A Moonlit Trio

NASA/Bill Ingalls

The Moon (left), Saturn, and Jupiter (lower right; Saturn is above and to the left of Jupiter) were seen in the sky above the Washington Memorial on Dec. 17, 2020. At the time, Saturn and Jupiter were nearing each other in the sky, culminating in a “great conjunction” on Dec. 21, where they appeared a tenth of a degree apart.

Great conjunctions between Jupiter and Saturn happen every 20 years, making the planets appear to be close to one another. This closeness...