ShadeFacts - The sun's daily & annual path


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	The sun's daily and annual path
Sun Risks Truths and myths About skin cancer UV radiation & the sun Ultraviolet (UV) radiation Direct & indirect UV radiation Factors affecting UV levels The UV index UV radiation and vitamin D Plotting Shade The sun's daily + annual path Finding North Protecting against UVR Shade - the best protection Controlling direct UV radiation Controlling indirect UV radiation Links to related sites	To achieve shade that falls in the right place at the right time you must be able to accurately predict where vegetation (trees, hedges etc) or built structures will cast shade. The shade depends on the position of the sun, which varies according to its daily and annual path. In WebShade, ShadeModeller allows you to model existing and proposed shade. Once WebShade knows your location and the direction of True North, it can plot your shade for you. The sun’s daily path Shadows move continuously as the sun passes from east to west over the course of a day: morning shadows fall in a westerly direction and are quite long, midday shadows will be close beneath the object and are short, afternoon shadows fall in an easterly direction and are longer again. Solar noon is the time of day when the sun is at its highest point in the sky and is located at True North. This is also the time when UV radiation levels are at their highest. Solar noon occurs around 1.00pm during daylight saving time and around 12 noon at other times of the year. The sun’s annual path The sun’s path also gradually changes throughout the year and so shadows vary according to the season. During the winter months the sun rises to the north of east and sets to the north of west and stays relatively low in the sky. During the summer months the sun rises to the south of east and sets to the south of west and is higher in the sky. The degree of these changes depends on your latitude. Four particular days of the year are important for understanding the sun’s annual path. 21 March and 23 September when day and night are of equal length (the equinoxes) 21 June the shortest day of the year (the winter solstice), and 22 December the longest day of the year (the summer solstice). Shade planners usually plot shade on these days so that they can predict how shade structures will perform at different times of the year.