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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 340 2012 October 7
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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/ BIG SUN-GRAZING COMET DISCOVERED
Spaceweather.com
The newly-discovered Comet Ison, currently still beyond the orbit of
Jupiter, is heading for a very close encounter with the Sun next year.
In 2013 November, it will pass less than 0.012 AU (1.8 million km)
from the solar surface. The fierce heating it will experience could
turn the comet into a bright naked-eye object -- but comets can and
often do fizzle out! Meanwhile, comet researcher John Bortle has
pointed out a similarity between the orbit of Comet Ison and that of
the Great Comet of 1680. "Purely as speculation," he says, "perhaps
the two bodies could have been one a few revolutions ago."
SHOCK WAVES SHAPED OUR SOLAR SYSTEM?
RAS
Certain scientists think that shock waves that might have been emitted
from the Sun when it was very young might have caused the planets in
the Solar System to form at different times. It seems that the waves
might have created a series of debris rings that eventually accreted
into planets, the outermost ones first.
DAWN SUGGESTS SPECIAL DELIVERY OF HYDRATED MATERIAL TO VESTA
RAS
The mechanism by which water was incorporated into the terrestrial
planets is a matter of debate. Now, observations of Vesta by the Dawn
mission suggest that hydrous materials were delivered to the asteroid
mainly through a build-up of small particles during an epoch when the
Solar System was rich in dust. Vesta's surface shows distinct areas
enriched with hydrated materials. Those regions are not dependent on
solar illumination or temperature, as we find in the case of the Moon.
The uneven distribution is unexpected and indicates ancient processes
that differ from those believed to be responsible for delivering water
to other airless bodies, like the Moon. Analysis of data from Dawn's
mapping spectrometer showed large regional concentrations of hydroxyl
(a hydrogen and an oxygen atom bound together) clearly associated with
features including ancient, highly-cratered landforms and the Oppia
crater. Hydroxyl on the surface of the Moon is thought to be created
continuously by the interaction of protons from the solar wind with
the lunar regolith. Highest concentrations are found in areas near
the lunar poles and in permanently shadowed craters where it is very
cold. By contrast, the distribution of hydroxyl on Vesta is not
dependent on significant shadowing or unusually cold temperatures.
It is also stable over time, so its origin does not appear to be due
to short-term processes.
The hydroxyl-rich regions on Vesta broadly correspond to its oldest
surfaces. Around relatively large and young impact craters, hydroxyl
detections are weak or absent, suggesting that the delivery of
hydroxyl is not an ongoing process. The spectrometer evidence
suggests that much of Vesta's hydroxyl was delivered by small
particles of primitive material, less than a few centimetres in
diameter, over a time-limited period, but it is not clear what period
that was.
SUPERNOVA 1006
ScienceDaily
Astronomers all over the world observed the supernova of the year
1006. Some of them, including Chinese astronomers, highlighted the
fact that it was visible for three years. The most explicit record,
made by the Egyptian Ali ibn Ridwan (988-1061), notes that the
phenomenon was about three times brighter than Venus, and that it
emitted light of a quantity equivalent to almost a quarter of the
Moon's brightness. Now a team of astronomers has studied the existing
stars in the area, regarding distance and possible contamination by
elements of the supernova, and the results show that there is no star
that could be considered the progenitor of the explosion and that the
event was probably the result of a collision and merger of two white
dwarf stars of similar mass.
MILKY WAY IS SURROUNDED BY HALO OF HOT GAS
Chandra X-ray Observatory / Harvard-Smithsonian Center for
Astrophysics
Astronomers have found evidence that the Milky Way Galaxy is embedded
in an enormous halo of hot gas that extends for hundreds of thousands
of light-years. The estimated mass of the halo is comparable to the
mass of all the stars in the Galaxy. If the size and mass of such a
gas halo is confirmed, it could also be an explanation for what is
known as the 'missing baryon' problem for the Galaxy. Baryons are
particles, such as protons and neutrons, that make up more than 99.9%
of the mass of atoms found in the cosmos. Measurements of extremely
distant gas haloes and galaxies indicate that the baryonic matter
present when the Universe was only a few billion years old represented
about one-sixth the mass and density of the existing unobservable, or
dark, matter. In the current epoch, about 10 billion years later, a
census of the baryons present in stars and gas in our galaxy and
nearby galaxies suggests that at least half the baryons are
unaccounted for. In a recent study, a team of astronomers used data
from Chandra, the XMM-Newton space observatory and the Suzaku
satellite to set limits on the temperature, extent and mass of the hot
gas halo. Chandra observed eight bright X-ray sources located far
beyond the Galaxy at distances of hundreds of millions of light-
years. The data indicated that X-rays from those distant sources are
absorbed selectively by oxygen ions in the vicinity of the Galaxy.
