Levels of Sunlight at Freshford Mill

Frome River Sunshine at Freshford Mill

Technical Note

In addition to the original calculation photographs have been taken at certain times of the day to determine the correct factor for Freshford Mill's location. The original factor for seeing the sun was calculated to be 14 degrees of celestial altitude. Since the mill is not at sea level the effect of the landscape needs to be taken into account. A revised calculation based on supporting photographic evidence is that a more accurate figure is 10 degrees.

Factor 1: High Land to the South

As Freshford Mill is located next to the river Frome it not only has a high probability of an annual risk of flooding but also lies North of the ridge of hillside that is the edge of the high land to the South. That land averages 120 metres and has parts in excess of 150 metres (130-160 feet) Freshford Mill is not more than 20 metres above sea level. The difference being not less than 100 metres above sea level for calculating levels of sunshine -given fine weather of course! In other words the hills obstruct the sunshine.

Factor 2: Woods to the South

The land South of Freshford Mill is also densely wooded with many mature deciduous and coniferous trees that together with the high ground also reduce the level of sunshine at the Mill site.  Furthermore, directly South of the Mill at Rosemary lane the land is so steep as to form a cliff. The closer one gets to the riverside the greater the effect of the geophysical features reduce the level of sunshine. The photograph below was taken on the 13th December 2007 at 2:36pm and shows quite clearly that the valley is not in sunshine. The sun can only be seen from the viewpoint of the camera because the camera is located at Iford lane (50 metres) Thus the level of Mid-Winter sunshine is such as to allow the Freshford Mill site only a few hours of sunlight during the day. When there is no sunshine the level of light is of course even further reduced. According to the way the proposed dwellings are arranged and the relative height of the buildings there will be very much reduced levels of light on the ground for much of the day.

Sunpath Diagrams

The diagram below is of the path of the sun throughout the year. The vertical axis is of the sun's altitude in degrees, the horizontal axis is of degrees East to West -the azimuth. The graphs have time intervals marked on them and it is to be noted that there are an equal number of segments for each of the graphs. The key factor is the altitude of the sun relative to the location both in terms of latitude and longitude but also in terms of altitude above sea level.. Freshford Mill is located at an effective altitude of 10 degrees in terms of the Sun.(Altitude: elevation: angular distance above the horizon (especially of a celestial object).   This means that because of the higher ground and trees to the South unless the altitude of the sun is 10 degrees it will not be seen. If Freshford Mill were to be  located at sea level the altitude factor would be zero and the sun would set at 4pm on the 21st December and at Midsummer the sun would set at 9pm. The hills and trees would have to be removed from the scenario though.

Since the altitude at Freshford Mill is calculated and confirmed by photographs  to be 10 degrees to see sunlight the sun sets on the 21st December at 2pm and rises at 10:30am.  The longest possible amount of sunshine for Freshford Mill is given by the Summer Solstice graph line where the sun can be traced to set at 7pm and rise at 5am giving 14 hours. The smallest possible amount of sunshine is given by the Winter Solstice and is less than 4 hours.

SunPath Diagram Designer

This resource is (no longer available, but see below) from: http://www.msa.ac.uk/colleges/bioclimatic/ Manchester School of Architecture (MSA) was voted the top school in the UK offering courses for the full range of qualifications necessary to become a professional architect. (Guardian newspaper poll result 2006). Although I doubt whether there can be any errors in the SunPath Diagram Designer there might be an error in my calculation of the effective altitude in degrees at Freshford Mill. Hopefully there might be sunshine on the 21st December and can I check to see whether the sun does set (disappear) at the calculated time. The best I could do was the 19th. December - Photos Download the Excel utility sun4a.xls