By Deborah Byrd
EarthSky Communications

Friday, Aug. 14
Earth flies between the sun and Jupiter today at 18:00 Universal Time. That is noon Mountain Daylight Time on Aug. 14. When it is opposite the sun, astronomers say that Jupiter is in opposition to the sun.

And, because it’s generally opposite the sun around now, you can see Jupiter at any time of night. Look near Jupiter for the beloved star Deneb Algedi in the arrowhead-shape constellation Capricornus the Seagoat. Deneb Algedi is Arabic for “the kid’s tail.”

You would need at least 80 Jupiters — rolled into a ball — to be hot enough inside for thermonuclear reactions to ignite. In other words, Jupiter is not massive enough to shine as stars do. But Jupiter is the largest planet in our solar system. So when the sun goes down on these August 2009 nights, you might — if you’re fanciful enough – imagine bright Jupiter as a tiny sun all night long.

Around the time we fly between Jupiter and the sun, our distance from this planet is least for 2009. Its greatest distance from us will come when Jupiter is behind the sun from Earth in February 2010. Let’s see . . . closest in August . . . farthest six months later in February 2010. You might see that Jupiter’s distance from us, as well as its location in our sky, is being driven primarily by Earth’s year-long orbit around the sun.

That’s because Earth travels around the sun in an orbit that’s closer to the sun than Jupiter. Our orbit is smaller, and we move faster in orbit than Jupiter. Earth travels at a speed of about 18 miles per second in orbit, in contrast to about 8 miles per second for Jupiter.

More online at www.EarthSky.org.