Astronomy in questions and answers
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The Earth [Questions 7-12]

7. Are summers warmer in the Southern than in the Northern Hemisphere?

Yes. The Earth is at perihelion in January, during the southern summer, and is about 5,000,000 kilometres closer to the Sun than it is in July during the northern summer. This difference, although it is less than 4% of the Sun's mean distance from the Earth, is large enough to make the summers warmer and winters colder in the Southern Hemisphere than in the Northern Hemisphere.

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8. Where is the International Date Line?

The International Date Line is the 180th meridian of longitude, which runs north and south at about the middle of the Pacific Ocean.
It marks the point where one civil day ends and the next begins on the Earth. Travellers crossing the International Date Line from east to west lose a day, while travellers travelling from west to east gain a day. Time on the Earth is not kept by the Sun. If it were, every town and village would have its own individual time, differing from every other town or village which was little to the east or west of it. This condition was until the end of the 19th century. Now there are different time zones. These time zones are areas running-north and south which are about 15 in width, because the Earth's rotation is 15 an hour. The boundaries of the time zones do not lie exactly on the meridians. Everywhere within one time zone, civil time is the same, and is known as standard time.

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9. What causes tides?

The gravitational attraction of the Sun and the Moon upon the Earth causes the tides.

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10. Do the tides affect the motion of the Earth?

Yes. The friction of the tides acts as a brake on the Earth's rotation, slowing it down. The Earth is rotating about one second more slowly every 100,000 years.

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11. What effect does the Sun have upon the tides?

When the Sun and the Moon are nearly in line with each other and with the Earth, as they are at new Moon and at full Moon, the Sun's gravitational force is added to that of the Moon and there are greater tides.

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12.Has the Sun or the Moon the greater tidal effect upon the Earth?

The Moon has about two-thirds (2/3) of the tidal effect upon the Earth and the Sun has one-third (1/3). The Sun is much bigger than the Moon, but it is also much farther away from the Earth.

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tides
See also
• The Sun
• The Moon
• Mercury, Venus and Mars
• Jupiter, Saturn, Uranus, Neptune and Pluto
• Meteors and Comets
• Stars
• The Constellations
• Galaxies
• Scientists and Astronomers
 
 
 

 
 
Related Internet Links
• The Nine Planets
• Earth Picture of the Day
   
  
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