Jupiter and Saturn will be so close today that they appear to form a “double planet.” Such a spectacular combination, as planetary alignment became known, has not taken place in almost 800 years.
When their orbits align every 20 years, Jupiter and Saturn get very close to each other. Jupiter orbits the sun every 12 years, while Saturn’s orbit lasts 30 years, so every few decades, Jupiter gives up Saturn, according to NASA.
The great conjunction of 2020 is particularly rare – the planets have not been so close to each other for almost 400 years and were not so observable at night in medieval times, in 1226.
“Alignments between these two planets are quite rare, occurring once every 20 years, but this conjunction is exceptionally rare because of how close the planets will be to each other,” Rice University astronomer said in a statement. Patrick Hartigan. “You should have returned by the morning of 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 both the four months of Jupiter – Io, Europa, Ganymede and Callisto – and the rings of Saturn. Not long after, in 1623, the two planets were observed aligning for the first time.
The conjunction is sometimes nicknamed the “Christmas Star” or “Star of Bethlehem” for its connection to the story of Christian Christianity. In the story, the star leads the sages to the house of Jesus, which many Christians believe was a miracle. Astronomers have tried to link the star to several rare celestial events – including a comet, a supernova and a conjunction.
Aligning with the winter solstice on December 21, 2020, the two planets will be only 0.1 degrees – less than the diameter of the 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 occurs between the two great planets in our solar system: Jupiter and Saturn.
The planets will be so close that they will appear, from certain perspectives, to completely overlap, creating a rare “double planet” effect. So close that a “pink finger at arm’s length will easily cover both planets in the sky,” NASA said.
However, although they may appear on Earth to be very, very close, in reality, they are still hundreds of millions of miles away.
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How to follow the great conjunction
During the last conjunction in 2000, Jupiter and Saturn were so close to the sun that the event was difficult to observe. But those who look at the sky should have a clearer view of the celestial event this time. The great conjunction will shine brightly shortly after sunset, low in the southwestern sky, as seen from the northern hemisphere, NASA said.
Throughout December, sky observers will be able to easily observe the two planets with the naked eye. You can look up every night to see them getting closer and closer to the sky – they are so bright that they are even visible in most cities.
Jupiter now looks brighter than any star in the sky. Saturn is slightly weaker, but still as bright as the brightest stars, with a recognized golden glow.
Saturn will appear slightly above and to the left of Jupiter and will look as close to the planet as some of its own moons, visible through binoculars or a telescope. Unlike the twinkling stars, both planets will keep a constant brightness, easy to find on clear nights.
“You can imagine that the solar system is a racetrack, with each of the planets as a runner on its own lane and the Earth toward the center of the stadium,” said Henry Throop, an astronomer in NASA’s Planetary Science Division. “From our point of view, we will be able to see Jupiter in the inner band, approaching Saturn all month and finally surpassing it on December 21.”
The event is observable from anywhere on Earth, provided the sky is clear. “The farther north a spectator is, the less time they will have to capture the conjunction before the planets sink below the horizon,” Hartigan said.
The planets will appear extremely close for about a month, giving observers in the air plenty of time to watch the spectacular alignment throughout the holiday season. The event coincides with the December solstice, marking the shortest day of the year in the northern hemisphere.
“Such conjunctions could happen on any day of the year, depending on where the planets are in their orbit,” Throop said. “The date of the conjunction is determined by the positions of Jupiter, Saturn and Earth in their orbits around the Sun, while the date of the solstice is determined by the inclination of the Earth’s axis. The solstice is the longest night of the year, so this rare coincidence will give people a great chance to go outside and see the solar system. “
To learn more about when and where to look up to see the conjunction, Throop will be live on NASA’s website to answer questions Thursday afternoon.
This will be the “biggest” big conjunction for the next 60 years, until 2080. Hartigan said that after this conjunction, the duo will not take such a close approach until sometime after 2400.