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Tuesday, 8 February 2011

SPA ENB No. 304

        Electronic News Bulletin No. 304   2011 February 6
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 Andrew Robertson, SPA Planetary Section Director
Note: all altitudes and timings below are given for the middle of the
month and my latitude of 52°.5 N.
JUPITER has been memorable this apparition which is now coming to
an end; it sets at 20:43.  At mid-month Jupiter will already be 2.5
hours past the meridian when the Sun sets at 17:04, but it will still be
at a tolerably healthy altitude of 30° then.  Early evening is generally
poor for planetary seeing -- the ground is cooling quickly and central
heating is coming on in houses.  However, at the risk of appearing to
contradict myself, I find that there is often about a half-hour window
just  after sunset when the seeing is very good, and I've been taking
every opportunity to grab those moments.
The SEB is fast becoming more and more prominent.
SATURN is better placed if you are able to observe throughout the
night, transiting at an altitude of 33° at 03:25.  It rises at 21:40
but does not reach 20° altitude until 00:15.  The rings are well
presented, being tilted 12°.
VENUS is fast sinking back towards the Sun, rising in the SE at 05:04.
By the time the Sun rises at 07:13 Venus is still only at an altitude
of 12°, although at mag -4.2 with a 66% gibbous phase it may still be
visible to the SSE in a clear sky.
URANUS is setting ahead of Jupiter.
MERCURY, MARS and NEPTUNE are too close to the Sun for observation.
Any reports of observations would be most welcome via:
A selection of members' images/sketches can be seen on the SPA
Planetary Section's Web Page:
According to two papers published recently, the scar that appeared in
Jupiter's atmosphere on 2009 July 19 was caused by a collision with a
small asteroid rather than with a comet.  Previously, it was thought
that the only objects that hit Jupiter were icy comets whose orbits
were perturbed by Jupiter, and that Jupiter had already cleared most
other objects, such as asteroids, from its sphere of influence.  The
scar was first noticed, as a dark spot at mid-southern latitude, by
Australian amateur astronomer Anthony Wesley.  Astronomers immediately
observed it in previously scheduled observing time at the infrared
telescope in Hawaii and obtained time for it at other observatories.
The impact was found to have warmed Jupiter's lower stratosphere by as
much as 3 to 4 °C about 42 km above its cloud tops; although 3 or 4
degrees does not sound much, it represents a large amount of energy
when it is spread over an enormous area.
Plunging through Jupiter's atmosphere, the object created a channel of
super-heated atmospheric gases and debris.  An explosion deep below
the clouds then launched debris material back along the channel, above
the cloud tops, to splash back down into the atmosphere, creating the
aerosol particulates and warm temperatures observed in the infrared.
Comparisons between the 2009 images and the Comet Shoemaker-Levy 9
results from 1994 suggest differences between the kinds of objects
that hit Jupiter.  The dark debris, the heated atmosphere, and
upwelling of ammonia were similar for this impact and Shoemaker-Levy,
but the debris plume in this case did not reach such high altitudes,
did not heat the high stratosphere, and contained signatures for
hydrocarbons, silica and silicates that were not seen before.  The
presence of hydrocarbons, and the absence of carbon monoxide, provide
strong evidence for a water-depleted impactor in 2009.  The newly
published papers deduce that the object was probably a rocky asteroid
rather than an icy comet.  The new conclusion is also consistent with
evidence from the Hubble telescope that the impact debris in 2009 was
denser than debris from Comet Shoemaker-Levy 9.
Carnegie Institution
Astronomers have pushed the Hubble telescope to its limits by finding
what they believe to be the most distant object so far seen -- at a
distance of 13.2 billion light-years and an age of about 3% of the age
of the Universe.  The dim object is a compact galaxy made of blue stars
that existed 'only' 480 million years after the Big Bang; it is tiny
-- over 100 such mini-galaxies would be needed to make up our Milky
Way.  It was identified in the Hubble infrared 'ultra-deep field' --
data taken in the late summers of both 2009 and 2010 -- as a faint dot
of starlight.  It is visible only at the farthest-infrared wavelengths
observable by Hubble, suggesting that the expansion of the Universe
