Sky & Telescope News Bulletin 14 Dec 2001
For images and Web links for these items, visit http://www.skypub.com
BRITAIN’S BIG ASTRONOMICAL PLANS
More than a year ago, British radio astronomers feared that that some
of their facilities were about to fall prey to a budgetary axe. It
turned out that the famed 76-meter Lovell radio telescope at Jodrell
Bank Observatory was never in danger of being mothballed. Other
astronomical facilities were at risk, however, specifically the
Multi-Element Radio Linked Interferometer Network (MERLIN), seven
dishes that combine to create an antenna 217 kilometers across using
the technique of very-long-baseline interferometry (VLBI).
Last week, Britain’s Particle Physics and Astronomy Research Council
(PPARC) announced that not only will MERLIN survive, it will receive
an upgrade. The $11-million improvement project will boost the array’s
sensitivity by a factor of 30. MERLIN director Philip Diamond explains
that the changes will “enable the enhanced instrument, called
e-MERLIN, to probe far deeper into the universe, achieving in one day
what would currently take three years of continuous observation.” The
project, largely an upgrade of network connections between the
antennas using fiber optics, is expected to be completed in 2007.
In another announcement, PPARC outlined the United Kingdom’s continued
steps toward joining the international consortium of the European
Southern Observatory (ESO). Britain will officially become ESO’s 10th
member in July 2002. As partners, U.K. astronomers will have access to
ESO facilities in Chile, including the Very Large Telescope (VLT), and
will help to fund and plan future projects, such as the Atacama Large
Millimeter Array (consisting of 64 dishes in the Chilean desert) and
the proposed 100-meter Overwhelmingly Large Telescope. “Joining ESO is
good for U.K. science,” says Martin Rees, the Astronomer Royal. “It .
. . restores the U.K.’s full competitiveness in optical astronomy.”
WAS MARS ALL WET?
Future astronauts roaming the surface of Mars will be hard-pressed to
find sources of water, but the red planet was not always so arid a
place. From minuscule gullies to giant flood plains, the face of Mars
bears mute witness to eras when water must have gushed forth onto the
surface — at least temporarily.
In fact, a recent study shows indirectly, but convincingly, that Mars
may have formed with enough water to cover its entire globe to a depth
of 1-1/4 kilometers (about 4,000 feet). The implication is that this
ruddy, arid world actually started out with more water, relative to
its overall mass, than we did. This provocative evidence comes not
from some robotic sentinel on Mars itself, but from the Far
Ultraviolet Spectroscopic Explorer orbiting 760 km above Earth.
In the November 30th issue of Science, Vladimir A. Krasnopolsky
(Catholic University of America) and Paul D. Feldman (Johns Hopkins
University) describe how they used FUSE to make the first-ever
detection of hydrogen molecules (H2) in the upper Martian atmosphere.
Present at just 15 parts per million, the hydrogen represents water
molecules that have been broken down by sunlight. Four years ago
Krasnopolsky used the Hubble Space Telescope to determine the extent
of deuterium (“heavy” hydrogen) in the Martian atmosphere (11 parts
per billion), and these two isotopic abundances provide important
clues to unraveling water’s history there.
Today Mars’s atmosphere has a deuterium-to-hydrogen (D:H) ratio 5.5
times higher than Earth’s. Yet Martian meteorites, ejected from Mars’s
surface 3-1/2 billion years ago, testify to a time when the D:H
enrichment was only 1.9 roughly. Sometime earlier than that, water
vapor was so abundant around Mars, it could escape wholesale into
space. When this so-called hydrodynamic escape shut off, water
continued to leak away, albeit gradually. The molecules first broke
down into their component atoms, followed by the H and D atoms flying
off into space. The process continues even today, and since the
lighter hydrogen escapes more readily than deuterium, the deuterium
becomes enriched over time.
Knowing the H2 abundance, Krasnopolsky has modeled the atmosphere’s
evolution and deduces that the D:H enrichment rise from 1.9 to 5.5
represents a loss of Martian water equivalent to a planetwide ocean
about 30 meters deep. What little water remains today in the polar
caps and hidden elsewhere is probably enough for a 20-meter-deep
layer. Thus 3-1/2 billion years ago, the ocean was some 50 meters
deep. Working further back through time, he calculates that
hydrodynamic escape likely robbed the planet of all but 4 percent of
its original water inventory, yielding an original water table of
1-1/4 km. Krasnopolsky’s model assumes Mars and Earth acquired their
water the same way and thus had equal D:H ratios to begin with.
However these assumed conditions could easily have been upset by
varying the proportion of incoming water-bearing comets (known to have
high D:H ratios).
