Using topographic maps, time reckoning and practical work

Time reckoning is based on the Earth’s rotation on its axis and its revolution around the Sun. The Earth rotates from west to east once in 24 hours, so a longitude difference of 360° : 24 = 15° equals one hour of time. Time is the same at all points of a meridian and is called local time; for convenience the Earth is divided into 24 time zones and one time is used inside a zone. Today the whole of Uzbekistan uses a single time, UTC+5 (the textbook calls it zone IV because it uses an older numbering of zones). The International Date Line runs along the 180° meridian: west of it the new date has begun, east of it it is still the previous date. A calendar is a system for counting long periods: the world uses the Gregorian calendar (12 months, February has 29 days in a leap year), and there are also the solar Hijri calendar, whose year begins on 21 March, and the lunar Hijri calendar based on the Moon’s motion (a year of 354 days).