DENVER (CBS4) – Monday is a special day for the northern hemisphere of planet Earth as it is the winter solstice, a day known as the shortest day of the year and the official start of the winter season. But on December 21st of this year something else will take place that involves two other planets in our solar system.

File photo of a group of amateur astronomers. (Photo: PHILIPPE HUGUEN / AFP / Getty Images)

Immediately after sunset on Monday you can experience the “great conjunction” of Saturn and Jupiter, as long as the weather cooperates. The conjunction should be visible from almost anywhere on earth and form what many call the poinsettia. To see this rare occurrence, look out toward the southwestern horizon about an hour after sunset.

(Credit: NASA)

According to NASA, it has been almost 400 years since these two planets were so close together, and it has been almost 800 years since such proximity happened at night. While you can see this celestial event with the naked eye, if you happen to have a telescope you can actually see each planet individually, including Saturn’s rings and Jupiter’s moons.

So why is that called a poinsettia? Is it because it happens so close to the Christmas holidays? Is there a biblical meaning? Is it because the two planets will briefly look like one big, bright star? Click here to read a great article by Larry Sessions and Deborah Byrd that explores these questions and more.