Rotation and Revolution

All of the above

Note — There is a misprint in option 1. The correct statement will be — The earth completes one rotation in 23:56:4.09 hrs.

66½°

Centrifugal Force

Both A and R are true but R does not explain A.

Explanation — The earth is always tilted in the same direction as it moves round the sun. The angle at which the earth is tilted is known as the inclination of the earth's axis. The earth's axis is always inclined towards its orbital plane at an angle of 66½°.

Both A and R are true and R is the correct explanation of A.

Explanation — Due to Coriolis effect, the winds and ocean currents move clockwise and are deflected to the right in the Northern Hemisphere and move in the anticlockwise direction and are deflected to the left in the Southern Hemisphere.

Elliptic

Aphelion: earth is farthest from the sun

4 minutes

All of the above

Both A and R are true and R is the correct explanation of A.

Explanation — Centrifugal force is an apparent outward force that acts on a rotating object. It is always directed outward, i.e., away from the axis of rotation. The speed of rotation has created a centrifugal force resulting in a bulge in the middle portion of the earth and flattened top at the poles.

Both A and R are true and R is the correct explanation of A.

Explanation — The earth rotates on an inclined axis in an elliptical path around the sun. The earth's axis is inclined at an angle of 23.5° from the perpendicular to this plane of the elliptic. As a result of this, in the course of the earth's movement around the sun, the North Pole remains inclined towards the sun for a part of the year while the South Pole is tilted away from it. For the remaining part of the year, the situation is reversed.

It occurs on 3 January.

Circle of Illumination

Aphelion

Summer in northern hemisphere

A is false but R is true.

Explanation — When the earth is closer to the sun, the gravitational pull makes the earth move faster than when it is away from the sun. Thus, the speed of revolution of the earth is not uniform.

Equinox

Midnight sun

Both (2) and (3)

all of the above

82½°

6:30 am

Both A and R are true and R is the correct explanation of A.

Explanation — The twilight continues as long as sun is 18° below the horizon. In temperate regions, the angle at which the sun rises and sets is more slanted, so it takes longer to reach 18° below the horizon, hence longer dawn and dusk.

Prime Meridian

December 22nd

23 1/2° S

The places lying beyond the arctic circle have night on this date.

66 1/2° S

June 21st

Sun will shine vertically on Tropic of Cancer (23 1/2° N).

Due to the inclination of the earth, all places on earth have different length of day and night.

The duration of day at the equator will be 12 hours at the equator and increase to 13.5 hours at 23 1/2° N and become 24 hours at 66 1/2° N. The remaining hours are night.

The earth is always tilted in the same direction as it moves round the sun. The angle at which the earth is tilted is known as the inclination of the earth's axis.

The axis of the earth makes an angle of 23 1/2° with the vertical or 66 1/2° with the plane of the earth's orbit.

The two chief motions of the earth are rotation and revolution.

Two characteristics of rotation are-

1. Direction- The earth completes one rotation from west to east on its axis in 23 hours, 56 minutes, 4.09 seconds.

2. Inclination of axis- The earth is always tilted in the same direction as it moves round the sun. The angle at which the earth is tilted is known as the inclination of the earth's axis.

Two possible consequences if the axis of the earth was vertical instead of inclined are-

1. The length of day and night would have been equal at all places on the earth.
2. All the places on the earth would have had the same temperature throughout the year. There would be no seasons.

We do not feel the motions of the earth because the force of gravity keeps everything attached to the earth. This keeps all objects at rest with reference to the motions of the earth.

The path of the earth around the sun is known as elliptic.

Two chief characteristics of the revolution of the earth are-

1. The earth moves round the sun in an elliptical orbit at an average speed of 29.8 km per second.
2. When the earth is closer to the sun, the gravitational pull makes the earth move faster than when it is away from the sun. Thus, the speed of revolution is not uniform.

Due to the elliptical orbit of the earth, the distance between the earth and the sun varies. When the earth is closest to the sun, the position is called perihelion and when the earth is farthest from the sun, the position is called aphelion.

The days and nights are equal all over the world on March 21st and September 23rd because the sun crosses the plane of the earth's equator making day and night of equal length.

March 21st is known as Spring or Vernal Equinox and September 23rd is known as Autumnal equinox.

The longest day in the Northern Hemisphere is June 21st as the sun's rays fall vertically at the Tropic of Cancer and the North Pole is tilted towards the sun.

The shortest day in the Northern Hemisphere is December 22nd as the sun's rays fall vertically at the Tropic of Capricorn and the North Pole is tilted away the sun.

The sun shines vertically overhead at the:

(a) Equator on 21st March and 23rd September
(b) Tropic of Cancer on 21st June
(c) Tropic of Capricorn on 22nd December

Noon is hotter than morning because at noon, the sun is overhead. So, vertical rays of the sun fall at noon making the place hotter than the morning when slanting rays of the sun fall at a place.

Days and nights are equal at all places on earth on September 23 because on this date, the sun shines vertically over the equator, making day and night of equal length.

It is autumn season in the northern hemisphere and spring season in the southern hemisphere.

On June 21, the northern hemisphere is tilted towards the sun and the sun is overhead at the Tropic of Cancer. So, the northern hemisphere enjoys the longest day. This day is called Summer Solstice.

We have Summer Solstice in the Northern Hemisphere on June 21st.

Equinox refers to the time when the sun shines vertically over the equator. At the equinoxes, the days and nights are of equal length throughout the world.

The duration of daylight on March 21st at 23°30'N and 66°30'S latitudes will be 12 hours because on March 21st, the sun shines vertically over the equator and so the length of day and night is equal all over the world.

The cycle of seasons is determined by the change in the angle of the sun's rays hitting the earth's surface, which is caused by the earth's axial tilt of approximately 23.5 degrees. As the earth orbits the sun, different parts of the earth are tilted towards or away from the sun at different times of the year, resulting in the four seasons.

