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PostPosted: Mon Nov 17, 2008 10:20 am 

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Electronic News Bulletin No. 255 2008 November 16

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
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By Alastair McBeath, SPA Meteor Section Director

Casual reports reaching the Section have suggested that a few bright
Taurids may have been present during late October to early November,
along with several UK reports of potential Taurid fireballs in the last
days of October, but none of these had sky-tracks well enough
established for certainty on their origins. See the list on the SPA's
Recent Fireball Sightings webpage at: for more
information. Although no meteor watch results have arrived from this
same period as yet, partly thanks to some unhelpful weather generally
over Britain, the International Meteor Organization (IMO) currently has
two "live" results' webpages for the Northern and Southern Taurids, at,
respectively, and . These
have indicated little sign that unusual Taurid Zenithal Hourly Rates -
ZHRs - were present in late October, though activity from both sources
seemed to have been above normal for a few days around November
3-5, and combined ZHRs from both branches could have been up to
20 or so on the latter date. However, caution has to be exercised with
these figures, because the values are based on limited datasets so far,
so are very preliminary only. If this activity is confirmed, it could support
another 'swarm' return having occurred, as hoped-for, though the
evidence so far is much less clear-cut than in the relatively fireball-rich
return of 2005.

By Alastair McBeath, SPA Meteor Section Director

The Orionid maximum, due on or around October 20, does indeed
seem to have been another interesting one in the sequence that began
in 2006, though rates were perhaps not quite so strong at best as
suggested in the initial report last time. The "live" IMO results, using
just a single, combined datapoint for each full day, have settled into a
pattern with highest ZHRs around 35-40 on both October 20 and 21,
probably marginally better on October 21. Surrounding this period,
ZHRs remained around 25-30 from October 19 to 24 inclusive. Given
that previous investigations of the shower had suggested activity at the
peak only this year might be 25-30, this was clearly another strong and
unusual return. There is still some uncertainty about the exact ZHR
values because of the bright Moon, but the extended period of good
activity after the maximum was unexpected.

Since ENB 254, Assistant Meteor Director David Entwistle and I have
examined the radio meteor data (see Radio Meteor Observation
Bulletin 183, October 2008, at: , for the reports and
details on the contributing observers' systems). David's initial
assessment using four datasets including his own, was that, as quite
typically, the Orionids failed to give a strong signature in many of the
radio results, but that a general peak of some sort was probably
present between roughly October 19-23 inclusive. I have just completed
a review of all the RMOB results this week, and concur with David's
findings for this overall appearance of the shower. However, a degree
of finer detail is apparent now. There was a curious difference to the
IMO visual results, where a slightly greater number of radio systems
favoured a peak on October 22. Activity seemed only marginally lower
than this on October 21 and 23 however, but significantly fewer
observers found a peak on October 20. Still more intriguingly, several
reports suggested a possible additional minor peak on October 25,
and close inspection of the data hints that this could have resulted from
an increased flux of fainter meteors.

There are still too few non-radio datasets in the Section's files to be
sure, but the early claims of brighter than normal Orionids, and perhaps
increased numbers of fireballs particularly on October 20 and 21, seem
not to have been borne out by subsequent results. As noted last time,
SPA visual magnitude distributions from October 20-21 and 21-22
seemed quite normal for the shower then. Video observations sent in
by Enrico Stomeo in Italy showed nearly identical magnitude
distributions for the Orionids on both October 18-19 and 19-20, for
example, with no fireballs, and his sporadic magnitudes on both nights
were also comparable to one another, suggesting it was not simply
different observing conditions at the root. The radio data failed to show
any good evidence for unusual numbers of fireballs during the shower
either (using longer-duration echo counts), though slightly better rates
of these may have been present on October 21.

While Britain's ever-unreliable weather thwarted many watchers here,
many thanks go to all the following observers for providing some data
over the shower, including those on the SPA and UK Weather World
Forums, and in October's RMOB. In the list, "V" = visual data were
provided, "I" = imaging - photography or video - and "R" = radio: Enric
Fraile Algeciras (R; Spain), Orlando Benitez (R; Canary Islands), Mike
Boschat (R; Nova Scotia, Canada), Jeff Brower (R; British Columbia,
Canada), Willy Camps (R; Belgium), Gaspard De Wilde (R; Belgium),
David Entwistle (R; England), "Halo" (V; England), Ed Majden (R;
British Columbia, Canada), Martin McKenna (V + I; Northern Ireland),
"Melanie" (V; England), Mike Otte (R; Illinois, USA), Jean-Louis Rault
(R; France), Robin Scagell (I; England), Andy Smith (R; England),
Enrico Stomeo (I; Italy), Dave Swan (R; England), Istvan Tepliczky (R;
Hungary), Maarten Vanleenhove (R; Belgium), Felix Verbelen (R;
Belgium), John Wardle (R; England) and the Director (V; England).

