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 Post subject: ENB No 248 July 20 2008
PostPosted: Sat Jul 19, 2008 9:22 am 

Joined: Fri May 16, 2008 10:09 pm
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Location: Headcorn, Kent, England
Electronic News Bulletin No. 248 2008 July 20

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

By Alastair McBeath, SPA Meteor Section Director

As some of you will be aware already, numerous problems with the
SPA website for most of this year have prevented any of the formerly
regular updates there being made since about February, including
those from the Meteor Section. Followers of the SPA's online Forum
will know that the Society has changed its webhost during the last
couple of weeks, and we hope we can put those difficulties behind us
quickly. The Recent Fireball Sightings page was fully updated for the
first time since January in early July, for instance, and we hope to
resume the normal routine updates of this page by August, as well as
the monthly meteor forecast pages. The transfer to the new host seems
to have gone fairly smoothly, but the e-mail addresses
were offline for a time during this switchover, so if you tried e-mailing
to one of those and had it returned to you, it should be possible to send
it through satisfactorily by this time.

Initial details from near Saint-Hilaire de Riez in Vendee, western
France suggested there may have been a further fireball sighting on
June 23-24 to tally with those received by the Section earlier from
Guernsey and Hampshire, reported last time. However, further
investigation now indicates the French report related to a fireball seen
to the southeast from Vendee, at around 23:30 UT on June 22-23
instead. Such an event would have been too far south to be spotted
from the UK, unfortunately.

There has been one fresh UK fireball observation reported since the
last ENB however, seen from East Yorkshire at around 02:00 UT on
July 7-8, the object of at least magnitude -3. Fireball reports made from
Britain and nearby (a fireball is any meteor that reaches at least
magnitude -3, so of Jupiter's current brilliance or more) are always
welcomed by the Section. Details to send are outlined on the "Fireball
Observing" page of the SPA website, at: .

By Alastair McBeath, SPA Meteor Section Director

Hopefully, much of the following information, plus radiant charts for most
of the showers, will shortly be available on the newly-revamped SPA
website (if so, off the Meteor homepage at:
but just in case there remain problems in doing so, and to allow people
to plan ahead, the full August meteor notes for British observers follow.
For further information on the showers mentioned, including radiant
positions, see the Meteor Showers List page for the present year, also
available off the SPA Meteor homepage.

August's popularity for UK astronomers stems from it bringing the end
of the midsummer overnight twilight season. It is also "Perseid month",
as this normally strong major meteor shower peaks in mid August, well-
timed to take advantage of the school and college summer holidays.
This year, the best Perseid rates may elude British observers, and
there is a waxing gibbous Moon then too, but conditions overall are still
quite favourable for seeing what happens, and stronger than normal
Perseid activity is a possibility. Overnight observing in mid August can
be very pleasant, with sometimes quite warm temperatures, and plenty
of meteors to see in clear, darker skies. August's weather can be
fickle however, on the cusp between late summer and early autumn, so
it can be cold and occasionally frosty by Perseid-time, notably further
north in the UK.

Continuing its steady trickle of meteors for much of the year, the
Antihelion Source (ANT) has a roughly oval radiant region, about 30
degrees in RA (two hours) by 15 degrees in Dec, which lies roughly
opposite the Sun in the sky, hence its name. The actual ANT's radiant
centre is about 12 degrees east of this point. Such positions for this
area are provided in the Section's Meteor Showers List. During August,
the ANT centre moves steadily northwards through Aquarius and just
into Pisces, an area that is on-view for most of the night, culminating
around 01h UT. In general, one or two meteors per hour is a good level
of ANT activity according to the latest International Meteor Organization
(IMO) analyses, but ZHRs may be a little better, around 2-3, till mid
August. Observations to check on Antihelion meteors are
recommended whenever there is no Moon after mid-evening. Such
meteors are of medium speed.

The July-August boundary brings some of the stronger near-ecliptic
meteor showers during the year, as noted in ENB 246
( ). The strongest of these is the Delta Aquarids
(previously called the "Southern Delta Aquarids", and thus still
abbreviated as "SDA"), which peaked in late July. Declining activity
from them should continue till August 19, but observed rates from Britain
usually peter out some days before this official end-date, thanks to
weak activity from a southerly radiant. Even so, Perseid maximum
watchers do sometimes spot the occasional meteor from this source, a
few of which can be bright.

