As Mecca is located within the tropics there are two days in each year when the sun passes nearly exactly over the Ka‘ba. This occurs on 27 or 28 May at 9:18 UTC [12:18 Saudi local time] and on 15 or 16 July at 9:27 UTC [12:27 Saudi local time]. Source and further reading: http://www.staff.science.uu.nl/~gent0113/islam/qibla.htm
