Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: Overview of Comet Hale-Bopp meeting at Tenerife, Feb. 2-5, 1998 [1/3]
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ESO Education and Public Relations Dept.
Text with all links is available on the ESO Website at URL:
http://www.eso.org/outreach/info-events/hale-bopp/report-rw-hbitp98.html
This is a provisional overview of some of the discussions that took place
at the First International Hale-Bopp Conference at Tenerife in February
1998. It was prepared by R. M. West (ESO, email: rwest@eso.org).
I. Introduction
Ten months after the perihelion passage, the First International Meeting
about Comet Hale-Bopp was held at the Conference Centre in Puerto de
la Cruz (Tenerife, Canary Islands, Spain) on February 2-5, 1998. Nearly
150 specialists from all major comet research groups in the world
participated. During 4 days of intensive debates and with the presentation
of approximately 150 papers, the participants surveyed the current status
of the many research programmes related to this most unusual comet.
The Local Organising Committee, headed by Mark Kidger and Monica
Murphy (IAC) had done a great job and the frame was excellent. The
conference provided a good opportunity for a discussion about some of
the fundamental issues connected to this spectacular astronomical event.
For instance: why was this comet so bright and in which respect(s) did it
differ from other comets observed with modern equipment? Although
many new results were presented and some main lines can be perceived,
those present were left with the impression that there are still many open
questions. There is no doubt that the associated research will continue for
some time. It is also obvious that further meetings on these subjects will
be held in due time.
The Hale-Bopp event provided observers with a long lead time, thanks to
the early discovery in July 1995 by Alan Hale and Tom Bopp who were
both at the conference. Thus, it was possible for the scientists to obtain a
substantial amount of observing time at the world's major observational
facilities and to prepare their runs well. Moreover, the Comet was visible
in the sky for an extremely long period. It was very bright and in the end, a
large number of telescopes and instruments were used at all wavelengths
from X-ray to radio. It is therefore no surprise that all the work by so many
scientists during the past months has resulted in important new knowledge,
as exposed at this meeting.
In what follows, some of the highlights of the conference will be reviewed.
They are arranged roughly in the order they were presented at the
meeting. Kindly note that not all contributions mentioned here are
attributed to individual speakers and various information by others has
been left out in order to keep this survey within a reasonable size.
However, a complete version of the conference summary, with full
references and more details, will ultimately appear in the Conference
Proceedings.
II. Motion and Early Observations
The meeting began with some basic information about the comet.
The Orbit
Based on more than 2600 astrometric observations from 1993-98, Brian
Marsden has calculated a new and improved orbit, now taking into
account non-gravitational forces arising from the jet effect associated with
the Comet's vigorous activity. He found that the original period was 4211
years and that the future period will be 2392 years with a formal
uncertainty of a few months only. However, the limited knowledge about
the future development of the Comet's activity may still change this period
somewhat.
Had it arrived about four months earlier this time, it would have passed
the Earth nearly as close as did Comet Hyakutake one year earlier. In that
case it would have been an incredible view. Interestingly, it appears that
Comet Hale-Bopp may have passed very close to Jupiter on June 7, 2216
BC. In view of the rather unstable orbit, it is unlikely that there have been
more than a few earlier, close perihelion passages.
Early Observations
Alan Fitzsimmons reviewed the various signs of very early activity which
are typical for this comet. In particular, investigations of early images of
the
dust tail by Hermann Boehnhardt and Marco Fulle have shown that the
Comet most probably was active already 4-5 years before discovery, that
is at pre-perihelion distance 18-20 AU. In addition to a UK Schmidt
pre-discovery image obtained in April 1993, an image of the Comet may
possibly be present on another photographic plate taken with the same
telescope in September 1991; this will now be investigated.
III. The Nucleus
Size
Harold Weaver and Philippe Lamy surveyed 7 different methods which
have led to reasonably consistent estimates of the size of Comet
Hale-Bopp's nucleus. Most of these lie in the interval between 20 and 40
km radius (i.e., 40 and 80 km diameter), but a few are somewhat larger.
There is also a possible indication that the nucleus may have elongated
shape. Particularly impressive among these observations were those
performed at radio wavelengths with the VLA in New Mexico and which
lasted more than 6 days -- they pointed towards a diameter of
approximately 50 km.
