Overview
This chapter explains the two main motions of the Earth — rotation and revolution — and shows how these motions produce everyday phenomena such as day and night, the apparent movement of the Sun, seasons, and time differences across the globe. Rotation is the spinning of Earth on its axis (west to east) once in about 24 hours and causes day and night and the apparent rising/setting of the Sun. Revolution is Earth’s movement around the Sun, taking about 365¼ days; combined with the tilt of Earth’s axis (about 23.5°) it produces seasons and varying day lengths. The chapter also introduces how time is calculated across different longitudes (15° = 1 hour), the idea of standard time (for example, Indian Standard Time), and the use of calendars including the reason for a leap year. Understanding these motions is important because they form the basis for later study of climate, weather, navigation and map skills, and they explain many familiar patterns in daily life and nature. Practical activities (like observing shadows) and simple diagrams help students visualise the Earth’s movements and their effects.
Learning Objectives
- Define rotation and revolution of the Earth and state their durations.
- Explain how Earth's rotation causes day and night and the apparent daily motion of the Sun.
- Describe the tilt of Earth's axis and explain its role in producing seasons.
- Illustrate by a labelled diagram the positions of Earth in different seasons (solstices and equinoxes).
- Distinguish between solstice and equinox, giving typical dates and key features of each.
- Relate the concept of inclination of axis to variation in day length and temperature across seasons.
- Identify how latitude affects the length of day and night and seasonal temperature changes.
- Compare the climatic effects of Earth's revolution on temperate, tropical and polar regions.
Topics in this chapter
6 topics · tap a topic title to jump straight to it.
Introduction to Motions of the Earth
Introduction to Motions of the Earth
Key Point: Circumference of Earth (approximate): C = 2 * π * R (R ≈ 6,371 km, so C ≈ 40,075 km)
Introduction to Motions of the Earth
The Earth moves in two main ways: rotation and revolution. These motions are responsible for daily changes (day and night), yearly changes (seasons), and other observable phenomena like the changing positions of the Sun and stars.
1. Rotation
Rotation is the spinning of the Earth around an imaginary line called its axis. The axis passes through the North and South Poles. Earth completes one full rotation in about 24 hours. Because of rotation:
- One half of Earth faces the Sun (day) while the other half faces away (night).
- The Sun, Moon and stars appear to move from east to west across the sky.
- Different longitudes experience different local times (this leads to time zones).
2. Revolution
Revolution is the motion of Earth as it travels around the Sun in an almost circular path called an orbit. Earth completes one revolution in about 365.25 days (one year). Important points about revolution:
- The Earth's axis is tilted by about 23.5° relative to the plane of its orbit. This tilt is the main reason we have seasons.
- When the Northern Hemisphere is tilted toward the Sun we get summer there and winter in the Southern Hemisphere — and vice versa.
- Key points in the yearly cycle are the solstices (longest and shortest days) and the equinoxes (day and night nearly equal).
Other consequences and examples
- Time zones: because Earth rotates 360° in 24 hours, it turns 15° of longitude each hour. This is how time zones are determined.
- Eclipses: when the Sun, Earth and Moon line up during their motions, we may see solar or lunar eclipses.
Understanding rotation and revolution helps explain everyday experiences like sunrise and sunset times, why seasons change, and why different places on Earth have different day lengths and local times.
- Day and night: When it is daytime in India, at the same moment it is night in parts of the Americas — this is due to Earth's rotation.
- Sunrise and sunset direction: The Sun appears to rise in the east and set in the west because Earth rotates from west to east.
- Seasons: When India (Northern Hemisphere) tilts closer to the Sun (around June), it experiences summer while Australia (Southern Hemisphere) experiences winter.
- Time difference: India (about 82.5°E) is roughly 5.5 hours ahead of Greenwich Mean Time because of longitude-based time calculation.
- Midnight Sun and Polar Night: Near the Arctic Circle during summer the Sun can stay above the horizon for 24 hours; in winter it can stay below the horizon for long periods.
- Eclipse example: A lunar eclipse happens when the Earth comes between the Sun and the Moon during revolution and the Moon passes through Earth's shadow.
