Jupiter and Saturn will be so close today that it looks like they are forming a ‘double planet’. Such a spectacular great conjunction, as the planetary alignment has become known, has not occurred in nearly 800 years.
When their orbits align every 20 years, Jupiter and Saturn become extremely close to each other. Jupiter orbits the sun every 12 years, while Saturn’s orbit lasts 30 years, so Jupiter rounds Saturn every few decades, according to NASA.
The great conjunction of 2020 is extremely rare – the planets haven’t been so close together in nearly 400 years and have not been seen so close together at night since the Middle Ages, in 1226.
“Alignments between these two planets are quite rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear,” Rice University astronomer Patrick Hartigan said in a statement. “You would have to go all the way back to just before sunrise on March 4, 1226, to see a closer alignment between these objects visible in the night sky.”
What is a great combination?
In 1610, the Italian astronomer Galileo Galilei discovered Jupiter’s four moons – Io, Europa, Ganymede and Callisto – as well as the rings of Saturn. Not long after, in 1623, the two planets were first seen aligned.
The conjunction is sometimes called the “Christmas Star” or “Star of Bethlehem” because of its connection to the Christian Christmas story. In the story, the star leads the wise men to the house of Jesus, which many Christians say was a miracle. Astronomers have tried to link the star to several rare celestial events – including a comet, a supernova, and a conjunction.
In line with the winter solstice on December 21, 2020, the two planets will be only 0.1 degrees apart – less than the diameter of a full moon, EarthSky said. The word “conjunction” is used by astronomers to describe the meeting of objects in our night sky, and the great conjunction takes place between the two largest planets in our solar system: Jupiter and Saturn.
The planets will be so close that, from some perspectives, they will completely overlap, creating a rare “double planet” effect. So close that a “pinky finger at arm’s length can easily cover both planets in the sky,” NASA said.
While they may appear very, very close from Earth, in reality they are still hundreds of millions of miles apart.
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How to view the great conjunction
During the last great conjunction in 2000, Jupiter and Saturn were so close to the sun that the event was difficult to observe. But skywatchers should have a clearer picture of the celestial event this time around. The great conjunction will shine brightly shortly after sunset, low in the southwestern sky as seen from the Northern Hemisphere, NASA said.
Throughout December, skywatchers will be able to easily see the two planets with the naked eye. You can look up every night to see them getting closer and closer in the sky – they are so bright that they are visible even from most cities.
Jupiter currently appears brighter than any star in the sky. Saturn is slightly fainter, but still as bright as the brightest stars, with a recognizable golden glow.
Saturn will appear slightly above and to the left of Jupiter, and will even appear as close to the planet as some of its own moons, visible with binoculars or a telescope. Unlike stars, which twinkle, both planets will maintain a constant brightness, easily found on clear nights.
“You can imagine the solar system as a race track, with each of the planets as a runner in their own orbit and the Earth toward the center of the stadium,” said Henry Throop, an astronomer with the Planetary Science Division at NASA headquarters. . “From our vantage point, we can see Jupiter on its inner orbit, approach Saturn for the entire month, and finally overtake it on December 21.”
The event is observable anywhere on Earth, provided the sky is clear. “The farther north a viewer is, the less time it takes them to glimpse the conjunction before the planets sink below the horizon,” Hartigan said.
The planets will appear extremely close for about a month, giving skywatchers plenty of time to witness the spectacular alignment throughout the holiday season. The event happens to coincide with the December solstice, the shortest day of the year in the Northern Hemisphere.
“Conjunctions like these can happen on any day of the year, depending on where the planets are in their orbits,” Throop said. The date of the conjunction is determined by the positions of Jupiter, Saturn, and the Earth on their paths around the sun, while the date of the solstice is determined by the tilt of the Earth’s axis. The solstice is the longest night of the year. , so this rare coincidence will give people a great opportunity to go out and see the solar system. “
To learn more about when and where to look up to see the conjunction, Throop will be live Thursday afternoon on NASA’s website answering questions.
This will be the “greatest” major conjunction for the next 60 years, through 2080. Hartigan said that, after that conjunction, the duo won’t get that close until sometime after the year 2400.