Universal Standard Time (UST) is the sun time on the Greenwich Meridian. Countries work out their Standard Time relative to the position of their longitude west or east of the Greenwich Meridian.

As South Africa takes its time from 30˚ East of Greenwich and therefore two hours ahead of UST, South African Standard Time (SAST) is UST +2 hours.

Because of the sun time differences between the eastern and western sides of wide countries (e.g. Russia, Canada, United States, Australia), some countries choose to have different time zones.

• United States has four time zones – Eastern Standard Time (UST -5 hours), Central Standard Time (UST -6 hours), Mountain Standard Time (UST -7 hours), and Pacific Standard Time (UST -8 hours). Alaska has its own time zone (one hour behind Pacific Standard Time, i.e. UST -9 hours) while Hawaii (USA’s 50^th state which is an island group far to the west of North America in the Pacific Ocean) is two hours behind Pacific Standard Time, i.e. UST -11 hours. Thus, when it is 12:00 in New York (Eastern Standard Time) it will be 09:00 in Los Angeles (Pacific Standard Time) and 07:00 in Hawaii.
• Russia has eleven time zones! Vladivostok which is a port in the east of Russia is 8 hours ahead of St Petersburg, a port in the west of Russia.
• Australia has three time zones. Sydney on the east coast is three hours ahead of Fremantle, a port on the west coast.
• Africa also has time zones : East African Time; Central African Time; West African Time. South Africa falls into Central African Time, and takes its time from 30˚E (UST +2 hours).