has reddened its light more than that of any other galaxy previously
identified in the field.  Astronomers are surprised to have found only
one; that may indicate that the Universe was changing very rapidly in
early times.  Previous searches had found 47 galaxies at somewhat
later times, when the Universe was about 650 million years old.  The
Carngie Institution item reported here somehow deduces from those
figures that the rate of star birth increased by about ten times while
the Universe aged by about a third, but the statistics are in any case
more than slightly shaky when they depend upon only one object.
The 'NanoSail-D' spacecraft has unfurled a sheet of space-age fabric
650 km above the Earth, becoming the first solar sail in Earth-orbit.
NanoSail-D spent the previous month and a half stuck inside its mother
ship, the Fast, Affordable, Science and Technology SATellite
(FASTSAT).  FASTSAT was launched in November with NanoSail-D and five
other experiments onboard.  In orbit, a spring was supposed to push
the 30 x 10 x 10-cm probe into an orbit of its own with room to unfurl
a sail.  But when the moment arrived, NanoSail-D became stuck in what
was seen as another failure in the long and troubled history of solar
sails.  (This one is actually NanoSail-D2; D1 was lost when its
launching rocket failed to reach orbit.)  The engineering team on the
ground began to give up hope as weeks went by and NanoSail-D remained
stubbornly and inexplicably onboard, but on January 17, for unknown
reasons, it spontaneously ejected itself.  It still had actually to
unfurl its sail.  That happened on January 20 and was set off by an
onboard timer: a wire burner cut the piece of fishing line holding the
spacecraft's panels closed and a second wire burner released the
booms.  Within seconds they unrolled, spreading a thin polymer sheet
of reflective material into a 10-square-metre sail.  Only one
spacecraft has done such a thing before: Japan's IKAROS probe deployed
a solar sail in interplanetary space and used it to fly by Venus in
2010.  IKAROS is using the pressure of sunlight as its primary means
of propulsion -- a landmark achievement, which has encouraged JAXA to
plan a follow-up solar-sail mission to Jupiter.  NanoSail-D will
remain much closer to home: its mission is to circle the Earth and
investigate the possibility of using solar sails as a tool to de-orbit
old satellites and space junk.  The sail's orbit skims the top of our
atmosphere, and the aerodynamic drag will bring it down.  Mission
planners expect it to return to Earth, meteor-style, in 70 to 120
The Channel Island of Sark has been recognised for the quality of its
night sky by the International Dark-sky Association (IDA), which has
designated it the world's first dark-sky island, the latest in a
select group of dark-sky places around the world.  The announcement
was hailed as a great success by astronomers.  Sark has no public
street lighting, and there are no paved roads or cars, so it does not
suffer from the effects of light pollution in the same way as towns
and cities do.  Many local residents and businesses have altered their
lighting to make them more sky-friendly, ensuring that as little light
as possible spills upwards,
2011 January
Rotations Nos. 2105, 2106
Much cloudy weather again hampered observers through the month.
NH AR 1140 was in view for the first few days, a fine spot, with small
SH ARs 1142, 1144 and NH AR 1145 following at a distance.  NH AR 1147,
another good-sized AR, came into view at the E limb on the 16th, its
large leader showing the 'Wilson Effect' well; by the 18th it showed
as a string of small sunspots behind the leader, which had split into
three pieces.  Traces of limb faculae were occasionally seen where ARs
had been.
MDF  1.44              R   20.83
A selection of small prominences was seen through the month, but on
the 18th a tall, finely shaped one spread northwards along the SW
limb, and on the 27th a tall complex arch stood out there.  On the
26th a large NE-limb prominence flowed as a filament onto the disc.
There was flare activity on the 9th, and on the 22nd a prominence,
filament and flare activity by AR 1147.  Flaring had been seen there
the previous day.  Plaging was seen to the larger ARs.  A full report
with high-resolution pictures can be seen on the Solar Section link
from the SPA home page.
MDF  3.82
Bulletin compiled by Clive Down
(c) 2011 the Society for Popular Astronomy
Good Clear Skies
Colin James Watling
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)

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