|
|
|
A B
C D
E F
G H
I J
K L
M N
O P-Q
R S
T-U V-W-X
Y-Z
Dhruv
Taaraa
From:
http://www.fact-archive.com/encyclopedia/Polaris
Dhruv Taaraa is also known as the
"North Star", the "Lode Star", or the "Pole star", Polaris, or sometimes
"Polaris Borealis". This star is always positioned in relation to Sapt
Rishi (Great Bear or Ursa Minor). It never displaces from its place. "
Because it lies nearly in a direct line with the axis of the Earth's
rotation "above" the North Pole—the north celestial pole—Polaris is
apparently motionless from the Earth, and all the stars of the Northern
sky appear to rotate around it. "
(1) It is written
in above lines that "It is nearly in direct line" but it is not written
that it is in direct line.
(2) It is written in above lines that "Polaris is apparently motionless"
but it is not written that it is motionless.
Only this mistake has created great mess in-fact.
Polaris (α UMi / α Ursae Minoris / Alpha
Ursae Minoris) is the brightest star in the constellation Ursa Minor. It
is also very close to the north celestial pole, making it the current
north pole star (but this is only a temporary situation due to
precession).
Because it lies nearly in a direct line with the axis of the Earth's
rotation "above" the North Pole—the north celestial pole—Polaris is
apparently motionless from the Earth, and all the stars of the Northern
sky appear to rotate around it. Therefore, it makes an excellent fixed
point from which to draw measurements for celestial navigation. The
antiquity of the use of this star is attested to by the fact that it is
found represented on the earliest known Assyrian tablets. At present,
Polaris is slightly under 1° away from the pole of rotation and hence
revolves around the pole in a small circle almost 2° in diameter. Only
twice during every sidereal day does Polaris accurately define the true
north azimuth; the rest of the time it is only an approximation and must
be corrected using tables.
Although Shakespeare wrote "I am as constant as the northern star",
Dhruv Taaraa will not always be the Dhruv Taaraa. This is due to
precession of the equinox over thousands of years. Other stars have been
the pole star in the past and will be again in the future, including
Thuban and Vega.
Dhruv Taaraa is due to become an even more accurate polar star in the
near future — the distance between it and the pole will reach a minimum
(of just under 1/2 degree) in 2100.
It is easy to find Polar Star by following the line traced from Merak to
Dubhe (β and α Ursae Majoris, also known as the Pointers), the two stars
at the end of the bowl of the Big Dipper. One can also follow the
central point of the W shape of Cassiopeia.
Polaris's fame as the North Star has given rise to a persistent
misconception that it is the brightest star in the sky. Although Polaris
is a relatively bright and conspicuous star, it is nowhere near the
brightest; it is actually the 51st brightest star. In fact the brightest
star in the sky (besides the Sun) is Sirius.
Polaris is 431 light years (132 parsecs) from Earth, according to
measurements made by the Hipparcos satellite. Around 1900, the star
varied between being 8% brighter than its average luminosity and 8%
dimmer (0.15 magnitudes in total) with a 3.97 day period. As of 2005,
the variations are about 2% from peak to trough. The star is also about
15% brighter (on average) than it was in 1900; the period has also
lengthened by about 8 seconds each year since then.
Recent research reported in "Science" suggests that Polaris is 2.5 times
brighter today than when Ptolemy observed it. The astronomer Edward
Guinan considers this to be a remarkable rate of change and is on record
as saying that "If they are real, these changes are 100 times larger
than [those] predicted by current theories of stellar evolution".
There is no real southern Pole Star. The star visible to the naked eye
that is closest to the south celestial pole is the dim Sigma Octantis,
sometimes called Polaris Australis. However, the bright Southern Cross
(Crux) points towards the south celestial pole.
|