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 Post subject: ENB No. 270 July 12 2009
PostPosted: Thu Jul 16, 2009 2:04 pm 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 270 2009 July 12
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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
visiting http://www.popastro.com/


IMAGED FIREBALLS IN JUNE-JULY
By Alastair McBeath, SPA Meteor Section Director

No fresh information has come in regarding the ~20:30 UT fireball on
June 15-16 since the previous ENB, but details on three fireballs
imaged from Europe since then have. The first was actually on June
15-16, a magnitude -6 event imaged from western France at 23:57
UT, which at least suggests more than one fireball passed not far from
the British Isles that night, though this one was not reported from the
UK. Karl Antier forwarded details about it, and the image can seen at
http://snipurl.com/n2uit .

The second event was still more spectacularly brilliant, and was
imaged from Italy on June 20-21, at 21:10 UT. The lucky imager
commented it was a little like a scene from the movie "Independence
Day"! Ferruccio Zanotti sent in notes about it, and you can find more
comments, some in English, some Italian, at: http://snipurl.com/n2uls
while the images are available here: http://snipurl.com/n2unf .

July 3-4 brought the third event, of about magnitude -6/-7 or more,
whose image was secured by Klaas Jobse's all-sky camera system
at Oostkapelle in the Netherlands, at 22:55 UT. It can be seen here:
http://snipurl.com/n2uow , including a close-up of the fireball's trail.
This event was also observed visually from England. Two observers,
one in Kent, the other the West Midlands, have reported seeing it so
far - see http://snipurl.com/n2vnc on the SPA's Observing Forum for
some preliminary comments, including from one of the lucky British
witnesses. Unfortunately, it has not been possible to determine a clear
trajectory for the object from these observations, but the meteor was
likely out high over the southern North Sea between southeast England
and western Holland, probably heading in a direction between
roughly southwest-northeast to south-north. It seems to have been
slow-moving, as one visual witness and Klaas' image, suggested it
was visible for around 5 to 6 seconds.

Many thanks go to all who provided details on these impressive
events. Sightings of fireballs (meteors of at least magnitude -3) made
from the British Isles and places nearby are always welcomed by the
Meteor Section. The details to report, including an e-mail report form,
are described on the "Making and Reporting Fireball Observations"
page of the SPA website, at: http://snipurl.com/kzlh7 .


"SKY LANTERNS" ARE STILL NOT FIREBALLS!
By Alastair McBeath, SPA Meteor Section Director

Back in ENB 228 (see http://snipurl.com/n2tp6 ), I gave some notes
on the increasing problems created by "sky lanterns" being
misidentified as meteoric fireballs. Since that notice appeared in late
2007, the problems have grown significantly worse. Between January 1
and July 4 this year, 43 genuine fireball-class meteors had been
reported to us from Britain and nearby, away from the main shower
maxima, plus 23 "lantern" sightings. In the whole of 2008, 72 fireballs
were similarly reported, plus just 7 "lanterns"! A recent discussion on
the SPA's Observing Forum (at: http://snipurl.com/n2xmq ) has
helped highlight what the things are and the difficulties they're now
creating for observers, plus the hazards they pose for aviation, their
obvious fire risk, and the false alarms they have caused for
coastguards, when mistaken for red distress flares over the sea.

"Sky lanterns" are roughly metre-high, paper hot air balloons, powered
by a burning wick suspended below them. Recent reports have
suggested some may be larger than this, however. Released singly or
sometimes in groups to go wherever the wind takes them, they first
started to appear as objects mistaken for meteoric fireballs in the
summer of 2007 over Britain. They can look like literal "balls of fire",
frequently yellow, orange or red in colour, sometimes showing a
flickering appearance, or even with clear flames seen, and a few have
apparently dropped burning material vertically below them. They drift
with the wind (remembering the surface wind is not always a guide to
how the wind may be behaving some tens to hundreds of metres
above ground-level), and remain visible for between tens of seconds
up to several minutes. Occasionally, they have been observed to
disappear into low cloud, and some have left a dark, smoky trail in the
sky for a short time. They can be very bright.