The scientists determined the temperature of the absorbing halo is
between 1 million and 2.5 million °C.
Other studies have shown that the Milky Way and other galaxies are
embedded in 'warm' gas with temperatures between 100,000 and 1 million
degrees. Studies have indicated the presence of a hotter gas with a
temperature greater than 1 million degrees. The new research provides
evidence that the hot gas halo enveloping the Milky Way is much more
massive than the warm gas halo. In an effort to estimate the size and
mass of the halo, the authors supplemented Chandra data on the amount
of absorption produced by the oxygen ions with XMM-Newton and Suzaku
data on the X-rays emitted by the gas halo. They concluded that the
mass of the gas is equivalent to the mass in more than 10 billion
Suns, perhaps as large as 60 billion Suns. The work shows that, for
reasonable values of parameters and with reasonable assumptions, the
Chandra observations imply a huge reservoir of hot gas around the
Milky Way. It may extend for a few hundred thousand light-years
around the Milky Way or it may extend further into the surrounding
local group of galaxies. Either way, its mass appears to be very
large. The estimated mass depends on factors such as the amount of
oxygen relative to hydrogen, which is the dominant element in the gas.
Nevertheless, the estimation represents an important step in solving
the question of the missing baryons, which has puzzled astronomers.
Although there are uncertainties, the work provides the best evidence
yet that the Galaxy's missing baryons have been hiding in a halo of
million-degree gas that envelopes the Galaxy. The estimated density
of the halo is so low that similar haloes around other galaxies would
have escaped detection. It must be noted that the weighty conclusions
proposed in this item all stem from a mere eight observations, and may
accordingly be open to some revision.
ULTRA-DISTANT GALAXY DISCOVERED
Johns Hopkins University
A team of astronomers has discovered what could be the most distant
galaxy ever detected. The young galaxy observed by the Hubble
telescope and Spitzer shone when the Universe was just 500 million
years old. The far-off galaxy existed within an important era when
the Universe began to emerge from the so-called 'Dark Ages', as it
went from a dark, starless expanse to a recognizable cosmos full of
galaxies. Technically speaking, the galaxy has a redshift of 9.6.
It is observable only because it has been enhanced by a 'gravitational
lens'.
FIRST TWO JAMES WEBB TELESCOPE MIRRORS DELIVERED
NASA
The first two of the 18 primary-mirror elements for the James Webb
space telescope have arrived at the Goddard Space Flight Center. The
rest will make their way from Ball Aerospace to Goddard over the next
12 months. Each of the 18 hexagonal tiles that make up the primary
mirror measures more than 1.3 metres across, and weighs about 40 kg.
PLANETS
By Alan Clitherow.
October offers some beautiful sights for the planetary observer.
For those prepared to be up before dawn, Jupiter is excellently placed
towards the south-east. From mid-UK latitudes the planet rises at
around 20.20 UT on the first of the month and by midnight UT is some
31° up, almost due east. As the night progresses its altitude climbs
and our view of it improves as we view through less and less
atmosphere. If you can wait until 4h UT Jupiter is nearly 60° up and
almost due south, and on a clear and steady night will reveal
beautiful detail in any astronomical telescope. On August 10 amateur
observers witnessed a bright fireball on Jupiter's limb as a small
comet or asteroid burnt up in the planet's atmosphere. Six such
events have been seen since Voyager 1 passed by in 1979, most by
amateurs. The recent fireball seen over the UK (September 21) puts
such observations in context, and it is likely that there are more
such events that go unobserved or un-reported.
The great disturbances in the planet's atmosphere seem to have settled
down a little, with the North Equatorial Belt and the North Temperate
Belt almost merged and the Equatorial Zone dark with activity and
festoons. The Great Red Spot is pale but still clearly visible, and
it is currently keeping company with Oval BA, or the little red spot,
which is moving past it, just to the South. It will be interesting to
see how those weather systems evolve in the coming months. By the end
of October Jupiter will be due south at around 2.25 UT, still 60° up,
and I urge you to view it at such anti-social hours if you can. The
planet will be beautifully placed for many months; however, frigid
winter nights often give poorer seeing conditions than those of late
autumn.
