Editing Visual binary (section)

===Trigonometric parallax===
In order to use this method of calculating distance, two measurements are made of a star, one each at opposite sides of the Earth's orbit about the Sun. The star's position relative to the more distant background stars will appear displaced.  The parallax value is considered to be the displacement in each direction from the mean position, equivalent to the angular displacement from observations one [[astronomical unit]] apart. The distance <math>d</math>, in [[parsec]]s is found from the following equation,
:<math> d = \frac{1}{\tan(p)} </math>
Where <math>p</math> is the parallax, measured in units of arc-seconds.<ref>{{cite book
 | author = Martin Harwit
 | title = Astrophysical Concepts 
 | date = 20 April 2000 
 | isbn = 0-387-94943-7
 | publisher = Springer
}}</ref>