Rotation and Revolution

 

Choose the correct option

Question 1

Which of the following is true about the rotation of the earth?

1.     The earth completes one rotation in 25:56:4.09 hrs

2.     The earth's axis passes through the poles

3.     The speed of rotation increases as we move towards the equator

4.     All of the above.

Answer

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.

Question 2

What angle does the earth's axis make with the plane of earth's orbit?

1.     0°

2.     23½°

3.     66½°

4.     90°

Answer

66½°

Question 3

An apparent outward force that acts on a rotating object:

1.     Centrifugal Force

2.     Sunset Effect

3.     Coriolis Effect

4.     Rotational Effect

Answer

Centrifugal Force

Question 4

What is the shape of the path of the earth around the sun?

1.     Oval path

2.     Spherical path

3.     Elliptic

4.     Coriolis

Answer

Elliptic

Question 5

Which of the following is correct?

1.     Aphelion : earth is closest to the sun

2.     Aphelion: earth is farthest from the sun

3.     Aphelion : moon is closest to the earth

4.     Aphelion : the equator is closest to the sun.

Answer

Aphelion: earth is farthest from the sun

Question 6

What is the time difference between two consecutive lines of longitude?

1.     7½ minutes

2.     4 minutes

3.     1 minute

4.     3 minutes

Answer

4 minutes

Question 7

Which of the following is true about the revolution of the earth around the sun?

1.     It results in the cycle of seasons

2.     The direction of motion is the same as rotation

3.     The speed is not uniform

4.     All of the above.

Answer

All of the above

Question 8

Which of the following is true about the perihelion position of the earth?

1.     It is farthest from the sun.

2.     It occurs on 3 January.

3.     The speed of revolution is the least.

4.     All of the above.

Answer

It occurs on 3 January.

Question 9

The lighted part of the earth is called the :

1.     Circle of Light

2.     Circle of Illumination

3.     Circle of Solstice

4.     Circle of Equinox

Answer

Circle of Illumination

Question 10

Perihelion : 147.4 million km :: ............... : 152 million km

1.     Aphelion

2.     Equinox

3.     Solstice

4.     All of the above

Answer

Aphelion

Question 11

Which of the following is true about the aphelion?

1.     Occurs on 4 July.

2.     Summer in northern hemisphere

3.     Speed of revolution is maximum

4.     All of the above.

Answer

Summer in northern hemisphere

Question 12

Solstice : Summer/Winter :: ................ : Spring/Autumn

1.     Solstice

2.     Equinox

3.     Vernal

4.     None of the above.

Answer

Equinox

Question 13

Name the phenomenon when the regions beyond the Arctic Circle experience 24 hours daylight.

1.     Daylight sun

2.     Midnight sun

3.     Arctic sun

4.     Regional sun

Answer

Midnight sun

Question 14

The period of diffused light between sunset and complete darkness is called ................ .

1.     dawn

2.     dusk

3.     twilight

4.     Both (b) and (c)

Answer

Both (b) and (c)

Question 15

The duration of twilight :

1.     increases to the poles

2.     might last for as much as 7 weeks at the poles

3.     is as long as the sun is 18° below the horizon

4.     all of the above.

Answer

all of the above

Question 16

World Standard Time: 0° :: Indian Standard Time : ...............

1.     23½°

2.     72½°

3.     66½°

4.     82½°

Answer

82½°

Question 17

Greenwich Mean Time : ............... :: Indian Standard Time : 12:00 pm

1.     6:30 am

2.     5:30 am

3.     6:30 pm

4.     5:30 pm

Answer

6:30 am

Question 18

World Standard Time : ............... :: Indian Standard Time : Standard Meridian of India

1.     World Standard Meridian

2.     Prime Meridian

3.     International Date Line

4.     Greenwich Mean Time

Answer

Prime Meridian

SAQ

 

1.     What is meant by the inclination of Earth’s axis? At what angle is the Earth’s axis inclined?

o    The inclination of Earth’s axis refers to the tilt of its rotational axis concerning the plane of its orbit around the Sun.

o    The Earth’s axis is inclined at an angle of approximately 23.5° with respect to the vertical or 66.5° with the plane of its orbit.

2.     Name the two chief motions of the Earth.

o    The two chief motions of the Earth are rotation and revolution.

3.     Describe two characteristics of rotation.

o    Direction: The Earth completes one rotation from west to east on its axis in approximately 23 hours, 56 minutes, and 4.09 seconds.

o    Inclination of Axis: The Earth’s axis remains tilted as it orbits the Sun.

4.     State two effects of the rotation of the Earth.

o    Day and Night: Rotation causes the alternation between day and night.

o    Time Differences: Different time zones result from the Earth’s rotation.