If you are up in the early morning, then once you have finished with
Jupiter, switch to Venus. Rising at 2.20 UT on the first of the month
a little north of east, Venus is shining at -4.0 magnitude and is a
brilliant beacon in the sky. By 5h UT the sky will be noticeably
lightening but Venus will still stand out clearly some 25° above the
eastern horizon and will present a disc of 15 arc-seconds across, of
which some 70% will be illuminated, giving an obvious visible phase.
If you can, observe with a dark-blue or violet filter (a Wratten
number 47 filter is often recommended) as that will not only help to
cut down the brilliant glare of the planet but may reveal subtle
details in its thick blanket of clouds. Venus is best observed early
in the month because it is moving quite rapidly away from us and its
separation from the Sun is decreasing as the month progresses.
Notwithstanding, the planet, once found, can easily be followed
through dawn and into daylight, so long periods of observation are
possible; just take great care whenever trying to observe anything
once the Sun is in the sky. You have been warned!
If we now switch to evening observation, there is less that is obvious
on view. Mercury reaches its greatest eastern elongation, that is its
greatest separation distance from the Sun in the evening sky, on
October 26, but it is extremely low on the horizon at sunset and you
are unlikely to get more than a glimpse of it before it sets.
Similarly Mars is very low in the south-west though you may catch it
as one of a pair of low red 'stars' as it is around 4° from Antares.
Saturn moves behind the Sun on the 25th (superior conjunction) so is
effectively invisible; so what does that leave us with? The answer is
Uranus.
At the start of the month Uranus can be found below the Great Square
of Pegasus in the south-eastern sky. If you draw a line from
Alpheratz in the top-left-hand corner of the Square and extend it down
to the bottom-left-hand-corner star Algenib, then extend the line the
same distance again downwards, you will almost be on top of a pale
blue-green star hovering on the edge of naked-eye visibility; it will
show clearly in binoculars. Since truly green stars are rather like
hens' teeth you will have, in fact, found Uranus. At only 3 arc-
seconds in diameter it will take larger telescopes and very steady
seeing to make out anything other than an obviously planetary-like
disc, but some faint banding detail is occasionally seen. I have
recently seen images taken with a large-aperture telescope using a
filter that passes only infra-red light from 685 Nm upwards (Baader
Planetarium filters) in which this banding was very obvious. By
midnight UT on the 1st of the month the planet reaches just under 40°
elevation, due south, and is well worth a look, it will remain
on show throughout October but viewing early in the month is
recommended if possible.
As usual, please submit any observing reports you may have via the
planetary section web site.
2012 SEP 21 UK FIREBALL
By Tony Markham, SPA Meteor Section Director
A bright slow moving fireball was seen by observers across much of the
UK shortly before 11pm BST on the night of Friday 21st September. The
start of the fireball was also seen by some observers in Belgium,
Denmark and the Netherlands and the end was seen from Ireland. This
fireball has attracted international attention and there has even been
speculation that the object may have been a very small Aten type
asteroid gravitationally "captured" by the Earth for some time before
finally entering the Earth's atmosphere. There has also been
speculation that, with the object entering the atmosphere at a very
shallow angle, part of it may have re-emerged from the atmosphere,
orbited the Earth again and then been responsible for a very similar
fireball seen over North America approx 155 minutes later. Another
possibility, of course, is that the latter was a different object on
a similar trajectory.
As is always the case, most eyewitnesses were non-astronomers with
little knowledge of the night sky and so the positions reported in
their accounts were often rather approximate. Reports that did quote
azimuths and altitudes or which described its path through the
constellations were particularly valuable. Based on the reports,
Alastair McBeath was able to produce a preliminary analysis.
Although there was scatter in the times reported, the average time
reported for its appearance was 21:57 ± 5 minutes UT. The mean
reported visible duration was estimated at 24 seconds, though this may
be somewhat under-estimated, as many people saw only part of the full
path. Magnitude estimates averaged in the -7 to -10 range, something
which was made still more difficult than normal because the fireball
was breaking up for much of its flight. Colours reported were many and
varied, but almost 80% were in the red-orange-yellow to white range,
the remaining 20% or so favouring predominantly green.