Interestingly, there may be more than one component of the nucleus. By
very careful analysis of high-resolution HST images obtained in 1996,
Zdenek Sekanina believes that the primary nucleus may have a lesser
companion of approximately half the size. This issue is still somewhat
controversial, but observations with the Adonis adaptive optics camera
at the ESO 3.6 m telescope in November 1997 and January 1998 by
three ESO astronomers also appear to show a double nucleus. More
observations with this facility in the coming months and/or with the HST
scheduled for later this month are expected to clarify this issue.
Rotation
In a review talk on this subject, Dave Jewitt listed the observational
possibilities for measuring the rotation period of Comet Hale-Bopp's
nucleus. With the nucleus hidden inside the coma already at the moment
of discovery, they include periodic fluctuations of that part of the light at
the centre of the coma which supposedly comes from the nucleus itself,
and also periodic changes in the coma structure (orientation of jets,
outward motion of shells, etc.).
Many such observations are available; the longest series was apparently
obtained by Mark Kidger and his group at the Teide Observatory on
Tenerife, right above the site of the conference. At this moment, there is
good agreement among the values published by 8 different groups and
the true rotation period of the nucleus must be close to 11.34 +/- 0.03
hours.
Although there were originally some signs of precession (wobbling of the
rotation axis), this is now less sure. The direction of the polar axis has
also not been unambiguously determined yet, but this may become
possible after further analyses.
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Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: Overview of Comet Hale-Bopp meeting at Tenerife, Feb. 2-5, 1998 [2/3]
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Composition and Structure
Dominique Bockelee-Morvan and Hans Rickman surveyed the many new
observations which will ultimately allow a better `look' into the still
unknown interior of a cometary nucleus. This is first of all due to the very
extensive observations which were made of the production rates of
various molecules, as the comet came closer to the Sun. These
observations show that not all of these species emerge in parallel and
there seem to be certain `transitory' periods during which changes in the
production rates can be observed. They are indicative of the composition
and structure of the upper layers of the nucleus.
For instance, a slowing down of the rate of increase of CO production was
observed at about the time when the water production started at a
heliocentric distance of approximately 3.5 AU. The production rates of
some, less abundant molecules, showed a very steep dependence on
heliocentric distance. All in all, the observed behaviour seems to follow
quite well what is predicted by the models which have been put forward
and which were described at the meeting by Dina Prialnik -- they include
in particular heat release by sub-surface cristallization of amorphous ice
in the nucleus.
It is also well established that the unusually great activity of Hale-Bopp
which was observed while it was still far from the Sun is mostly caused by
the outgassing of CO from its interior; this process pushed large amounts
of dust into space. The more dust there is around the nucleus, the more
sunlight is reflected and the brighter will the comet appear.
IV. The Gas Phase
Many gaseous molecules and atoms were observed in the coma. Some
of these are electrically uncharged (neutrals), others have lost one or
more electrons (ions). Sodium, a neutral atom observed extensively in
Hale-Bopp, plays a particular role and was discussed in a special session.
Neutrals
Didier Despois reviewed extensive radio observations which have led to
the discovery of a total of 8 new molecules never seen before in a comet
(SO, SO2, H2CS, HC3N, HNCO, NH2CHO, HCOOH, CH3OCHO).
Observations of isotopes (now also including DCN, HC15N and C34S for
the first time) indicate that this comet is similar to Comet Halley and that it
was formed in the solar system. In particular, the HDO/H2O ratio was
found to be twice that measured in the Earth's oceans, and 10 times larger
than the protosolar value.
Thanks to great technological advances, it has now become possible to
produce detailed maps of the distribution of individual molecules in the
coma. This has led to very interesting research which will ultimately help
to understand the extremely complex chemistry of a cometary coma. In
particular, this may allow to determine which of the molecules observed
really come from the nucleus itself (as parents) and which are secondary
products (daughters).
Jacques Crovisier reported equally exciting new observations in the
infrared spectral region, from the ground with several of the largest
infrared telescopes and from space (ISO). This includes hydrocarbons
(organic molecules) and also water for which the ortho-to-para ratio was
equal to that measured at Halley and indicates the very low spin
temperature of 25 K. It is not clear whether this is also the temperature of
formation.
Unfortunately, at least for this type of research, the very large dust-to-gas
ratio observed in Comet Hale-Bopp made observations of spectral
emission lines difficult since they were recorded on top of a very strong
continuum spectrum of solar light reflected from the dust in the coma.
