A Close Encounter with Jupiter
See IoFlyby.com for details.
Right: Duane Hilton's rendering of Jupiter and the full moon on October 23, 1999 as seen near 10 p.m. local time from Bryce Canyon.
On October 23, 1999 Jupiter will be "at opposition." That's an astronomical term that simply means you can draw a perfectly straight line between the Sun, the earth, and Jupiter as shown below. This geometry isn't unusual; Jupiter is at opposition about once a year. However, there is something special about this year's opposition. Jupiter is passing through the part of its elliptical orbit that is closest to the Sun. That means it will also be closest to Earth. On October 23 Jupiter will be 368 million miles away from our planet -- just a hop, skip, and a jump by cosmic standards.
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This is a good time to look at Jupiter through a telescope. Jupiter will appear to be nearly 50 arc seconds in diameter, approximately 36 times smaller than the full moon. That's big! Even inexpensive department store telescopes will be powerful enough to reveal light and dark bands crossing Jupiter's equator and Jupiter's four largest moons: Io, Europa, Ganymede and Callisto. It's also a good time to view Jupiter's famous Great Red Spot, a gigantic storm system that has been churning for at least 300 years. Tonight, October 22, the Red Spot will move across the center of Jupiter's disk, as seen from Earth, around 9:19 p.m. EDT. A six-inch or larger telescope and good viewing conditions are recommended for seeing the red spot. The Galilean satellites can easily be seen through a good pair of binoculars. (As an interesting exercise, see how steadily you can hold the binoculars as you're viewing Jupiter. It's not as easy as it sounds!)
If you're out this weekend admiring Jupiter, don't forget that NASA is watching the giant planet, too, although with a better view. NASA's Galileo spacecraft has just marked the tenth anniversary of its launch aboard the Space Shuttle Atlantis on October 18, 1989. Galileo entered orbit around Jupiter in December 1995. Since then it has revolutionized our understanding of Jupiter and its moons by sending a probe into Jupiter's atmosphere, finding new evidence for water on Europa, and most recently zipping a mere 600 km above the volcanoes of Io. Many of Galileo's impressive accomplishments are described at JPL's new Galileo home page: http://galileo.jpl.nasa.gov. The current Galileo Extended Mission will conclude later this year with a daring pass less than 300 km above Io, possibly flying through the plume of a sulfurous volcano. For more information about the Io flybys, please visit IoFlyby.com.
This week's sky at a glance -- from Sky & Telescope
Jack Star Gazer -- Jack Horkheimer's naked eye astronomy web site
Jupiter - from the SEDS Nine Planets web site
Saturn - from the SEDS Nine Planets web site
More NASA Science News
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Dr. John M. Horack , Director of Science Communications
|Author: Dr. Tony Phillips
Curator: Bryan Walls
NASA Official: Frank M. Rose