Sky and Telescope’s News Bulletin 28 Dec 2001

For images and Web links for these items, visit http://www.skypub.com

JUPITER’S SHRINKING RED SPOT

Telescopic observers from the 19th century may not have had the
technological wizardry available to modern-day skywatchers — but they
apparently had an easier time spotting Jupiter’s signature feature,
its Great Red Spot. According to Amy Simon-Miller (NASA/Goddard Space
Fight Center), today this giant cyclonic storm is only about half as
big as it was in the 1880s. Simon-Miller and three colleagues
confirmed the shrinkage during a careful comparison of historical
records and contemporary images from the Voyager, Galileo, and Cassini
spacecraft. She presented their results last month at a meeting of
planetary scientists.

Astronomers have known since the early 1900s that the Great Red Spot’s
longitudinal extent has been decreasing. Late in the 19th century the
spot was nearly 35 degrees wide, which corresponds to about 40,000
kilometers, or more than three times Earth’s diameter.

By 1979, when Voyagers 1 and 2 swept past, it had shrunk to 21 degrees
(about 25,000 km), yet its latitudinal "height" remained essentially
unchanged, about 12,000 km from top to bottom.

Simon-Miller has discovered that the contraction seems to have picked
up steam since the Voyager visits: at its present rate of shrinkage
(0.19 degree in longitude per year), the spot will become the "Great
Red Circle" by the year 2040. However a perfectly round shape is
unlikely, she explains, because the strong, opposing jet streams that
confine the spot’s northern and southern boundaries will always
distort it into an oval.

No one knows why the not-so-Great Red Spot has shrunk — or, for that
matter, why its color intensifies and fades over time. One clue is
that the winds around its circumference are whirling 70 percent faster
now (about 700 km per hour) than they were in the Voyager era. Some
historical observations suggest that the Red Spot grows and shrinks in
a decades-long sequence. "I’m not sure the behavior is really
cyclical," Simon-Miller comments, "but I certainly would not be
surprised in the least if this shrinking trend slowed or reversed."

One possible explanation is that deep-seated bursts of
thunderstorm-like convection periodically energize the overlying cloud
layers, causing the spot to bloat in size, then gradually contract as
the turbulence subsides. "All of the weather on Jupiter seems to have
sporadic increases in activity," she notes, "so whatever feeds the
Great Red Spot likely will too."

THE LEONIDS’ BEST HOME VIDEOS

Thanks to some high-tech videography, researchers at last have meteor
images detailed enough to probe the insides of shooting stars. The
results were presented at a meeting of the American Geophysical Union
earlier in the month.

Hans Stenbaek-Nielsen (University of Alaska, Fairbanks) captured the
meteors on video as part of NASA/Ames Research Center’s Leonid
Multi-Instrument Aircraft Campaign (MAC). His camera can take video at
a rate of 1,000 frames per second. The instrument was originally used
to study mysterious sprites, fleeting columns of light sometimes seen
above massive thunderstorms.

Stationed at Poker Flat Research Range in Alaska, Nielsen pointed the
camera skyward and spent the night of November 17-18 watching a video
monitor that displayed only a 6-degree-square field. When he saw a
Leonid cross the field, he stopped the recording and manually saved
the hundreds of images. "I managed to save three good meteors,"
Nielsen says. "I did see more, but it was rather tiring observational
circumstances."

Nielsen’s video clearly shows how the initial pinpoint glow of the
heating meteoroid quickly develops a bow shock and a tail. Peter
Jenniskens (SETI Institute) explains, "Our images for the first time
confirm that most meteor light comes from a bright plasma just behind
the meteoroid."

FUSE IN SAFE MODE

Just as it began its third year of observations, NASA’s Far
Ultraviolet Spectroscopic Explorer (FUSE) went into safe mode on
December 10th when the second of four orientation-holding reaction
wheels malfunctioned. The first of the wheels went out of action on
November 25th. The FUSE mission team at NASA’s Goddard Space Flight
Center and Johns Hopkins University is optimistic that new software
will be written to control the pointing of the satellite with the
remaining two wheels. FUSE also has a system that uses the Earth’s
magnetic field to change the craft’s orientation.

The first sign of trouble came in August 2000 when a wheel temporarily
rubbed against its housing when trapped gas made the surrounding
insulation bulge. The spacecraft was down again briefly in February
2001 with a similar problem. Until a fix is ready — probably in weeks
if the wheels can be restarted, but several months if a new control
method is needed — FUSE will sit in emergency configuration with its
solar panels aimed directly at the Sun for maximum power.

FUSE was launched in June 1999 and since science operations began the
following November, the mission has been largely trouble free. In 2001
alone, FUSE observed more than 600 different astronomical objects, and
more than 50 papers based on FUSE observations are scheduled for
presentation at the American Astronomical Society meeting next month.
Earlier this month, ancient Martian oceans were inferred using FUSE
observations.

COMET LINEAR FAR SOUTH

Comet LINEAR (C/2000 WM1) shines at about 6th magnitude, but is only
visible for Southern Hemisphere observers. This coming week, the comet
moves from the constellation Grus into Indus, as it nears its closest
approach to the Sun — called perihelion — on January 22nd. As
twilight fades, the comet will be about 25 to 35 deg. above the
southwestern horizon. Here are positions for the coming week in 2000.0
coordinates:

           R.A.      Dec. 

Dec 29   22h 27   -50.6 deg.

Dec 31   22  16   -51.7

Jan  2   22  05   -52.6

Jan  4   21  54   -53.4 

THIS WEEK’S "SKY AT A GLANCE"

Some daily events in the changing sky, by the editors of Sky &
Telescope.

