The sky is a clock that never stops. By day, you read the shadow; at night, the stars and the moon.
UNDERSTAND
The Earth spins once every twenty-four hours. From here, the whole sky turns: the sun crosses it at fifteen degrees per hour and peaks at solar noon, due south in the northern hemisphere. At that moment, shadows are at their shortest of the day.
At night, the stars turn around the Pole Star, counterclockwise when you face north. They make a full turn in a little under twenty-four hours: a quarter turn every six hours.
The moon falls behind: it rises about fifty minutes later each day. So its shape tells you where it is on its path relative to the sun, and so what time it is.
ACT
By day: the shadow of a stick
- Push a straight stick into flat ground. Mark the tip of its shadow from time to time.
- The shortest shadow is solar noon. In the northern hemisphere, it then points north.
- After that, the shadow turns clockwise (northern hemisphere), about fifteen degrees per hour on average: a bit faster around noon, a bit slower morning and evening. Once noon is marked, you have a rough sundial: a quarter turn of the shadow is roughly six hours.
Late in the day: your hand
Arm outstretched, count the fingers between the bottom of the sun and the horizon: each finger is about a quarter of an hour of daylight at mid-latitudes. See Measuring with your hand.
At night: the Big Dipper is the clock hand
- Find the Pole Star using the Big Dipper (method in Finding your way without instruments).
- At dusk, note where the Big Dipper sits around the Pole Star, like a hand on a clock face.
- It turns counterclockwise, a quarter turn every six hours. An eighth of a turn: three hours have gone by.
You're not reading the exact time, but the time that has passed: enough to know whether it's midnight or dawn is coming.
At night: the moon
- Full moon: rises at sunset, is highest around midnight (solar time), sets at dawn.
- First quarter (right half lit, in the northern hemisphere): highest at sunset, sets around midnight.
- Last quarter (left half lit): rises around midnight, is highest at dawn.
- A thin crescent in the evening, low in the west: the night is just starting. A thin crescent in the morning, in the east: dawn is near.
ADAPT
Noon on your watch isn't noon for the sun. Depending on your time zone, daylight saving time and where you are in the zone, solar noon can fall an hour or two after 12:00 on the clock. In France, it's around 1:30 to 2:30 pm in summer, 12:30 to 1:30 pm in winter, later in the west than in the east.
Southern hemisphere. At noon the shadow points south and turns the other way. At night, the Southern Cross turns around the south celestial pole clockwise when you face south.
Under an overcast sky. Even behind clouds, the sun lights its side of the sky a little more: look for the brightest patch, and for a faint shadow of a small stick held on your fingernail.
What you really need is how long until dark. Your fingers are enough. For what comes next, moving at night: Se déplacer de nuit.