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Electronic News Bulletin No. 172 2005 April 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
using 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

Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this bulletin. For information on
certain Philip's titles see the end of this Bulletin.

By Alastair McBeath, SPA Meteor Section Director

An unhelpfully moonlit Lyrid maximum is forthcoming shortly, due around
10h30m UT on April 22, which timing is in daylight for Britain anyway.
The bright Moon, full on April 24, is a severe hindrance throughout the
shower this year (the Lyrids are active from April 16-25), as the radiant,
on the Hercules-Lyra border and not near Vega as some people expect,
rises to a usable elevation only after 22h30m UT or so for the UK.
Anyone wishing to brave the moonlight in the hopes of spotting a few
Lyrids should look generally northwards (that is, away from the Moon,
but not too close to the Lyrid radiant), after midnight UT on April 21-22
for the best chances of doing so. The peak timing is not certain, and the
most recent detailed analysis of International Meteor Organization (IMO)
data indicated it could occur between about 02h30m UT to 13h30m UT
on April 22. The ~10h30m UT timing would be most likely to bring more
active Zenithal Hourly Rates (ZHRs), 20-25 or more, though the average
is 18, and can be lower the further the maximum happens away from the
ideal time. Rare stronger ZHRs, up to 90 (last in 1982 over the USA),
may occur too. Lyrids are medium-swift meteors, which sometimes can
be very bright.

Beginning their activity around April 19, May 3-10 should see the
strongest, swift-moving, Eta Aquarid rates, with ZHRs of perhaps 30+
on every night during this time, rising to around 50-60 at best on May
5-6, according to the most recent IMO long-term analysis. This
suggested a previously-suspected 12-year periodicity in activity,
governed by Jupiter's orbit, may be real, with the next high-point in
ZHRs (perhaps up to 85) falling around 2008-2010. Unfortunately, the
shower's radiant is in the little "Y"-shaped Water Jar asterism of Aquarius
(Gamma, Zeta, Eta and Pi Aquarii) on the UK morning of May 6 which
rises only shortly before dawn, so it is rare to glimpse more than one or
two Eta Aquarids a night here, and even this low rate is not guaranteed.
The slim waning crescent Moon for the peak will add more attraction
than nuisance, assuming it can be seen at all in the bright twilight, rising
barely half an hour or so before sunrise. From the southern hemisphere,
this is one of the strongest, reliable, annual meteor showers, and anyone
planning a trip to places at latitude 35 degrees south or so in early May
can enjoy over two hours of virtually moonless, twilight-free sky before
dawn to observe Eta Aquarids in. Meteors from this source are slightly
easier to see later in May, when their radiant (by May 15, very near
Beta Piscium) rises slightly earlier before dawn, but rates are of course
lower then. The shower ends around May 28.

More details on these and the other, less-active, showers present during
April and May can be found on the monthly webpage during the month
in question, off the Meteor Section's homepage at:


Known forms of life require liquid water, defining the habitable zone
around a star as the region where liquid water can exist on the
surface of a planet. The Sun's habitable zone is presently estimated
to range from about 0.95 to 1.67 AU. Other stars have habitable zones
at various distances, depending on their brightnesses and spectral
types. Stars become brighter as they age, pushing the habitable zone
further out and possibly bringing a period of warmth and life to
planets originally too far away. A new study considered the movement
of the habitable zone when stars reach the sub-giant and red-giant

There is indirect evidence that it took between half a billion to a
billion years for the emergence of life on Earth. According to the
study, the transit of the habitable zone, for planets between 2 and 9
AU from a solar-mass star, lasts from a few hundred to two thousand
million years, about the same time as the estimate for the development
of life. As an example of what might happen, it is pointed out that
Mars is a small planet with a thin atmosphere that does not hold heat
well, so even though Mars is just inside the estimated outer limit of
the Sun's habitable zone, it remains frozen today. However, a few
billion years from now, the inner limit of the Sun's habitable zone
will move out from Earth to Mars, so Martian life may get a second

The Register

Astronomers now have evidence that stars form when galaxies collide.
Data from the ISO infrared observatory have shown that the shock wave
caused by the collision of two galaxies has excited the gas from which
new stars could form. It is already known that shock waves from
supernovae excite clouds of gas, which causes the clouds to collapse
and eventually to form new stars. Hydrogen molecules radiate at a
particular frequency when they are excited by that process, and it is
that signature that scientists have observed in the colliding galaxies
known collectively as the Antennae. The two galaxies are located 60
million light-years away in the constellation Corvus and are at a very
early stage in their encounter. The region where they overlap is very
rich in excited molecular hydrogen. Although the excitation of the
gas has been detected, there are relatively few supernovae in the
region, so winds from them cannot be responsible for the excitation of
the hydrogen -- it has to be a result of the collision. The
researchers believe that new stars will be born over the next million
years or so, causing the galaxies to become twice as bright in the