Torrid zone receives almost vertical rays of the sun and temperate zone and frigid zone receive slanting rays of the sun.

The duration of twilight is influenced by seasons because it is related to the angle at which the Earth's axis tilts towards the Sun, which changes as the Earth orbits around the Sun throughout the year.

In summer, the Sun sets at a shallower angle, causing longer periods of twilight. The twilight period is defined as the time between sunset and when the Sun is 18° below the horizon. Since the angle of the Sun's descent is more gradual in summer, it takes longer for it to reach the 18° mark, resulting in longer periods of twilight.

In winter, the Sun sets at a steeper angle, causing it to reach the 18° mark more quickly, resulting in shorter periods of twilight.

During the summer solstice in the Northern Hemisphere, the rays of the sun fall vertically on the Tropic of Cancer. The duration of sunlight increases from 12 hours at the equator to 13 hrs 27 minutes at 23 1/2° N and further to 24 hrs at 66 1/2° N. Beyond the Arctic Circle, the regions experience 24 hours daylight. This phenomena is called the ‘Midnight Sun’ and it only takes place at the poles.

The effect of seasons in low and high latitudes is distinct through various phases of different seasons. Low latitude areas experience high temperature and get ample rainfall while the high latitude areas are cold and receive less rainfall.

Tropical regions are always warm with heavy rainfall season, the temperate regions are cold with scanty rainfall and the polar regions are covered with snow throughout the year due to extremely low temperature.

The spinning of the earth on its axis from west to east once in 24 hours is called rotation of the earth.

Three effects of the rotation of the earth are:

1. Day and night are caused by the rotation of the earth on its axis.
2. Rotation causes difference in time over various places on the earth.
3. Sunrise and sunset are caused by the rotation of the earth from west to east.

Due to the inclined axis of the earth, the duration of day and night is different at different places of the earth. The time of day at any place is determined by the height of the sun in the sky.

(i) Kuala Lumpur rotates faster on the earth's axis than London because Kuala Lumpur is closer to the equator while London is away from the equator and the speed of rotation is greater at the equator and decreases towards the poles.

(ii) We always see the sun rising in the east because the earth rotates from west to east.

(iii) Norway is called the Land of the Midnight Sun as Norway lies beyond the Arctic circle and hence, the sun is visible just above the horizon continuously for almost three months.

As the angle of incidence changes from 0° to 90° from Poles towards the Equator, the duration of sunlight also changes.

On June 21st, the equator receives 12 hours of sunlight which increases to 24 hours at the North pole and decreases to 0 hours at the South pole.

Similarly, on December 22nd, the equator receives 12 hours of sunlight which decreases to 0 hours at the North pole and increases to 24 hours at the South pole.

Due to the tilted axis of the earth, the Northern Hemisphere gets maximum sunlight from March to September and Southern Hemisphere from September to March. So, the seasons are also reversed e.g. the summer season in Northern Hemisphere correspond by winter in Southern Hemisphere and the spring is exchanged with Autumn season.

(i) The length of day and night is not equal at all places on the earth due to the tilted axis of the earth and the migration belt of the sun between Tropics of Cancer and. Capricorn.

(ii) The period of twilight and dawn increases polewards because of the oblique path of the sun rays towards the poles than the vertical path along the equator. Thus, the length of dawn and twilight is greater, as it is nearly one hour near equator and 50 days at the poles.

(iii) On December 22, the southern hemisphere is tilted towards the Sun. The sun shines directly overhead the Tropic of Capricorn. The places in the southern hemisphere experience the summer season. Therefore, 25th of December, i.e., Christmas is celebrated in summer in New Zealand.

If the Earth stopped rotating on its axis, it would have devastating effects on the planet and its inhabitants. Some of the specific impacts would be:

1. Drastic temperature differences — One side of the Earth would be perpetually facing the Sun, leading to incredibly high temperatures, while the other side would be facing away from the Sun, causing it to freeze.
2. Disruption of weather patterns — The rotation of the Earth is what drives weather patterns around the globe. If the rotation were to stop, weather patterns would be disrupted, causing extreme storms and potentially leading to droughts or floods.
3. Increase in seismic activity — The Earth's rotation helps to balance tectonic plates and magma pressure, so if the rotation were to stop, there could be a significant increase in seismic activity, including earthquakes and volcanic eruptions.
4. Changes in gravity — The Earth's rotation generates centrifugal force, which helps to counteract the pull of gravity. Without this force, the planet's gravitational field would change, leading to potential impacts on the orbit of the Moon and other celestial bodies.

If the earth stops rotating, it would have catastrophic consequences for life on the planet, making it one of the most significant natural disasters imaginable.

I went to Australia for winter vacation. I found the following climatic differences between India and Australia:

1. Since Australia is in the southern hemisphere, its seasons are opposite to those in India. Therefore, when it was winter in India, it was summer in Australia.
2. The northern parts of Australia are tropical and experience hot and humid weather year-round, while the southern parts of the country have a more temperate climate.
3. The ocean currents surrounding Australia also affect its climate. The warm waters of the Indian Ocean to the west and the cooler waters of the Pacific Ocean to the east create different climate zones.

On June 21, the summer solstice occurs in the northern hemisphere and the winter solstice occurs in the southern hemisphere. The tilt of the Earth's axis causes different parts of the planet to receive different amounts of sunlight at different times of the year. During the summer solstice, the northern hemisphere is tilted toward the Sun, while the southern hemisphere is tilted away from it, causing opposite seasons.

New York is located in the northern hemisphere, so it experiences summer on June 21. Jakarta, on the other hand, is located in the southern hemisphere, so it experiences winter on the same date.