Jupiter will appear unusually bright in the night sky, outshining even Venus, on September 20 as two astronomical phenomena are coinciding on the day — the planet is going to be in opposition to the Sun and will be at a distance closest to the Earth since 1963.
The orbits of planets Mars, Jupiter, Saturn, Uranus and Neptune are at a distance greater than that of the Earth and thus the group is known as superior planets. When a superior planet, the Earth and the Sun align in a straight line with the Earth in between, it is known as opposition, says D.P. Duari, Director (Research and Academics) at the Birla Planetarium here.
“At or near opposition, the Earth comes closest to Jupiter for the year, and Jupiter, in turn, shines most brightly in our sky,” said Dr. Duari.
The phenomenon of opposition is not particularly rare as it occurs every 13 months. The Earth revolves around the Sun in one year, while Jupiter takes 12 years. In the time the Earth has taken to come back to the previous point of opposition, Jupiter has moved along one-twelfth of its orbit, so it takes Earth an extra month to catch up, Dr. Duari said.
“This year on September 20, Jupiter will be about 590 million km away from Earth. This is the closest it has come since 1963 and the next time the approach will be this close is in 2022,” Dr. Duari said.
On the night of September 20 and 21, the size of Jupiter will be about 50 arc seconds (an arc second is 1/3600 th of a degree) and the planet will be the brightest object, barring the moon, in the night sky.
On both these days Jupiter will remain in the sky exactly for 12 hours from sundown to sunrise the next day, Dr. Duari added.
He said the event would be an ideal opportunity for astronomy enthusiasts to observe certain interesting features of Jupiter. The largest of its satellites, called the four Galilean moons after Galileo Galilee, will be in clear view through even a small telescope, he said.
