A Christmas Star That Is Not a Star

The conjunction that appears as a “star” – Image: NASA

Popularly known as the “Christmas Star,” at this time of 2020 you can observe this “star” that is actually the planetary conjunction of the bright planets Jupiter and Saturn.  The conjunction culminates on the night of December 21, but is visible in the evening sky now.

We know that Galileo Galilei in 1610 discovered the four moons of Jupiter – Io, Europa, Ganymede, and Callisto. He also saw in his telescope a strange oval surrounding Saturn. Later that halo would be seen in better telescopes as Saturn’s rings.

In 1623, our solar system’s two giants, Jupiter and Saturn, moved together until Jupiter caught up to and passed Saturn. This astronomical event is known as a “Great Conjunction.”

The planets regularly appear to pass each other in the solar system. Jupiter and Saturn align in the sky about once every 20 years.

You can imagine ancient skywatchers seeing this conjunction as a bright star at this time of solstice or Christmas as something miraculous.

But this year has several additional celestial wonders. First, it has been almost 400 years since the planets passed this close to each other in the sky. Astronomers tell us that it has been nearly 800 years since the alignment of Saturn and Jupiter occurred at night so that people around the world can see this conjunction.

The 21st is also the Winter Solstice. These two planets will be so close (a tenth of a degree apart)  and will appear on the long solstice night to be one “star.” No telescope needed to observe the conjunction. Actually, the naked eye will blur the two together more than an optical view.

If you believe in coincidences, this is an interesting one. If you don’t believe in coincidences, this is more interesting.

Like many celestial events when viewed from Earth, these giants will appear close together, but they will remain hundreds of millions of miles apart in space.

On this snowy night, I will venture out to an unobstructed view of the sky, an hour after sunset, and look to the southwestern sky. Jupiter will look like a bright star and Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter. At the solstice, Jupiter will overtake it and they will reverse positions in the sky.  If you do have a telescope or good binoculars you might see Jupiter’s four large moons. The Moon will be at its First Quarter tonight with 45% of it illuminated.

You might want to watch the NASA Science Live episode on the conjunction live at 3 p.m. EST today on NASA Television and the agency’s website, along with the NASA FacebookYouTube, and Periscope channels.

the planets
Our solar system –  Image by Comfreak from Pixabay


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A lifelong educator on and off the Internet. Random by design and predictably irrational. It's turtles all the way down. Dolce far niente.

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