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Small-angle formula
The small-angle formula is a mathematical approximation, used in astronomy. It relates the linear size (D) of an object to its angular size (α) and its distance from the observer (d) and is a valid approximation if α is small.
The approximate formula is:
- D = α d / 206,265
Here, α has to be measured in arcseconds.
The number 206,265 is approximately equal to the number of arcseconds in a circle (1,296,000), divided by 2π.
The exact formula is
- D = 2 d tan(απ/1,296,000)
and the above approximation follows from this because tan(x) is approximately equal to x if x is small.
Last updated: 10-18-2005 07:57:11
10-26-2009 08:16:03
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details