On Dec. 21, don’t forget best look at cosmic Christmas Star in 800 years

Don’t forget to check out Monday’s cosmic event: the Christmas Star — which is actually Jupiter and Saturn in their closest visible alignment in nearly 800 years.

If cloud cover allows — fingers crossed — the planets will appear almost as one, creating an usually bright point of light in the southwest, about 45 minutes after sunset and roughly 15 degrees above the horizon. That’s about the width of your hand at arm’s length.

Orbits of the two gas giants line up every few decades, but it’s not always in December or this close. And we’ll be the first humans since 1226 who’ve gotten a shot at this view against the canvas of a night sky.

It won’t last long — the planets will set after about an hour. But if you miss it, or the weather doesn’t cooperate, Dec. 21 is just the peak. The alignment — known as a Great Conjunction — will remain striking for several days while the planets gradually part company.

Naked eyes will do, but if there’s a telescope under that tree, hand it over early.

Joanne Kimberlin, 757-446-2338, joanne.kimberlin@pilotonline.com