Partly for this reason, it appears that it has not been possible to gain new
knowledge about the interesting emission lines from organic molecules
seen in the 3.2 - 3.6 micron band. Nevertheless, many new mineral bands
were seen in the infrared region (see below).
Many spectral observations in the optical region were reported by Claude
Arpigny. They generally show that Hale-Bopp is similar to other
long-period comets. Several groups have reported detailed, very
high-resolution spectroscopic monitoring of the various emission lines in
this wavelength region. There is obviously still much work to be done on
all of these high-dispersion spectra.
In the ultraviolet spectral region observations were made with a number
of spacecraft and also with several sounding rockets. Paul Feldman
described the spectra obtained with HST and the IUE Space
Observatories which include many atomic lines. Further towards shorter
wavelengths, a line of singly ionized oxygen (O+) has been detected by
the EUVE satellite at 538 A, but unexpectedly, neon (Ne) was not
etected in the same spectral region. This points to a very low
neon-to-oxygen ratio in this comet, at least 25 times less than the solar
value.
An enormous Lyman-alpha halo of hydrogen, about 150 million km
diameter, that is the distance from the Sun to the Earth, was observed by
the SOHO Observatory when the comet was near perihelion. It was also
possible to view the comet in the ultraviolet light of various atoms; when
compared to images obtained at other spectral wavelengths, they will
contribute to the understanding of the processes in the coma.
Ions
Heike Rauer reported that most of the ions known in earlier comets have
also been observed in Comet Hale-Bopp. Strangely, emission from CO+
was first detected quite late (at a heliocentric distance of 3.6 AU); the
reason for this is still unclear. Very complex coma and tail structures were
observed by Steve Larson and others in the light of CO+ and other
selected ions, indicating an exceedingly complex interaction between the
solar wind and the cometary ions (streamers, sunward arcs, etc.). In this
respect, the detailed mapping of the spatial distribution in the coma and
the corresponding velocity field of HCO+ by groups in Europe and the
USA provided very valuable observational information.
There has clearly been tremendous progress in the modelling of the solar
wind/comet interaction in recent years. Tamas Gombosi showed that new
and very complex computer software running on the fastest machines
available now make it possible to reproduce in quite some detail the
observed structure (distribution of ions, magnetic field lines, cavities,
sheets, etc.). In this context, the discovery by the Ulysses Spacecraft that
the solar wind moves faster at high ecliptic latitudes and therefore interacts
stronger with the comet when it is far from the ecliptic plane, has provided
an important breakthrough in this field.
Sodium
While sodium has been seen since 1910 in comets that come close to the
Sun, the first signs of a sodium tail was reported in 1957 from an objective
prism spectrum obtained of the unusual Comet Mrkos. However, it was in
mid-April 1997 that the now famous third cometary tail of neutral sodium
atoms and measuring more than 50 million km was discovered by
Gabriele Cremonese and his colleagues of the European Comet
Hale-Bopp Team. Already at that time, the correct interpretation was
brought forward, that is fluorescence acceleration of sodium atoms
released in the coma.
Meanwhile, this and other groups have also reported the presence of
neutral sodium in the normal dust tail, demonstrating that these atoms are
also released from the dust in this tail. It is still unclear, however, from
where the sodium in the inner coma comes. Interestingly, no NaOH (soda)
or NaCl (salt) was found in gaseous form in the coma (but may still be
present in the dust grains).
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Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: Mars Global Surveyor Update - February 12, 1998
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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www. jpl.nasa.gov
Mars Global Surveyor Mission Status
February 12, 1998
Mars Global Surveyor is currently in its 128th orbit around
Mars. Aerobraking continues to go normally and is being aided by
the relatively calm state of the Martian atmosphere. Atmospheric
stability allows the spacecraft to dip lower into the Martian
atmosphere, experience more air resistance and lower its orbit at
a faster rate.
The spacecraft's closest approach to Mars is currently
bringing it to within 117 kilometers (about 73 miles) of the
surface and has reduced the time it takes to complete one orbit
around the red planet to 17 hours. The flight team reported that
there have been no additional issues with the slightly damaged
attachment structure on one of the spacecraft's two solar panels.
Global Surveyor's science instruments are scheduled to be
turned off on Wednesday, Feb. 18 and remain off until late March.
The payload is being shut off because of Surveyor's much-
diminished orbital period, which no longer allows enough time to
both send aerobraking commands to the spacecraft and to transmit
to Earth the scientific data stored onboard.
