Thursday, October 2, 2008

Spot the mistake! answer

Hey all! I'm so glad that exams are all over =D Now, back to our usual activities...

A few weeks ago I posted this.
Anyone managed to spot the mistake? If you couldn't, no matter, read on!

Everyone must be familiar with the terms "Big Dipper" and "Pole star", etc. both of which are supposedly useful in helping you locate the North direction and navigate your way when you're lost, as depicted in popular culture.

Now popular culture, more often than not, uses the terms interchangeably, while there is a marked distinction between the two.
A quick glance back to a diagram of the celestial sphere shows you this:

As seen, the North Celestial Pole (NCP) is the point where the entire celestial sphere, or "sky", appears to rotate about. The NCP also happens to be marked by a star of apparent magnitude 1.97, thus it appears stationary as the sky rotates about the NCP. Polaris therefore is a good pointer to the North.

Polaris aka Pole Star belongs to the asterism Little Dipper, whose picture is shown below:

Another good North pointer is the Big Dipper.

Big Dipper and Little Dipper share a little bit of resemblance, thus explain the names.

The bigger asterism, due to its close angular distance from the NCP (as seen at 2 o'clock on 1st picture), is also a good North pointer. It however does not stay motionless on the sky, and thus rotates about the NCP just like the rest. Its stars are brighter and the asterism is more recognisable than Polaris, thus Big Dipper can be used to find Polaris, then North.

As such, referring back to the image we had last time...
The image shown was that of Big Dipper, NOT Little Dipper, therefore our Pole Star appears to have been misplaced, removed from Little Dipper and placed at Big Dipper instead. Big Dipper thus is not stationary, or "always there", and as it goes, the boy deceived the poor little girl -_-
ALSO, Polaris, at an apparent magnitude of 1.97, is not "the brightest star". Our brightest star excluding the Sun would have to be Sirius of Canis Major, at apparent magnitude -1.46. For more information, just wiki.

Hope this clears up some's misconceptions!

Clear skies (:

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