Jupiter, Saturn draw closer in nearest visible alignment in 800 years

NEW YORK • For months, Saturn and Jupiter have appeared to be courting, as the giant celestial bodies have gradually drawn nearer in the night sky.

Over the next two weeks, as their orbits align more closely, the planets will pull closer until they appear to be just a tenth of a degree apart - about the thickness of a dime held at arm's length, according to the United States' National Aeronautics and Space Administration.

The encounter, known as a great conjunction, happens about every 20 years. But this one - arriving on Dec 21, the winter solstice - is special, astronomers said.

It will be the closest alignment of Saturn and Jupiter, the largest planets in our solar system, since 1623.

But that conjunction, just 14 years after Italian astronomer Galileo Galilei built his first telescope, was 13 degrees away from the Sun, making it almost impossible to view from Earth, said Ms Amy Oliver, a spokesman for the Centre for Astrophysics, Harvard & Smithsonian.

This one will be the closest visible encounter between the two giants since the Middle Ages, in 1226, Ms Oliver added.

The next time the planets will be this close is 2080, she said, making the event a once-in-a-lifetime spectacle for most adults.

Across the US, the best view of the two coming into near-alignment will be just after sunset, in the south-western portion of the sky.

"It's a very elegant astronomical event to watch in the night sky," said Professor Renu Malhotra, a planetary sciences expert at the University of Arizona. "It's a very romantic event - to see these planets approaching each other."

Although best viewed with binoculars or a telescope, the encounter should be visible to the naked eye.

California Institute of Technology associate professor of planetary science Konstantin Batygin said he had been watching Jupiter, his favourite planet, and Saturn draw closer to each other on nightly walks with his dog.

"It's the rare astronomical event where you can appreciate the motion of the planets around the sun without being some kind of astronomer," Prof Batygin said.

"You can still go outside close to Christmas and say, 'Wow, those two planets sure are close to one another, and they aren't usually'. It's one of these rare times when the majesty of the solar system presents itself to the naked eye."

But such encounters were not always viewed so lyrically.

Prof Malhotra said that in ancient times, people considered planetary alignments to be bad omens, portending calamity.

"There was reason to fear that the gods were conspiring when they got closer in the night sky," she said. "It might have ominous meaning to people on earth."

The conjunction is the result of the orbital paths of Jupiter and Saturn coming into line, as viewed from Earth. Jupiter orbits the sun about every 12 years, and Saturn about every 29 years.

Although they will appear to be close together - resembling a bright ball or a tipped-over snowman in the sky, Ms Oliver said - the planets will not actually be that close.

In fact, they will be more than 64 million km apart, she said.

NYTIMES