The flight team has begun commands to rotate the spacecraft
twice per orbit so that different parts of Global Surveyor are
better exposed to the Sun. Normally, Surveyor spends the majority
of its time with its high-gain antenna pointed directly at the
Earth. The new commands are necessary to keep the temperatures
onboard the laser altimeter from falling below 10 degrees Celsius
(50 degrees Fahrenheit). Current analysis suggests that the
rotations will be necessary until September.
After 462 days in flight, Mars Global Surveyor is currently
about 340 million kilometers (211 million miles) from Earth,
circling Mars about once every 17 hours. The spacecraft's
current elliptical orbit takes it about 117 kilometers (73 miles)
above the surface of Mars at the closest point and about 25,000
kilometers (15,500 miles) from the planet at the farthest point
in the orbit. At present, one-way light time from Global
Surveyor to Earth is 18 minutes, 9 seconds.
Real-time orbital information about Mars Global Surveyor is
available on the Internet at
http://marsnt3.jpl.nasa.gov/mgs/realtime/orbit.html. The
information is automatically updated every 30 seconds.
#####
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Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: NASA Radar Reveals Hidden Remains At Ancient Angkor
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MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary A. Hardin (818) 354-0344
FOR IMMEDIATE RELEASE February 12, 1998
NASA RADAR REVEALS HIDDEN REMAINS AT ANCIENT ANGKOR
New evidence of a prehistoric civilization and remnants of
ancient temples in Angkor, Cambodia have been discovered by
researchers using highly detailed maps produced with data from an
airborne imaging radar instrument created by NASA.
Experts say the findings, made possible by the Airborne
Synthetic Aperture Radar (AIRSAR) developed by NASA's Jet
Propulsion Laboratory (JPL), Pasadena, CA, may revolutionize the
way archaeologists view the ancient city's development.
Angkor is a vast complex of some 1,000 temples covering more
than 160 square kilometers (about 100 square miles) of northern
Cambodia. Little is known of the prehistoric occupation of this
fertile flood plain, but at its height the city housed an
estimated population of 1 million people. The famous temples were
built from the 8th to 13th century AD and were accompanied by a
massive hydrological system of reservoirs and canals. Today,
much of the civilization of Angkor is hidden beneath a dense
forest canopy and is inaccessible due to poor roads, land mines
and political instability.
"The radar data have enabled us to detect a distribution of
circular 'prehistoric' mounds and undocumented temples far to the
northwest of Angkor," said Dr. Elizabeth Moore, Head of the
Department of Art & Archaeology at the School of Oriental and
African Studies at the University of London. "The site's
topography is highlighted by the radar, focusing our attention on
previously neglected features, some at the very heart of the
city.
"The radar maps not only bring into question traditional
concepts of the urban evolution of Angkor, but reveal evidence
of temples and earlier civilization either absent or incorrect on
modern topographic maps and in early 20th century archaeological
reports," she said.
"The radar images make apparent many features that are not
readily identifiable on the ground," said Dr. Anthony Freeman, a
radar scientist at JPL who has collaborated with Moore for the
past three years studying the use of radar on the Angkor site.
"We can see differences in vegetation structure and some features
that are obscured by vegetation cover."
In December 1997, Moore surveyed a small mound on the
perimeter of the famous 12th century AD temple, Angkor Wat, that
Freeman had first noticed in the radar image. "Previous
archaeological accounts from 1904 and 1911 note only two temples
and make no mention of the distinct circular form of the mound.
We found four to six temple remains, including pre-Angkorean
structures," Moore said. "This suggests occupation of the 12th
century site some 300 years earlier, radically changing accepted
chronologies of Angkor."
Angkor's beauty is seen its in temples, but the greatness
of the Khmer city lies in the multitude of water-related
constructions, according to Moore. The Khmer kings nominally
dedicated temples to Hindu and Buddhist deities, but the
underlying significance was veneration of ancestral spirits,
ensuring fertility of the land. Management of water was
essential, both for control during the monsoon rains and
conservation during the dry season and involved the construction
of moats, dikes, canals, tanks, and reservoirs. The largest of
these reservoirs, dated to the 12th century AD, is eight
kilometers (five miles) long and its function remains a matter of
archaeological debate.
"These new detailed topographic maps have shown us many
more hydrological features and highlighted how they function in
the rituals and daily life of the Khmer people," Moore explained.
