Search the Discovery Encyclopedia

Geography Weather and climate Weather is what the air outside is like right now: hot or cold, wet or dry, windy or calm. It can change from hour to hour. Climate is the usual weather of a place over a long time. Scientists work it out by averaging about 30 years of weather. Weather tells you what to wear today; climate tells you what clothes to pack for a trip.
Geography Weathering and erosion Weathering is rocks breaking apart where they are: ice in cracks, rain, wind-blown sand and growing roots all do it. Erosion is the next step, when gravity, rain, rivers, waves, wind and glaciers carry the broken pieces away. Over thousands to millions of years, they carve valleys, cliffs and canyons.
Life around the world Living with snow in Yakutsk Yakutsk, a city of more than 300,000 people beside the Lena River in Siberia, is one of the coldest cities in the world: in January, the average daily high is about -35°C. People dress in layers, many buildings stand on stilts above frozen ground called permafrost, and young children stay home from school on the coldest days.
Life around the world The polar night in Tromsø, Norway Tromsø lies far north of the Arctic Circle. From about 26 November to 17 January the sun stays below the horizon all day, a time called mørketid in Norwegian, the dark time. Around midday there are still a few hours of twilight. People wear reflectors on dark roads, and a study found that people farther north in Norway tended to feel more positive about winter.
Life around the world Six months of night at the South Pole At the Amundsen-Scott South Pole Station, the Sun sets once a year, around 20 March, and does not rise again for about six months. Up to 42 people spend the dark, freezing winter there with no flights in or out, sharing chores, meals and science.
Life around the world Northern lights over Fairbanks, Alaska Fairbanks, in the middle of Alaska, sits under a ring-shaped zone where the aurora often appears. The University of Alaska Fairbanks says its viewing season runs from about 21 August to 21 April, when nights are dark enough. Around the winter solstice there are fewer than four hours of daylight, and winter cold shapes daily life.
Geography Where our food grows Where a crop can grow depends on climate, soil and water. Rice needs warm weather, wheat can sprout in the cool, and cocoa for chocolate grows only in a hot, rainy belt near the Equator. An FAO atlas from 1995 found that just three crops, rice, maize and wheat, gave the world most of its food energy.
Geography Seeing Earth from satellites Earth-watching satellites carry cameras and other instruments that measure light and heat from far above. Their images cover huge areas at once, so scientists can track weather, map fires, and see how forests, farms, cities and ice change over the years. Landsat satellites have imaged Earth's land since 1972.