A close encounter with Jupiter
Marshall Space Flight Center

This weekend the Solar System’s largest planet will be brighter and nearer
to Earth than at any time in the past 12 years.

October 22, 1999: Lately, you may have noticed a bright light in the sky
that rises above the eastern horizon around dinnertime. It’s not an airplane
or a UFO — it’s Jupiter, the largest planet in the solar system. This
weekend Jupiter will be brighter and closer to the Earth than it has been
for a dozen years.

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. 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.

To see Jupiter this week, simply go outside shortly after the sun sets and
look toward the east. Jupiter, blazing at magnitude -3, will be rising above
the eastern horizon. The giant planet will be visible all night long. It
crosses the southern meridian at local midnight and sets in the western sky
at dawn.

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:


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.