"Using a technique known as radar interferometry, which
combines two images to create a three-dimensional topographic
map, we can construct a map of the area surrounding Angkor that
is more accurate than most maps we have of the United States,"
said Dr. Scott Hensley, a radar engineer at JPL. "This map lets
us see both natural and human-made water management features at
the site with great clarity."
"Angkor is situated on the edge of the Tonle Sap lake, a
unique body of water that doubles in size during the rainy
season. These maps give us new insights into the human impact on
this ecosystem, from the ancient Khmer to the present day, and
are of importance in the study of our changing Earth," Freeman
continued.
The Angkor radar images were taken in late 1996 as part of
the AIRSAR Pacific
Rim Deployment and were a follow-up to the 1994 study of Angkor
with data collected by the Spaceborne Imaging Radar-C/X-band
Synthetic Aperture Radar (SIR-C/X-SAR) that flew on NASA's Space
Shuttle Endeavour.
Like SIR-C/X-SAR, AIRSAR transmits and receives three radar
frequencies in both horizontal and vertical polarizations. While
both systems use C-band and L-band wavelengths, AIRSAR has the
added benefit of P-band, a longer wavelength that can penetrate
below the forest canopy. In addition, AIRSAR can be flown in a
mode called TOPSAR that allows it to measure topography and
create three-dimensional images of the surface.
AIRSAR images of the Angkor region will be posted to the
Internet at this address: http://www.jpl.nasa.gov/news/
AIRSAR flies on a NASA DC-8 aircraft that is managed at
NASA's Dryden Flight Research Center, Edwards, CA. The AIRSAR
instrument is managed by JPL, a division of the California
Institute of Technology for NASA's Office of Earth Sciences,
Washington, DC. This office manages NASA's Earth Science
enterprise, an internationally coordinated effort to study
natural and human-induced changes in the Earth's land, oceans,
atmosphere, ice and life.
The AIRSAR flight over Cambodia was funded by the Government
of Thailand. Ground verification has been made possible by Vann
Molyvann, Minister of State for Culture and Fine Arts,
Territorial Management, Urban Planning and Construction; and Dr.
Ang Choulйan of the Cambodian Authority for the Protection and
Management of Angkor and the Region of Siem Reap.
#####
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Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: NASA Selects 335 Innovative Small Business Projects
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Donald Nolan
Headquarters, Washington, DC February 12, 1998
(Phone: 202/358-1983)
RELEASE: 98-25
NASA SELECTS 335 INNOVATIVE SMALL BUSINESS PROJECTS
NASA has selected 335 research proposals for negotiation of
Phase I contract awards for NASA's Small Business Innovation
Research (SBIR) Program.
SBIR goals are to stimulate technological innovation,
increase the use of small business (including women-owned and
disadvantaged firms) in meeting federal research and development
needs, and increase private sector commercialization of results of
federally funded research.
The 1997 solicitation closed on Oct. 14, 1997. NASA received
2,665 proposals submitted by small, high technology businesses
from across the United States. The combined award total for the
335 Phase I contracts is expected to be approximately $23 million.
The nine NASA field centers and the Jet Propulsion
Laboratory, Pasadena, CA, reviewed proposals for technical merit
and feasibility and relevance to NASA research and technology
requirements. The selected firms will be awarded fixed-price
contracts valued up to $70,000 each to perform a six-month Phase I
feasibility study.
Companies that successfully complete the Phase I activities
are eligible to compete for Phase II selection the following year.
The Phase II award allows for a two-year, fixed-price contract in
the amount up to $600,000.
The NASA SBIR Program Management Office is located at the
Goddard Space Flight Center, Greenbelt, MD, with executive
oversight by NASA's Office of Aeronautics, NASA Headquarters,
Washington, DC. Individual SBIR projects are managed by the NASA
field centers and the Jet Propulsion Laboratory.
-end-
EDITOR'S NOTE: A printed listing of companies selected for the
program is available in the NASA Headquarters Newsroom (Phone:
202/358-1600) and also can be accessed on the Internet at URL:
http://sbir.nasa.gov
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Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: Sky & Telescope News Bulletin - February 13, 1998
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SKY & TELESCOPE'S NEWS BULLETIN
FEBRUARY 13, 1998
HERE COMES THE BLAST WAVE
The Hubble Space Telescope has provided a new view of the remnants of
Supernova 1987A in the Large Magellanic Cloud that illustrate the debris'
continued expansion. The image from Hubble's Wide Field and Planetary
Camera 2 taken by Peter Garnavich (Harvard-Smithsonian Center for
Astrophysics) reveals a brightened knot in an encircling ring of gas cast
off the star prior to the supernova. The gas was set glowing by the
supernova's radiation, and had been fading since the explosion a decade
ago. Now, the blast wave has caught up to the ring and astronomers expect
the gas to brighten considerably. The gaseous collision should greatly
increase the amount of X-ray and radio emissions for the next few years.
