The SOCIETY for POPULAR ASTRONOMY Electronic News Bulletin No. 375

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                    The SOCIETY for POPULAR ASTRONOMY
              Electronic News Bulletin No. 375  2014 May 4

    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
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    Data from the AIM spacecraft (described below) have been interpreted
    as indicating 'teleconnections' in the Earth's atmosphere that stretch
    from the North Pole to the South Pole and back again, linking weather
    and climate more closely than simple geography would suggest.  For
    example, scientists have found that the winter air temperature in
    Indianapolis, Indiana, is well correlated with the frequency of
    noctilucent clouds over Antarctica.  Noctilucent clouds (NLCs) are the
    highest type of cloud.  They form at the edge of space, 83 km above
    the polar regions, in a layer called the mesosphere.  Seeded by
    'meteor smoke', NLCs are made of tiny ice crystals that glow electric
    blue in sunlight.
    AIM was launched in 2007 to investigate NLCs, to discover how they
    form and to learn about their chemistry.  As is often the case,
    however, when exploring the unknown, researchers found something they
    weren't looking for — teleconnections.  When the AIM mission was
    being planned, attention was focused on a narrow layer of the
    atmosphere where NLCs form.  Now scientists are finding that the layer
    manifests evidence of long-distance connections in the atmosphere far
    from the NLCs themselves.  One connection links the Arctic
    stratosphere with the Antarctic mesosphere.  Stratospheric winds over
    the Arctic control circulation in the mesosphere.  When northern
    stratospheric winds slow down, a ripple effect around the globe causes
    the southern mesosphere to become warmer and drier, leading to fewer
    NLCs.  When northern winds pick up again, the southern mesosphere
    becomes colder and wetter, and the NLCs return.
    This January, a time of year when southern NLCs are usually abundant,
    the spacecraft observed a sudden decline in the clouds.  About two
    weeks earlier, winds in the Arctic stratosphere were strongly
    perturbed, leading to a distorted polar vortex.  It is *believed* that
    that triggered a ripple effect that led to a decline in noctilucent
    clouds half-way round the world.  The same polar vortex made headlines
    in the USA last winter when parts of that country experienced unusual
    cold.  Researchers found that there was indeed a statistical link
    between winter weather in the USA and the decline in noctilucent
    clouds over Antarctica.  In many northern US cities cold air
    temperatures on the ground were correlated with NLC frequencies high
    above Antarctica two weeks later.  The two-week delay is, apparently,
    the time it takes for a signal to propagate through three layers of
    atmosphere (the troposphere, stratosphere and mesosphere), and from
    pole to pole.
    [Note by editor: The above item alleges a seemingly improbable
    statistical correlation, for which no plausible mechanism is
    suggested, that involves a fortnight's delay.  If the alleged
    correlation really exists, the delay provides an opportunity to test
    its reality by forecasting Antarctic NLC frequencies a fortnight in
    advance from the weather experienced in the USA.  It would have been
    so easy to make such a simple and obvious test of what is being
    alleged that one might expect that it would have been undertaken and
    its results described before this item was rushed into print.  It is
    easy to look for, and sometimes to find, temporary apparent
    correlations between things that can not really be connected at all.
    There are so many different things that one can try to correlate that
    it is inevitable that there will be coincidental 'successes' from time
    to time.  I remember seeing on one occasion a supposedly convincing
    correlation between the appearance of new large sunspots and the dates
    of matinees of the Folies Bergere!  But when the next season's
    programme was to hand and the dates of matinees known, those dates
    ought to have been (but weren't, as far as I know) promulgated to
    astronomers as forecasts of the dates of appearance of new large
    sunspots.  No doubt that was hardly worth doing, since the forecasts
    would have been bound to fail.  If the correlation had held up season
    after season I feel sure that we should have heard a lot more about it
    by now.]