The IAU has approved the following new designations and names of
satellites of Jupiter:

Jupiter XXXIX Hegemone = S/2003 J 8
Jupiter XL Mneme = S/2003 J 21
Jupiter XLI Aoede = S/2003 J 7
Jupiter XLII Thelxinoe = S/2003 J 22
Jupiter XLIII Arche = S/2002 J 1
Jupiter XLIV Kallichore = S/2003 J 11
Jupiter XLV Helike = S/2003 J 6
Jupiter XLVI Carpo = S/2003 J 20
Jupiter XLVII Eukelade = S/2003 J 1
Jupiter XLVIII Cyllene = S/2003 J 13


Using the XMM Newton space observatory, a team of astronomers is
unravelling the complex interactions that occur as clusters containing
hundreds of galaxies and enormous amounts of gas and dark matter
interact and merge. From observations of many clusters, it is
possible to estimate the distribution of mass in the Universe as a
whole, which may have a bearing on what the Universe is made of, how
it began, and how will it end. However, it seems that only 5% of the
mass of galaxy clusters lies in stars and galaxies. The space between
the galaxies is filled with gas which is so hot (10--100 million
degrees Celsius) that it can be seen only at X-ray wavelengths.

It is collisions between cluster of galaxies that makes the gas so
hot. Colliding clusters interact and finally merge. Mergers are the
most energetic events to have taken place since the Big Bang. The
energy released in cluster collisions irreversibly modifies the
physical conditions within the cluster through compression waves and
shocks which heat the gas to temperatures 10,000 times those on the
surface of the Sun. It should be remarked that the temperature of a
gas at very low density is a measure of the random speeds of the
individual atoms of the gas and is not what might be registered by a
conventional thermometer.

By working at X-ray wavelengths, the observers been able to measure
the origins and energy of X-rays from galaxy clusters. From the
positional information, they were able to map the distribution of the
gas in the clusters. From the X-ray energy, they were able to measure
the gas temperature. By combining the two, they could map the
temperature structure of the cluster gas and calculate that clusters
can collide at velocities greater than 2,000 km/s.


Scientists from Durham have been trying to solve a decades-old puzzle
regarding the distribution of the eleven small satellite galaxies that
surround the Milky Way. Galaxies are thought to be built up piece by
piece as sub-galactic fragments merge together; theoretically, that
should lead to the formation of a tightly-bound galaxy at the core
surrounded by a diffuse sphere of satellite structures. Cosmologists
have been puzzled by the fact that not only do the Milky Way's
satellites lie on a flat circle, approximately perpendicular to the
Galactic Plane, but also there are far too few satellite galaxies in
comparison with predictions.

The Durham team developed a computer model that built up a complete
history of all mergers between galactic building blocks, resulting in
a family tree for each satellite galaxy formed. They carried out six
simulations in total, and in each case found not only the correct
number of satellites but also, surprisingly, that the eleven most
massive satellite galaxies showed the same pancake-like distribution
around the core galaxy that is observed in the satellites of the Milky
Way. The team tried to understand that result by making animations of
the simulations and looking at the evolution of the dark-matter halo
in which the principal galaxy was supposed to have formed. The
findings of the Durham group are consonant with the 'cold dark matter'
model that has enjoyed some favour with cosmologists recently, and
offer hope that a coherent picture of how galaxies like the Milky Way
emerged from the Big Bang may now be beginning to fall into place.

Pennsylvania State University

The Swift mission, launched in 2004 November, has measured the
distance to two gamma-ray bursts, from opposite parts of the sky, and
found that both were from over nine billion light-years away. They
represent the mission's first direct red-shift measurements. The
Swift science team said that such measurements will become routine,
allowing scientists to create a map to understand where, when and how
the bursts of light are created.

Swift, with three telescopes, is designed to detect bursts and turn
autonomously within seconds to focus its telescopes on the burst
afterglow, which can linger for minutes to weeks. Swift detected
bursts on March 18 and 19, at estimated red-shifts of 1.44 and 3.24,
respectively, corresponding to distances of about 9.2 and 11.6 billion
light-years. Swift has detected 24 bursts so far, of which the one on
March 18 was the first in which an afterglow was detected.


