The seasons of the year When it is summer in one hemisphere, it is winter in the other hemisphere. When it is spring in one hemisphere, it is autumn in the opposite hemisphere. In summer, one of the two hemispheres receives more direct sunlight. At the same time, it is winter in the other hemisphere, because the Sun's rays are less intense. During spring and autumn, the Sun's rays strike the two hemispheres in a similar way. The dates of the solstices and equinoxes mark the changes in seasons. Solstices: days that mark the beginning of winter and summer. The solstices take place around the 21st December and the 21st June. At those times, the Sun's rays are perpendicular to one of the tropics, which receives much more sunlight than the other tropic. Equinoxes: days that mark the beginning of autumn and spring. They take place around the 23rd September and the 21st March . On those days the Sun's rays are perpendicular to the Equator and day and night both last 12 hours in each hemisphere. The only exception is at the poles: the day lasts for six months and the night for six months. Investigate Find out where in Norway Lofoten is located. Look at your atlas. If you wanted to see the midnight sun, which countries could you travel to? Investigate the effects that the midnight sun can have on sleep. How do you think it would affect you? The midnight sun In areas north of the Arctic Circle, around the time of the summer solstice, the Sun can be seen 24 hours a day. This is because the Sun does not go below the horizon and there is constant twilight. This natural phenomenon is known as the midnight sun. It is caused by the tilt of the Earth's axis relative to the horizontal plane of the Earth's orbit, which exposes the North Pole to the Sun . (7) In the Southern Hemisphere, the winter solstice occurs on the same date. In areas close to the South Pole, the opposite phenomenon occurs: the so-called polar night, which is the absence of sunlight for 24 hours a day. Around the time of the winter solstice in the Northern Hemisphere, the situation is reversed: the polar night arrives in the Northern Hemisphere and the midnight sun in the Southern Hemisphere. E X P L O R E 7. Lofoten (Norway) COMMUNICATION Do you think you could easily adapt to living in a place with six months of day and six months of night? Discuss with your partner. Describe the two movements of the Earth. List and explain the effects of the Earth's rotation and revolution on our lives. Define leap year and explain why it occurs. When is the next leap year? K E Y Q U E S T I O N S 13 1
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