ENB No. 244 May 25 2008

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ENB No. 244 May 25 2008

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Electronic News Bulletin No. 244 2008 May 25

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://popastro.c.topica.com/maalEUjabHvndcixLLVb/

By Alastair McBeath, SPA Meteor Section Director

A couple of fresh sightings of the May 6-7, ~22:16 UT fireball have
arrived since the last ENB, bringing the tally now to seven, all from
places scattered across western Britain south of Merseyside, and east
as far as Hampshire. Unfortunately, no more accurate track than the
rough "possible" one suggested last time has been established still.

Further investigation of the radio Lyrids in the last fortnight, using
details from Radio Meteor Observation Bulletin 177 for April 2008
(see: http://popastro.c.topica.com/maalEUjabHvnecixLLVb/ ), has suggested two possible peaks on
April 22, one around 01h-03h UT, and a second, similarly strong, one
around 08h UT. This second peak was unexpected, since it coincided
with the shower radiant's culmination for those European sites that
registered it, a time when, due to the complexities of radio echo-
reflection geometries, we often find a dip in observed echo counts.
Both these peaks were seen just in the European results, however.
None of the active North American systems found clear signs of the
Lyrid maximum at all, and unfortunately, there are no Japanese data
available so far, which might have helped clarify the situation. Visual
results remain virtually nonexistent, so we cannot be sure what really
took place, and investigations continue. The preliminary radio findings
discussed in ENB 243 still stand, of course.

The Eta Aquarid maximum, due in early May, probably centred on May
5, seems to have been recorded quite well in the preliminary
International Meteor Organization results (IMO; available via the
http://popastro.c.topica.com/maalEUjabHvnfcixLLVb/ homepage), though the relatively few southern
hemisphere observers made the details less certain than we would
have liked. Best Zenithal Hourly Rates (ZHRs) seem to have been ~75
on May 6, around 01h UT, quarter of a day later than expected, with
rates of 30-50 seen from May 3-8 inclusive. Veteran SPA observer
Tony Markham in Staffordshire reported spotting his first-ever probable
Eta Aquarid, but after his meteor watching ended on May 6-7, while he
was packing up his gear to head home!

A lot less welcome has been the return of sightings of "sky lanterns",
coincident with the spell of fine weather over much of the UK in early
May. Notes on two separate incidents have come through so far, on
May 9-10 over Manchester, the other the following night observed from
Bedfordshire. Regular ENB readers may recall these became rather
problematic in generating false fireball reports from late last summer,
with peaks in sightings in late August to early September, around
November 5 and December 25. Some notes on them and how to
identify them from genuine meteoric fireballs were given in ENB 228,
archived at: http://popastro.c.topica.com/maalEUjabHvngcixLLVb/ .

Another non-meteoric phenomenon, flashes from artificial satellites
catching the Sun as they rotate, has surfaced recently on the
Observing Forum, at: http://popastro.c.topica.com/maalEUjabHvnhcixLLVb/ , where I gave some
notes in regard to separating such flashes from point-source meteors
(that is, meteors heading straight towards you through the atmosphere,
and thus appearing like short-lived points of light).

In the case of "sky lanterns" or possible satellite flashes, if, after
following the suggestions for segregating them from real meteors,
you're still not certain what you saw, do contact me at the Meteor
Section, with as full a description as possible of what you saw, when
and where from. If the event was particularly bright, of magnitude -3 or
brighter, you may have seen a fireball-class meteor (though some
satellite flares, especially from the Iridium satellites, can reach well into
this brightness range). If so, I need still more detailed information from
you ideally, as outlined on the "Fireball Observing" page of the SPA
website, at: http://popastro.c.topica.com/maalEUjabHvnicixLLVb/ .

By Alastair McBeath, SPA Meteor Section Director

All-night twilight for British watchers, and the year's strongest daytime
radio showers, characterise June. As most meteor watchers prefer
dark-sky visual observing, this tends to mean a lot of people ignore the
month, but there are still occasional notable events to be seen. The
wholly unexpected June Bootid outburst in 1998 was well-viewed from
some luckier clear-sky British sites, while the minor June Lyrids (a
shower that may be only irregularly active) was independently
discovered by watchers in California and Britain in 1966.

