This year’s winter solstice is bringing an early Christmas present to onlookers. As the sun sets on Dec. 21, Jupiter and Saturn will appear closer together than they have since the Middle Ages, creating what is referred to as the “Christmas Star.”
According to Rice University astronomer Patrick Hartigan, the last time the solar system’s two largest planets appeared close enough for Earth to view was in March of 1226.
The last time Jupiter and Saturn created this “double planet” effect was in 1623, but the spectacle was too close to the sun, making it impossible to view from Earth.
“Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to one another,” Hartigan explained.
Jupiter and Saturn have been moving closer to each other since summer. By Dec. 16, the two planets will be less than the diameter of a full moon apart- just more than 2,000 miles.
On the evening of Dec. 21, that gap between the planets will have lessened to 20 percent of the moon’s diameter, which is just shy of 500 miles. According to NASA, this distance is equivalent to the thickness of a dime held at arm’s length.
The closeness of the two planets and their respective moons will form what astronomers refer to as a “conjunction,” which is when the orbit of two or more planets align.
Many double and even triple planet conjunctions have happened in Earth’s history. In fact, some astronomers believe that the star of Bethlehem was a triple planet conjunction between Jupiter, Saturn and Mars.
Hartigan is encouraging stargazers to start looking for the planets now, as it will make it easier to find them on Dec. 21.
Weather permitting, the event will be visible to anyone on Earth, but it will be more difficult for people living in high northern latitudes.
“The further north a viewer is, the less time they’ll have to catch a glimpse of the conjunction before the planets sink below the horizon,” Hartigan explained. “People are going to have to work a bit.”
A telescope is not needed to see the planets; however, punctuality and a good viewing spot are key. Too early, and Saturn may look faint. Too late, and the planets may already be out of sight.
Hartigan warns that the conjunction won’t be obvious, suddenly appearing as a bright “Christmas Star” in the sky, but shouldn’t be hard to find for those who know where to look.
Avoid tall mountains or buildings and look towards the low, southern horizon just after sunset. In Raleigh County, the sun should begin to set at 5:10 p.m.
Amy Oliver, spokeswoman for the Harvard Smithsonian Center for Astrophysics, says that the best chance to view the event is at dusk and anywhere from 15 to 20 minutes after dark.
The spectacle will not be visible during the day, but the United States should have no problem seeing the conjunction at night, weather permitting.
Those who miss this year’s conjunction may live long enough to see the next conjunction in March of 2080. After that, the pair won’t conjunct again until sometime after 2400, according to Hartigan.
If possible, the astronomer says to make an effort to look for the two planets on Dec. 21.
“Astronomy gives you a different kind of perspective on the universe, which is different from our day-to-day experiences. Things are going on above us all the time, they mark eras… It’s an important connection between generations.”
Visit nasa.gov for information on the great conjunction and other celestial events.