- \[Circumference of Earth (approximate): C = 2 * π * R (R ≈ 6,371 km\]\[so C ≈ 40,075 km)\]
- \[Rotational (linear) speed at equator: v = 2 * π * R / T (T = 24 hours → v ≈ 40,075 km / 24 h ≈ 1,670 km/h)\]
- \[Angular speed of rotation: ω = 360° / T (T = 24 h → ω = 15° per hour)\]
- \[Orbital (average) speed of Earth around Sun: v_orbit = 2 * π * a / P (a ≈ 1 AU\]\[P ≈ 365.25 days → v_orbit ≈ 30 km/s)\]
- \[Time-zone rule: Earth rotates 360° in 24 hours → 360° / 24 = 15° of longitude corresponds to 1 hour difference in local time\]
Rotation of the Earth
Rotation of the Earth
Key Point: Angular speed (degrees per hour): ω = 360° / 24 h = 15° per hour
What is rotation? Rotation is the spinning of the Earth around an imaginary line called its axis. The axis passes through the North and South Poles. The Earth rotates from west to east.
How long does one rotation take? One complete rotation takes about 24 hours. This 24-hour period is the reason we have day and night.
Direction and apparent motion: Because the Earth turns eastward, the Sun, Moon and stars appear to rise in the east and set in the west. If you watch the sky through the night, the stars seem to move from east to west.
Important effects of Earth's rotation:
- Day and night: At any moment, half of the Earth faces the Sun (day) while the other half faces away (night). As the Earth rotates, places move into and out of sunlight, creating the daily cycle.
- Local time and time zones: Because the Earth is round and rotates, local time changes with longitude. The Sun reaches its highest point at different times in different longitudes, so the world is divided into time zones.
- Different speeds at different latitudes: Points on the equator travel fastest through space during rotation; points near the poles move much slower. Linear speed decreases with latitude.
- Small flattening at the poles: Centrifugal force from rotation makes the Earth slightly bulge at the equator and flatten at the poles (this effect is small but measurable).
- Evidence of rotation: A Foucault pendulum (seen in some science museums) and time-lapse photos of Earth's night lights show rotation.
What rotation is not: Rotation causes day and night, but it is not the reason for seasons. Seasons are caused by the Earth's tilt and its revolution around the Sun.
Simple classroom demonstration: Use a globe (Earth model) and a torch (Sun). Shine the torch on the globe and slowly turn the globe to show how different places move into daylight and into night.
- Day and night: When India faces the Sun it is day there; while at the same time it is night in parts of the Americas.
- Sunrise in the east and sunset in the west: Observers everywhere see the Sun appear in the eastern sky and disappear in the western sky because of Earth's eastward rotation.
- Time zones and local time: If it is noon in London, it will be later in locations east of London and earlier in locations to the west. Each 15° of longitude equals one hour of time difference.
- Foucault pendulum: A swinging pendulum slowly changes its plane of swing as the Earth rotates beneath it — visible proof of rotation.
- Equatorial speed: A person standing on the equator moves eastward at about 1,670 km/h because of Earth's rotation.
- Sunset times across longitudes: When it is sunset in one city, cities eastward see sunset a bit earlier and cities westward later (roughly 4 minutes per degree of longitude).
- \[Angular speed (degrees per hour): ω = 360° / 24 h = 15° per hour\]
- \[Angular speed (radians per second): ω = 2π / T ≈ 2π / (24×3600 s) ≈ 7.27 × 10⁻⁵ rad/s\]
- \[Linear speed at equator: v = 2πR / T ≈ 40,030 km / 24 h ≈ 1,670 km/h (≈ 465 m/s)\]\[where R ≈ 6371 km\]
- \[Linear speed at latitude φ: v(φ) = (2πR / T) × cos φ ≈ 1,670 km/h × cos φ (example: at 45°\]\[v ≈ 1,670×0.707 ≈ 1,180 km/h)\]
- \[Time difference with longitude: Δt = Δλ × 4 minutes per degree (because 24 h / 360° = 4 min/°)\]
- \[Centrifugal acceleration (near equator): a = ω²R ≈ (7.27×10⁻⁵)² × 6.371×10⁶ m ≈ 0.034 m/s² (a very small effect compared to gravity)\]
Time and Longitude
Time and Longitude
Key Point: Time difference (hours) = Longitude difference (degrees) / 15
What is longitude? Longitude are imaginary north–south lines (meridians) that run from the North Pole to the South Pole. They measure angular distance east or west of the Prime Meridian (0°) which passes through Greenwich, London.