The other leading, if much less active, July-August near-ecliptic source,
is the Alpha Capricornids (CAP), which also peaked, albeit at a much
lower level than the SDA, in late July. As the CAP radiant actually
overlaps that of the large ANT area's, we are not sure if it will still be
sensibly observable as separate from the ANT as a result. This is
particularly true by early August, as in the past, it was unusual to spot
any CAP meteors from Britain after the first week in August or so,
though the shower's official end date is not until August 15. Occasional
slow, bright to fireball-class, shower members may still occur until then.

The Perseid maximum is due between 11h30m-14h00m UT on August
12 this year, and should produce typical healthy Perseid numbers.
Zenithal Hourly Rates (ZHRs) thus should be around 80-100. Though
this timing is obviously poor for British visual observers, the peak
should still remain observable by radio methods even here (as long as
interference permits, at least). However, Finnish meteor expert Esko
Lyytinen has suggested the Earth may encounter a denser meteoroid
trail for perhaps an hour or so centred on 05h26m UT that morning,
producing an additional stronger maximum ahead of what would be
usually the main peak, much as was seen back in 1991-98 and again
in 2004. Esko suggested ZHRs could reach 100-300, perhaps higher,
and there seems a good prospect for brighter than normal Perseid
meteors to be involved. This timing too is unhelpful for British visual
observers of course, but we should catch part of the rising activity this
way later in the night of August 11-12, with luck, and again radio
observers should be able to cover this potential peak interval from
here. Meteor rates will likely remain most acceptable by August 12-13
too, if doubtless below their best. The Moon is waxing gibbous, near its
lowest in the sky, and will set around midnight UT for most UK sites on
each night, leaving much of the second half of the night free for dark-sky
watching. This is so as the shower's radiant, a few degrees northeast
of Eta Perseii, first reaches a useful elevation by about 22h UT, and
improves all night after then, to culminate well after sunrise, around 06h.
Perseids are swift, often bright, and commonly trained meteors. Lower
Perseid activity can be followed away from the main peak for most of
the month, ending around August 24 (the shower began back in mid
July). The waxing Moon in early August should allow some coverage
right up to the maximum date under better conditions, if skies are clear.
The post-midnight observing window does close quickly, only a couple
of nights after the maximum, however. Activity tends to drop steeply
once the maximum is past anyway, so this is less of a nuisance than
it might have been.

The minor Kappa Cygnid maximum should happen on August 17, the
day after full Moon, so is liable to pass entirely unobserved. The shower
produces wonderfully slow, typically bright, meteors from August 3-25,
but its peak ZHRs are just ~3. Occasional fireballs have been seen from
it, and these may recur in periodic bursts every 6 or 7 years. In addition,
because the shower's radiant, between Cygnus' western wing-tip and
Draco's neck, is almost overhead for much of the night, observed rates
can equal the ZHR in dark, clear skies at the peak, if not in 2008 sadly.
As the radiant lies close to the ecliptic pole in Draco, its daily drift is
almost negligible.

As August draws to a close, some Alpha Aurigids may be spotted, as
they begin around August 25, lasting into early September. Their activity
is from one of a number of suspected radiants in Auriga, Cassiopeia,
Perseus, Aries and Triangulum during the early autumn, and is probably
the strongest. Others include the September Perseids and Delta
Aurigids, neither of which is active before early September. The Alpha
Aurigids were recently re-evaluated by IMO analysts using global data
from 1986-2000, and were found to usually produce ZHRs of ~7
around August 31 to September 1. The peak is most likely on the
former date this year, excellent news with the month's second new
Moon falling on August 30. Regrettably, no strong outburst like that
seen under moonlit skies from across the western USA in 2007, when
ZHRs reached about 120 for a short time (see ENB 228, ), is predicted for this year. Previous,
unexpected, Alpha Aurigid outbursts occurred in 1935, 1986 and 1994,
which produced ZHRs of ~30-40, though none of these was widely-
seen. Alpha Aurigid meteors are swift, like Perseids, but not usually so

Good luck for all your late summer observing, and clear skies!

Carnegie Institution

New tests of increased sensitivity have indicated that tiny beads of
volcanic glasses collected by two of the Apollo missions to the Moon
contain traces of water. It is being suggested that the water came
from the Moon's interior and came to the surface in volcanic eruptions
long ago. That would call into question some critical aspects of the
'giant impact' theory, which holds that the Moon was formed after a
Mars-size body collided with the Earth in the early days of the Solar
System, melting both objects and sending into Earth orbit molten
debris some of which coalesced to form the Moon. In that case the
light elements would have been volatilized.

