@stro object for the week of 04/17/2000
(c) 1997 Roger D. Herzler
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
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.
information for Polaris (Northern Hemisphere):
Approximately 384 light-years +/- 54 LY
APOD of Polaris...
on Cepheid Variables...