NOCTILUCENT CLOUDS ACCORDING TO NASA
NASA
-- or DON'T BELIEVE EVERYTHING YOU ARE TOLD
[Part of the editing of the first paragraph has been left explicit.]
Noctilucent clouds are a mystery dating back to the late 19th century.
[Not so -- their nature has been known for a long time -- ED.}.
Northern sky watchers first noticed them in 1885, about two years
after the eruption of Krakatoa. Ash from that Indonesian volcano
caused such splendid sunsets that evening sky-watching became a
worldwide pastime. One observer in particular, a German named
T.W. Backhouse [Not so -- he was born, lived, and died, in Sunderland.
He published a paper in Astronomische Nachrichten, but that did not
make him a German! -- ED.], who is often credited with the discovery
of NLCs, noticed something odd. He stayed outside longer than most
people, long enough for the twilight to fully darken, [an
extraordinary thing for NASA to say about an astronomer! -- ED.] and
on some nights he saw wispy filaments glowing electric blue against
the black sky. [He was very observant, and had very acute sight, as
witness the facts that (a) he discovered the Gegenschein for himself,
and routinely observed it, from Sunderland, and (b) he published a
catalogue of the 9842 stars that he said were "very conspicuous" to
the naked eye -- far more than most people could hope to see even
from a dark site; the number *now* visible from Sunderland is probably
about 30!] Scientists of the day figured [a NASA expression normally
expurgated from these Bulletins] that they were some manifestation of
volcanic dust. Eventually Krakatoa's ash settled and the sunsets
faded, but the noctilucent clouds didn't go away. They're still
present today, stronger than ever. [Not so: they can be seen only
for 6--8 weeks on either side of the summer solstice,when they are
illuminated by sunlight shining 'over the Pole'.] Researchers aren't
sure what role Krakatoa's ash played in those early sightings. One
thing is clear, however: the dust behind [i.e. in] the clouds we see
now is space dust. The researchers used the Solar Occultation for
Ice Experiment (SOFIE) and found that about 3% of each ice crystal in
a noctilucent cloud is meteoritic. The inner Solar System is littered
with meteoroids of all shapes and sizes -- from asteroid-sized chunks
of rock to microscopic specks of dust. Every day the Earth scoops up
tons of the material, mostly the small stuff. When meteoroids hit our
atmosphere and burn up, they leave behind a smoke of tiny particles
suspended 70 to 100 km above the surface -- the height of NLCs.
Specks of meteor smoke act as gathering points where water molecules
can assemble themselves into ice crystals. The process is called
nucleation. Nucleation happens all the time in the lower atmosphere.
In ordinary clouds, airborne specks of dust and even living microbes
can serve as nucleation sites. Tiny ice crystals, drops of water, and
snowflakes grow around such particles, falling to earth if and when
they become heavy enough. Nucleating agents are especially important
in the rarefied realm of NLCs. The clouds form at the edge of space
where the air pressure is very small. The odds of two water molecules
meeting is slim, and of sticking together slimmer still. Meteor smoke
helps them to do so. According to Aeronomy of Ice in the Mesosphere
(AIM) data, ice crystals can grow around meteoritic dust to sizes
ranging from 20 to 70 nanometres. For comparison, cirrus clouds in
the lower atmosphere, where water is more abundant, contain crystals
10--100 times larger. The small size of the ice crystals explains the
NLCs' blue colour: small particles scatter short wavelengths of light
(blue) more strongly than long wavelengths (red). Meteor smoke
explains much about NLCs, but not why the clouds seem to be
brightening and spreading. They used to be seen only between about
50° and 70° latitude, but in recent times they have been observed from
latitudes as low as 40°. There has been a suggestion that that is due
to the increase in the atmosphere of the 'greenhouse gas' methane,
which comes from landfills, natural gas and petroleum systems, farming
activities, and coal mining. In the upper atmosphere it is oxidized
by a complex series of reactions to form additional water vapour,
which is then available to grow ice crystals for NLCs.
PLENTY OF DARK MATTER NEAR THE SUN
RAS
Astronomers have found large amounts of invisible 'dark matter' near
the Sun. Their results are consistent with the idea that the Milky
Way galaxy is surrounded by a massive halo of dark matter, but this is
the first study of its kind to use a method tested against mock data
from simulations. The team also finds tantalising hints of a new
dark-matter component in our Galaxy. Dark matter was first proposed
by the Swiss astronomer Fritz Zwicky in the 1930s. He found that
clusters of galaxies must contain a lot of dark matter, otherwise
their total mass would not be enough to keep them from flying apart.
