The Astronomical Size (SAF) calculator uses the small angle formula (SAF) to compute the size of an astronomical body based on the distance to the object (D) and the angle subtended (α).
INSTRUCTIONS: Choose units and enter the following:
Size (S): The calculator returns the size in Astronomical Units (ua). However, this can be automatically converted to compatible units via the pull-down menu.
Use theto compute the :
S = α • D
This is an essential step in computing distance with the parallax method. Note: some textbooks show this formula with a coefficient of 2.06 x 105. This is the equivalent to the formula used here, because vCalc makes the appropriate unit conversions from arc-seconds to radians and does not require the 2.06 x 105 coefficient.
Related Astro Calculators:
Dr. Spicklemire has an instructional YouTube video on the using the Small Angle Equation ().