5.     Mention two possible consequences if the axis of the Earth was vertical instead of inclined.

o    Equal day and night lengths worldwide.

o    Uniform temperatures throughout the year (no seasons).

6.     State one reason why we do not feel the motions of the Earth.

o    The force of gravity keeps everything attached to the Earth, preventing us from feeling its motions.

7.     What is an elliptic?

o    The path of the Earth around the Sun is known as an ellipse.

8.     Define ‘revolution’.

o    Revolution refers to the Earth’s motion around the Sun in an elliptical orbit.

9.     State two chief characteristics of the revolution of the Earth.

o    The Earth moves around the Sun in an elliptical orbit at an average speed of 29.8 km per second.

o    The speed of revolution varies due to gravitational pull (faster when closer to the Sun, slower when farther away).

10. Mention two effects of revolution.

o    Seasons: Revolution causes different seasons due to varying heating of the Earth.

o    Heat Zones: The spherical shape of the Earth, combined with revolution, leads to distinct heat distribution zones.

11. What do you understand by perihelion and aphelion?

o    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.

12. On which two days are the days and nights equal all over the world and why? What name do you give to these days?

o    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.

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

13. Which is the longest and which is the shortest day in the Northern Hemisphere and why?

o    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.

o    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 from the Sun.

14. On which dates does the Sun shine vertically overhead at:

o    (a) Equator: On March 21st and September 23rd.

o    (b) Tropic of Cancer: On June 21st.

o    © Tropic of Capricorn: On December 22nd.

15. Why is noon hotter than morning?

o    Noon is hotter than morning because at noon, the Sun is overhead. Vertical rays of the Sun fall at noon, making the place hotter than in the morning when slanting rays of the Sun fall.

16. Why are days and nights equal at all places on Earth on September 23? What are the seasons in the Northern and Southern Hemispheres on this date?

o    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.

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

Question 21: How is the duration of twilight influenced by seasons?

• The duration of twilight varies with the changing seasons due to the Earth’s axial tilt and its orbit around the Sun.
• In summer, the Sun sets at a shallower angle, resulting in longer twilight periods. Twilight is the time between sunset and when the Sun is 18° below the horizon. The gradual descent of the Sun in summer prolongs this period.
• Conversely, in winter, the Sun sets at a steeper angle, causing twilight to be shorter. The Sun reaches the 18° mark more quickly, leading to shorter twilight.

Question 22: How has the phenomenon of the ‘Midnight Sun’ come about?

• The Midnight Sun occurs in polar regions during the summer solstice (around June 21st) in the Northern Hemisphere.
• On this day, the rays of the Sun fall vertically on the Tropic of Cancer (23.5°N).
• Beyond the Arctic Circle (66.5°N), regions experience continuous daylight for 24 hours. This phenomenon is known as the Midnight Sun.

Question 23: Mention one effect of seasons in low and high latitudes.

• Low Latitudes (Tropical Regions):
• Experience high temperatures throughout the year.
• Receive ample rainfall due to the consistent warmth.
• High Latitudes (Polar Regions):
• Are cold and have extremely low temperatures.
• Receive less rainfall and are often covered with snow.

Question 24

Draw a well labelled diagram to show changes in the altitude of the midday sun at different times of the year.

 

1.     Rotation and Revolution:

o    Rotation:

§  It refers to the spinning of the Earth on its axis.

§  The Earth completes one full rotation approximately every 23 hours and 56 minutes.

§  Rotation causes the alternation between day and night.

o    Revolution:

§  It is the motion of the Earth around the Sun in an elliptical orbit.

§  The time taken for one revolution is approximately 365 days, 5 hours, and 48 minutes.

§  Revolution causes seasonal changes.

2.     Vertical and Slanting Rays:

o    Vertical Rays:

§  Vertical rays of the Sun travel over a shorter distance through the atmosphere.

§  Consequently, they lose less heat during their journey.

§  These rays fall within the migration belt between the Tropics of Cancer and Capricorn.

o    Slanting Rays:

§  Slanting rays of the Sun travel over a larger distance through the atmosphere.

§  As a result, they lose more heat.

§  These rays fall in temperate and polar regions.

3.     Equinox and Solstice:

o    Equinox:

§  Refers to the time when the Sun crosses the plane of the Earth’s equator.

§  On equinox days (around March 21st and September 23rd), day and night are of equal length.

§  It marks the start of spring and autumn.

o    Solstice:

§  Occurs when the Sun reaches its highest or lowest point in the sky at noon.

§  On solstice days (around June 21st and December 22nd), we experience the shortest and longest days of the year.

§  It corresponds to summer and winter.