    The Cassini spacecraft has documented the formation of a small icy
    object within the rings of Saturn.  Astronomers think they may be
    looking at the act of birth, where this object is just leaving the
    rings and heading off to be a moon in its own right.  Images taken
    with Cassini's narrow-angle camera on 2013 April 15 show disturbances
    at the very edge of Saturn's A ring — the outermost of the planet's
    large, bright rings.  One of the disturbances is an arc about 20%
    brighter than its surroundings, 1200 km long and 10 km wide.
    Scientists also found unusual protuberances in the usually smooth
    profile at the ring's edge, and believe that the arc and protuberances
    are caused by the gravitational effects of a nearby object.  The
    object is not expected to grow any larger, and may even be falling
    Cassini's orbit will move closer to the outer edge of the A ring in
    late 2016 and provide an opportunity to study the postulated object,
    which is too small to see in images so far; it is estimated to be no
    more than about a kilometre in diameter.  Saturn's icy moons range in
    size more or less according to their proximity to the planet — the
    farther from the planet, the larger.  And many of Saturn's moons are
    comprised primarily of ice, as are the particles that form Saturn's
    rings.  Researchers recently speculated that the icy moons formed from
    ring particles and then moved outward, away from the planet, merging
    with other moons on the way.  The theory holds that Saturn long ago
    had a much more massive ring system capable of giving birth to larger
    moons.  As the moons formed near the edge, they depleted the rings.
    It is possible that the process of moon formation in Saturn's rings
    has ended with this object, as Saturn's rings now are, in all
    likelihood, too depleted to make more moons.
    [Note by editor: Received wisdom used to be exactly the reverse of
    what is now being suggested: it was that the rings are the debris of
    satellites that were tidally disrupted by Saturn when they approached
    within the Roche limit.  That idea did at least provide a plausible
    origin for the rings, whereas the item above seems to take the rings
    for granted as being just a natural source of material for the
    manufacture of new satellites, without any concern for how the
    material got there in the first place.  And the cheerful way in which
    unidentified astronomers are said to suggest that a moon can form and
    then be “just leaving the rings and heading off to be a moon in its
    own right”, as if it had its own motor, could choose its own
    itinerary, and could just go where it likes without there being any
    dynamical reason that would make its path differ from the paths of the
    rest of the ring particles, hardly inspires confidence in any
    scientific underpinning that there may be for this report.]


    The Wide-field Infrared Survey Explorer (WISE) and Spitzer Space
    Telescope have discovered what appears to be the coldest brown dwarf
    known — a dim, star-like body that, surprisingly, is as frosty as the
    Earth's North Pole.  Named WISE J085510.83-071442.5, the brown dwarf
    appears to be 7.2 light-years away, making it the fourth-closest
    system to us.  It has a temperature between -48 and -13°C.  Previous
    record-holders for the coldest brown dwarfs, also found by WISE and
    Spitzer, were about room temperature.  WISE was able to spot the
    object because it surveyed the entire sky twice in infrared light.
    Cool objects like brown dwarfs can be invisible when viewed by
    visible-light telescopes, but their thermal glow — even if feeble —
    stands out in infrared light.  In addition, the closer a body, the
    more it may appear to move in images taken months apart.  After
    noticing the fast motion of the WISE object, astronomers spent time
    analyzing additional images taken with Spitzer and the Gemini South
    telescope in Chile.  Spitzer's infrared observations helped determine
    the temperature of the brown dwarf.  Combined detections from WISE and
    Spitzer, taken from different positions around the Sun, gave the
    object's parallax, and thus its distance.
    The WISE object with the long name appears to be 3 to 10 times the
    mass of Jupiter.  With such a low mass, it could be a gas giant
    similar to Jupiter that was ejected from its star system.  But
    scientists think [this is what the item says; I am not making it up —
    ED.] it is probably a brown dwarf rather than a planet, on the
    [remarkably weak] grounds that brown dwarfs are known to be fairly
    common.  If so, it is one of the least-massive brown dwarfs known.


