Motion of the Earth

Q14. Explain the following terms.

     a.   Rotation

Rotation is the movement of the earth on its axis.

     b.   Revolution

The movement of the earth around the sun in a fixed path or orbit is called revolution.

     c.   Orbital Plane

The plane formed by the orbit is known as orbital plane.

     d.   Circle of illumination

The portion facing the sun experiences day while the other half away from the sun experiences night. The circle that divides the day from night on the globe is called the circle of illumination.

     e.   Leap year

A year with 366 days is called a leap year.

     f.    Equinox

On 21^st March and September 23^rd, 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.

Q15. What would happen if the earth did not rotate?

Ans. The portion of the earth facing the sun would always experience day, thus bringing continuous warmth to the region. The other half would remain in darkness and be freezing cold all the time. Life would not have been possible in such extreme conditions.

Q16. Why do we have leap year?

Ans. The earth takes 365 ¼ days to revolve around the sun. We consider a year as consisting of 365 days only and ignore six hours for the sake of convenience. Six hours saved every year 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. Such a year with 366 days is called a leap year.

Q17. Differentiate between Summer Solstice and Winter Solstice.

Ans.