Frequently Asked Questions
What units should I use?
Use the same unit for the actual size and the distance, such as kilometers and kilometers. The result is an angle, so the units cancel.
Why does the calculator use arctangent?
The arctangent form is exact for any angle, so it stays accurate even for nearby objects that span a wide angle in the sky.
How do I convert the angular size to arcseconds?
One degree contains 3600 arcseconds, so multiply the result in degrees by 3600. The calculator reports both degrees and arcseconds, since small, distant objects are easier to express in arcseconds. For example, 0.5 degrees equals 1800 arcseconds.
How big does the Moon look in the sky, and what is the Sun's angular size?
Both the full Moon and the Sun span about 0.5 degrees, roughly half a degree or about 30 arcminutes. That near-match is exactly why total solar eclipses are possible: the Moon can just cover the Sun's disk. For a quick comparison, a fingernail held at arm's length also covers about one degree, so the Moon looks about half a fingernail wide.
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Estimates for informational purposes only.
Important Disclaimer: Estimates for informational purposes only.
This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.