Anyone who still has observations from the Orionids to submit is
welcome to do so, preferably as soon as possible, please!

By Alastair McBeath, SPA Meteor Section Director

The September 25-26, circa 20:55 UT re-entry fireball, mentioned last
time as due to part of a Russian Proton rocket launched about half a
day earlier, now has a total of 21 sightings in the SPA files, thanks to
our French colleague Karl Antier very kindly making available
translations of the fifteen observations of it he received. The French
data confirmed how unusually slow-moving and long-lasting the event
was (in some cases for between 30 seconds to 2 or 3 minutes), and
described some heavy fragmentation late in its track. As far as the
uncertainties in the visual reports allow, this re-entry seems to have
approximately followed its expected atmospheric path, which is
reassuring at least!

On the SPA's General Chat Forum, at , David
Entwistle has provided a link to and some discussion of a fresh image
of the very persistent train produced when asteroid 2008 TC3 came
down over Sudan on October 7, as predicted shortly before (on which
event see also ENB 254). The train itself appears to have lasted for an
hour or more, and was imaged after the start of morning twilight from
David's calculations.

By Peter Grego, SPA Lunar Section Director

I will be offering a live webcast of the occultation of Venus on the
evening of December 1 on my website

The first webcast is from 15:15-45 UT (immersion is at 15:40 UT), the
second is from 17:00-17:30 UT (emergence is at 17:13 UT). Location:
St Dennis, Cornwall. The instrument will be a 102-mm achromat
(Celestron NexStar 102 SLT), imaged afocally with a ToUcam
PCVC740K. If the events are clouded out a real-time computer
simulation of the occultation will be substituted.


After more than two years of few sunspots, and even fewer solar
flares, the Sun is finally showing signs of life. During October,
five sunspot groups were observed. That may not sound like much, but
in a year with record-low numbers of sunspots and long stretches of
spotlessness, five is significant and represents a real increase in
solar activity. Even more significant is the fact that four of them
belonged to Solar Cycle 24, the long-awaited next instalment of the
Sun's 11-year solar cycle. Solar Cycle 23 peaked in 2000 and has
since decayed to low levels. Meanwhile, the new Cycle 24 has been
slow to get started. 2008 is a year of overlap, with both cycles
weakly active at the same time. From January to September, the Sun
produced a total of 22 sunspot groups, 18 of which belonged to the old
Cycle 23. October added five more, but this time four belonged to
Cycle 24.

At first glance, old- and new-cycle sunspots look the same, but they
are not. To tell the difference, solar physicists check two things:
a sunspot's heliographic latitude and its magnetic polarity.
(1) New-cycle sunspots always appear at high latitude, while old-cycle
spots cluster around the sun's equator. (2) The magnetic polarity of
new-cycle spots is reversed compared to that of old-cycle spots. Four
of October's five sunspot groups satisfied those two criteria for
membership in the new cycle.


The Messenger spacecraft has passed by Mercury for the second time
this year and imaged a further 30% of the previously unseen part of
the surface. When combined with data from the first fly-by and from
Mariner 10, the latest coverage means that we have now seen about 95%
of the planet. Cameras took more than 1,200 pictures of the surface,
while the laser altimeter obtained profiles of the topography. The
comparison of the new magnetospheric observations with those from the
spacecraft's first flyby in January provides new insight into
Mercury's internal magnetic field and reveals new features of its

Previous fly-bys by Messenger and Mariner 10 provided data only about
Mercury's eastern hemisphere. The most recent fly-by observed the
western hemisphere, and showed that the planet's magnetic field is
highly symmetrical. The probe's laser altimeter allowed topographic
measurements to be correlated with images for the first time at high
resolution. A spectrometer observed Mercury's thin atmosphere, known
as its exosphere. The instrument searched for emissions from sodium,
calcium, magnesium, and hydrogen atoms. Observations of magnesium
were the first detection of that element in Mercury's exosphere. Now
that Messenger has imaged more than 80% of Mercury, it is clear that,
unlike the Moon and Mars, Mercury's surface is more homogeneously
ancient and heavily cratered, with large extents of younger volcanic
plains lying within and between giant impact basins.


The Mars Reconnaissance Orbiter has observed a new category of
hydrated minerals spread across large regions of Mars. Deposits of
such minerals indicate where and when water was present. The new
observations have identified hydrated silica, commonly known as opal,
whose presence suggests that water may have existed as recently as
2 billion years ago, a billion years later than scientists had
previously supposed. Until now, spacecraft orbiting Mars had observed
only two major groups of hydrated minerals, phyllosilicates and
hydrated sulphates.