Active all month, though generally producing rates no better than one or
two meteors per hour, is the Antihelion Source. This Source is a roughly
oval 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 Source's centre is about 12 degrees east of this point. Video
results suggest it is active virtually throughout the year, producing
generally low rates, and radiant centre positions for this oval area are
provided in the Section's online Meteor Showers List, available off the
homepage at: http://popastro.c.topica.com/maalEUjabHvnjcixLLVb/ . During June, the Antihelion
Source is near the most southerly part of the ecliptic, in Ophiuchus to
Sagittarius, an area that is on-view for most of the brief nights,
culminating around 01h UT. The very low radiant elevation will have an
adverse effect on its observed meteor rates from the UK however, and
although ZHRs may be up to 4 in the first and last few days of June
(only), this can reduce observed counts to negligible proportions, though
at least the Moon will be little additional problem at either "better" time.
Antihelion meteors are of medium speed, and observations to check
on them are recommended whenever there is no Moon after mid-evening.

Three major annual showers have maxima this month, but all are in the
daytime sky, thus observable from Britain solely by radio or radar
methods, when summertime interference, often from Sporadic-E,
permits. All three were discovered by radar observations from Jodrell
Bank in Cheshire in 1947. Two have peaks before mid-month, the
Arietids and Zeta Perseids. The Arietids are active from about May
22 to July 2, with a peak on June 7 from a radiant at RA 02h56m,
Dec +24 degrees. The estimated peak ZHR could be around 60, but
the radiant is barely 30 degrees west of the Sun at maximum, so only
visual observers near the equator might spot the occasional medium-
speed Arietid shortly before dawn in early June. The Zeta Perseids last
from May 20 to July 5 or so, and reach maximum on June 9 (visual-
equivalent ZHRs perhaps ~40). Their radiant then is at RA 04h08m,
Dec +23 degrees, actually between the Hyades and Pleiades star
clusters in Taurus, not especially near the star Zeta Perseii at all. This
location is a mere 15 degrees west of the Sun, so visual observations
are impossible. The proximity of the Arietid and Zeta Perseid radiants,
and their peaks coming so close together in time, means even radio
operators usually cannot separate the two sources, though echo counts
are typically elevated for much of early to mid June as a result.

Hunting for any potential June Lyrid activity between June 11-21,
perhaps at maximum on June 15, will be extremely difficult thanks to
the Moon, full on June 18. Theoretically, the radiant at maximum lies
near Vega, Alpha Lyrae, around RA 18h32m, Dec +35 degrees, well
on-view all night, but IMO investigations have failed to find it in recent
observations. At most, low rates of slow-medium speed meteors might
be seen, but only with extreme difficulty this year because of the twilight
and moonlight. The clearest and best-confirmed June Lyrid return was
back in 1969, when British observers made a significant contribution to
the data-pool despite that twilight, and ZHRs reached 9-10. Subsequent
returns produced lower activity, which dwindled to nothing significant by
the late 1970s. Independent reports of weak activity by several
observers were last made in 1996, though nothing definite has been
detected since. The source may be active only in some years, however.
Interested observers should carefully plot any suspected June Lyrids
onto gnomonic charts to allow a proper analysis, and should be aware
that not all previous reports agree well with even the theoretical radiant
suggested here.

The June Bootids burst back to life in 1998 with Zenithal Hourly Rates
(ZHRs) of 50-100 for one night only, after being virtually inactive since
1927. This event probably resulted from material shed in the 19th
century by the shower's parent comet, 7P/Pons-Winnecke, along with
a similar outburst, yielding ZHRs of 20-50, on 2004 June 23 - a date
before the shower was previously thought detectable! Prior to 1998, just
three earlier more probable returns had been recorded from this source,
in 1916, 1921 and 1927, all apparently strong and all near the time of
Pons-Winnecke's perihelion, unlike more recently. Currently, the
comet's orbit lies about 0.24 astronomical units - about 36 million km -
outside the Earth's, so a direct influence on potential shower activity is
unlikely, though it returns to perihelion again this September. No
predictions are in-force for activity in 2008 as yet, but if anything does
manifest this summer, it is most likely between June 22 and July 2, with
a repeat of the 1998 peak due within six hours of 02h30m UT on June
26-27. Last quarter Moon then will be only a minor additional nuisance
for observers, rising shortly before midnight from Britain. Very slow
meteors are characteristic, emanating from a diffuse radiant in northern
Bootes centred at RA 14h56m, Dec +48 degrees, an area well on-view
throughout the short nights.

