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(IAAC) Polaris : the @stro object for the week of 04/17/2000



@stro object of the week
drafted by the @stro pages
the week of 04/17/2000
highlighted this week: Polaris
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Polaris, commonly referred to as "the North Star", is a star visible in the
northern hemisphere who's most commonly known trait is that it is very close
to the North Celestial Pole (NCP). The NCP is the imaginary point in the
northern sky around which the stars seem to circle as the Earth rotates
during the night. The NCP in the sky corresponds to the North Pole on Earth.
Polaris is circumpolar meaning that it never sets so its visible all night
from sunset to sunrise. It is this property plus its closeness to the NCP
that allowed Polaris to be used as a major navigational reference point for
sailors and others who were traveling at night. Even today Polaris is used
for navigation and is often used by astronomers aligning their equatorially
mounted telescopes to the night sky.
All stars appear to "drift" very slowly through the constellations (not to
be confused with the normal nightly rotation of the Earth) and change their
absolute positions due to their motion and the Earth's motion through space.
This means that Polaris hasn't always been the "North Star" and other stars
have been closer to the NCP in Earth's history. Polaris is very close to the
NCP right now but sometime around the year 2100 it will slowly begin to
drift away from the NCP from our perspective and another star will
eventually take its place as the star closest to the NCP.
Polaris is a Class F yellow supergiant star and is a "Cepheid Variable".
Cepheid Variables are stars with a regular dimming and brightening pattern
that has earned them importance in astronomy because they can be used to
determine celestial distances. Polaris is only around magnitude 2.0 and even
though its often thought of as a "bright star", its magnitude is much lower
than some other stars in the sky. It can be difficult to see with the naked
eye in light-polluted urban environments.
Photos taken of Polaris by using the technique called "star trails" can
produce images like the example above. The star in the center of the image
that displays the least amount of trailing is Polaris.
For more information visit:
APOD of Polaris...
http://antwrp.gsfc.nasa.gov/apod/ap991006.html
more on Polaris...
http://www.astro.uiuc.edu/%7Ekaler/sow/polaris.html
more on Cepheid Variables...
http://www.windows.umich.edu/cgi-bin/tour_def/kids_space/cepheid_variable.ht
ml
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Clear skies,
Roger Herzler
the @stro pages
http://theastropages.com
Copyright (c) 2000 the @stro pages
Permission granted to reprint this article
if you include this footer with credits.
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