    55 Cancri is a star bright enough to be seen with the naked eye, with
    a planetary system.  Its radial velocity has been measured at four
    different observatories over a thousand times in total, giving the
    planets in that system much more attention than most exo-planets
    receive.  Astronomers first discovered that 55 Cancri is orbited by a
    giant planet in 1997.  Long-term observations later detected five
    planets orbiting the star, ranging from a cold giant planet with an
    orbit very similar to that of Jupiter to a scorching-hot “super-Earth”
    — a type of planet with a mass more than the Earth's but much less
    than that of Neptune, which has a mass 17 times greater than the
    Numerous studies since 2002 had failed to identify a plausible model
    for the masses and orbits of two giant planets located closer to 55
    Cancri than Mercury is to the Sun.  Astronomers had struggled to
    understand how those massive planets orbiting so close to their star
    could avoid a catastrophe such as one planet being flung into the
    star, or the two planets colliding with each other.  Now, a new study
    led by Pennsylvania State University has combined thousands of
    observations with new statistical and computational techniques to
    measure the planets' properties more accurately, showing that their
    particular masses and orbits are preventing the system from
    self-destructing at all soon.  The 55 Cancri planetary system is
    unique both in the diversity of its known planets and the number and
    variety of astronomical observations.  The complexity of the system
    makes it unusually challenging to interpret the observations.  In
    order to perform the new analyses, astronomers collaborated with
    computer scientists to develop a tool for simulating planetary systems
    using graphics cards to accelerate the computations.  By combining
    multiple types of observations, the Penn State astronomers determined
    that one of the planets in the system (55 Cnc e) has eight times the
    Earth's mass, twice the Earth's radius, and thus the same mean density
    as the Earth.  The planet is far too hot to have liquid water, as its
    surface temperature is estimated to be 2100°C.  It was only in 2011,
    8 years after the discovery of 55 Cnc e, that astronomers recognised
    that it orbits its star in less than 18 hours, rather than nearly
    3 days, as originally thought.  Soon after, astronomers detected the
    planet in transit in front of the star, allowing them to measure the
    relative size of the planet too.
    The two giant planets of 55 Cancri interact so strongly that we can
    detect changes in their orbits.  The rapid interactions between the
    planets present a challenge, since modelling the system requires time-
    consuming simulations for each model to determine the trajectories of
    the planets and therefore the likelihood of their survival for
    billions of years without a catastrophic collision.  One must account
    precisely for the motions of the giant planets in order to measure the
    properties of the super-Earth-mass planet.  Most previous analyses had
    ignored the planet-planet interactions.  A few earlier studies had
    modelled those effects, but had performed only simplistic statistical
    analyses owing to the huge number of calculations required for a
    proper analysis.


    The Universe we can see is made up of billions of galaxies, each
    containing anywhere from hundreds of thousands to hundreds of billions
    of stars.  Large numbers of galaxies are elliptical in shape, red and
    mostly made up of old stars.  Another (more familiar) type is the
    spiral, where arms wind out in a blue thin disc from a central red
    bulge.  On average stars in spiral galaxies tend to be much younger
    than those in ellipticals.  Now a group of astronomers has found a
    (relatively) simple relationship between the colour of a galaxy and
    the size of its bulge — the more massive the bulge the redder the
    galaxy.  The team used data from the Sloan Digital Sky Survey to group
    together over half a million galaxies of all different colours,
    shapes, and masses.  They then used pattern-recognition software to
    measure the shape of each one, to see how the proportion of red stars
    in a galaxy varies with its other properties.  They found that the
    mass in the central bulge (regardless of how big the disc surrounding
    it may be) is the key to knowing the colour of the whole galaxy.
    Above a given bulge mass, galaxies are red and have no new young
    stars.  Almost all galaxies have massive black holes at their centres.
    The mass of the bulge is closely related to the mass of the black
    hole; the more massive the black hole the more energy is released into
    the surrounding galaxy in the form of powerful jets and X-ray
    emission, which can blow away and heat up gas, stopping new stars from
    forming.  Thus a relatively simple result, that large galaxy bulges
    mean red galaxies, has profound consequences: big bulges mean big
    black holes, which can put an end to star formation.

    Bulletin compiled by Clive Down

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