The third major radio shower peak in June is from the Beta Taurids,
often quite an ill-defined maximum around June 28, the shower overall
active from roughly June 5 to July 17. Their maximum visual-equivalent
rates are about 25 meteors per hour, from a diffuse radiant centred near
RA 05h44m, Dec +19 degrees, some 10 degrees west of the Sun near
the Southern Horn of Taurus, thus, as for the Zeta Perseids, with which
they have sometimes been associated, no visual observations are
practical. This, perhaps with the Zeta Perseids, is the Earth's second
annual encounter with the Taurid showers we see visually overnight
each year in October-November. They have also sometimes been
suggested as the origin for the Tunguska airburst event over Siberia
exactly a century ago this June 30th, though that is far from certain.

Good luck, and clear skies, for your observing!


Hydroxyl, a 'free radical' or incomplete molecule, is made up of one
hydrogen atom and one oxygen atom. It has now been found in the upper
reaches of the Venusian atmosphere about 100 kilometres above the
surface by a spectrometer on Venus Express. The molecule was detected
by turning the spacecraft away from the planet and looking along the
faintly visible layer of atmosphere surrounding the planet's disc.
The instrument detected the hydroxyl molecules by measuring the
infrared light that they give off. The layer of the outer atmosphere
containing the glowing hydroxyl molecules is only about 10 kilometres
thick. By looking at the limb of the planet, Venus Express looked
along that faint atmospheric layer, increasing the signal strength by
about 50 times.

Hydroxyl is thought to be important for any planet's atmosphere
because it is highly reactive. On Earth it has a key role in purging
pollutants from the atmosphere. On Mars it is thought to help
stabilize the carbon dioxide, preventing it from converting to carbon
monoxide, and also to sterilize the soil, making the top layers
hostile to microbial life. The reactive molecule has been seen around
comets, but the method of production there is thought to be completely
different from the way it forms in planetary atmospheres. On Earth,
the glow of hydroxyl in the atmosphere has been shown to be closely
linked to the abundance of ozone, so maybe the same is true at Venus.
Now, scientists can try to estimate the amount of ozone in the
planet's atmosphere. Venus Express has shown that the amount of
hydroxyl at Venus is highly variable. It can change by 50% from one
orbit to the next, possibly because of changing amounts of ozone in
the atmosphere.


New observations from the Mars Reconnaissance Orbiter indicate that
the crust and upper mantle of Mars are stiffer and colder than
previously thought. The findings suggest that any liquid water that
might exist below the planet's surface would be located deeper than
scientists had suspected. The discovery was made using the 'Shallow
Radar' instrument, which has provided the most detailed pictures to
date of the interior layers of ice, sand and dust that make up the
north polar cap on Mars. The radar images reveal long, continuous
layers stretching up to 600 miles. Images also show a smooth, flat
border between the ice cap and the rocky Martian crust. On Earth, the
weight of a similar stack of ice would cause the planet's surface to
sag. The fact that the Martian surface is not bending means that its
strong outer shell, or lithosphere, a combination of its crust and
upper mantle, must be very thick and cold. Temperatures in the outer
portion of a rocky planet like Mars increase with depth toward the
interior. The thicker the lithosphere, the more gradually the
temperature increases. The discovery of a thicker Martian lithosphere
therefore implies that any liquid water lying in aquifers below the
surface would have to be deeper than previously supposed, where
temperatures are warmer.

Johns Hopkins University

Using data from the Pluto-bound 'New Horizons' spacecraft, an
international team has found that the storm represented by Jupiter's
'Little Red Spot' (LRS) has some very high wind speeds. The spot is
nearly the size of the Earth and is as red as the similar, but larger
and better known, Great Red Spot. The LRS formed by the merging of
three smaller white storms that had been observed since the 1930s.
Two of them coalesced in 1998, and the combined pair merged with the
third storm in 2000. In late 2005, for reasons unknown, the combined
storm turned red. The winds in the LRS have increased substantially
over the wind speeds in the precursor storms, which had been observed
by the Voyager and Galileo missions previously. The wind speeds and
directions were determined from two images that were taken by New
Horizons 30 minutes apart in order to track the motions of cloud
features. The LRS's maximum winds speeds proved to be about 400 mph.
Jupiter's venerable Great Red Spot has decreased steadily in size over
the past several decades. A rare upheaval in Jupiter's atmosphere,
involving a number of spectacular cloud changes, began before New
Horizons visited last year.


