Chapter 1 of 10/5 min read
Finding your way in the sky
Cardinal points, height above the horizon and how to measure the sky with your hand.
Two pieces of information are enough to say where something is in the sky: its direction along the horizon (north, east, south, west) and its altitude, how high it is above the horizon, from 0° (on the horizon) to 90° (the zenith, straight overhead).
Finding the cardinal points
- The Sun rises roughly in the east and sets roughly in the west; exactly so only at the equinoxes.
- In the northern hemisphere the Sun is towards the south at midday.
- At night, in the northern hemisphere, Polaris marks north to within one degree.
- A phone compass works, but keep it away from metal objects.
Measuring the sky with your hand
With your arm fully stretched, your hand becomes a protractor: the ratio between arm and hand is similar for almost everyone.
- Your little finger covers about 1° (twice the width of the full Moon).
- Three fingers together cover about 5°.
- A closed fist covers about 10°.
- An open hand, thumb to little finger, covers about 20–25°.
When GAIA says "low in the east, 10° above the horizon", it means one fist above the horizon towards the east.