“What’s THAT thing?” people are asking. A big bright “star” greets you if you look up on any clear night this September. It’s low in the east after twilight, and higher in the southeast as the evening grows late. It completely overpowers every actual star in the night sky.

What you’re looking at is the planet Jupiter. “Jupiter is always bright, but if you think it looks a little brighter than usual this month, you’re right,” says Robert Naeye, editor in chief of Sky & Telescope magazine. “Jupiter is making its closest pass by Earth for the year. And this year’s pass is a little closer than any other between 1963 and 2022.”

Jupiter is nearest to Earth on the night of Monday, September 20th: 368 million miles away. But it remains nearly this close and bright throughout the second half of September.

At the closest point of its previous swing-by, in August 2009, Jupiter was 2% farther than this time. That translated into 8% dimmer, all things considered. At its next pass, in October 2011, it will be a little less than 1% more distant than now.

In addition, Jupiter is an additional 4% brighter than usual because one of its brown cloud belts has gone missing. For nearly a year the giant planet’s South Equatorial Belt, usually plain to see in a small telescope, has been hidden under a layer of bright white ammonia clouds.

Uranus Too

Coincidentally, Jupiter is also passing almost in front of the planet Uranus just now. Uranus is 5 times farther away and almost 3,000 times dimmer, so it’s invisible to the unaided eye and contributes no light to speak of. But binoculars or a telescope will show Uranus less than 1 degree from Jupiter now through September 24th. (You’ll need a detailed chart showing which tiny point of light it is; see http://SkyandTelescope.com/uranus).

On the other end of the brightness scale, the full Moon joins this celestial scene around the same time too — shining above Jupiter on the evening of September 22nd and left of it on the 23rd.

More coincidences are also happening here. Jupiter and Uranus find themselves close to the point on the sky known as the vernal equinox, where the Sun crosses the celestial equator on the first day of spring. (“Spring” here means spring in the Northern Hemisphere.)

And, all of this takes place around the date when fall begins in the Northern Hemisphere: on September 22nd. (Fall begins at 11:09 p.m. Eastern Daylight Time on that date.)

What do all these coincidences mean? “Nothing at all,” says Alan MacRobert, a senior editor at Sky & Telescope. “People forget that lots of things are going on in the sky all the time. Any particular arrangement might not happen again for centuries, but like the saying goes, there’s always something. Enjoy the show.”

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Publication-quality images: http://www.skyandtelescope.com/about/pressreleases/102862454.html

For more skywatching information and astronomy news, visit SkyandTelescope.com or pick up Sky & Telescope, the essential magazine of astronomy since 1941.