Winter solstice one must be able to observe a change in azimuth or elevation less than or equal to about 1/60 of the angular diameter of the sun. Observing that it occurred within a two-day period is easier, requiring an observation precision of only about 1/16 of the angular diameter of the sun. Thus, many observations are of the day of the solstice rather than the instant. This is often done by observing the sunrise and sunset or using an astronomically aligned instrument that allows a ray of light to be cast on a certain point around that time. Length of day
Labours of the Months Ice Age has been detected in differences between early and late examples. Most sculptured cycles in Europe, especially when compressed into the archivolt of a portal, consist of an astrological symbol beside, above or incorporated in a sculpture or relief illustrating a monthly labour. A few sculpted examples of the many surviving are: The Labours of the months often occur in those rose windows that are dedicated to the Creation, the circular nature of the window suiting the cyclic theme. In these windows, the months are part of a complex iconographical scheme. Other windows have the Labours of the Months