Sunday, September 19, 2010

Big Bright Jupiter

Jupiter is the largest planet in our solar system, and it is located at 3.95 Astronomical Units (AU) or 368 million miles from the Earth. In our night sky the planet is always bright, but this month it is even brighter than usual as it makes its closes pass by Earth for the year, and closest since 1963 and until 2022. Jupiter's orbit varies in distance about 10-11 million miles over a period of about 60 years, but in terms of brightness to use you have to look at this relatively small variation in terms of magnitude factors. Normally, the brightness varies between -1.6 and -2.94, with the latter being the brightest. But a change as small as 1% can mean a brightness change in either direction of up to 4%. In the current case, we're talking 4% brighter than normal. Tomorrow, Monday, September 20 will be the nearest point to Earth in this near pass. And on Tuesday, September 21, the Earth will pass between Jupiter and the Sun. So grab your telescope and head outside to take a look!

On the topic of looking at the planets through a telescope, Jupiter is one of the largest planets in terms of how much of the telescope's eyepiece it fills up at about 31 arc seconds across. If you have a standard amateur or backyard telescope then that's about a 12th of your field of view, and with this simple of an instrument you can see some good banding around the planet and some moons. Don't have a telescope? Try some binoculars, the view will still be good and you might even see some of Jupiter's moons (hint: keep your arms nice and steady).

If you are in the mid-northern latitudes then look for Jupiter to the lower right of the Great Square of Pegasus. The "celestial trio," Mars, Venus, and the star Spica, will rise at or just after dusk, and as this trio sets you will see Jupiter rise in the east. Or, just look for a bright "star" near the moon. In these, mid-northern latitudes, you'll see it in the early evening and you should be able to see the planet all night long. As you go further north the earlier and longer you'll see Jupiter, and as you go south the later and less you'll see it.

Also, while you are gazing at Jupiter on September 21st move your telescope or binoculars less than a degree to catch sight of the planet Uranus. Its possible that both of the planets will be visible in the same field of view. The planets line up, or are in opposition, on the same night making finding and viewing them easy.

Learn lots more about this event here:

(image from
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