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South Africa
South Africa uses a single time zone: South Africa Standard Time (SAST). This is two hours in advance of UT. Daylight Saving Time / Summer Time is not used. To obtain local (zone) time, add two hours to UT. If the result is greater than 24, subtract 24 hours. If the initial or subsequent result is less than 12:00, the zone time is a.m.; if greater, subtract 12 hours to get the time p.m.
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The aim of this Guide is to help people find their way around the night sky, by showing how the stars that are visible change from month to month and by including details of various events that occur throughout the year. The objects and events described may be observed with the naked eye, or nothing more complicated than a pair of binoculars.
The conditions for observing naturally vary over the course of the year. During the summer, twilight may persist throughout the night and make it difficult to see the faintest stars. There are three recognized stages of twilight: civil twilight, when the Sun is less than 6° below the horizon; nautical twilight, when the Sun is between 6° and 12° below the horizon; and astronomical twilight, when the Sun is between 12° and 18° below the horizon. Full darkness occurs only when the Sun is more than 18° below the horizon. During nautical twilight, only the very brightest (navigation) stars are visible. During astronomical twilight, the faintest stars visible to the naked eye may be seen directly overhead, but are lost at lower altitudes. At Sydney, full darkness persists for about six hours at mid-summer. Even at Christchurch, NZ (not shown), full darkness lasts about four hours. By contrast, as far south as Cape Horn, at mid-summer nautical twilight persists, so only the very brightest stars are visible.
Another factor that affects the visibility of objects is the amount of moonlight in the sky. At Full Moon, it may be very difficult to see some of the fainter stars and objects, and even when the Moon is at a smaller phase it may seriously interfere with visibility if it is near the stars or planets in which you are interested. A full lunar calendar is given for each month and may be used to see when nights are likely to be darkest and best for observation.