Nocturnal and Tide Predictor,

How to use a nocturnal

How to use a nocturnal

Length: 126.000 mm
Width: 80.000 mm
Height: 21.000 mm

M&ME 1857,11-16.2

Telling the time using the stars

Using a sundial is fine when the sun is out, but what if it's night time? A long time ago, people noticed that the stars moved across the sky at night, like the sun does during the day. You can see this yourself if you ever stay up late. If you are in the northern hemisphere, there's a bright star you can see over the North Pole called the Pole Star, which all the other stars seem to rotate around.

As with the sun, the position of the stars can be used to tell the time. To do this, you need an instrument like this one called a nocturnal, which means 'night time'. Have a look at the drawing to see how to do this. You set the instrument to the right time of year, then look for the Pole Star through the hole in the middle. Adjust the index arm to align with the 'pointer stars', which seem to point to the Pole Star. Where the arm meets the hour scale, you read off the time.

There are nocturnals to make for both the northern and the southern hemispheres inside the Time book.