The SOCIETY for POPULAR ASTRONOMY
Electronic News Bulletin No. 177 2005 July 10
Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
at our secure site and can take credit and debit cards. You can join
or renew via a secure server or just see how much we have to offer by
Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this Bulletin. There is information
on certain Philip's titles and a special offer at the end.
By Alastair McBeath, SPA Meteor Section Director
Further to the fireball sightings given in the Special ENB of June 19, Steve
Evans in Gloucestershire has reported on a couple of events he recorded
using his meteor video system, which operates throughout most clear nights.
He did not catch any of the late May events, but he did record an ambient
brightening of the camera field on May 27-28 at 22:19 UT. These sudden
brightenings can be due to non-meteoric causes of course, but it is possible
that another fireball not spotted by observers elsewhere may have
appeared at around this time. Steve then recorded an in-field fireball at
01:31 UT on June 7-8. Although the correlation between CCD video and
visual meteor magnitudes is not exact, he estimated its peak brightness at
around video magnitude -4/-5, which might have been similar to,
perhaps a magnitude or two fainter than, this for a visual observer. No
visual sightings are yet to-hand. Unfortunately, Steve was not able to run
the camera on June 8-9, when the mysterious "meteoric flash" (?) was
spotted from elsewhere in Glos and Hants.
Observations of these or any other fireballs - meteors of visual magnitude
-3 or brighter - should always be submitted to the Section without delay.
Information on what to report and where to can be found on the "Fireball
Observing" page of the SPA website, off the Meteor homepage at:
METEORIC NON-EVENTS IN JUNE
By Alastair McBeath, SPA Meteor Section Director
A very late call for observations on June 12 of a possible meteor shower
associated with Comet P/2005 JQ5 (Catalina), was issued on June 11 on
the IMO-News e-mail list. The Earth was due to pass closest to the
comet's orbit around midday on June 12, roughly seven days before the
comet. However, the separation between the two, 0.024 astronomical
units (about 3.6 million kilometres), was rather large in meteoric terms.
The theoretical radiant for the very slow meteors was on the Libra-
Ophiuchus border, about 5 degrees south-south-west of the wide unaided-
eye pair Delta and Epsilon Ophiuchi, so was on-view overnight, though
moderately low, from Britain. Unfortunately, clouds seem to have prevailed
then here, but no positive reports were received even from clearer-skied
sites elsewhere. One preliminary report of increased radio meteor counts
from the UK has not been confirmed by any others as yet, and may have
been due to the summertime radio interference known as Sporadic-E
Later in June, as the Special ENB of May 29 noted, we were anticipating
a moonlit opportunity for potential June Bootid hunting after the solstice.
Initial reports sent to the SPA and the International Meteor Organization,
suggest observed rates were of the order of zero to one possible Bootid
an hour around June 26 to 28 - in other words, apparently there was no
detectable shower activity this year! Always a period worth monitoring
though, just in case.
BROWN DWARF JET
For the first time, a jet of matter has been detected streaming from a
brown dwarf, mimicking a process seen in young stars. The observation
suggests that brown dwarfs may form like other stars. Researchers
using the VLT in Chile have observed a jet, moving at 45 km/s and
stretching as far as from the Sun to Saturn, coming from a young brown
dwarf in the star-forming region around Rho Ophiuchi. Similar jets
have been detected around young, massive stars and are thought to form
from material in the disc that swirls around them. The stars grow
when matter falls on them from the disc, but the stars' magnetic
fields throw about a tenth of that matter back out through the jets.
PLANETARY CONSTRUCTION ZONE
Harvard-Smithsonian Center for Astrophysics
Located about 180 light-years away in the constellation Hydra is the
variable star TW Hydrae. It is a 10-million-year-old star about
four-fifths as massive as the Sun. Astronomers using the Very Large
Array to measure radio emissions from it have detected radiation from
a cold, extended dust disc containing centimetre-sized pebbles. Such
pebbles are a prerequisite for planet formation, created as dust
collects together into larger and larger clumps. Over millions of
years, the clumps grow into planets. A dusty disc like that in TW
Hydrae tends to emit radio waves with wavelengths similar to the size
of the particles in the disc. The scientists observed the young
star's disc with the VLA at several centimetre-range wavelengths. Not
only does TW Hydrae show such evidence of ongoing planet formation,
but it also shows signs that at least one giant planet may have formed
already: previously published infrared observations show that there is
a gap in the disc, extending from the star out to a distance of about
400 million miles -- similar to the distance to the asteroid belt in
our Solar System. The gap might have formed when a giant planet swept
up all the nearby material, leaving a hole in the middle of the disc.
The proto-planetary disc surrounding TW Hydrae contains about
one-tenth as much material as the Sun -- more than enough to form
several Jupiter-sized planets.