Clay-like phyllosilicates formed more than 3.5 billion years ago where
igneous rock came into long-term contact with water. During the next
several hundred million years, until approximately 3 billion years
ago, hydrated sulphates formed from the evaporation of salty and
sometimes acidic water. The newly discovered opaline silicates are
the youngest of the three types of hydrated minerals. They formed
where liquid water altered materials created by volcanic activity or
meteorite impact on the Martian surface. One such location is the
large Martian canyon system Valles Marineris.


When Comet Holmes unexpectedly erupted in 2007, astronomers around the
world turned their telescopes toward the spectacular event. People
would naturally like to know why the comet had suddenly exploded, but
observations recently reported from the Spitzer space telescope do not
answer the question, showing only oddly-behaving streamers in the
shell of dust surrounding the nucleus. The Comet Holmes explosion
gave us a rare glimpse of material from the inside of a comet nucleus,
and the data do not look like anything we typically see in comets.

Every six years, Comet Holmes heads inwards towards the Sun from the
distance of Jupiter's orbit. Usually it travels without incident, but
twice in the last 116 years, in 1892 November and 2007 October, it
suffered an explosion as it approached the asteroid belt, and
brightened a millionfold overnight. Spitzer observed the comet last
November and again in March. Its infrared spectrograph gave
indications of the composition of Holmes' solid interior. The
November observations showed a lot of fine silicate dust and materials
similar to those seen around other comets where grains have been
treated violently, as in the Deep Impact mission, which smashed a
projectile into Comet Tempel 1. Comet dust is very easily destroyed
and it is thought that the fine silicates are produced in violent
events by the destruction of larger particles originating inside the
comet nucleus. When Spitzer observed the same portion of the comet
again in March, the fine-grained silicate dust was gone and only
larger particles were present, so there seems to be only a small
window of time for studying comet dust after a violent event. Comet
Holmes not only has unusual dusty components, but it also does not
look like a typical comet. Pictures taken from the ground shortly
after the outburst showed streamers in the shell of dust surrounding
the comet. Scientists suspect that they were produced after the
explosion by fragments escaping the comet's nucleus. In 2007 November
the streamers pointed away from the Sun, which agreed with the idea
that radiation from the Sun was pushing the fragments straight back.
However, when Spitzer imaged the same streamers in March, they were
still pointing in the same direction even though the comet had moved
and sunlight was arriving from a different direction.

Harvard-Smithsonian CfA

The Spitzer infrared telescope has observed Epsilon Eridani, a star
that is younger and slightly smaller and cooler than the Sun and, at a
distance of only 10.5 light-years, is the ninth-closest star. The
star proves to have three rings of cool material that emit radiation
only in the infrared. It is conjectured that the radiation arises
from bands of asteroid-like objects. The innermost band is about 3
astronomical units from the star, just like the asteroid belt in the
Solar System, and judged by its brightness it contains an amount of
material comparable with that in our asteroid belt. The second ring
seen in the infrared is at about 20 astronomical units from the star
(about the distance of Uranus from the Sun) and appears to hold about
20 times as much material as the first. A third ring, that has
been observed previously, extends from about 35 to 100 astronomical
units from Epsilon Eridani. A possibly analogous band in the Solar
System is called the Kuiper Belt; however, judged from its brightness,
Epsilon Eridani's outer ring holds about 100 times more material than
ours. The Spitzer data show gaps between the successive rings
surrounding Epsilon Eridani. Such gaps might be explained by the
presence of planets that constrain the rings gravitationally, just as
the moons of Saturn constrain its rings.

New Scientist

The arrival of spring in the southern hemisphere of Mars is reviving
the two venerable Mars rovers as deepening autumn in the arctic north
freezes the Phoenix lander, which failed to wake up on November 2.
After hibernating for the winter on the northern edge of a plateau,
the 'Spirit' rover moved uphill in October to collect more sunlight.
On the other side of the planet, the 'Opportunity' rover, which
climbed out of a large crater called Victoria at the end of August,
has completed the first month of a 12-kilometre trek towards an even
bigger crater called Endeavour. That journey is expected to take more
than two years. Designed to last only 90 days, the two rovers have
survived for nearly five years.

Once it started moving, Spirit was able to climb slopes of up to 30°.
However, two weeks of movement has not dislodged the dust that limits
the power generated by its solar arrays. Winds have blown dust off
Opportunity's solar panels, so they generate more than 25 watts and
allow the rover to move faster, but it must navigate carefully across
ground that includes soft dunes where it could get stuck. The rover
can travel up to 100 metres in an hour, but it can see only 20 to 30
metres ahead. That means that it has to stop regularly to send
pictures of the prospect so that controllers can pick out a safe
path. Both rovers will have to be parked during an interruption in
communications from November 29 to December 15, when the Sun will be
between Mars and the Earth.

Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

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