Much of this behaviour is quite unlike that of genuine meteors, which
follow straight-line paths, are always above even the very highest
tropospheric clouds, and rarely remain visible for more than a few
seconds as they streak across part of the sky. Man-made re-entry
fireballs, which are much slower than natural meteors, can
occasionally last up to a minute or two, but again they usually show a
glowing streak across the sky. Any train left after a meteoric object
has disappeared, a column of ionized gas, will glow rather than be
dark. A very large meteoroid can leave a dark smoke trail which is not
self-luminous, but this is opaque, and has the appearance of roiling
clouds, something like the effect seen in volcanic dust clouds, or more
commonly the "cauliflower" appearance of "fluffy" cumulus clouds, and
it always lies along the original straight-line path only at first (though it
may drift away from that area, and spread, with time). The smoky trails
left by "sky lanterns" seem to be quite thin to transparent in parts, by contrast.

In theory, mass-releases of "sky lanterns" are supposed to be notified
to the aviation authorities in advance, and coastguards have begun
asking for similar information on ANY such near-coastal releases (not
just for groups of "lanterns"). It is though already clear this notification
to the aviation authorities does not always happen - indeed such
advance warnings seem rather the exception, judging by the
numerous "UFO" reports in the media recently, almost all of which
seem to have been due to these "sky lanterns".

The best way to tell "sky lanterns" apart from genuine fireballs or other
astronomical targets like artificial satellites, is to examine them with
good, firmly-held, properly-focused, binoculars. This should enable an
easy confirmation of what they were. If the object vanished before you
could swing your binoculars into action, even when they were slung
ready around your neck, chances-are that object was meteoric, though
it may also have been a brief satellite flare, or aircraft lights. To check
for those, keep watching the same area of sky for any repeat flashes
of light over the next half minute or so. If, even after careful checking,
you couldn't be sure whether what you saw was a meteor or something
else, please send a fully-detailed sighting to the Meteor Section. Of
course, if your object was a genuine fireball-class meteor, I would be
delighted to have a similarly-detailed observation of that from you too!


LATE JULY'S METEOR ACTIVITY
By Alastair McBeath, SPA Meteor Section Director

As the Perseid maximum in mid-August will have a bright waning
Moon to contend with this summer, the lower-activity southern-sky
showers that peak with fewer moonlight problems near the end of July
become a more appetizing prospect than normal. The stronger source
is the Delta Aquarids, whose maximum Zenithal Hourly Rates (ZHRs)
should be about 15-20, usually achieved for a day or two around July
28-30. However, their radiant lies sixteen degrees below the equator
then, so the shower is never seen at its best from Britain, and observed
rates will be well below the ZHR as a result. The radiant though is
above the horizon all night, while the Moon, at first quarter on July 28,
will set during the late evening hours UT for the peak, and by midnight
even as late as August 1.

This early-setting Moon favours the other leading, if much less active,
late July shower peak, that of the Alpha Capricornids, around July
30-31. Highest ZHRs are usually only ~5, though a minor
enhancement to ~10, with several fireballs, was observed from Europe -
including Britain - in 1995, and the shower is noted for occasionally
producing wonderfully bright, slow meteors.

Be aware during your observations that the Antihelion Source is active
simultaneously, near both these radiants (indeed it partly overlaps that
of the Alpha Capricornids), centred on the ecliptic about 12° east of
the point opposite the Sun in the sky, but extending in a roughly oval
region away from that centre-point for about 30° in RA (two hours) and
15° in Dec. The centre culminates around 01h UT. Antihelion ZHRs are
liable to be about one or two for most of the month, rising to perhaps
2-3 by late July. As with the Delta Aquarids, their deep southerly
radiant will likely reduce observed numbers from the UK to negligible
proportions other than in late July. Don't forget too that some early
Perseids should be present from July 17 onwards, radiating from
"below" the "W" of Cassiopeia. Activity will not be plentiful from them
either - their ZHRs usually do not rise above ~10 until the first week
of August - though the combined effect of all these sources, plus the
omnipresent sporadic meteors, can produce quite healthy observed
hourly meteor counts, under clear, dark skies.