LAKE-LIKE FEATURE ON TITAN
The Cassini spacecraft has captured a series of images showing a
marking that is darker than anything else around it. It is remarkably
lake-like, with smooth, shore-like boundaries unlike any seen
previously on Titan. Scientists say that it is definitely the best
candidate they have seen so far for a liquid hydrocarbon lake on
Titan. The suspected lake measures 234 by 73 kilometres. Its
perimeter is intriguingly reminiscent of terrestrial lakes' shorelines
that are smoothed by water erosion and deposition. The feature lies
in Titan's cloudiest region, which is presumably the most likely site
of recent methane rainfall. Other possibilities are that the feature
was once a lake but has dried up, leaving behind dark deposits, or
that the 'lake' is simply a broad depression filled by dark, solid
hydrocarbons that have fallen from the atmosphere onto Titan's surface.
In that case, the smooth outline might be the result of a process
unrelated to rainfall. Another 39 Titan fly-bys are planned for
Cassini's prime mission, and the scientific teams will have
opportunities to observe the lake feature again and to look for
mirror-like reflections, that would strongly suggest the presence of
liquids, from smooth surfaces elsewhere on Titan.
SATURN'S RINGS HAVE ATMOSPHERE
Saturn's ring system has its own (extremely tenuous) atmosphere --
separate from that of the planet itself -- according to data from the
Cassini spacecraft. By making close fly-bys of the ring system,
Cassini has been able to determine that the atmosphere around the
rings is composed principally of molecular oxygen. The finding was
made by two experiments on Cassini -- the mass spectrometer and
plasma-science instrument -- which show the atmosphere to be very
similar to those of Jupiter's moons Europa and Ganymede.
PLANET WITH LARGE CORE
HD 149026, an 8th-magnitude Sun-like star in Hercules, has been found
to have a planet whose mass similar to that of Saturn but which is
significantly smaller in diameter and is therefore denser. That is
not remarkable, since the mean density of Saturn is only 0.7 times
that of water. The planet takes just 2.87 days to circle the star.
Modelling of the planet's structure suggests that it has a solid core
approximately 70 times the Earth's mass. That is the first
observational evidence in favour of the 'core accretion' theory of
planetary formation, in which planets start as small rock--ice cores
that grow as they acquire additional mass gravitationally. (It is not
clear that that is the same idea as was implicit in the first two
items in this Bulletin.) Scientists believe that the large rocky core
of the planet could not have formed by cloud collapse; they think the
core must have grown first, and then acquired gas.
MINERAL FROM ANCIENT SUPERNOVA
University of Arizona
NASA and University of Arizona researchers who have been using
high-flying research aircraft to collect extra-terrestrial dust,
probably delivered to the Earth's upper atmosphere by a comet or
asteroid, have discovered pristine mineral grains that formed in an
ancient supernova explosion. The grains offer clues as to how much
material supernovae contributed to making our Sun and planets,
including radioactive material used in isotopic age-dating techniques.
The discovery also provides a partial check on numerical models of
supernovae explosions. The grains have oxygen isotopic ratios that
have never been seen in meteorites or cometary dust, but are predicted
in astrophysical models of supernova explosions.
SUPERNOVA 2005cs IN M51
Astronomers believe that they have identified a possible 24th-
magnitude progenitor for this young type-II supernova in Hubble Space
Telescope images of M51. The identification is consistent with a red
supergiant with an approximate absolute I magnitude of -5.8 that
implies an initial mass for the progenitor of about 10 solar masses.
The supernova occurred in a crowded field, and there are several other
red sources and a bright, blue, possible compact star cluster within
0".3 of the supernova location.
NOVA SAGITTARII 2005 No. 2
The IAU has announced the discovery of an 8th-magnitude nova in
Sagittarius. The co-ordinates are R.A. 18h 17m.9, Dec. -30 27'
(2000.0). Attempts to find the precursor star have so far failed.
COMET'S HUGE PLUME HIDES CRATER
The Deep Impact spacecraft may have missed its chance to see the
crater made in Comet Tempel 1 because of the large plume of material
kicked out. Seeing the crater was a key objective of the mission;
scientists hoped that the impact depression would tell them more about
the structure of the comet. But the team might be able to base an
estimate of the crater's dimensions upon the amount of material
thrown out, and might yet be able to resolve part of the crater by
use of image-processing software.
PHILIP'S NEW TITLES AND SPECIAL OFFER
Special Offer! Â£10 off the retail price of Â£30 and free p&p on Atlas
of the Universe, the definitive guide to stars, planets and the
Universe, by Sir Patrick Moore. To order call 01903 828 503 quoting
Philip's 52. Offer ends July 29.
NEW EDITION of PHILIP'S GUIDE TO THE NIGHT SKY (48-page paperback,
Â£4.99, ISBN 0540087017). SIR PATRICK MOORE takes the novice
astronomer on a guided tour of the stars and constellations of the
northern hemisphere. An accessible work, clearly and concisely
Bulletin compiled by Clive Down
(c) 2005 the Society for Popular Astronomy
Current and previous news bulletins from the SPA
1 post • Page 1 of 1