observation is very accurate, but it requires an accurate determination of the local time of culmination as well as making the correct observation at that exact moment. Another common method is using the compass, which is more practical because it can be done at any time; the disadvantage is that the north indicated by a magnetic compass differs from true north. This magnetic declination can measure up to 20°, which can vary in different places on Earth and changes over time. Shadow observation As observed from Earth, the sun appears to "shift" between the Northern and Southern Tropics seasonally; additionally, it appears to move from east to west daily as a consequence of the earth's rotation. The combination of these two apparent motions means that every day the sun crosses the meridian once, usually not precisely overhead but to the north or to the south of the observer. In locations between the two tropics—latitudes lower than 23.5° north or south—at certain moments of the year (usually twice a year) the sun passes almost directly overhead. This happens when the sun crosses the meridian while being at the local latitude at the same time. The city of Mecca is among the places where this occurs, due to its location at 21°25′ N. It occurs twice a year, firstly on 27/28 May at about 12:18 Saudi Arabia Standard Time (SAST) or 09:18 UTC, and secondly on 15/16 July at 12:27 SAST (09:27 UTC). As the sun reaches the zenith of the Kaaba, any vertical object on earth that receives sunlight cast a shadow that indicates the qibla (see picture). This method of finding the qibla is called rasd al-qiblat ("observing the qibla"). Since night falls on the hemisphere opposite of the Kaaba, half the locations on Earth (including Australia as well as most of the Americas and the Pacific Ocean) cannot observe this directly. Instead, such places observe the opposite phenomenon when the sun passes above the antipodal point of the Kaaba (in other words, the sun passes directly underneath the Kaaba), causing shadows in the opposite direction from those observed during rasd al-qiblat. This occurs twice a year, on 14 January 00:30 SAST (21:30 UTC the previous day) and 29 November 00:09 SAST (21:09 UTC the previous day). Observations made within five minutes of the rasd al-qiblat moments or its antipodal counterparts, or at the same time of the day two