Tonight for March 11, 2012
While you’re gazing in awe at tonight’s very bright planets in
early evening – Venus and Jupiter close together in the direction of
sunset (west) and Mars now at its best for two years in the opposite direction (east)
– you might wonder about some other famous sky objects. Have you ever
wanted to find the Big Dipper – known as the Plough in the U.K. or, in
Hindu astronomy Saptarishi, after the seven rishis – but just
couldn’t spot this famous pattern? Then today’s chart is for you. It
shows the Big Dipper on an evening in March, ascending in the northeast
during the evening hours. See the Dipper shape? In the early evening
in March, the handle of the Dipper is pointing down toward the horizon
as it rises.
Illustrated guide to Venus and Jupiter conjunction in March 2012
How to see Mars in March 2012
The two outer stars in the Bowl of the Big Dipper always point to Polaris.
Still not sure the Pattern you’ve found is the Dipper? Try to notice
if the pattern you see matches the chart shown at right. That chart
shows a well-known trick for finding the North Star, or Polaris. That
is, the two outermost stars in the bowl of the Big Dipper point to
Polaris. Those stars are Dubhe and Merak. They are well known among
amateur astronomers as The Pointers. If you extend a line about five
times the distance between Dubhe and Merak from the star Dubhe – and don’t find a medium-bright star (Polaris) – then the pattern you see is not the Big Dipper. Keep looking.
An ancient eye test for those wishing to join the Roman army involved
spotting stars in the handle of our modern-day Big Dipper. You can take
this ancient eye test, too.
Go outside around 9 p.m. You should see the Big Dipper just off the
northeast horizon. The middle star in the “tail” of the question mark is
Mizar. If you look for a couple seconds longer, you may see a little
starry point right next to Mizar. This star is called Alcor. If you had
lived in the time of the early Romans and could see Alcor, you would
have been eligible to be an archer in the Roman army. If not, you likely
would have served in another capacity for the Caesar. It’s said that
sultans of the past also tested their soldiers’ eyesight in this way.
Mizar (brighter) and Alcor (fainter) as seen from Earth. Image Credit: ESO Online Digitized Sky Survey
Mizar and Alcor
are a “visual double” star. There are an estimated three light-years
between Mizar (78 light years away) and Alcor (81 light years away).
This three-light-year distance makes it unlikely that Mizar and Alcor
are gravitationally bound to each other. Mizar is a true multiple star,
though. It has several companion stars that are gravitationally bound to
it and revolve around it.
Bottom line: On these March 2012 evenings, while you’re watching Venus and Jupiter close together after sunset (look west) and Mars now at its best for two years (look east) – you might also spot the Big Dipper or Plough ascending in the northeast during the evening hours.
Illustrated guide to Venus and Jupiter conjunction in March 2012
How to see Mars in March 2012
http://earthsky.org
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