Solar Alignments - Scanistle (IS5) Map ref 4108 6724
An unimpressive stone about 1.2 x 1.0 x 0.4m. Â and leaning to the SE.
It is situated in open farmland  with a clear view of the mountains on the nearby Island of Jura - the 'Paps of Jura
A double alignment was found for the northern solstice by means of the method of 'halving the difference'Â Â (see below) and for epochs 3 & 5 each 22 or 23 days before/after the solstice:-
The idea that some alignments were used for determining particular days in the year using the movement of the sun ( and hence the development of a solar calendar) has been discussed earlier.  The full list of all the solar alignments in Mull and Islay is given in the Summary later. Once the numbers of days for each of the 16 ‘months’ or epochs had been determined, then the setting up of alignments in a new region (i.e. finding a suitable site for the rising/ setting of the sun on the day for each epoch by counting days from the solstice) would not have been particularly difficult – except for the determination of the day of the solstice. The sun is almost stationary for several days at the solstice. In theory it is possible to determine the actual day by use of a very long alignment of over 20km. This may have been done at Kintraw and Ballochroy in Argyll (Thom 1971: 36-38). This is disputed. However there is an alternative and much easier method of finding the day of the solstice. If a backsight position is chosen such that the sun passes a distinct feature a few days before the solstice, then by counting the number of days to its return to the same feature, then by ‘Halving the Difference’, the solsticial day is found. Two sites on Mull (Ardnacross and Gruline) and Scanistle on Islay all make use of this method:-
Note. By counting the number of days (14) before/after the solstice when the sun’s lower limb just touched the ridge below the sun  and halving it gives the day of the solstice  (By careful positioning of the backsight a second alignment for the epochs 3 and 5 was possible).