Dr. Locke Spencer (Photo provided by the University of Lethbridge)

By Justin Goulet

See the Christmas star: rare celestial event to occur on the Winter Solstice

Dec 20, 2020 | 7:30 AM

LETHBRIDGE, AB – You might be able to catch a glimpse of the Christmas star this week.

That’s the celestial event when Jupiter and Saturn appear very close together in the southwestern sky a few hours after sunset. On Monday, December 21, Jupiter and Saturn will share the same celestial longitude and appear to pass each other in the sky. This is known as a great conjunction, because they are the two largest planets in our solar system.

Jupiter has an orbital period of about 12 years while Saturn’s is approximately 30 years.

“These great conjunctions take place about every 20 years,” said Dr. Locke Spencer, Canada Research Chair in Experimental Astrophysics with the Department of Physics and Astronomy at the University of Lethbridge.

“Some are greater than others because their elliptical orbits do not always bring them as close together from our perspective on Earth.”

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The last great conjunction was in May 2000. Then, Saturn and Jupiter appeared to be two full-moon widths apart. This time around, they’re expected to appear much closer, separated by the thickness of a dime held at arm’s length.

“Another grand feature of this upcoming great conjunction is that it is taking place on the Winter Solstice, the longest night of the year for those in the Northern Hemisphere, so, weather permitting, it should be visible to many. It should be visible in the southwest sky between Capricornus and Sagittarius, not too far above the horizon,” added Dr. Spencer.

“While both are visible to the naked eye, one should be able to see Jupiter’s Galilean moons and a faint glimpse of Saturn’s rings with good binoculars.”

The last great conjunction as close and as visible as this year’s happened almost 800 years ago in March of 1226.