Ever since the Apollo missions, the consensus has been that the Moon
is dry. The new analysis used a technique called secondary-ion mass
spectrometry that can detect as little as 5 parts per million, ten
times less than could be measured previously. The samples yielded up
to 46 ppm. That would be only a small proportion of the total amount
of water in the eruptions that created the volcanic glass. Most of
the volatile materials in the magma would have escaped into space, but
some may also have found its way to the cold poles of the Moon where
ice may be present in permanently shadowed craters. One of the goals
of the 'Lunar Reconnaissance Orbiter' mission, to be launched later
this year, is to look for such ice.


In January the spacecraft 'Messenger' made the first of three planned
fly-bys of Mercury needed before it can enter orbit round the planet
in 2011. Pictures taken in the first fly-by suggest that the planet
has contracted by more than 1.5 km in diameter over its history. The
shrinkage is being attributed to the planet's core slowly cooling.
There is also evidence of volcanic activity, previously hinted at by
Mariner 10. By combining Mariner 10 and MESSENGER data, the
scientific team tried to understand the great Caloris basin, which
must have been formed by an asteroid impact during the 'heavy
bombardment' period in the first billion years of Solar-System
history. As with the lunar maria, a period of volcanic activity
produced lava flows that filled the basin interior. The vulcanism
produced the comparatively light, red material of the plains within
Caloris, intermingled with impact-crater deposits. Spacecraft
measurements also found that craters on Mercury are about a factor of
two shallower than those of analogous sizes on the Moon. Sensors
recorded silicon, sodium and even water ions around Mercury. The
scientists think that the ions are blasted from the surface by the
solar wind and are then trapped by the planet's magnetic field.

University of Maryland

It has only recently been recognized that many asteroids have their
own moons; it is currently estimated that about 15% of near-Earth and
main-belt asteroids with diameters less than 10 kilometres have
satellites. It seems that these small binary asteroid pairs could not
have lasted since the beginning of the Solar System, so some process
that is still at work must have created them. Researchers now say
that the process depends on sunlight, which can increase or decrease
the spin rate of an asteroid through what is known as the Yarkovsky
effect, named after the nineteenth-century Russian scientist who first
recognized it. Owing to the time that it takes a surface exposed to
sunlight to heat up, the 'afternoon' side of a body is always warmer
than the 'morning' side, and radiates more heat. The heat is radiated
in the form of photons, which carry away momentum, albeit in tiny
quantity. The principle of conservation of momentum requires that the
body itself -- an asteroid is the case of interest here -- acquires
corresponding momentum in the opposite direction, implying a nett
force directed towards the nadir of the afternoon side of the
asteroid. Operating over a long time, a tiny force can achieve
macroscopic effects, affecting both the spin and the orbit of the
asteroid. The sign of the effect depends on whether the asteroid is
initially spinning in the prograde or retrograde direction. In a time
that is only of the order of a million years -- short by cosmic
standards -- a kilometre-sized body can be spun up to bursting point.

A team of US and French astronomers has outlined a model showing that
when solar energy spins up a rubble-pile asteroid to a sufficiently
fast rate, material is thrown off round the asteroid's equator.
If the spun-off bits of the asteroid shed sufficient excess motion
through mutual collisions, then the material coalesces into a
satellite that continues to orbit its parent. The model closely
matches observations of binary asteroids. The proposed process would
also cause a drift of material from the poles towards the equator of
the asteroid, leaving previously deeply buried material exposed near
the poles, so a sample-return mission to a pole of such a binary
asteroid could bring back pristine material and thereby probe the
internal composition of the asteroid without having to dig into it.

University of California at Berkeley

A survey of 250 stars in the central region of the Orion Nebula has
found that fewer than 10% of them emit the 1.3-mm-wavelength radiation
typically signifying a warm disc of dust. Even fewer were judged to
have dust discs with masses above 1/100 of a solar mass, a mass
thought to be the lower limit for formation of Jupiter-sized planets.
Because stars like the Sun probably formed in hot open clusters like
Orion, the finding suggests that Sun-like stars have a low probability
of forming planets, at any rate planets the size of Jupiter or larger.
The implication is that systems like ours may be the exception rather
than the rule. That is consistent with the results of current planet
searches, which are finding that only about 6% of stars surveyed have
planets the size of Jupiter or larger.


