The summer solstice occurs today, 21 June, at 11.38 UTC (GMT).
The summer and winter solstices mark the times when the Sun is at its furthest from the celestial equator (the projection of the Earth's equator onto the sky). The world 'solstice' comes from the Latin solstitium meaning 'Sun stands still' because the apparent movement of the Sun's path north or south stops before changing direction.
The summer solstice does not always fall on 21 June. Because the Earth takes approximately 365.25 days to go around the Sun, the precise time of the solstices and equinoxes occurs about 6 hours (0.25 days) later each year, with a jump of a day backwards on leap years. The last time the summer solstice was not on 21 June was 1975 when it occurred on 22 June at 00.27, and in the year 2012 it will occur on 20 June at 23.09.
Find out more about solstices and equinoxes in our fact file.
To mark the solstice, the Royal Observatory is hosting Hour Angle by composer John Eacott, a free musical performance sonifying the exact moment of the summer
solstice. A real-time calculation of the Sun's declination will be
transformed into live notation played by 12 musicians. The piece will
allow visitors the chance to experience the solstice in an
unforgettable way. The performance will start promptly at 12.08. Visitors are advised to