The Antelope Valley Observatory

Hoping to pique the interest of all who enter in astronomy and the related sciences

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Astronomy by the numbers

Here are some simply formulae that every amateur astronomer should know. All dimensions are in millimeters unless otherwise noted.

Aperture Gain; Objective #1 diameter divided by Objective #2 diameter Quantity squared. (Objective #1 diameter/Objective #2) squared

Dawes Limit; 4.56 seconds of arc divided by Objective diameter in inches

Exit Pupil; Objective diameter divided by Magnification Or Eyepiece focal length divided by Telescope focal ratio

Focal Ratio; Focal length divided by aperture equals the focal ratio (Fl/A)

Magnification; Focal length of the scope (Fl) divide by focal length of the eyepiece (fl). Fl/fl=magnification Or Telescope Aperture divided by Exit Pupil. A/exit pupil

True Field; In degrees... Eyepiece Apparent Field of View divided by Magnification. OR Eyepiece field stop divided by Telescope Focal length times 57.3 degrees

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