A flare is an explosive release of energy from a star, caused by a
sudden reorganization of the magnetic field in an area of its surface.
The field stores increasing amounts of magnetic energy through being
twisted up by the relative motions of large volumes of plasma within
which it is trapped. The motions are driven by convection and
probably ultimately in ways associated with the star's rotation. The
field builds up until it suddenly lets go into a simpler configuration,
and the stored energy is radiated at wavelengths throughout the
spectrum, from gamma-rays to radio waves, and particles are accelerated
to very high energies, including jets of electrons that constitute
electric currents analogous to very powerful lightning discharges.

The 'Swift' satellite recently observed the brightest flare ever seen
from a normal star other than our Sun. It came from a variable star
called EV Lacertae, which is a red dwarf, by far the most common type
of star. EV Lacertae shines with only 1% of the Sun's light and
contains only a third of the Sun's mass. At a distance of only 16
light-years, it is one of our closest stellar neighbours, but with its
feeble light output it appears as a star of magnitude 10, well below
unaided-eye visibility. It is relatively young, with an estimated age
of a few hundred million years. It rotates once every four days, much
faster than the Sun, which rotates once every four weeks, and its
rapid rotation apparently allows it to generate magnetic energy 100
times greater than the Sun's.

The flare was first seen by the Russian-built Konus instrument on the
Wind satellite early on April 25. Swift's X-ray telescope caught the
flare less than two minutes later, and quickly slewed to point toward
EV Lacertae. When Swift tried to observe the star with its
ultraviolet/optical telescope, the flare was so bright that the
instrument shut itself down for safety reasons. The star remained
bright in X-rays for 8 hours before settling back to normal. At the
time of year that the flare appeared, the constellation of Lacerta is
visible only from the Northern Hemisphere, and only just at the end of
each night. If the star had been more easily visible, the flare
probably would have been bright enough for the star to have been
seen with the unaided eye for an hour or so. EV Lacertae is only about
a fifteenth of the age of the Sun, but it does not necessarily
represent closely what the Sun may have been like at the corresponding
age, since it is so much less massive than the Sun. But in general,
younger stars rotate faster, and that enables them to wind up their
magnetic fields more and to generate more powerful flares, so it is
quite probable that in its first billion years the Sun produced
frequent energetic flares that could have affected the Earth and the
other planets.

National Radio Astronomy Observatory

Astronomers have discovered a pulsar in association with a Sun-like
star in an elongated orbit, a combination that has never been seen
before. The pulsar, called J1903+0327, was discovered in a long-term
survey with the Arecibo radio telescope in Puerto Rico. It is
spinning on its axis 465 times every second. Nearly 21,000 light-
years from the Earth, it is in a highly elongated orbit with a period
of 95 days. An infrared image made with the Gemini North telescope in
Hawaii shows a Sun-like star at the pulsar's position. If it is
really the orbital companion to the pulsar, it is unlike any
companions of other rapidly rotating pulsars. The pulsar, a neutron
star, also is unusually massive for its type. Astronomers think that
most millisecond pulsars are speeded up by material falling onto them
from a companion star. That requires the pulsar and its companion to
be in a tight orbit that becomes more and more circular with time.
The orbits of some millisecond pulsars are perfect circles, so the
elongated orbit of the new one is a mystery.

