Читать книгу How to predict the weather with a cup of coffee: And other techniques for surviving the 9–5 jungle - Matthew Cole - Страница 46

Before deciding how to mark your dial on the ceiling you need a basic grasp of how a sundial works. I’ll cover it in three points.

1 Everything the sun does outside is the inverse of what happens on the ceiling. As it moves across from east to west the reflected beam moves across the ceiling west to east. The lower the sun in the sky, the further into your room the beam is projected.

2 The route of the spot changes daily, sweeping across the ceiling between two extremes: the winter and summer solstices. In the middle of these extremes is the equinox; that’s the moment every 21 March and 22 September when the sun follows the same course in the sky and the days are exactly the same length as the nights. Mark out your dial on a date that’s as close to the equinox as possible; this will help you position the equinox line (the mid point of your dial) close to the middle of the ceiling.

3 The hours fall within flared bands that radiate from a centre point somewhere outside your window.