1.     Kuala Lumpur vs. London Rotation Speed:

o    Geographical Reason: Kuala Lumpur is closer to the equator, while London is farther away.

o    Explanation: The speed of rotation is greater at the equator due to its larger circumference. As we move away from the equator toward the poles, the rotational speed decreases. Therefore, Kuala Lumpur, being near the equator, rotates faster than London.

2.     Why We Always See the Sun Rising in the East:

o    Geographical Reason: Earth’s rotation from west to east.

o    Explanation: The Earth rotates on its axis, causing the Sun to appear to rise in the east and set in the west. This daily rotation gives us the consistent pattern of sunrise and sunset.

3.     Norway as the Land of the Midnight Sun:

o    Geographical Reason: Norway lies beyond the Arctic Circle.

o    Explanation: Beyond the Arctic Circle (approximately 66.5°N), during the summer solstice (around June 21st), the Sun remains visible just above the horizon for almost three months. This phenomenon is known as the Midnight Sun.

Question 1(d)

Draw a well labelled diagram to show inclination of the earth on its axis.

1.     What is meant by rotation of the Earth? State three effects of the rotation of the Earth.

o    Answer:

§  Rotation of the Earth: It refers to the spinning of the Earth on its axis from west to east once in approximately 24 hours.

§  Effects of Rotation:

1.     Day and Night: Rotation causes the alternation between day and night.

2.     Time Differences: Different time zones result from the Earth’s rotation.

3.     Sunrise and Sunset: Rotation causes the apparent movement of the Sun across the sky, leading to sunrise and sunset.

2.     What is the effect of the inclined axis of the Earth on day and night?

o    Answer:

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

3.     Give a geographical reason for each of the following:

o    (i) The length of day and night is not equal at all places on Earth.

§  Geographical Reason: The tilted axis of the Earth and the migration belt of the Sun between the Tropics of Cancer and Capricorn.

o    (ii) The period of twilight and dawn increases polewards.

§  Geographical Reason: The oblique path of Sun rays toward the poles compared to the vertical path along the equator.

o    (iii) 25th of December in New Zealand may be one of the hottest days of the year.

§  Geographical Reason: On December 22nd, the Southern Hemisphere is tilted toward the Sun, resulting in summer in New Zealand.

Thinking Skills

Certainly! Here are the questions along with their answers:

1.     Imagine if the Earth stops its rotation on its axis. What would be its impact on the inhabitants of the Earth? Give examples to support your answer.

o    Answer:

§  If the Earth stopped rotating on its axis, it would have devastating effects on the planet and its inhabitants.

§  Examples of impacts:

1.     Drastic Temperature Differences: One side of the Earth would face the Sun perpetually, leading to scorching temperatures, while the other side would experience freezing cold.

2.     Disruption of Weather Patterns: The rotation drives weather patterns globally. Without rotation, extreme storms, droughts, and floods could occur.

3.     Increased Seismic Activity: Earth’s rotation balances tectonic plates and magma pressure. Stopping rotation might lead to more earthquakes and volcanic eruptions.

4.     Changes in Gravity: Centrifugal force from rotation counteracts gravity. Stopping rotation would alter the gravitational field, affecting orbits of celestial bodies.

2.     You travel for winter vacation to Australia from India. What type of climate will be there in Australia? Give reasons to support your answer.

o    Answer:

§  Australia experiences opposite seasons compared to India due to its location in the southern hemisphere.

§  During India’s winter (December to February), Australia has summer. The northern parts of Australia are tropical and hot, while the southern parts have a temperate climate.

§  Ocean currents (warm Indian Ocean to the west and cooler Pacific Ocean to the east) create distinct climate zones in Australia.

3.     On June 21, your uncle who lives in New York experiences summer, whereas your cousin who lives in Jakarta experiences winter. Give reasons to support your answer.

o    Answer:

§  On June 21, the summer solstice occurs in the northern hemisphere, while the southern hemisphere experiences winter.

§  Earth’s axial tilt causes varying sunlight distribution. During the summer solstice, the northern hemisphere tilts toward the Sun, resulting in summer in New York. Jakarta, in the southern hemisphere, experiences winter on the same date.

Question 1

Name the correct date depicted in your diagram.

Answer

December 22nd

Question 2

Name the latitude where the sun is shining vertically overhead.

Answer

23 1/2° S

Question 2

Name the part of the globe where there is night on this date.

Answer

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

Question 4

Name the latitude on which length of the day will be 24 hours.

Answer

66 1/2° S

Question 5

Give the date when the earth will be directly opposite to the above position.

Answer

June 21st

Question 6

What will be the vertical position of the sun on that date?

Answer

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

Question 7

What is the effect of the inclination of the earth upon the length of day and night?

Answer

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

Question 8

What will be the probable length of day and night on that date?

Answer

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.