Motions of the Earth – Chapter 3 Geography Class 6 NCERT Solutions

1. Answer the following questions briefly.

(a) What is the angle of inclination of the earth’s axis with its orbital plane?

Ans. Earth’s orbital plane is known as the ecliptic plane, and Earth’s tilt is known to astronomers as the obliquity of the ecliptic, being the angle between the ecliptic and the celestial equator on the celestial sphere. It is denoted by the Greek letter ε. Earth currently has an axial tilt of about 23.4°.

(b) Define rotation and revolution.

Ans. Rotation:- Rotation is where the Earth spins on its own axis. The axis is an imaginary line through the center of the planet between the north and south poles. As the Earth rotates, the Sun looks like it’s traveling around the Earth, rising in the east and setting in the west – but what really happens is the other way around. As the Earth rotates, the spot where you’re standing is moving past the Sun from west to east.

Revolution:- Revolution is where the Earth travels, or revolves, around the Sun in a roughly circular path. (Mathematically, it’s actually an ellipse rather than a circle.) Each revolution takes the Earth around one complete orbit of the Sun, back to the same point a second time, and is called a year.

(c) What is a leap year?

Ans. A leap year is a calendar year containing one additional day added to keep the calendar year synchronized with the astronomical or seasonal year. Because seasons and astronomical events do not repeat in a whole number of days, calendars that have the same number of days in each year drift over time with respect to the event that the year is supposed to track. By inserting an additional day or month into the year, the drift can be corrected. A year that is not a leap year is called a common year.

(d) Differentiate between the Summer and Winter Solstice.

Ans. Summer Solstice:-

  •     Falls on 21st June.
  •     Longest day and shortest night in northern hemisphere.
  •     Summer season in northern hemisphere.
  •     Winter in southern hemisphere.

Winter Solstice:-

  •     Falls on 22nd December.
  •     Longest day and shortest night in southern hemisphere.
  •     Summer in southern hemisphere.
  •     Winter in northern hemisphere.

(e) What is an equinox?

Ans. It’s common knowledge the days are longer than nights in summer, and that in winter, the days are shorter. However, this is not quite true during some parts of the year: during equinoxes. An equinox is a point in the year when daytime and nighttime are exactly the same length, 12 hours each. Equinoxes occur twice a year, usually on March 20 and Sept. 22, when the Earth is tilted neither toward nor away from the sun. The word is derived from Latin: ‘equi,’ which comes from aequus, meaning equal, and nox-‘, meaning night. In actuality, day and night are not exactly the same length on the equinox, but they are very close. There are various reasons for this minor difference in duration. The way we define day and night uses the edge of the sun instead of the center as a point of measurement. Also, refraction allows people to see sunlight sooner than the sun actually rises above the horizon.

(f) Why does the Southern Hemisphere experience Winter and Summer Solstice in different times than that of the Northern Hemisphere?

Ans. This happens because of the angle between earth’s axis and its orbit. On 21st June, the sunlight falls directly on the Tropic of Cancer. Hence, it is summer solstice in the northern hemisphere. On 22nd December, the sunlight falls directly on the Tropic of Capricorn. Hence, it is summer solstice in southern hemisphere.

(g) Why do the poles experience about six months day and six months night?

Ans. The poles experiences 6 months of days and 6 months of nights due to the tilt of the earth on its own axis. Because of this tilt each pole is tilted towards and away from the earth for about 6 months each. When the north pole is tilted towards the sun,it experiences continuous day light for six months.

2. Tick the correct answers.

(a) The movement of the earth around the sun is known as

(i) Rotation (ii) Revolution (iii) Inclination

(b) Direct rays of the sun fall on the equator on

(i) 21 March (ii) 21 June (iii) 22 December

(c) Christmas is celebrated in summer in

(i) Japan (ii) India (iii) Australia

(d) Cycle of the seasons is caused due to

(i) Rotation (ii) Revolution (iii) Gravitation

3. Fill in the blanks.

(a) A leap year has _______________ number of days.

366

(b) The daily motion of the earth is _______________.

Rotation

(c) The earth travels around the sun in ______________ orbit.

Elliptical

(d) The sun’s rays fall vertically on the Tropic of ___________ on 21st June.

Tropic of Cancer

(e) Days are shorter during ___________ season.

Winter

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