. ETHOS Volunteer
Michiana Astronomical Society Member
References:
1. Observer's Handbook 2O2O The Royal Astronomical Society of Canada
2. The Backvard Astronomers Guide 3.d ed. Dickinson and Dyer, Firefly books 2008
3. Solar Slzstem: A Visual Exploration Of The Planets. Moons. And Other Heavenly Bodies That
Orbit Our Sun Chown, Marcus, Black Dog and Leventhal Publishers, Inc. 2016 4. Sky and Telescope American Astronomical Society Vol 140, No.6, December, 2O2O 

​Learn more about conjunctions at 1 Degree of SkyTime: https://youtu.be/DILtQlBPF_4