More information about the expected fireworks can be found in the January
issue of SKY & TELESCOPE, page 18.
BUDGET BOOSTS FOR ASTRONOMY
The National Science Foundation's budget for fiscal year 1999 includes some
funding increases for astronomical facilities. Of the $792 million
earmarked for mathematical and physical sciences, the Gemini Observatories
-- twin 8-meter reflectors in Hawaii and Chile -- had an 11.5 percent boost
to nearly $7 million. Other national astronomy centers will receive $70
million -- a 6 percent increase over the previous year. The money will go
toward upgrading instrumentation and the operation of projects such as the
Global Oscillation Network Group (GONG). And funding has been nearly
tripled to almost $20 million for the Laser Interferometer Gravitational-
Wave Observatory (LIGO).
MOON GETS OUT OF COMETS' WAY
A waning Moon leaves the evening sky behind this week (and heads toward the
total solar eclipse on the 26th) improving the odds of seeing a pair of
comets in the west after sunset. Comet 55P/Tempel-Tuttle, the parent of the
Leonid meteor stream, continues to move south through Pisces at 8th
magnitude. Observers in mid-northern latitudes should look soon after
sunset, as the earlier you look in the west (to the upper right of Saturn)
the higher up in the sky the comet will be. More information about the
comet can be found in the February issue of SKY & TELESCOPE, page 91, and
on SKY Online Comet Page http://www.skypub.com/comets/comets.html. Here are
positions for Tempel-Tuttle at 0 hours Universal Time in 2000.0
coordinates:
R.A. Dec.
February 15 01h 15m +15.4 deg.
17 01 15 +14.2
19 01 15 +13.2
Slightly higher above the horizon is Comet 103P/Hartley 2, which is about
9th magnitude. It is moving east through Aries. Its positions for the week
are:
R.A. Dec.
February 15 03h 10m +02.0 deg.
17 03 19 +02.5
19 03 38 +02.9
THIS WEEK'S "SKY AT A GLANCE"
Some daily events in the changing sky, from the editors of SKY & TELESCOPE.
FEB. 15 -- SUNDAY
* The waning gibbous Moon rises with Spica at its lower right very late this
evening. By dawn Monday morning, Spica is below the Moon.
FEB. 16 -- MONDAY
* Have you been watching the slow fading of Mira, after its January maximum?
This red variable star is visible with binoculars, and still possibly the
naked eye, in Cetus well to the upper left of Saturn. It's marked on the
fold-out constellation map in the February Sky & Telescope.
FEB. 17 -- TUESDAY
* Orion shines at its highest in the south in early evening this week. In
its center is Orion's diagonal Belt. Have you ever noticed that the Belt
is not straight but slightly curved to the upper right? Below the Belt is
Orion's fainter, vertical Sword. Use binoculars to look for the Great Orion
Nebula in the middle of the Sword.
FEB. 18 -- WEDNESDAY
* It's just eight days to the eclipse of the Sun on February 26th! The
eclipse will be total in parts of northern South America and the Caribbean.
It's partial for much of the United States and eastern Canada (south and east
of a line from Southern California through Kansas, Michigan, Quebec, and
Labrador). See the map and other information in the February Sky & Telescope,
page 82 (it's also on SKY Online at
http://www.skypub.com/eclipses/eclipses.html). The article also has tips
for viewing the Sun safely and projecting its image for classroom viewing.
FEB. 19 -- THURSDAY
* Last-quarter Moon (10:27 a.m. EST).
* Pre-dawn telescope users will find the Moon having an interestingly
large libration for the next few days; the lunar southwest limb (the Mare
Humorum area) is tilted unusually far into view. Can you see the Cordillera
Mountains and Mare Orientale?
* Saturn's largest moon, Titan, is three or four ring-lengths to Saturn's
west this evening through Sunday evening. A small telescope will show it.
FEB. 20 -- FRIDAY
* Venus is at its greatest brilliancy, low in the southeast just before and
during dawn.
