View Full Version : Parsecs

2003-Dec-19, 12:44 AM
What is the purpose of a Parsec, who named a parsec a parsec. And why is it 3.26 ly?


2003-Dec-19, 12:58 AM
"a non-metric unit of distance used in astronomy. As the Earth makes
its orbit around the Sun, nearby stars appear to shift their
positions in relation to the background of distant stars. The
shift, called the parallax of the star, is very small, less than
one arcsecond even for the nearest stars. If it can be measured,
however, then simple trigonometry can be used to find the distance
from the Earth to the star. One parsec is the distance at which a
star appears to shift its position by one arcsecond over the course
the time (about 3 months) in which the Earth moves a distance of
one astronomical unit (au) in the direction perpendicular to the
direction to the star. Using this unit makes it easy to compute
distances: the distance to a star, in parsecs, is simply one
divided by the amount of the parallax. If the parallax is 0.01
seconds, the distance is 100 parsecs. The length of
a parsec, divided by one astronomical unit (the radius of the
Earth's orbit) is the trigonometric function of the parallax called
the cotangent; from this relation we can compute that one parsec
equals 206 264.8 au. This is the same as 3.261 631 light years,
30.856 78 petameters (30.856 78 x 1012 kilometers), or about
19 173 510 000 000 miles."

too lazy to talk about it :P

2003-Dec-19, 01:48 AM
Thankyou for clearing that up. :D