Why longitude matters for time — The Earth rotates once in 24 hours (360°). So it turns 360°/24 = 15° every hour. Because of this rotation, the Sun appears to move across the sky from east to west. Local solar time is set by the Sun's highest point (local noon) when the Sun crosses a place's meridian. Every 15° of longitude change corresponds to one hour difference in local solar time.
Direction rule: places east of the Prime Meridian are ahead of Greenwich Mean Time (GMT); places west are behind GMT.
Standard time and time zones — Using local solar time for every meridian would be confusing. So the world is divided into time zones, generally following meridians about 15° apart. Each zone uses a standard time for convenience. Countries may choose a standard meridian that does not exactly match local solar time (for example, India uses 82.5°E as its standard meridian so Indian Standard Time is 5 hours 30 minutes ahead of GMT).
Conversions and sign convention — To compute local time from GMT: Local time = GMT + (longitude in degrees / 15) hours, where longitude east of Greenwich is positive and west is negative. If the result crosses 24:00 or goes below 0:00, adjust by adding or subtracting 24 hours.
Important points:
- 15° longitude = 1 hour of time difference
- 1° longitude ≈ 4 minutes of time (60 min / 15°)
- Standard time zones smooth out local solar differences; political boundaries and convenience often determine zone borders.
- If it is 12:00 noon at Greenwich (0°), what is local solar time at 75°E? Calculation: time difference = 75/15 = 5 hours ahead → local solar time = 12:00 + 5:00 = 17:00 (5:00 PM).
- New Delhi longitude ≈ 77.2°E. Local solar time difference from GMT = 77.2/15 ≈ 5.15 hours ≈ 5 hours 9 minutes. So when it is 12:00 GMT, local solar time in Delhi is about 17:09. But India uses IST based on 82.5°E (82.5/15 = 5.5 hours), so official time is 17:30.
- New York longitude ≈ 74°W. Time difference = 74/15 ≈ 4.93 hours ≈ 4 hours 56 minutes behind GMT. If GMT is 12:00, local solar time in New York ≈ 07:04 AM.
- Air travel example: A flight departs London (GMT) at 18:00 and lands in a city 30°E two hours later by clock-time. The local time at the destination is GMT + 30/15 = GMT + 2 hours, so local time on arrival will be 18:00 + 2:00 (flight duration) + 2:00 (time zone change) = 22:00 local time.
- Every 1° of longitude equals 4 minutes of time. So two places 7.5° apart differ by 30 minutes.
- \[Time difference (hours) = Longitude difference (degrees) / 15\]
- \[Time difference (minutes) = Longitude difference (degrees) × 4\]
- \[Local time = GMT + (Longitude° / 15) hours (take longitude east as positive\]\[west as negative)\]
- \[Degrees = Hours × 15\]
- \[Indian Standard Time (IST) = GMT + 5 hours 30 minutes (based on 82.5°E)\]
Revolution of the Earth
Revolution of the Earth
Key Point: Time for one revolution (sidereal year) ≈ 365.25 days (365 days 6 hours).
What is revolution? Revolution of the Earth means the movement of the Earth around the Sun along a path called its orbit. One complete trip of the Earth around the Sun is called a revolution.
Duration and shape of orbit: Earth takes about 365 days and 6 hours (365.25 days) to complete one revolution. The orbit is not a perfect circle but slightly elliptical (oval-shaped).
Tilt and its importance: The Earth’s axis is tilted at about 23.5 degrees to the plane of its orbit. Because of this tilt, as the Earth revolves around the Sun, different parts of the Earth receive different amounts of sunlight at different times of the year. This difference causes the seasons.
Seasons:
- When the Northern Hemisphere is tilted towards the Sun, it receives more direct sunlight and has summer there while the Southern Hemisphere has winter.
- When the Northern Hemisphere is tilted away from the Sun, it has winter and the Southern Hemisphere has summer.
- Equinoxes (around March 21 and September 23) are the two days when day and night are nearly equal everywhere (12 hours each).
- Solstices (around June 21 and December 22) are the days of maximum and minimum daylight in each hemisphere (longest and shortest day).
