Next week in the night sky, Jupiter and Saturn will look as if they are merging and are closer together than they have been since Galileo’s time in the 17th century.
According to astronomers, so-called conjunctions between the two of the largest planets in our solar system are not particularly rare.
Every 20 years, Jupiter moves past its neighbor Saturn as they make their rounds around the sun.
However, the one coming up on Monday is particularly close: from our perspective, Jupiter and Saturn will be just one-tenth of a degree apart, or about one-fifth the width of a full moon.
If weather permits, they should be easily visible around the world shortly after sunset.
Together with the winter solstice in the northern hemisphere, the longest night of the year, and the summer solstice in the southern hemisphere, this spectacle promises to be one of the biggest conjunctions just in time for Christmas.
“A close conjunction occurring in our night sky is extremely rare,” David Weintraub, professor of astronomy at Vanderbilt University, said.
“I think it’s fair to say that such an event typically occurs only once in a person’s lifetime, and I think ‘once in a lifetime’ is a pretty good test of whether something deserves to be called rare or special.”
It will be the closest Jupiter-Saturn pairing since July 1623, when the two planets appeared slightly closer.
However, this conjunction was barely visible because of its proximity to the Sun.
Much closer and easily visible was the conjunction of the two planets in March 1226 – when Genghis Khan conquered Asia.
Monday’s conjunction will be the closest pairing visible since then.
Saturn and Jupiter have been converging in the south-southwestern sky for weeks.
Jupiter – larger and closer to Earth – is noticeably brighter.
“I love watching them get closer and closer, and the fact that I can see it with my naked eyes from my porch,” Virginia Tech astronomer Nahum Arav said in an email.
Despite appearances, Jupiter and Saturn will actually be more than 730 million km apart.
Earth, on the other hand, will be 890 million km from Jupiter.
A telescope will not only capture Jupiter and Saturn in the same field of view, but also some of their brightest moons.
Their next super-close pairing will occur on March 15, 2080.