* rMDNMЇSrMDNMЇmall-telescope users throughout the Americas can watch the
eclipsing
variable star Theta-1 Orionis A in one of its periodic dimmings. Theta-1
Orionis is the quadruple star in the heart of the Great Orion Nebula.
Component A is the westernmost of the four stars. Normally A is magnitude 6.5,
as bright as the easternmost component, D. But every 65 days it is eclipsed by
a dimmer companion and fades to about magnitude 8.0. This makes it as faint as
the northern component, B. Minimum light should come around 9:43 p.m. EST. The
star will remain near minimum for about 2 and 1/2 hours centered on that time,
then will take about 7 hours to rebrighten.
FEB. 21 -- SATURDAY
* Tonight the faint asteroid 153 Hilda should occult a 9.8-magnitude star in
Corvus along a path from Florida to the Southwest. You can try timing this
event with at least a 6- or 8-inch telescope and the instructions in the
February Sky & Telescope, page 86 (also at
http://www.skypub.com/occults/occults.html.) The occultation should happen
within a few minutes of 5:13 Universal Time in Florida and 5:15 UT in Texas.
For any late updates check the Web site, or call the voice recording at
301-474-4945, a few hours before the event.
============================
THIS WEEK'S PLANET ROUNDUP
============================
MERCURY is hidden in the glare of the Sun.
VENUS shines brightly (magnitude -4.7) in the southeast during dawn.
MARS, magnitude +1.2, is very low in the west-southwest during dusk, far to
the lower right of Saturn.
JUPITER is hidden in the Sun's glare.
SATURN, in Pisces, shines at magnitude +0.7 in the west-southwest after dusk.
URANUS and NEPTUNE are in the glow of sunrise.
PLUTO, magnitude 13.8 at the Ophiuchus-Scorpius border, is in the southeast
before dawn.
(All descriptions that relate to the horizon or zenith 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
minus 5 hours.)
More details, sky maps, and news of other celestial events appear each month
in SKY & TELESCOPE, the essential magazine of astronomy. See our Web site at
http://www.skypub.com/. Clear skies!
SKY & TELESCOPE, P.O. Box 9111, Belmont, MA 02178 * 617-864-7360 (voice)
Copyright 1998 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). Illustrated versions,
including active links to related Internet resources, are available via SKY
Online on the World Wide Web at http://www.skypub.com/.
In response to numerous requests, and in cooperation with the Astronomical
League (http://www.mcs.net/~bstevens/al/) and the American Association of
Amateur Astronomers (http://www.corvus.com/), S&T's Weekly News Bulletin and
Sky at a Glance are available via electronic mailing list too. For a free
subscription, send e-mail to skyline@gs1.revnet.com and put the word "join"
on the first line of the body of the message. To unsubscribe, send e-mail
to skyline@gs1.revnet.com and put the word "unjoin" on the first line of the
body of the message.
SKY & TELESCOPE, the Essential Magazine of Astronomy, is read by more than
200,000 enthusiasts each month. It is available on newsstands worldwide.
For subscription information, or for a free copy of our catalog of fine
astronomy books and products, please contact Sky Publishing Corp., P.O. Box
9111, Belmont, MA 02178-9111, U.S.A. Phone: 800-253-0245 (U.S. and
Canada); 617-864-7360 (International). Fax: 617-864-6117. E-mail:
custserv@skypub.com. SKY Online: http://www.skypub.com/. Clear skies!
Hа сегодня все, пока!
=SANA=
Дата: 14 февраля 1998 (1998-02-14)
От: Alexander Bondugin
Тема: Voyager 1 Now Most Human-Made Ojbect In Space
Привет всем!
Вот, свалилось из Internet...
MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary A. Hardin (818) 354-0344
FOR IMMEDIATE RELEASE February 13, 1998
VOYAGER 1 NOW MOST DISTANT HUMAN-MADE OBJECT IN SPACE
In a dark, cold, vacant neighborhood near the very edge of
our solar system, the Voyager 1 spacecraft is set to break
another record and become the explorer that has traveled farthest
from home.
At approximately 2:10 p.m. Pacific time on February 17,
1998, Voyager 1, launched more than two decades ago, will cruise
beyond the Pioneer 10 spacecraft and become the most distant
human-created object in space at 10.4 billion kilometers (6.5
billion miles.) The two are headed in almost opposite directions
away from the Sun.
As with other spacecraft traveling past the orbit of Mars, both
Voyager and Pioneer derive their electrical power from onboard
nuclear batteries.
