A rare celestial phenomenon will take place on Monday evening when the two biggest planets of the solar system – Jupiter and Saturn – will appear in the night sky as if they are nearly touching. In India, the best view of the two planets coming in near-alignment is expected to be just after sunset between 6:30 pm and 7:30 pm.

The encounter, known as a great conjunction, happens about every 20 years. But the one that will take place on Monday will be the closest alignment since 1623, Amy C Oliver, a spokesperson for the Center for Astrophysics, Harvard & Smithsonian, told The New York Times. However, that conjunction of 1623 was 13 degrees away from the sun, making it almost impossible to view from Earth, she added.

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Therefore, Monday’s event will be the “closest visible encounter” between the two planets since the Middle Ages, in 1226, Olivia said. The next time the planets will be this close is 2080.

The National Aeronautics and Space Administration, or NASA, said the closest alignment will appear just a tenth of a degree apart, about the thickness of a coin held at arm’s length. It will be visible to the naked eye.

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.

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Astrophiles around the world are excited. At the Regional Science Centre and Planetarium in Kozhikode, Kerala, an observation session will be organised on Monday evening, reported The Hindu.

The planets will be easy to see with naked eye by looking toward the southwest. Jupiter, the largest planet and also relatively closer to Earth, will be vastly brighter.

Saturn will be slightly fainter and will appear slightly above and to the left of Jupiter until December 21, when Jupiter will overtake it and they will reverse positions in the sky, according to The Business Standard. Although the planets will be visible to the naked eye, one might be able to see the Jupiter’s four large moons with the help of binoculars or a small telescope.

The conjunction also coincides with the longest day of the year as the sun reaches a point where it appears to shine farthest to the south of Equator over the Tropic of Capricorn, marking the start of the winter solstice.

The Google doodle on Monday was also about the great conjunction. Source: Google