More details, including radiant charts for all these sources, are
available on the monthly meteor webpage of the SPA site, off the
homepage at: http://snipurl.com/n2url . Good luck!


TUNGUSKA EVENT CAUSED BY COMET
Geophysical Research Letters

In recent years there has increasingly been a consensus that the
object that caused the 1908 Tunguska explosion that levelled a large
area of Siberian forest was of the nature of a comet. That conclusion
is supported by Cornell University research from an unlikely direction
--- the exhaust plume from the space shuttle launched a century later.
The research connects the two events by what followed each about a day
later: bright night-visible clouds, or noctilucent clouds, that are
made up of ice particles and form only at very high altitudes and in
extremely cold temperatures. The researchers contend that the massive
amount of water vapour thrown into the atmosphere by the comet's icy
nucleus was caught up in eddies by a process called two-dimensional
turbulence, which explains why the noctilucent clouds formed a day
later many thousands of miles away. Noctilucent clouds are the
highest type of clouds, forming naturally in the mesosphere at about
55 miles over the polar regions during the summer months when the
mesosphere is around -117 C.

A single space-shuttle flight injects 300 tons of water vapour into
the Earth's thermosphere, and the water particles have been found to
travel to the Arctic and Antarctic regions, where they form the clouds
after settling into the mesosphere. Researchers saw the noctilucent-
cloud phenomenon days after the space shuttle Endeavour was launched
on 2007 August 8. Similar cloud formations had been observed after
launches in 1997 and 2003. Following the 1908 explosion, known as the
Tunguska Event, the night skies shone brightly in the north for several
days across Europe, particularly Great Britain.


LANDFORMS INDICATE 'RECENT' WARM CLIMATE ON MARS
Science and Technology Facilities Council

New research indicates that Mars had a significantly warmer climate in
its recent past than previously thought. Scientists came to that
conclusion by studying high-resolution images, obtained by the Mars
Reconnaissance Orbiter, of equatorial landforms that formed by melting
of ice-rich soils. The work indicates that the Martian surface
experienced freeze-thaw cycles as recently as 2 million years ago, and
that Mars has not been locked in permafrost conditions for billions of
years as had been previously thought.

The features were previously interpreted to be the result of volcanic
processes but are now attributed to the expansion and contraction of
ice, and by thawing of ice-rich ground, and suggest a climate very
different from what we find today. All of the landforms observed are
in an outflow channel, thought to have been active as recently as 2 to
8 million years ago. Since the landforms exist within, and cut
across, the pre-existing features of the channel, they too must be
supposed to have been created within that time. The pictures show
polygonally patterned surfaces, branched channels, blocky debris and
mound/cone structures, all of which are similar to landforms on Earth
typical of areas where permafrost terrain is melting. The observations
demonstrate not only that there was ice near the Martian equator in the
last few million years, but also that the ice melted to form liquid
water and then re-froze, probably for many cycles.


LARGEST MAP OF COLD DUST REVEALED
ESO

A new atlas has been produced, showing the inner regions of the Milky
Way at sub-millimetre wavelengths. It covers a strip about two
degrees wide and over 40 degrees long along the galactic plane, and
was created from observations made with the APEX telescope in Chile.
APEX is located at an altitude of 5100 m on the arid plateau of
Chajnantor in the Chilean Andes -- a site that permits observations in
the sub-millimetre wavelength range. The Universe is relatively
unexplored at sub-millimetre wavelengths, as extremely dry atmospheric
conditions and advanced detectors are required for such observations.
Images at those wavelengths are useful for studies of the birthplaces
of stars and the structure of the crowded Galactic core. The new
atlas, known as the APEX Telescope Large Area Survey of the Galaxy
(ATLASGAL), offers a fresh view of the Milky Way. It should give us
an overview of the large-scale structure of our Galaxy, and provide a
guide for observations to be made with the forthcoming ALMA telescope
and with the recently launched Herschel space telescope.

