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Tuesday, 12 March 2013

SPA ENB No. 349b


          Electronic News Bulletin No. 349b  2013 March 12

By Alan Clitherow, SPA Planetary Section Director.

While many people will be looking into the western sky shortly after
sunset, trying to catch a glimpse of comet 2011 L4 (PANSTARS), it
should be remembered that early evening twilight can be an excellent
time to observe the planets. The air can be somewhat steadier than it
would otherwise be later into the night, giving a window of improved
'seeing' conditions, allowing excellent detail to be seen on the
planets; and the same can also be true for a period as the air settles
after midnight. With this in mind, mid to late March is an excellent
time to observe Jupiter in the evening and Saturn in the early morning

As the sky darkens Jupiter is still more than 40 degrees above the
south-western horizon, showing a disc some 36 seconds of arc across
and shining brightly at magnitude -2. There have been a number of
interesting developments in the atmosphere of Jupiter very recently
and these will be on show to careful observers and imagers. Look at
the southern half of the planet; this will be seen as the 'top' part
when using a Newtonian telescope or the 'bottom' part with a refractor
or Schmidt-Cassegrain telescope when using a star diagonal to hold the
eyepiece. The large and obvious dark belt, dominating the southern
hemisphere, is the South Equatorial Belt (SEB) and you may see the
Great Red Spot (GRS) sitting in an obvious cut-out within that belt.
Looking further south (towards the nearest pole) is another narrower
dark belt, the South Temperate Belt (STB),  and it is here that recent
action has been going on. If you can, viewing through a blue filter
may improve the visibility of these features.

The STB does not currently stretch around the whole planet and at its
leading edge it is interrupted by another red spot often called
'Little Red' but more correctly known as 'Oval BA'.  This spot has
been moving around the planet slightly slower than the dark STB
element that trails it; now the STB has caught up and a titanic
atmospheric collision is under way. Precisely what will happen next is
unclear but there are likely to be a number of observable consequences
in the next month or so before this region settles down into any kind
of stability. Perhaps Oval BA will be pushed along from behind and
accelerate in its path around the planet. Perhaps this red anti-
cyclonic storm will eat into the encroaching belt behind it spawning
further giant eddies, spots or storms. Now is certainly a good time to
go outside, observe and find out! Imagers who have access to Infra-Red
pass filters or even Methane band filters may well detect the up-
swelling of new storm activity before it becomes fully visible to the
naked eye.  Around 2 hours after midnight in late March, Saturn will
be some 20 degrees up in the south; shining at around magnitude 0.3 in
the western part of the constellation of Libra.  The beautiful rings
are well displayed and the dark band known as the 'Cassini Division'
that runs around the rings should be clearly visible if the air is
steady. Markings on the planet's surface tend to be subtle; there is
a similar cloud belt system to that of Jupiter but the colder
temperatures in the upper atmosphere of Saturn tends to produce a thin
veil of methane cloud through which the banding of the lower
atmosphere is less obvious. None the less careful observation, and
imaging, will reveal those belts and, occasionally, violent pale-white
storms in the upper atmosphere. As mentioned before, this time of the
morning can have very steady 'seeing' conditions allowing observers to
make the most of Saturn's relatively low elevation above the horizon.
If you are an early-bird then I really do urge you to take the
opportunity to look.

Bulletin compiled by Clive Down

(c) 2013 the Society for Popular Astronomy

Good Clear Skies
Colin James Watling
Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
Lyra Website:
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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