At nearly the same time, Jan Oort in the Netherlands discovered that
the density of matter near the Sun was nearly twice what he estimated
from the probable total mass of stars and gas alone. In the decades
since, astronomers developed a theory of dark matter and structure
formation that explains the properties of clusters and galaxies in the
Universe, but the amount of dark matter in the solar neighbourhood has
remained uncertain. For decades after Oort's measurement, studies
found 3-6 times more dark matter than expected. Then last year new
data and a new method claimed far less than expected. The community
was left puzzled, generally believing that the observations and
analyses simply were not sensitive enough to perform a reliable
measurement.
In this latest study, the authors are much more confident in their
measurement and its uncertainties. [Authors always are!] That is
because they used what they considered to be a realistic simulation
of our Galaxy to test their mass-measuring technique before applying
it to the real data. They found that standard techniques used over
the past 20 years were biased, always tending to underestimate the
amount of dark matter. They devised what they claim to be an
unbiased technique and showed that it recovered the correct answer
from the simulated data. Applying that technique to the positions and
velocities of thousands of K-dwarf stars near the Sun, they obtained a
new measure of the local dark-matter density. [According to the
authors of the item reported here,] astronomers are 99% confident that
there is dark matter near the Sun. In fact, the favoured dark-matter
density is a little high. There is a 10% chance that this is merely a
statistical fluke. But with 90% confidence, they find more dark
matter than expected. [But it is odd that the item still does not tell
us how much that is.]
ASTRONOMERS UNDERSTAND 'MONSTER STARS'
RAS
In 2010 scientists discovered four monster stars in the giant star
cluster R136 in the Large Magellanic Cloud (LMC), the most massive
being more than 300 times as massive as the Sun. No such objects have
so far been found anywhere else. Now a group of astronomers at the
University of Bonn has suggested an explanation: the ultra-massive
stars were created from the mergers of stars in tight binary systems.
The LMC, at a distance of 160,000 light-years, is the third-nearest
satellite of the Milky Way galaxy and has many star-forming regions.
By far the most active one is the Tarantula Nebula, also known as the
30 Doradus (30 Dor) complex -- a region 1000 light-years in diameter,
near the centre of which is R136. R136 is by far the brightest
stellar nursery not just in the LMC but in the entire 'Local Group' of
more than 50 galaxies (including our own).
Until 2010, observations of the Milky Way and other galaxies suggested
a universal upper limit for the masses of stars of about 150 times the
mass of the Sun. In an effort to understand the exceptional case of
R136, the Bonn team modelled the interactions between stars in an
R136-like cluster. Their simulations assembled the model cluster star
by star, so as to resemble the real cluster as closely as possible,
creating a cluster of more than 170,000 stars packed closely together.
At the outset it was ensured that the stars all conformed to a normal
mass distribution. Such highly intensive, star-by-star calculations,
known as 'direct N-body simulations', are the most reliable and
accurate way to model clusters of stars. The Bonn researchers used
the N-body integration code NBODY6, developed by S.J. Aarseth at the
Institute of Astronomy in Cambridge, and used video-gaming cards --
operating much faster than mere scientific hardware! -- installed in
otherwise ordinary workstations. Cluster simulations are complicated
by the effects of the energy released by each star and what happens
when two stars happen to collide, a frequent event in a crowded
environment. When the calculations were done, the origin of the
ultra-massive stars was clear. They start appearing very early in the
life of the cluster. With so many massive stars in tight binary
pairs, themselves packed closely together, there are frequent random
encounters, some of which result in collisions where two stars
coalesce. The resulting stars can quite easily end up being as
massive as those seen in R136.
GALAXY CLUSTER FORMS STARS AT RECORD PACE
Chandra X-ray Center
Astronomers have been observing the Phoenix cluster, which is about
5.7 billion light-years away and is one of the largest objects in the
Universe, with the Chandra X-ray observatory and several ground-based
telescopes. While galaxies at the centres of most clusters appear to
have been largely dormant for billions of years, the central galaxy in
the Phoenix cluster seems to have come back to life with a new burst
of star formation. Like other clusters, Phoenix contains a vast
reservoir of hot gas, which itself holds more normal matter -- not
dark matter -- than all of the galaxies in the cluster combined. The
reservoir can be detected only with X-ray telescopes. It used to be
thought that the gas should cool over time and sink to the galaxy at
the centre of the cluster, forming huge numbers of stars, but in fact
most clusters seem to have formed very few stars during the last few
billion years. Astronomers now think that the super-massive black
hole that probably exists in the central galaxy of a cluster pumps
energy into the system, preventing cooling of the gas from causing a
burst of star formation. The well-known Perseus cluster is an example
where jets emanating from a black hole are releasing a lot of energy
and preventing the gas from cooling to form stars at a high rate.