COMET LINEAR FAR SOUTH
Comet LINEAR (C/2000 WM1) dips even farther south this coming week,
moving from Sculptor into Grus. Observers report that the comet
remains at about magnitude 5.5, making it a naked-eye object. It is
nearly gone from the evening skies for skygazers in midnorthern
latitudes. The comet is only a few degrees above the southern horizon
by the end of twilight and it sets shortly thereafter. The view is
much better in the Southern Hemisphere; the comet is more than halfway
up the sky in the southwest as dusk fades. For finder charts, see the
Special Sky Events page at
http://www.skypub.com/sights/skyevents/0112skyevents.shtml . Here are
positions for the coming week in 2000.0 coordinates:
R.A. Dec.Dec 15 23h 47m -35.3 deg.
Dec 17 23 34 -38.6
Dec 19 23 22 -41.5
Dec 21 23 11 -43.9
THIS WEEK’S “SKY AT A GLANCE”
Some daily events in the changing sky, by the editors of Sky &
Telescope.
DEC. 16 — SUNDAY
* Some doorstep astronomy: After about 7 p.m. look east-southeast
(well to the right of brilliant Jupiter) for the winter constellation
Orion, the Hunter. Bright orange Betelgeuse, in the constellation’s
left-hand corner, marks Orion’s shoulder. Bright white Rigel, farther
right, is one of Orion’s feet. Look midway between Betelgeuse and
Rigel for the three-star row of Orion’s Belt, nearly vertical.
To identify constellations all around your sky, use the printable
evening star map and instructions at
http://www.skypub.com/sights/northern/0112skyn.shtml (if you’re in the
mid-latitudes of the Northern Hemisphere. South of the equator, use
our Southern Hemisphere sky map at
http://www.skypub.com/sights/southern/0112skys.html .)
* 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 9:45 p.m. EST. 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 list of all predicted Red Spot transit times, at
http://www.skypub.com/sights/moonplanets/redspot.html, is good
worldwide.
DEC. 17 — MONDAY
* Jupiter’s largest satellite, Ganymede, casts its tiny black shadow
on Jupiter’s face tonight from 9:19 p.m. to 12:20 a.m. Tuesday morning
EST. Ganymede itself crosses the planet from 10:45 p.m. to 1:47 a.m.
EST.
DEC. 18 — TUESDAY
* More doorstep astronomy: Forming a roughly equilateral triangle
with Jupiter and Saturn, high to their upper left in the eastern
evening sky, is the bright star Capella.
* Jupiter’s Red Spot transits around 11:23 p.m. EST.
DEC. 19 — WEDNESDAY
* Saturn’s largest and brightest moon, 8.5-magnitude Titan, lies
four ring-lengths east of the planet tonight. A small telescope will
show it.
* Jupiter’s Red Spot transits around 7:14 p.m. EST.
* Jupiter’s moon Callisto slowly disappears into eclipse by
Jupiter’s shadow around 7:11 p.m. EST. Callisto is the moon appearing
closest to the planet at the time. It slowly reappears (practically on
Jupiter’s northwest limb) around 9:45 p.m. EST, then disappears behind
the planet itself 18 minutes later.
For the month’s complete listing of Jupiter’s satellite phenomena,
good worldwide, see the December Sky & Telescope, page 106.
DEC. 20 — THURSDAY
* Look to the upper right of the Moon this evening for Mars. Much
farther to the Moon’s lower left is Fomalhaut.
* Jupiter’s Red Spot transits around 1:00 a.m. Friday morning EST.
DEC. 21 — FRIDAY
* The December solstice occurs at 2:21 p.m. Eastern Standard Time,
when the Sun ends its annual journey south and begins returning north
for the year. This moment marks the beginning of winter in the
Northern Hemisphere and summer in the Southern Hemisphere. Tonight is
the longest night of the year.
* Jupiter’s Red Spot transits around 8:52 p.m. EST.
DEC. 22 — SATURDAY
* First-quarter Moon (exact at 3:56 p.m. EST).
* The eastern side of the Great Square of Pegasus (the upper left
side) points down toward the Moon this evening.
* Saturn is now at its closest to Aldebaran (3.6 degrees north of
it).
============================
THIS WEEK’S PLANET ROUNDUP
============================
MERCURY and VENUS are hidden in the glare of the Sun.
MARS (magnitude +0.6, in Aquarius) is the orange “star” in the south
during twilight. It’s lower in the southwest later in the evening.
JUPITER (magnitude -2.7, in Gemini) rises in twilight. The brightest
point of light in the sky, it blazes 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 during
evening far to Jupiter’s upper right. The star Aldebaran sparkles just
4 degrees (two or three fingers’s-widths at arm’s length) to Saturn’s
lower right for much of the evening. Aldebaran is directly below
Saturn later at night. Compare their colors. Saturn is pale yellow;
Aldebaran is more orange.
URANUS and NEPTUNE (6th and 8th magnitude, respectively, in
Capricornus) are getting low in the southwest right after dark, to the
lower right of Mars. Finder charts for them are in the April Sky &
Telescope, page 104, and at
http://www.skypub.com/sights/moonplanets/outerplanets01.html .
PLUTO is hidden in the glow of sunrise.
(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://www.skypub.com/ . Clear skies!
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and Sky at a Glance stargazing calendar are provided as a service to
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