Measuring the distance to stars for A Level physics - parsec


parsec - distance to stars

When it comes to distances involved in the objects in space, three major units are used. They are,
  • astronomical unit
  • light-year
  • parsec
Astronomical unit - AU
This is the average distance between the Sun and the Earth.
1AU = 150 million km = 1.5 x 1011 m
The astronomical unit, AU,  is used to express the distance between the Earth and the other planets in our solar system.

Light-year - ly 
The distance travelled by light in one year is called a light-year.
1 light-year = 3 x 108 x 3600 x 24 x 365 = 9.46 x 1015 m

parsec -pc
The distance at which 1AU subtends an angle of 1 arcsecond is called a parsec.
1 arcsecond - (1/3600)°
tan (1 arcsecond) = 1AU/1pc
1 pc =  1AU x tan(1 arcsecond)
1pc = 1.5 x 1011 x tan(1 arcsecond)
1pc = 3.1 x 1016 m or 1 pc = 3.26 ly

You can calculate the angle in arcseconds and pc with the following simulation:


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