Bright star? Planet Jupiter closer on September 20, 2010 than since 1963

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On September 20, 2010, Jupiter will be closer to Earth than since 1963. On September 21, Earth will pass between Jupiter and the sun. Look for Jupiter! It'll look like a very bright 'star.'

September 14th, 2010 - Astronomy Essentials

What is the bright ’star’ in the night sky in September and October 2010? The brightest ’star’ up throughout the night is really a planet, Jupiter, which will be closer on September 20 than it has been since 1963.

Júpiter en septiembre 2010, en Español …

Jupiter – biggest planet in our solar system, central to its own system of orbiting moons – is rising in the east just after sunset in mid-September. You can’t miss it. It looks like a star, but it’s much brighter than any star in our night sky. We on Earth are in a very good place to see Jupiter in September and October 2010 for two reasons.

First, Earth will fly between Jupiter and sun on September 21, 2010. We go between Jupiter and the sun every 13 months. Each year, when that happens, our two worlds are always relatively close together.

We go between Jupiter and the sun that often because Earth takes a year to complete one orbit around the sun, while Jupiter – with its bigger orbit and slower motion in orbit – needs 12 years to orbit the sun once. Nearly every year, our world’s faster motion in orbit places Jupiter opposite the sun in our sky. Astronomers call this event an opposition of Jupiter.

Every year around the time of opposition, people notice Jupiter. Around September 21, 2010 the planet will be rising in the east as the sun sets in the west. It will be highest in the sky at midnight, and it will set in the west when the sun comes back to the east at dawn. By October, 2010 Jupiter will be minutely fainter as Earth flies ahead in orbit. But it will be even more noticeable because it will already be in the east when night falls.

Second, Jupiter will be closer on September 20 than it has been since 1963. That’s happening because Jupiter’s orbit – like Earth’s orbit – isn’t perfectly round. Jupiter’s closest point to the sun in its 12-year orbit will come about six months from now, in March, 2011.

So we will be passing between Jupiter and the sun (Jupiter’s opposition) on September 21, 2010. And Jupiter will be closest to the sun in March, 2011. That is why Jupiter comes closest to us – at a distance of 368 million miles – around the time of this opposition. The exact date of Jupiter at its closest is September 20, 2010 – the day before opposition. The giant planet will be closer that day than it has been since 1963, and it won’t come so close to Earth again until the year 2022.

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So look for Jupiter in the night sky, and expect it to be big and bright!

If you have ordinary binoculars lying around the house, be sure to turn them in Jupiter’s direction. Jupiter is always a fun object to see through binoculars, and that will be especially true this year since the planet is closest. Through binoculars, you can see one, two or more of the planet’s four largest moons, known as the Galilean satellites. They will appear as tiny ’stars’ strung out in a line bisecting the planet.

A telescope would reveal even more detail within Jupiter’s cloudtops. Dedicated observers, who track this detail over years and decades, know that the planet has recently lost its South Equatorial Belt. At the same time, the Great Red Spot has intensified in color.

By the way, at opposition this year – around September 20, 21, 22 – Jupiter will have company on the sky’s dome. For one thing, it’ll be not far from the moon on the night of opposition,September 21. Also, the planet Uranus – shining barely within the limit of visibility to the unaided eye, and best seen in a dark sky – will be less than a degree from Jupiter on the night of opposition. When the moon is not nearby, shedding its glare on the scene, look through binoculars for Uranus near Jupiter. Both planets will be visible in the same field of view.

Uranus is in opposition on the same night as Jupiter, by the way. The two come to opposition only 5 hours apart. People love it when planets and moons line up in space. On the night of Jupiter’s opposition – September 21, 2010 – Jupiter and Uranus will make a tiny line-up, a line-up of two, in space. For a finder chart showing how to identify Uranus in 2010, look here.

In an earlier version of this article, we indicated that Jupiter would be closer in 2010 than it had been since 1951. In fact, Jupiter was slightly closer (and therefore appeared slightly larger) in 1951 than it will in 2010. There was one intervening year (1963) when Jupiter’s diameter in Earth’s sky was very slightly greater than the 2010 diameter. Here is data on Jupiter’s closest approach (in astronomical units) for the three years in question (1951, 1963 and 2010):

1951 October 2: 3.94871 AU

1963 October 7: 3.95245 AU

2010 September 20: 3.95393 AU

So Jupiter was a tiny bit closer (and larger) in 1963 than it will be in 2010. But Jupiter was even closer in 1951 than in 1963 or 2010. Whew! Lots of numbers. But the main thing is to look at Jupiter in the night sky in September and October, 2010.

And especially mark your calendar for September 20 and 21! On September 20, Jupiter will be closer to Earth than it has been since the year 1963. On September 21, Jupiter will be opposite the sun as seen from Earth, rising at sunset and dominating the sky all night, shining more brightly than any star.

Enjoy Jupiter in 2010!