An annular eclipse occurs when the Earth, Sun and Moon line up, with the Moon in mid position – but with the Moon in the further part of its orbit, so that its disk is not quite big enough to cover the Sun completely. The Sun’s mean angular diameter is 32 min 1 s of arc; the apparent diameter of the Moon ranges between 33 min 21 s and <30 min, with a mean of 31 min 8 s. The length of the Moon’s shadow varies between 237,000 and 227,000 miles, with a mean of 231,000 miles. The Moon’s mean distance from the Earth is 238,700 miles, and from this distance the shadow is too short to reach the Earth’s surface. It follows that annular eclipses are more frequent than totals in the ratio of 5:4. This is brought out by the dates of totals and annulars in Great Britain between 1800 and 2100; six annulars (1820, 1836, 1847, 1858, 1921 and 2003) and only two totals (1927 and 1999), though it is true that the track of totality on 30 June 1954 just grazed the tip of the northernmost of the Shetland Isles (I do not believe that anyone actually saw it from there). The next British totalities will be on 3 September 2081(Channel Islands) and 23 of September 2090 (Southern Ireland and Cornwall).