Starship Asterisk*

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Jupiter among the evening stars. (Credit: TWAN/Babak A. Tafreshi)

What’s THAT thing?

If you look up on any clear September night, a big bright “star” will greet you. 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. 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% or so 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 is it; see SkyandTelescope.com/uranus).

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

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.”

Jupiter is cozying up to Earth this month. At its closest approach, the giant planet will swing closer and shine brighter than at any time between 1963 and 2022.

You can already see Jupiter twinkling low in the east after twilight, and higher in the southeast as the evening wears on. But it will be brightest in the second half of September. The gas giant’s closest approach will be at a distance of 368 million miles on Monday, September 20. Its previous swing-by in August 2009 was 2 percent farther, and the next approach in October 2011 will be a little less than 1 percent more distant.

Jupiter is also brighter than usual by about 4 percent because one of its brown cloud belts is hidden.

Uranus will be visible in the same part of the sky until September 24, though you’ll need binoculars or a telescope to see it. The full moon will appear right above Jupiter on September 22, which is coincidentally the fall equinox.

Ann wrote:Personally I wonder about the double red "trail". Could it have been made by an observer being caught on a long-exposure image as he(?) walked by the camera carrying some sort of red lamp to light his way across the undoubtedly nearly pitch-dark landscape?

S&T wrote:In this time exposure, the red lines were made by the photographer walking toward Jupiter with a red flashlight aimed at the ground.

bystander wrote:

S&T wrote:In this time exposure, the red lines were made by the photographer walking toward Jupiter with a red flashlight aimed at the ground.

owlice wrote:When my son and I left the house this morning, I pointed Jupiter out, low in the western sky.

"So what? I don't care!," came his reply.

~~~ sigh ~~~

owlice wrote:When my son and I left the house this morning, I pointed Jupiter out, low in the western sky.

"So what? I don't care!," came his reply.

neufer wrote: If I had to get up that early in the morning I would probably say pretty much the same thing.

owlice wrote:

neufer wrote:
If I had to get up that early in the morning I would probably say pretty much the same thing.

Had I not been giving him a lift to the Metro, he'd have left the house even earlier to catch a bus to the subway.
He's the one who set up his class schedule, not I!!

Science@NASA reader Tamas Ladanyi took this picture of a friend photographing Jupiter over a lake in the Bakony mountains of Hungary on Sept. 5th. The giant planet was remarkably bright, said Tamas.

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Been outside at midnight lately? There's something you really need to see. Jupiter is approaching Earth for the closest encounter between the two planets in more than a decade--and it is dazzling.

The night of closest approach is Sept. 20-21st. This is also called "the night of opposition" because Jupiter will be opposite the sun, rising at sunset and soaring overhead at midnight. Among all denizens of the midnight sky, only the Moon itself will be brighter.

Earth-Jupiter encounters happen every 13 months when the Earth laps Jupiter in their race around the sun. But because Earth and Jupiter do not orbit the sun in perfect circles, they are not always the same distance apart when Earth passes by. On Sept. 20th, Jupiter will be as much as 75 million km closer than previous encounters and will not be this close again until 2022.

[url=http://www.spaceweather.com/submissions/large_image_popup.php?image_name=Fredrik-Broms-SW-broms_1284638891.jpg]Jupiter and Uranus surrounded by Northern Lights[/url] [i]Copyright: Fredrik Broms - 15 Sept 2010[/i]

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Jupiter is at opposition on Sept. 21st, meaning the giant planet will be directly opposite the sun, soaring overhead at midnight with dazzling brilliance. In a coincidence of interplanetary proportions, Uranus is at opposition on the very same night! Fredrik Broms of Kvaløya, Norway caught the two converging during a geomagnetic storm on Sept. 15th:

"It's amazing to be able to observe two giant planets next to each other--and never have I seen such a pair against a completely green background!" says Broms.

While Jupiter is outshining everything in the midnight sky (except the Moon), Uranus is barely visible to the naked eye. It's a difference of scale: Uranus is almost three times smaller than Jupiter and five times farther away. Nevertheless, Uranus is still a pretty sight. A telescope pointed at Jupiter on Sept. 21st will reveal the aqua-colored disk of Uranus less than a degree away. And if the sky turns green at the same time, well, that's just a bonus.

More images: from Jean-Paul Godard at Pic du Midi Observatory, France; from Tamas Ladanyi in the Bakony mountains of Hungary; from Peter Rosén of Stockholm, Sweden