Astronomers have new evidence that the formation of the first galaxies
may have begun earlier than previously thought. The team used
Space-Telescope data to identify remote galaxies that were suitable
for further study and then analysed archived images, taken at infrared
wavelengths by Spitzer, of a part of the southern sky in Fornax.
Spectra taken by the 10-m Keck telescope showed that the galaxies have
redshifts of about 6, which means they are so far away that light from
them has taken about 13 billion years to reach us. We see them as
they were when the Universe was less than a billion years old -- eight
billion years before the Earth and Sun formed. The Hubble images tell
us about the new-born stars, but the new infrared images give extra
information about the light that comes from older stars. The
observations suggest that some of the very distant galaxies were
already 300 million years old when the Universe was young, so star
formation must have started very early in the history of the Universe.


A UK-led team of astronomers has discovered a completely new type of
star cluster around the Andromeda galaxy (M31). The new-found
clusters contain hundreds of thousands of stars, like the familiar
globular clusters. What distinguishes them from the globular clusters
is that they are much larger -- several hundred light-years across --
and hundreds of times less dense. The distances between the stars
are, therefore, much greater within the newly discovered 'extended
clusters'. The new clusters are distributed in a spherical region
extending about 200,000 light-years around M31. Like the globular
clusters, they appear to be ancient. They may have been originally
created not in M31 but in dwarf galaxies, which have subsequently
between tidally disrupted by the giant M31 galaxy and merged with it.
If so, they might be more properly considered as the very smallest
galaxies rather than as star clusters.


For the last five years, a team of astronomers at the University of
Cambridge and the Anglo-Australian Observatory in Sydney has been
building a special instrument to search for distant galaxies. Known
as DAZLE (Dark Age Redshift Lyman Explorer), it is hoped to be able to
look back to the time when the very first stars were appearing from
the 'dark ages' that dominated the Universe shortly after the Big
Bang. It is optimised to detect faint emission lines in the spectra
of distant galaxies. The lines are hard to detect because they are
apt to be swamped by intense infrared emission created high in the
Earth's atmosphere. DAZLE uses specially designed filters that block
out 99.99% of that glow from the Earth's atmosphere. The first
observing run is planned to take place on the ESO VLT in Chile later
this year, when DAZLE will search a narrow window between night-sky
emission lines at an infrared wavelength that corresponds to the
Lyman-alpha line (emitted by hydrogen that has been heated by very hot
young stars) at a redshift of 7.8, equivalent to 12.8 billion
light-years. That means that the light would have left any such
galaxies 12.8 billion years ago, when the Universe was 500 times
smaller in volume than it is now. If the search at redshift 7.8 is
successful, the team plans to search another window in the sky
emission at a redshift of 8.8 although previous attempts to look back
so far in time have been unsuccessful.

The Register

NASA has approved another 18 months' operation for the two Mars
rovers, Spirit and Opportunity. The rovers, which were originally
designed to explore the surface of Mars for just three months, are
holding up so well after fourteen months that mission scientists say
they are having to make long-term plans for them. Scientists warn,
however, that with the rovers already performing well beyond their
original design lifetimes, having a part wear out and disable a rover
is a distinct possibility at any time. Both rovers are showing their
age. Spirit's drill's teeth seem to have worn away after grinding
through five times as much rock as expected, and Opportunity's
miniature thermal emission spectrometer is playing up.

Harvard-Smithsonian Center for Astrophysics

When the distant planetoid Sedna was discovered on the outer edges of
our Solar System, it posed a puzzle to scientists because it appeared
to be spinning very slowly. Astronomers hypothesized that it must
possess a moon whose tidal effects had slowed its rotation, but no
moon could be seen. New photometry with the 6.5-m MMT in Arizona,
however, has shown periodic fluctuations that demonstrate that the
originally claimed rotation period was a mistake. Sedna actually
rotates in a period of 10 hours, which is typical of the smaller
bodies in the Solar System and requires no external influences to


A book by Society member Robin Scagell has been published. 'Night
Sky Atlas' is a practical guide for observers with binoculars or
telescopes and contains maps, images and explanations to assist people
viewing the night skies anywhere in the world. Also 'Stargazing 2005'
by Heather Couper and Nigel Henbest, £6.99; 'Dark-Sky Observer'
pack that contains the new guide book by Neil Bone, a star chart and an
observer's calendar, £12.99. For more information on those and other
Philip's titles please visit

Philip's Dark Skies map of the UK (ISBN 0-540-08612-6) is also
available from bookshops. It was produced in collaboration with the
BAA Campaign for Dark Skies, and Pierantonio Cinzano, author of
'Atlas of Artificial Sky brightness'. Cost £6.99.

Bulletin compiled by Clive Down

(c) 2005 the Society for Popular Astronomy

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