CBSE Class 6 Social Science Geography: Motions of the Earth NCERT Solutions

(a) The Earth's axis is tilted at an angle of $66½^\{\backslash circ\}$ with respect to its orbital plane. This tilt is responsible for the changing seasons.

(b) Rotation: Rotation refers to the movement of the Earth spinning on its own axis. This motion takes approximately 24 hours to complete and causes day and night.

Revolution: Revolution is the movement of the Earth as it orbits around the Sun in a fixed path or orbit. This journey takes approximately 365.25 days to complete and is responsible for the cycle of seasons.

(c) A leap year is a year that contains an extra day, making it 366 days long instead of the usual 365 days. This extra day is added to February, which has 29 days in a leap year. Leap years occur approximately every four years to synchronize the calendar year with the solar year.

(d) The key differences between the summer solstice and winter solstice are:

Summer Solstice:

• Occurs around June 21st in the Northern Hemisphere.
• It is the longest day and shortest night of the year in the Northern Hemisphere.
• Simultaneously, the Southern Hemisphere experiences its shortest day and longest night.
• This position is called the summer solstice for the hemisphere tilted towards the Sun.

Winter Solstice:

• Occurs around December 22nd in the Northern Hemisphere.
• It is the shortest day and longest night of the year in the Northern Hemisphere.
• Simultaneously, the Southern Hemisphere experiences its longest day and shortest night.
• This position is known as the winter solstice for the hemisphere tilted away from the Sun.

(e) An equinox is a phenomenon that occurs twice a year, around March 21st and September 23rd. On these dates, the direct rays of the Sun fall on the Equator. At this time, neither of the Earth's poles is tilted towards or away from the Sun. As a result, the entire Earth experiences approximately equal lengths of day and night.

(f) The Southern Hemisphere experiences winter and summer solstices at different times than the Northern Hemisphere because the Earth's axis is tilted. When the Northern Hemisphere is tilted towards the Sun, experiencing summer, the Southern Hemisphere is tilted away from the Sun, experiencing winter. Conversely, when the Northern Hemisphere is tilted away from the Sun (winter), the Southern Hemisphere is tilted towards it (summer). Therefore, the position of the Earth that causes a solstice in one hemisphere results in the opposite season in the other hemisphere.

(g) The poles experience approximately six months of continuous daylight and six months of continuous night due to the tilt of the Earth's axis. As the Earth revolves around the Sun, the tilt causes the North Pole to be continuously illuminated by the Sun for about six months (during the Northern Hemisphere's summer) and the South Pole to be in darkness. The opposite occurs when the Earth is on the other side of its orbit, with the South Pole receiving sunlight for six months and the North Pole in darkness.

(a) (ii) Revolution. The movement of the Earth around the Sun is called revolution.

(b) (i) 21 March. On March 21st, the direct rays of the Sun fall on the Equator, marking an equinox.

(c) (iii) Australia. Since Australia is in the Southern Hemisphere, it experiences summer in December when Christmas is celebrated.

(d) (ii) Revolution. The cycle of seasons is caused by the Earth's revolution around the Sun combined with the tilt of its axis.

(a) A leap year has 366 number of days.

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

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

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

(e) Days are shorter during winter.

(i) (a) imaginary line. The axis of the Earth is an imaginary line passing through the North and South Poles.

(ii) (d) Sun. The Earth receives light and heat from the Sun, which is its primary source of energy.

(iii) (a) 24 hours. The time taken by the Earth to complete one rotation on its axis is approximately 24 hours, commonly known as an Earth day.

(iv) (c) 365 1/4 days. The Earth completes one revolution around the Sun in approximately 365.25 days, which is often represented as 365 1/4 days.

(v) (b) 21st March. On March 21st, it is the vernal (spring) equinox in the Northern Hemisphere and the autumnal equinox in the Southern Hemisphere.

(i) Days and nights occur due to the rotation of the Earth on its axis.

(ii) Only half of the Earth gets light from the Sun at a time due to its spherical shape.

(iii) The period of rotation is known as the Earth day.

(iv) The Sun's rays fall vertically at the Tropic of Capricorn on 22nd December.

(v) On 23rd September, it is autumn season in the Northern Hemisphere and spring in the Southern Hemisphere.

(i) False. The axis of the Earth makes an angle of 66½ degrees with its orbital plane. The angle it makes with the perpendicular to the orbital plane is 23½ degrees.

(ii) False. A leap year, where February has 29 days, occurs approximately every four years, not every five years.

(iii) True. Season changes are primarily caused by the Earth's revolution around the Sun combined with the tilt of its axis.

(iv) False. When there is summer in the Northern Hemisphere, it is winter in the Southern Hemisphere, not spring.

(v) True. While life exists in various conditions, extreme environments like the deep sea or polar regions present significant challenges for life as we know it.