Download december 2010 - Holt Planetarium

FRIENDS OF THE PLANETARIUM NEWSLETTER – DECEMBER 2010
Season’s greetings to one and all. There are a couple of interesting astronomical events this month.
On December 21 there is a total eclipse of the Moon. The total phase of this eclipse lasts for just over
72 minutes, with the partial umbral eclipse spanning almost 3.5 hours. All stages of the total eclipse
of the Moon are visible from North America and the eastern Pacific. South America will see the
earlier stages up to totality. On the other side of the Pacific, the start of the eclipse is before Moon
rise in New Zealand. In northern parts of New Zealand to just south of Auckland, moonrise occurs
just before the onset of totality, so all parts of the total stage of the eclipse are visible. Further south
only the later parts of the total phase will be visible. More than half of the total eclipse is visible in all
of the North Island and the top half of the South Island. At Timaru the Moon rises about 1 minute
before the time of mid eclipse. Further south only the final stages of totality are visible; at
Invercargill moonrise is just over 15 minutes before the end of the total part of the eclipse. Although
this is an interesting event, it is a poor eclipse for the southern hemisphere. It occurs with the moon
at is greatest northerly declination so at its lowest in southern skies and its occurs on the shortest
night of the year.
This brings us to the second event this month,
the summer solstice. On the 22nd of December,
daylight will last more than 18 hours for all of
New Zealand. The Sun will have reached its
most southerly declination, sitting directly
above the Tropic of Capricorn at midday. Solar
activity is increasing as the Sun approaches the
peak of its latest cycle. Here is a photo of a
filament wrapping itself around the limb of the
Sun. It appears as a dark line starting just
below the centre of the disc and disappearing
around the lower left edge. This filament is a
strand of solar plasma that has been ejected
from the surface and is caught up in magnetic
field lines emanating from the solar interior. It
is more than 700,000 kms. long. That’s almost
twice the distance from the Earth to the Moon.
Don’t forget your sunblock!
The short hours of darkness mean that planet
viewing is very limited this summer. Mercury
and Mars have disappeared in to the western evening twilight. Venus and Saturn are in the morning
sky with Venus being the more easily visible of the two. Venus will move to the east through the
stars, taking it from Virgo in to Libra while Saturn remains in Virgo. Jupiter dominates the
northwestern night sky. It will be the brightest star like object in the evening sky and so be an easy
and obvious target for viewing throughout the summer.
Stripes are back in season on Jupiter. New
NASA images support findings by amateur
astronomers that one of Jupiter's stripes that
"disappeared" last autumn is now showing
signs of a comeback. After follow-up
observations in Hawaii with NASA's Infrared
Telescope Facility, the W.M. Keck
Observatory and the Gemini Observatory
telescope, scientists now believe the
vanished dark stripe is indeed returning.
Every few decades or so, the South
Equatorial Belt turns completely white for
perhaps one to three years, an event that has
puzzled scientists for decades. This extreme
change in appearance has only been seen
with the South Equatorial Belt, making it
unique to Jupiter and the entire solar system.
Scientists are particularly interested in
observing this latest event because it's the
first time they've been able to use modern instruments to determine the details of the chemical and
dynamical changes of this phenomenon. Observing this event carefully may help to refine the
scientific questions to be posed by NASA's Juno spacecraft, due to arrive at Jupiter in 2016. The event
also signifies another close collaboration between professional and amateur astronomers. The white
band wasn't the only change on the big, gaseous planet. At the same time, Jupiter's Great Red Spot
became a darker red colour.
Last month, NASA’s Deep
Impact EPOXI spacecraft
flew past the unusual comet
Hartley 2. It is unusual not
only for its odd shape but
also because it is
experiencing a significant
winter snowstorm. Deep
Impact photographed the
unexpected tempest when
it flew past the comet's
nucleus on Nov. 4th at a
distance of only 700 km. At
first, researchers only
noticed the comet's hyperactive jets. The icy nucleus is studded with them, flamboyantly spewing
carbon dioxide from dozens of sites. A closer look revealed an even greater marvel, however. The
space around the comet's core is glistening with chunks of ice and snow, some of them possibly as
large as a basketball. The 'snowstorm' occupies a roughly spherical volume centered on Hartley 2's
spinning nucleus. The dumbbell-shaped nucleus, measuring only 2 km from end to end, is tiny
compared to the surrounding swarm. The ice cloud is a few tens of kilometers wide, and possibly
much larger than that. Well, it is Christmas time so let it snow, let it snow, let it snow! If you are
looking for a last minute gift idea, how about a 2011 New Zealand Astronomical Almanac. They are
available at the Planetarium for just $20. The Planetarium is open throughout the holiday season.