In Astronomy, there is a way to measure lengths in the sky (for determining the distance between two stars, for example). The units are degrees (thanks to no comply for correcting me).
If you hold your arm straight and towards the sky, your hand can be used as a rough ruler:
- 1 degree: the width of your pinky
- 5 degrees: the width of your middle three fingers, held together (ie. like a scout's salute)
- 10 degrees: the width of your fist
- 15 degrees: the distance between your pinky and index finger if they are held in a 'Y' shape
- 25 degrees: the distance between your pinky and thumb if they are held out in a 'Y' shape
You will need to calibrate your hand, using the Big Dipper (or Ursa Major). If you are not familiar with the big dipper, please refer to sockpuppet's excellent node, How to locate Polaris, the North Star for a picture. The two star on the right side of the "bowl" of the spoon are about 5 degrees apart. The two stars across from each other on the top of the bowl are about 10 degrees apart. From the right-most star in the "bowl" to the left-most star in the constellation is about 25 degrees. From the right-most star in the "bowl" to the second star in the handle from the "bowl" is about 15 degrees.
Most of this I learned at an open house at Rothney Astrophysical Observatory, outside of Calgary, Alberta, Canada. Rothney has open houses each month in the summer.