"For 25 years, the Pioneer 10 spacecraft led the way,
pressing the frontiers of exploration, and now the baton is being
passed from Pioneer 10 to Voyager 1 to continue exploring where
no one has gone before," said Dr. Edward C. Stone, Voyager
project scientist and director of NASA's Jet Propulsion
Laboratory.
"At almost 70 times farther from the Sun than the Earth,
Voyager 1 is at the very edge of the Solar System. The Sun there
is only 1/5,000th as bright as here on Earth -- so it is
extremely cold and there is very little solar energy to keep the
spacecraft warm or to provide electrical power. The reason we
can continue to operate at such great distances from the Sun is
because we have radioisotope thermal electric generators (RTGs)
on the spacecraft that create electricity and keep the spacecraft
operating," Stone said. "The fact that the spacecraft is still
returning data is a remarkable technical achievement."
Voyager 1 was launched from Cape Canaveral on September 5,
1977. The spacecraft encountered Jupiter on March 5, 1979, and
Saturn on November 12, 1980.
Then, because its trajectory was designed to fly close to
Saturn's large moon Titan, Voyager 1's path was bent northward by
Saturn's gravity, sending the spacecraft out of the ecliptic
plane - the plane in which all the planets except Pluto orbit the
Sun.
Launched on March 2, 1972, the Pioneer 10 mission officially
ended on March 31, 1997. However NASA's Ames Research Center,
Moffet Field, CA, intermittently receives science data from
Pioneer as part of a training program for flight controllers of
the Lunar Prospector spacecraft now orbiting the Moon.
"The Voyager mission today presents an unequaled technical
challenge. The spacecraft are now so far from home that it takes
nine hours and 36 minutes for a radio signal traveling at the
speed of light to reach Earth,"said Ed B. Massey, project manager
for the Voyager Interstellar Mission. "That signal, produced by
a 20 watt radio transmitter, is so faint that the amount of power
reaching our antennas is 20 billion times smaller than the power
of a digital watch battery,"
Having completed their planetary explorations, Voyager 1 and
its twin, Voyager 2, are studying the environment of space in the
outer solar system. Although beyond the orbits of all the
planets, the spacecraft still are well within the boundary of the
Sun's magnetic field, called the heliosphere. Science
instruments on both spacecraft sense signals that scientists
believe are coming from the outermost edge of the heliosphere,
known as the heliopause.
The heliosphere results from the Sun emitting a steady flow
of electrically charged particles called the solar wind. As the
solar wind expands supersonically into space in all directions,
it creates a magnetized bubble -- the heliosphere -- around the
Sun. Eventually, the solar wind encounters the electrically
charged particles and magnetic field in the interstellar gas. In
this zone the solar wind abruptly slows down from supersonic to
subsonic speed, creating a termination shock. Before the
spacecraft travel beyond the heliopause into interstellar space,
they will pass through this termination shock.
"The data coming back from Voyager now suggest that we may
pass through the termination shock in the next three to five
years," Stone said. "If that's the case, then one would expect
that within 10 years or so we would actually be very close to
penetrating the heliopause itself and entering into interstellar
space for the first time."
Reaching the termination shock and heliopause will be major
milestones for the mission because no spacecraft have been there
before and the Voyagers will gather the first direct evidence of
their structure. Encountering the termination shock and
heliopause has been a long-sought goal for many space physicists,
and exactly where these two boundaries are located and what they
are like still remains a mystery.
Science data are returned to Earth in real-time to the 34-
meter Deep Space Network (DSN) antennas located in California,
Australia and Spain. Both spacecraft have enough electricity and
attitude control propellant to continue operating until about
2020, when electrical power produced by the RTGs will no longer
support science instrument operation. At that time, Voyager 1
will be almost 150 times farther from the Sun than the Earth --
more than 20 billion kilometers (almost 14 billion miles) away.
On Feb. 17, Voyager 1 will be 10.4 billion kilometers (6.5
billion miles) from Earth and is departing the Solar System at a
speed of 17.4 kilometers per second (39,000 miles per hour). At
the same time, Voyager 2 will be 8.1 billion kilometers (5.1
billion miles) from Earth and is departing the solar system at a
speed of 15.9 kilometers per second (35,000 miles per hour).
JPL, a division of the California Institute of Technology,
manages the Voyager Interstellar Mission for NASA's Office of
Space Science, Washington, D. C.
#####
Hа сегодня все, пока!
=SANA=
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