The interstellar medium is composed of gas and grains of cosmic dust,
rather like fine sand or soot. The gas is mostly hydrogen, which is
difficult to detect, so the dense regions are often identified instead
from the faint heat glow of the cosmic dust grains. Sub-millimetre
radiation shows the dust clouds as shining, even though they obscure
the view of the Universe at visible-light wavelengths. Accordingly,
the ATLASGAL map includes the denser central regions of our Galaxy, in
the direction of the constellation Sagittarius, that are otherwise
hidden behind a dark shroud of dust clouds. The map also shows
thousands of dense dust clumps, many never seen before, which mark the
future birthplaces of massive stars. The clumps are typically a
couple of light-years in size and have masses of between ten and a few
thousand times the mass of our Sun.


THE NATURE OF 'BLOBS' AND THE LIMIT TO THE SIZES OF GALAXIES
Chandra X-Ray Center

About ten years ago, astronomers who were making surveys of young
distant galaxies found great reservoirs of hydrogen gas, which they
called 'blobs', near them. The blobs glowed brightly in optical
light, but their nature and the source of the energy that powered the
glow and were unknown. It is thought that recent observations by the
Chandra X-ray satellite, the Spitzer infrared satellite, and other
instruments have answered the main questions. They have observed 29
blobs in one particular field. The blobs appear to be galaxies in
course of formation, several hundred thousand light-years across, and
are seen as they were when the Universe was only about two billion
years old. In five of the blobs, Chandra saw a point-like source of
X-ray emission, which has been taken to be the signature of a growing
super-massive black hole. Other observations indicate that there is a
lot of star-formation going on in the blobs. The radiation and
outflows from the black holes and the star formation is calculated to
be sufficient to light up the surrounding hydrogen in the blobs. It
may also be enough to arrest the infall of further gas and prevent the
blobs growing indefinitely into galaxies much larger than are actually
observed; some such process must be at work to limit the sizes of
individual galaxies.


ULYSSES SPACECRAFT ENDS MISSION
JPL

Ulysses, a joint NASA/ESA mission, ceased operations on June 30. The
spacecraft charted the unexplored regions of space above the poles of
the Sun for more than 18 years. When the space shuttle Discovery
launched Ulysses in 1990, the spacecraft had an expected lifetime of 5
years. It gathered information about the heliosphere -- the bubble
carved in space by the solar wind -- and made nearly three complete
orbits of the Sun in a plane almost perpendicular to the ecliptic..
The probe revealed for the first time the three-dimensional character
of Galactic cosmic radiation, energetic particles produced in solar
storms and the solar wind. In addition to measuring the solar wind
and charged particles, Ulysses measured small dust particles and
neutral gases that penetrate into the heliosphere from local
interstellar space. It also had three chance encounters with comet
tails, registered more than 1,800 cosmic gamma-ray bursts, and
provided findings for more than 1,000 scientific articles and two
books. On June 10, Ulysses became the longest-running ESA-operated
spacecraft, overtaking the International Ultraviolet Explorer, which
logged 18 years and 246 days of operations. Ulysses' orbital path is
carrying the spacecraft away from the Earth. The ever-widening gap
has progressively limited the amount of data transmitted, and the
project managers, with the concurrence of ESA and NASA, decided that
it was an appropriate time to end the mission..


Bulletin compiled by Clive Down

(c) 2009 the Society for Popular Astronomy


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