Science Daily

Supernovae are the explosions of massive stars -- stars more than 8
times the mass of the Sun -- whose cores run out of nuclear fuel and
collapse in on themselves to form a neutron star or a black hole. In
the process they launch a powerful shock wave that blows up the star.
Until now, observations of such objects have been of the aftermath,
typically several days after the initial explosion; no one had
witnessed one actually occurring in real time. While observers were
using the orbiting Swift X-ray telescope to look at another supernova
in the spiral galaxy NGC 2770 in the constellation Lynx, they detected
an extremely luminous blast of X-rays released by a new supernova
explosion. They alerted 8 other orbiting and ground telescopes to
observe that first-of-its-kind event. Astrophysicists had proposed
nearly 40 years ago that the first sign of a supernova would be an
X-ray blast; now that one has been seen and astronomers know what
X-ray pattern to look for, they may be able to find more supernovae at
the critical moment, opening up avenues of research that previously
seemed nearly impossible.

New Scientist

A supernova remnant near the centre of the Milky Way has turned out to
be the youngest known in our Galaxy. Known as G1.9+0.3, the remnant
lies about 28,000 light-years away. It was first identified as a
ring-like supernova remnant in the early 1980s. Now, observations by
the Chandra X-ray observatory and the Very Large Array radio telescope
in New Mexico have shown that the diameter of the glowing gas shell
has expanded by 16% over the past 22 years. If the speed of expansion
is roughly constant, then the remnant is only about 140 years old,
making it the youngest in the Milky Way. Previously, the most recent
supernova was thought to have occurred around the year 1680, creating
the ghostly remnant Cassiopeia A. The supernova would not have been
visible to 19th-century astronomers because it would have been totally
obscured in visible light by the dense gas and dust near the Galactic
Centre, but the remnant shines also in radio waves and X-rays, so
radio and X-ray telescopes can see it. Measurements of supernova
rates in other galaxies suggest that about three supernovae should
occur in the Milky Way every century. If so, our Galaxy ought to
contain roughly 10 remnants younger than Cassiopeia A.


An international team of astronomers has calculated that the Universe
is actually twice as bright as previously thought because dust is
obscuring approximately half of the light that the Universe is
currently generating. While astronomers have known for some time that
the Universe contains small grains of dust, they had not realised the
extent to which that is restricting the amount of light that we can
see; the dust absorbs starlight and re-emits it, making it glow.
They knew that existing models were flawed, because the energy output
from glowing dust appeared to be greater than the total energy
produced by the stars!

The team combined a new model of the dust distribution in galaxies
with data from the Millennium Galaxy Catalogue, a high-resolution
catalogue of 10,000 galaxies. Using the new model, the astronomers
could calculate the fraction of starlight blocked by the dust. The
key test that the new model passed was whether the energy of the
absorbed starlight equated to that detected from the glowing dust.
The astronomers claim that the equation balanced perfectly, and that
for the first time they have a total understanding of the energy
output of the Universe over the whole wavelength range. The results
demonstrate very clearly that interstellar dust grains have a serious
effect on measurements of the energy output from even 'nearby'
galaxies, but with the new calibrated model in hand the astronomers
are now more confident of being able to assess the fraction of
starlight blocked by the dust.


The Phoenix Mars Lander is expected to end its long journey today and
begin a three-month mission to taste and sniff Martian soil and buried
ice. Phoenix will enter the top of the Martian atmosphere at almost
13,000 mph. In seven minutes, the spacecraft must complete a
challenging sequence of events to slow to about 5 mph before its three
legs reach the ground. Internationally, fewer than half of all
attempts to land on Mars have succeeded. Rocks large enough to spoil
the landing or prevent opening of the solar panels present the
greatest known risk. However, images from the Mars Reconnaissance
Orbiter, detailed enough to show individual rocks smaller than the
lander, have helped lessen that risk.

In 2002 the Mars Odyssey orbiter discovered that ice lies just beneath
the surface in many places at high latitudes on Mars. NASA chose the
Phoenix proposal over 24 other proposals to become the first endeavour
in the 'Mars Scout' programme. Phoenix will land farther north on
Mars than any previous mission, and will study the permafrost region.
The solar-powered robotic lander will manipulate a 7.7-foot arm to
scoop up samples of soil and, supposedly, underground ice. On-board
laboratory instruments will analyse the samples. Cameras and a
weather station will supply other information about the site's
environment. One research goal is to assess whether conditions at the
site have ever been favourable for microbial life. The composition
and texture of soil above the ice could give clues to whether the ice
ever melts in response to long-term climate cycles.

The SPA Electronic News Bulletins are sponsored by the Open University.
Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

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