Читать книгу Exploring the Solar System - Peter Bond - Страница 100

1 1 The braking action of the tides causes Earth's period of rotation to slow by between 1.5 and 2 milliseconds per century. In order to ensure that clocks remain linked to Earth's rotation, an extra second is sometimes added to the year. This is known as a leap second.

2 2 Mercury is rather different because its orbit is much more elliptical than those of the other planets, so its surface is noticeably cooler when it nears aphelion.

3 3 There are small year‐to‐year variations in the dates and times of solstice and perihelion due to the leap‐year cycle in the calendar and the effect of the Moon on Earth's motion.

4 4 The average decrease in temperature – the normal lapse rate or environmental lapse rate – is 6.5°C per 1,000 m of altitude.

5 5 It is this jet stream which causes flights from Europe to North America to take much longer than flights in the opposite direction.

6 6 They are called hurricanes in the Atlantic, typhoons in the Asian Pacific, and cyclones in the Indian Ocean and Australia.

7 7 Colder or saltier water is denser and tends to sink.

8 8 In Spanish, El Niño means “the boy,” a reference to the baby Jesus, since historically the phenomenon has been observed near Christmas. The reverse situation is called La Niña, “the little girl.”

9 9 There is some evidence that, during at least two periods between 550 and 800 million years ago, ice sheets reached all the way from the poles to the equator, a situation known as “snowball Earth.”

10 10 It has been estimated that a 1% rise in water vapor could raise Earth's global average temperature by more than 4°C.

11 11 The Arctic and Antarctic are also extremely dry. Only the slow rate of evaporation prevents these regions from being classed as deserts.

12 12 The disappearance of species from the Earth at the present time, resulting from human activity, is often regarded as another mass extinction.

13 13 At present, Mercury is the only planet with the same polarity as Earth.

14 14 A third, temporary, belt was discovered in September 2012, possibly caused by the arrival of a shock wave following a major eruption on the Sun a few days earlier.