It seems, however, that not all clusters are subject to the same
inhibition. With the Phoenix cluster not producing powerful enough
jets to prevent star formation, its centre is teeming with stars that
are forming about 20 times faster than in the Perseus cluster. The
rate is the highest seen in the centre of a cluster of galaxies, but
is not actually the highest seen anywhere in the Universe. However,
other areas with the highest rates of star formation, located outside
clusters, have rates only about twice as high. The frenetic pace of
star birth and cooling of gas in the Phoenix cluster is causing the
galaxy and the black hole to add mass very quickly -- an important
phase that researchers say must be relatively short-lived, otherwise
the galaxy and black hole would become much bigger than their
counterparts in the 'nearby' Universe.
CHINESE LAUNCHER TO SEND SPANISH ROVER TO THE MOON
RAS
A Barcelona-based company, Galactic Suite, leading the industrial
conglomerate Barcelona Moon Team, has signed a launch-service contract
for a Chinese rocket to carry a Spanish robot to the Moon in 2014
June to attempt to win the $30 million Google Lunar X Prize. That
prize, the largest incentivized competition offered to date,
challenges space professionals and engineers from across the globe to
build and launch to the Moon a privately funded spacecraft capable of
completing a series of exploration and transmission tasks. The prize
is one of four active competitions from the X Prize Foundation, the
leading non-profit organization for creating and managing large-scale,
global incentivized competitions.
The contract states that China will provide the services of a Long
March 2C launcher with an upper stage CTS2 for insertion into the
lunar transfer orbit. The launcher will carry the Spanish lander
module that, once released, will make the correction and deceleration
operations for insertion into lunar orbit before landing. The team
has designed its mission to carry up to 25 kg of additional payload
besides the rover participating in the competition. The extra
payload is offered to universities, commercial or pharmaceutical
companies, and national agencies, which can see the Spanish mission as
a demonstration mission for future operations on the Moon.
PERSEIDS 2012
By Tony Markham, SPA Meteor Section Director
Although the moonlight prospects for the 2012 Perseids were more
favourable than those of 2011, the weather was doing no favours for UK
observers, with most areas enduring a high proportion of cloudy
nights. For the nights closest to maximum, Aug 10-11, 11-12 and
12-13, there was cloud across much of the UK, but on each night there
were some areas with at least some cloud breaks. However, it appears
that no-one had the long clear spells that are so desirable for meteor
observing. Some observers have already reported their observations
via the SPA Forum or have mailed them directly to me. If you still
have Perseid observations to report, please do so as soon as possible.
Fortunately, meteor observing is coordinated internationally nowadays
and we can look to the International Meteor Organisation's live
Perseid ZHR graph (
http://imo.net/live/perseids2012 ) for an early
indication as to what we in the UK were largely missing. The early
indications are that the peak ZHR in 2012 was around 80-90 and
occurred, as predicted, during the daytime of Aug 12. That would make
it a fairly typical Perseid return and somewhat better than the
peak ZHR of around 60 that occurred in 2011.
CENTENARY OF THE BIRTH OF GEORGE ALCOCK
By Tony Markham, SPA Meteor Section Director
2012 August 28 marks the centenary of the birth of George Alcock
(1912-2000), one of the UK's greatest amateur astronomers. From the
1930s to the early 1950s, Alcock was a prolific meteor observer.
In the mid 1950s, however, he switched his efforts to searching for
comets, and five discoveries bear his name. From the mid 1960s, he
also started memorising the star patterns visible through binoculars
-- a momentous task -- and through careful sweeping of the night sky
on every clear night went on to discover five novae.
Below is a summary of his discoveries:
1959 Comet C/1959 Q1 (Alcock) = 1959e. Discovered August 24
1959 Comet C/1959 Q2 (Alcock) = 1959f. Discovered August 30
1963 Comet C/1963 F1 (Alcock) = 1963b. Discovered March 1
1965 Comet C/1965 S2 (Alcock) = 1965h. Discovered September 26
1967 HR Del = Nova Del 1967. Discovered July 8
1968 LV Vul = Nova Vul 1968 No 1. Discovered April 15
1970 V368 Sct = Nova Sct 1970. Discovered July 31
1976 NQ Vul = Nova Vul 1976. Discovered October 21
1983 Comet C/1983 H1 (IRAS-Araki-Alcock) = 1983d. Discovered May 3
1991 V838 Her = Nova Herculis 1991. Discovered March 25
A fuller account of his achievements can be found at
http://martinmobberley.co.uk/Alcock.html
Topic: Late August astronomy bulletin (Read 1361 times)