How to Easily Measure Angles on the Sky

An easy way to measure angles on the sky (e.g. when you learn sky naked-eye, or when you want to narrow a position) is to use the following tricks:

• closed fist, at arm's length is 10° on the sky
• closed fist, thumb stretched, at arm's length, is 15°
• hand, fingers stretched, at arm's length, is 25° between thumb and last finger

For smaller scales:

• fingertip, at arm's length, is 1° on the sky (this, by the way, means that a fingertip may hide Sun -don't try! Sun is dangerous! check at our dedicated tutorial- or the Moon. These two bodies indeed are just ½° on the sky whatever larger their brightness may make them look like. This, by the way, allows another trick: Moon has a diameter of ½° and this may be used for quick and small angles assessments, or during a moon or a sun eclipse
• thumb, at arm's length, is 2.5° on the sky

Celestial hints:

• the Great Dipper's width is 25° from the end of the handle to the last side of the bucket
• the Orion's Belt is 3° wide
• the distance between Pollux and Castor, of Gemini, the Twins, is 5°
• note: one hour of R.A. (right ascension) is worth 15°

Much useful!