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sábado, 10 de marzo de 2012

Tonight for March 11, 2012 How to see the Big Dipper

How to see the Big Dipper

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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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