DEC. 30 — SUNDAY

* The Moon shines brightly in the eastern sky this evening, with
brilliant Jupiter to its upper right and Pollux and Castor to its
left.

* Jupiter’s Great Red Spot should cross Jupiter’s central meridian
(the imaginary line down the center of the planet’s disk from pole to
pole) around 11:14 p.m. Eastern Standard Time. The "red" spot is very
pale orange-tan. It should be visible for at least 50 minutes before
and after in a good 4- or 6-inch telescope if the atmospheric seeing
is sharp and steady. Our complete list of Red Spot transit times, at
http://www.skypub.com/sights/moonplanets/redspot.html , is good
worldwide.

DEC. 31 — MONDAY

* The Moon is up in the eastern sky by midevening. Above it look for
Pollux and Castor. To their upper right is much brighter Jupiter.

* Jupiter is at opposition tonight, opposite the Sun in our sky.

* Jupiter’s Red Spot transits around 7:07 p.m. EST.

* Jupiter’s moon Europa reappears from eclipse out of the planet’s
shadow, just barely off Jupiter’s eastern limb, around 7:15 p.m. EST.

JAN. 1 — TUESDAY

* The naked-eye eclipsing variable star Algol should be in one of
its periodic dimmings, magnitude 3.4 instead of its usual 2.1, for a
couple hours centered on 6:39 p.m. EST. Algol takes several additional
hours to fade and to brighten. Our timetable of all its predicted
minima, at http://www.skypub.com/sights/variables/algol.html , is good
worldwide.

* Jupiter’s Red Spot transits around 12:54 a.m. Wednesday morning
EST.

JAN. 2 — WEDNESDAY

* Earth is at perihelion, its closest to the Sun for the year (3.3
percent closer than at aphelion in July).

* Jupiter’s Red Spot transits around 8:45 p.m. EST.

* The Quadrantid meteor shower may be active before dawn Thursday
morning, but bright moonlight interferes.

JAN. 3 — THURSDAY

* Jupiter’s moon Io crosses Jupiter’s face from 11:28 p.m. to 1:42
a.m. EST Friday morning. Its tiny — but much more visible — black
shadow follows just 4 minutes behind.

* Saturn’s largest moon, Titan, is located three or four
ring-lengths east of Saturn tonight through Saturday night. A small
telescope will show it.

JAN. 4 — FRIDAY

* Jupiter’s largest moon, Ganymede, reappears from eclipse out of
Jupiter’s shadow around 10:23 p.m. Eastern Standard Time. A small
telescope will show it gradually swelling from invisibility to its
normal brightness just off the planet’s eastern limb.

* Coincidentally, Jupiter’s Red Spot also transits around 10:23 p.m.
EST.

JAN. 5 — SATURDAY

* Last-quarter Moon (exact at 10:55 p.m. Eastern Standard Time).

============================

THIS WEEK’S PLANET ROUNDUP

============================

MERCURY is beginning to appear through the glow of sunset. Look for it
just above the southwest horizon about 40 minutes after sundown. It’s
getting a little higher and easier to see each day.

VENUS remains hidden in the glare of the Sun.

MARS (magnitude +0.8, at the Aquarius-Pisces border) is the orange
"star" in the south-southwest during twilight. It sinks lower in the
southwest later in the evening and sets around 10 p.m.

JUPITER (magnitude -2.7, in Gemini) is at opposition this week: in the
opposite direction from the Sun as seen from Earth’s viewpoint. It’s
the brightest point of light in the sky — blazing white in the east
during evening, high in the south in the middle of the night, and in
the west before dawn.

SATURN (magnitude -0.3, in Taurus) shines high in the east far to
Jupiter’s upper right for much of the evening. It’s in the south
directly to Jupiter’s right by about 10 p.m. The star Aldebaran
sparkles just 4 degrees (two or three fingers’s-widths at arm’s
length) to Saturn’s lower right in early evening. (Later at night,
Aldebaran is directly below Saturn and then to its lower left.)
Compare their colors. Saturn is pale yellow; Aldebaran is more orange.

URANUS and NEPTUNE are disappearing into the sunset.

PLUTO (magnitude 14, in Ophiuchus) is barely up in the east-southeast
before dawn.

(All descriptions that relate to the horizon or zenith — including
the words up, down, right, and left — are written for the world’s
midnorthern latitudes. Descriptions that also depend on longitude are
for North America. Eastern Standard Time, EST, equals Universal Time
[GMT] minus 5 hours.)

More celestial events, sky maps, observing projects, and news of the
world’s astronomy research appear each month in SKY & TELESCOPE, the
essential magazine of astronomy. See our enormous Web site and
astronomy bookstore at http://SkyandTelescope.com/ . Clear skies!

SKY & TELESCOPE, 49 Bay State Rd., Cambridge, MA 02138 *
617-864-7360

Copyright 2001 Sky Publishing Corporation. S&T’s Weekly News Bulletin
and Sky at a Glance stargazing calendar are provided as a service to
the astronomical community by the editors of SKY & TELESCOPE magazine.
Widespread electronic distribution is encouraged as long as these
paragraphs are included. But the text of the bulletin and calendar may
not be published in any other form without permission from Sky
Publishing (contact permissions@skypub.com or phone 617-864-7360).
Updates of astronomical news, including active links to related
Internet resources, are available via SKY & TELESCOPE’s site on the
World Wide Web at http://www.skypub.com/.