What do altitude and azimuth mean?

Altitude is how high an object is above the horizon, from 0° on the horizon to 90° straight overhead. Azimuth is its direction around the horizon, measured clockwise from north: 0° north, 90° east, 180° south, 270° west. Together they tell you exactly where to look from where you stand right now.

Reading the numbers

Say an app shows Jupiter at altitude 35°, azimuth 120°:

1. Face north, then turn a third of the way towards south through east. 120° is between east (90°) and south-east (135°).
2. Hold your fist at arm’s length on the horizon. Each fist is about 10°. Stack three and a half fists.
3. The bright point there is Jupiter.

Hand measures at arm’s length

Hand shape	About
Little finger	1°
Three middle fingers	5°
Fist	10°
Spread hand, thumb to little finger	20°

They work for adults and children alike, because longer arms come with bigger hands.

Why the values change

These coordinates are local. The sky turns about 15° an hour, so a star’s altitude and azimuth change through the night, and a friend in another city sees different numbers at the same moment. Star charts use right ascension and declination instead, which stay fixed to the sky.

A handy check: the altitude of Polaris is roughly your latitude in the northern hemisphere.

In Sky Map

Sky Map (my app) shows altitude and azimuth for stars and planets, alongside the live AR view over the camera. If the AR view seems off, the numbers give you a second way to aim. A compass that needs calibrating is the usual cause; see fixing compass and AR drift.

More: the Sky Map guides.