Astronomical distances

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  • Created on: 02-09-13 16:45
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Astronomical Distances
1 astronomical unit (AU) is equal to 1.496x1011m
One astronomical unit is the mean distance from the centre of the Earth to the centre of the Sun. It is
used whilst studying the Solar System. The Earth's orbit is elliptical so at the start of the year the
distance between the Earth and the sun is 1.471x1011 whereas later on in the year it is slightly further
away, 1.521x1011. The average of these results is 1.496x1011m.
1 Light Year is equal to 9.461x1015
The light year is the distance light will travel through a vacuum in one year. It is not measured in time it
is measured in distance. To work out 1 light year you multiply the number of days in a year, 365.25
by how many seconds there are in a day x24x60x60, and then times that by the speed of light.
X2.9979x108. It's just Distance=Speed X Time.
The Parsec
To work out the distances between stars a triangulation method was used. The length of B
was taken and the angle A and C were measured. This enabled the distances of C and A to be
measured. However both angles A and C are always 900 instead a length of two astronomical
units are used. (2AU) The angles will always be small.
You then get an equation of sin=2AU/X and the distance (X) = 2AU/ where the angle is
measured in Radians.
The Parsec is a unit related directly to this method of Astronomical distances. It is a
shortening of parallax of one second. It is the distance away an object must be to have a
parallax of one arc second when observed.
An arc second is 3600th of a degree
An arc minute is 60th of a degree
1 Parsec (1pc)= 2.1x105 AU
1 Parsec (1pc)= 3.3 light years
1 Parsec (1pc)= 3.1x1012m


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