خطوط العرض والطول والمناطق الزمنية
Geography · Key Stage 2 · The School
Two numbers locate anywhere
LATITUDE measures how far north or south of the Equator a place is, in degrees from 0° at the Equator to 90° at each pole. Lines of latitude run across the globe and are parallel. LONGITUDE measures how far east or west of the PRIME MERIDIAN, which runs through Greenwich in London. Lines of longitude run pole to pole and meet at both ends. Together the two give any place on Earth a unique address.
The named lines
Some lines of latitude have names because something happens there. The EQUATOR at 0° splits the Northern and Southern Hemispheres. The TROPIC OF CANCER at 23.5°N and the TROPIC OF CAPRICORN at 23.5°S mark the furthest points where the Sun can be directly overhead. The ARCTIC and ANTARCTIC CIRCLES at 66.5° mark where at least one day a year has no sunset, and one no sunrise.
Why clocks differ
The Earth turns once in about 24 hours, so at any moment half of it faces the Sun and half does not. Rather than everyone using one clock, the world is divided into TIME ZONES roughly following lines of longitude, each about an hour apart, counted from Greenwich. Travel far enough east or west and you cross the International Date Line, where the calendar date itself changes.
London sits on 0° longitude. New York is at about 74° west. The Earth turns 360° in 24 hours, so 15° per hour. 74 ÷ 15 is about 5, so New York is 5 hours behind: 3pm in London is 10am in New York. Now Sydney, at about 151° east: 151 ÷ 15 is about 10 hours AHEAD, so 3pm in London is 1am the next day in Sydney. Longitude is a clock.