Motions Of The Earth

The tilted position of the earth’s axis is called the inclination. The earth makes an angle of with the orbital plane.

Rotation: Rotation can be defined as the movement of the earth on its axis.

Revolution: The movement of the earth around the sun in a fixed path or orbit is known as a Revolution.

A year with 366 days is called a leap year. It takes 365¼ days (one year) to revolve around the sun. Six hours saved every year are added to make one
day (24 hours) over a span of four years. This surplus day is added to the month of February. Thus every fourth year, February is of 29 days instead of 28 days.

Summer Solstice: It occurs on 21^st June and is also known as the longest day of the year in the Northern Hemisphere. This is due to the position of the earth when there is summer in the Northern Hemisphere and winter in the Southern Hemisphere.

Winter Solstice: Winter Solstice occurs on 22nd December, which is also known as the shortest day of the year. At this time, the earth’s North Pole is tilted farthest from the sun. It is summer in the Southern Hemisphere and winter in the Northern Hemisphere.

Equinox is that time of the year when day time and night time are of equal length. The word Equinox is derived from the Latin; ‘equi’ means equal and ‘nox’ means ‘night’. It occurs on two such, 21st March and 23rd September.

Due to the revolution of the earth on its axis, the Southern hemisphere receives direct sunlight in the month of December and the Northern Hemisphere is away and receives less sunlight. Since a large portion of the Southern Hemisphere faces the sun, it experiences Summer Solstice while the other half away from the sun experiences Winter Solstice.

Due to the angle of inclination of the earth, both the poles experience day for 6 months and night for 6 months. The pole that is tilted towards the sun receives sunlight continuously for 6 months and the pole away from the sun experiences night for 6 months.

The movement of the earth around the sun in a fixed path or orbit is known as a Revolution. It takes 365¼ days (one year) to revolve around the sun. We consider a year as consisting of 365 days only and ignore six hours for the sake of convenience.

On 21st March and September 23rd, direct rays of the sun fall on the equator. At this position, neither of the poles is tilted towards the sun; so, the whole earth experiences equal days and equal nights. This is called an equinox.

Due to the revolution of the earth on its axis, the Southern hemisphere receives direct sunlight in the month of December and experiences Summer Solstice.

Due to the revolution of the earth on its axis, the position of the earth around the sun changes. This causes seasons to change.

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

A year which has 366 days and not days is called a leap year.

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

Rotation can be defined as the movement of the earth on its axis in 24 hours.

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

The shape of the earth’s orbit is not round but elliptical. 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.

21^st June is the longest day, also known as the Summer Solstice. On this day the sun’s rays fall directly over the Tropic of Cancer.

(e) Days are shorter during winter season.

The days are shorter in winter than in summer, because of the tilt of the earth’s axis.