Long Questions: Motions of the Earth | NCERT Summary: UPSC PDF Download

Q1: How are seasons caused?
Ans:

• The Earth revolves round the Sun on an elliptical orbit.
• Its axis is inclined in the same direction (east) on its orbit by 2314°.
• The revolution of the Earth and the inclination of the earth’s axis in a fixed direction cause seasons.
• A year is divided into four seasons.
• They are Spring, Summer, Autumn and Winter.
• Seasons change with the change in the position of the Earth around the Sun.

On 21st June, Northern hemisphere is tilted towards the Sun.

• On that day the Sun shines directly on the Tropic of Cancer (231/2° N). Hence, these areas receive more heat.
• The areas near the poles receive less heat because the rays of the Sun are slanting there.
• The North hemisphere is inclined towards the Sun and the places beyond the Arctic Circle experience continuous day light.
• As a large portion of the Northern hemisphere gets light from the Sun, therefore, it is Summer in the Northern hemisphere.
• The duration of day is longer and that of night shorter here.

At this time in the Southern hemisphere all these conditions are opposite.

• It is winter season there.
• Nights are longer than days.
• This position of the Earth is called summer solstice.

On 22nd December, the Tropic of Capricorn receives the direct rays of the Sun and Southern hemisphere tilts towards it.

• On this day the Sun shines vertically on the Tropic of Capricorn (23W S).
• Hence a larger portion of the Southern Hemisphere gets light.
• It is summer in the Southern hemisphere with longer days and shorter nights.
• The opposite conditions are prevalent in the Northern hemisphere.
• This position of the Earth is called winter solstice.

On 21 March and 23 September, The Sun shines vertically on the equator.

• In this position neither of the hemispheres is tilted towards the Sun, so the whole of the Earth experiences equal days and equal nights.
• It is neither very cold nor very hot all over the world.
• The Northern hemisphere experiences spring on 21st March and autumn on 23rd September.
• Exactly the opposite happens in the Southern hemisphere. Here, it is spring on September 23rd and autumn on March 21st.
• These positions are called Spring and Autumn Equinoxes respectively.

Q2: Where do six months-long nights and days take place and why?
Ans: For around six months, the tilt of the earth on its axis causes each of the poles to be slanted either towards or away from the Sun. The poles endure around six months of night and six months of day due to this tilt. There is continuous daylight for six months when the North Pole is turned towards the Sun. The South Pole is tilted away from the Sun at this time, and it is night for the duration. When the South Pole is turned towards the Sun, it receives continuous daylight for six months.

Q3: Explain the equinox.
Ans: The equinox is the point on Earth where the Sun's rays fall squarely on the equator. The South Pole and the North Pole are not tilted toward the Sun in this situation. The days and nights are the same all throughout the world. This occurs on March 21st and September 23rd. On the equinox, all of the earth's nights and days are equal. The Sun receives an equal amount of sunrays in the Northern and Southern Hemispheres on this day.

Q4: What are rotation and revolution?
Ans: The rotation and revolution of the Earth are two different motions. Rotation is the movement of the earth on its axis. The Earth follows a set orbit or path around the Sun. Revolution is the name given to this movement. The earth takes approximately 24 hours to complete one rotation around its axis. This is known as Earth Day. The earth revolves around the Sun in about 365 days. The earth's revolution around the Sun is known as the revolution of the earth around the Sun.

Q5: Explain the following:

1. Revolution of the Earth.
2. Leap year.

Ans: 1. Revolution of the Earth:

• Earth’s movement around the Sun on its orbit is called revolution.
• The earth takes 36514 days (one year) to revolve round the Sun.
• We take a year of 365 days only and ignore 6 hours for the sake of convenience.

2. Leap Year:

• Six hours saved every year in revolution are added for four years.
• They become 24 hours or one additional day.
• The day is added to the month of February every four years.
• It is because of this that every fourth year February has one more day – 29 days instead of 28 days.
• Such a year of 366 days is called a leap year.

Q6: What is the difference between the Winter Solstice and Summer Solstice?
Ans: The position of the earth during the Summer Solstice is when the Sun's rays fall directly on the Tropic of Cancer. The earth's position at the Winter Solstice is when the Sun's rays fall directly on the Tropic of Capricorn. The North Pole is inclined towards the Sun during the summer solstice and away from the Sun during the winter solstice.
The light from the Sun falls on the majority of the Northern Hemisphere during the summer solstice, and it is summer there when the days are longer than the nights. The majority of the Southern Hemisphere receives sunlight during the winter solstice, while it is winter in the Northern Hemisphere, and the nights are longer than the days.

Q7: Why is the Winter and Summer Solstice experienced at different times in the Southern and Northern Hemispheres?
Ans: The summer solstice occurs when the North Pole tilts towards the Sun in the Northern Hemisphere. The South Pole is tilted away from the Sun in this situation, causing the Southern Hemisphere to experience winter solstice. When the South Pole is tilted towards the Sun, the Summer Solstice occurs, and when the North Pole is inclined away from the Sun, the Winter Solstice occurs. This explains why the winter and summer solstices occur at different times in the Southern and Northern Hemispheres.