# How is the distance between stars and the earth calculated?

##### 1 Answer

Using stellar parallax.

#### Explanation:

Stellar parallax is the apparent angular displacement of a star when observed from two sufficiently-spaced known locations

A convenient choice is the same observatory, with time spacing that is (sufficiently large integer) N days.

If N is the exact number of 24-hour days and

where

For conversion to light years (ly), use 1 AU =

The arc of the Earth's orbit for N days subtends N

Sample Data: N = 7,

The approximation to the distance of the star

=

= 8.259 E+06 AU

= 131.3 light years.

(It is assumed that the precision in the Radio Telescope for parallax is as good as 0.001".)