A method for measuring the course of the sun
A great circle with the earth (m) at its centre, sunrise and sunset, day and night marked
A single large circle drawn across the sheet stands for the daily path of the sun, with the earth placed at its centre (m) and the moments of sunrise and sunset set at either side. Leonardo proposes a way to gauge the sun's course by choosing a season in which the night, measured between sunset and sunrise, is twice the length of the day. The short accompanying note keys the lettered points b, e, a and d to sun, day and night positions on the ring. Beyond this block the sheet carries further faint, untranscribed writing showing through the paper.
On this page
Timing the sun's course from the ratio of night to day
Leonardo sets out a method for measuring the sun's course. One is to take a time of year in which the night, enclosed between the setting and the rising of the sun, is twice as long as the day. The point m is to be reckoned as the body of the earth, sitting at the centre of the great circle.
The great circle of the sun's daily path
A single large compass-drawn circle spans the leaf, with a horizontal line through its centre and small ringed marks where sun positions are noted. The labels place the sun (e, a) at the sides and mark day and night about the central earth m, with points d above and b below. The figure serves as a schematic of the sun travelling around the earth over a day and night.