A very distant galaxy is conjectured to be making stars at rate of
more than 1,000 a year. For comparison, our own Milky Way galaxy
turns out an average more like 10 stars a year. The discovery goes
against one of the theories of galaxy formation, that galaxies
increase their star content by absorbing pieces of smaller ones --
not by making stars in one big burst as seems to be happening in the
one described here. That one belongs to a class of galaxies called
starbursts and is the brightest starburst galaxy so far observed in
the very distant part of the Universe. Brightness is taken to be a
measure of star-formation rate. At its present rate, if maintained,
it would take 'only' 50 million years, not very long on the cosmic
time-scale, to grow into a galaxy equivalent to the most massive ones
we see 'nearby' today. In visible light the galaxy is faint, but it
stands out at infrared and sub-millimetre wavelengths, supposedly
because it has a huge number of youthful stars. When stars are born,
they shine with a lot of ultraviolet light and produce a lot of dust.
The dust absorbs the ultraviolet light and as it warms up it re-emits
the energy at infrared and sub-millimetre wavelengths.


Taking advantage of a rare cosmic coincidence, astronomers have
measured an effect predicted by Einstein's general theory of
relativity in the extremely strong gravity of a pair of super-dense
neutron stars. The scientists used the Green Bank radio telescope to
study a double-star system consisting of a pair of neutron stars, both
of which are seen as pulsars that emit lighthouse-like beams of radio
waves. Of about 1700 known pulsars, it is the only case where two
pulsars are in orbit around one another. The average distance between
the two is only about twice the distance from the Earth to the Moon,
and the orbital period is just under 2.5 hours. By specially good
fortune, their orbital plane is aligned so nearly with the line of
sight from the Earth that one passes behind a region of ionised gas
surrounding the other, eclipsing the signal from the pulsar behind.

Einstein's 1915 theory of relativity predicted that, in such a close
system of two very massive objects, one object's gravity, along with
an effect of its spinning around its axis, should cause the spin axis
of the other to precess. The eclipses have allowed astronomers to pin
down the geometry of the double-pulsar system and to track changes in
the orientation of the spin axis of one of them. The results
indicate that the 93-year-old theory has passed yet another test.


Spacecraft controllers have woken Rosetta from hibernation to prepare
for its encounter with asteroid Steins on September 5, on its way to
comet Churyumov-Gerasimenko. Launched in 2004, Rosetta will reach its
final destination in 2014. Rosetta has passed close to the Earth
twice and to Mars once, performing gravity-assist manoeuvres that gave
it the necessary boost to continue on its journey. The third and last
Earth fly-by is scheduled for 2009 November. The spacecraft will also
fly by two asteroids and study them on its way, Steins this year and
Lutetia in 2010 June. As it closes in on Steins in September, Rosetta
will have travelled about 3,700 million kilometres and will be 2.1 AU
from the Sun. Steins has been classified as an E-type asteroid, a
relatively rare type composed mainly of silicates and basalts, but its
properties are not at present known in detail.


Scientists, engineers and astronauts are finishing plans to fly the
space shuttle in early October on a mission to the Hubble telescope to
repair and upgrade it. The long-delayed servicing mission will be the
last, but it is hoped to allow the telescope to perform better than
ever for the remaining five or six years of its operating life. The
last repair mission will also deliver two new instruments, the 'Cosmic
Origins Spectrograph' (which will observe at extreme ultraviolet
wavelengths) and the 'Wide-Field Camera 3' (which will allow the
telescope to operate across the light spectrum from ultraviolet to
optical and infrared).

The final Shuttle to be launched before the whole fleet goes into
retirement is currently expected to be Endeavour, which will carry
parts for the International Space Station in 2010. By that time NASA
hopes to have demonstrated the replacement technology with an unmanned
test flight of its 'Ares' launch vehicle which is intended to carry
the proposed new 'Orion' module that should eventually take astronauts
back to the Moon. After the shuttle is retired, the space station
will rely on Russian, European and Japanese craft for supply.

BBC Online

The future of Jodrell Bank is secure, according to the site's owner,
Manchester University. Jodrell's existence had been in doubt because
of uncertainty over where money would come from to finish and run its
key new project, the e-Merlin network. However the university says
that funding for the network, which ties together radio dishes across
the UK, is now safe. e-Merlin is an upgrade to a network of seven
radio telescopes, from the 250-foot Jodrell telescope to Lord's Bridge
at Cambridge. By linking the stations together with fibre-optic
cables, e-Merlin can mimic a single radio telescope spanning 217 km.

The SPA Electronic News Bulletins are sponsored by the Open University.

Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

The Society for Popular Astronomy has been helping beginners to
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