The long atmospheric flight for the meteor created problems in
determining where it may have flown above, but the information
available suggested that it probably followed a roughly east to west
trajectory (or perhaps ENE to WSW) across northern England, most
likely passing overhead around the Durham/North Yorkshire to southern
Cumbria/Lancashire region. Three reports of possibly associated sonic
booms were made between 30 seconds to three or four minutes after the
meteor had passed-by from Co. Durham (two) and Lancashire, which help
to confirm this possible overflight zone, albeit tentatively. The
start was likely out over the North Sea, and the end may have been
somewhere above central-western Ireland or over the Atlantic off the
western coast.
Early press coverage also suggested the event may have been a man-made
re-entry. However, if we assume the average visible duration noted
above was roughly correct, and that the full visible path was between
circa 500 to 1000 km long as a crude estimate, the object's velocity,
not allowing for deceleration, would have been well above any near-
Earth man-made objects, but comfortably within the expected meteor
atmospheric-entry range, between ~20 to 40 km/sec."
Subsequent reports have required minimal change to Alastair's analysis.
The only significant change has been to push the start point further
East, probably beyond the Dutch-German border, suggesting a path
length for the fireball of at least 1100km.
ORIONID METEORS
By Tony Markham, SPA Meteor Section Director
The Orionid Meteor shower is active during the second half of October,
with the highest rates likely during Oct 20-23. The meteors are
typically swift moving, with many leaving good persistent trains. The
peak ZHR is typically around 25-30, although stronger returns have
occurred in some years.
The Moon is at First Quarter on Oct 22, but is in the Sagittarius/
Capricornus area and although it will provide some interference while
the radiant is still low in the sky, it will not be an issue later in
the night.
Note that the Orionid radiant actually lies beyond the top left of
the main pattern of Orion, close to the border with Gemini. Be aware
also that the Orionid radiant doesn't rise until after 10pm BST and
so no Orionids will be seen before then. Rates should then increase
as the radiant altitude increases and will be best late in the night.
Alongside the Orionid activity, you may well also see a few Taurid
meteors each hour.
Charts showing the locations of the Orionid and Taurid radiants can
be found at:
http://snipurl.com/256pzla SPA SOLAR SECTION
By Richard Bailey, Solar Section Director
SEPTEMBER 2012 (edited edition) Rotation Nos. 2127, 2128
WHITE LIGHT
Activity during the month resembled that in August. A maximum of 9
AR's showed across both hemispheres until the 9th; then diminished
activity was seen until the 25th; when a surge of up to 8 AR's gave
a stronger end to the month. Between the 13th. to 19th. only one AR
was recorded in the NH, AR1566. Over the time, the SH was slightly
more active than the NH. One NH AR,1560, was by the equator, the
highest latitude ones in each hemisphere being around 25 degrees.
The return of previously seen AR's increased in number. No large AR's
were seen, SH AR1564 developing rapidly to have the most individual
spots. Faculae was seen each day in limb areas of both hemispheres.
No(protected) naked eye sunspots were seen.
Week 1: Up to 9 AR's were seen daily, mostly in the SH. NH AR1560
was by the equator, showing a loose line of small spots and with SH
AR1564, a scattered collection of them, were the two largest AR's of
the month. Both decayed during the week.
Week 2: Around the E limb on the 12th. came SH AR1569, a run of small
spots, closely followed in line by SH AR 1571, the strongest AR's of
the week.
Week 3: The two main AR's diminished as they went westwards. NH AR
1566 was the only NH AR from the 13th. to 19th.
Week 4 to end of month. Up to 8 AR's were on the disc until the
30th. when 4 were seen. Most were small, often just single sunspots.
MDF 4.00 R 53.15
H-ALPHA
As in recent months, prominences of varied shapes and sizes were to
be seen daily, similarly filaments. Numbers of both followed the AR
activity. One large horse-shoe shaped filament west of AR1579 was a
feature for some days in the last week. A small amount of minor
flare activity was reported, in addition to plaging to larger AR's.
MDF 4.86
The un-edited version of this Report can be seen on the Solar link
from the SPA homepage, accompanied by a selection of pictures of
solar activity during the month. Click on pictures to see the
original full resolution ones.
Owing to holidays, the next scheduled bulletin will be issued on
October 28.
Bulletin compiled by Clive Down
(c) 2012 the Society for Popular Astronomy
Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
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