Direction and relation with rotation: From above the North Pole the Earth revolves around the Sun counterclockwise. Revolution and rotation (spin of Earth on its axis) together determine day/night and seasonal patterns, but revolution itself causes the yearly change of seasons.
Perihelion and aphelion: Because the orbit is elliptical, Earth is closest to the Sun (perihelion, about 147.1 million km) in early January and farthest (aphelion, about 152.1 million km) in early July. Distance differences are small and are NOT the main cause of seasons—tilt is.
Leap year: The extra 0.25 day (6 hours) each year is why every 4th year we add one day (29 February) to keep the calendar in step with the seasons. Century years are leap only if divisible by 400 (e.g., 2000 was leap, 1900 was not).
Effects of revolution (summary):
- Causes seasons (spring, summer, autumn, winter).
- Changes the length of day and night through the year at different latitudes.
- Produces equinoxes and solstices.
- Explains why climate and daylight patterns vary with latitude.
Simple classroom demonstration idea: Use a lamp (Sun) and a tilted globe (Earth). Move the globe around the lamp keeping the tilt pointing in the same direction to show how seasons change.
- When it is summer in India (Northern Hemisphere tilted towards the Sun), Australia (Southern Hemisphere) has winter at the same time.
- On around March 21 (vernal equinox) and September 23 (autumnal equinox) nearly every place on Earth has about 12 hours of day and 12 hours of night.
- Because of the extra 6 hours each year, 2020 and 2024 were leap years (February had 29 days).
- Although Earth is closest to the Sun in January (perihelion), the Northern Hemisphere has winter then; this shows seasons are due to axial tilt, not distance from the Sun.
- \[Time for one revolution (sidereal year) ≈ 365.25 days (365 days 6 hours).\]
- \[Approximate orbital speed: v = 2πa / T\]\[where a = mean distance to Sun (1 AU ≈ 1.496 × 10^11 m) and T = orbital period in seconds\]\[For Earth v ≈ 29.8 km/s.\]
- \[Kepler's third law (simple form): T^2 ∝ a^3\]\[For planets using years and astronomical units: T^2 = a^3 (Earth: T = 1 year\]\[a = 1 AU).\]
Seasons and Related Phenomena
Seasons and Related Phenomena
Key Point: Earth's axial tilt: 23.5° (approx).
What are seasons? Seasons are recurring periods of the year with characteristic weather patterns (temperature, rainfall, day-length) — for example spring, summer, autumn (fall) and winter. In many parts of the world (especially tropics) people also recognise wet (monsoon) and dry seasons.
Why do seasons occur? Seasons are caused mainly by two facts about Earth:
- Earth's axis is tilted by about 23.5° with respect to the plane of its orbit around the Sun (the ecliptic).
- Earth revolves around the Sun once every ~365.25 days while maintaining that tilt direction relative to the stars.
Because of the tilt, during different parts of the year different hemispheres lean toward the Sun. The hemisphere tilted toward the Sun receives more direct sunlight (solar rays fall more vertically), so it receives more energy per unit area and therefore becomes warmer (summer). The hemisphere tilted away receives less direct sunlight (more slanted rays), so it is colder (winter).
Direct vs. indirect rays: When sunlight strikes the ground directly (near perpendicular), energy is concentrated on a small area → higher temperature. Slanted rays spread energy over a larger area → lower temperature.
Key dates — solstices and equinoxes:
- Summer solstice (~June 21): Northern Hemisphere tilted most toward the Sun — longest day in north, start of astronomical summer in north.
- Winter solstice (~Dec 21): Northern Hemisphere tilted most away — shortest day in north, start of astronomical winter in north.
- Vernal (spring) equinox (~Mar 21) and autumnal equinox (~Sept 23): Both hemispheres receive nearly equal sunlight and day and night are approximately equal length.
Day length and seasons: Tilt causes the Sun to rise earlier and set later in the hemisphere having summer, giving longer days. Near equator day length changes little through the year; at high latitudes day length changes a lot. Above the Arctic/Antarctic Circles there are continuous daylight (midnight sun) in summer and continuous night (polar night) in winter.
Common misconceptions: Seasons are NOT caused by Earth being closer to or farther from the Sun. Earth's orbit is slightly elliptical, but the change in distance is too small and the tilt effect dominates. For example, Earth is closest to the Sun (perihelion) in early January while it is winter in the Northern Hemisphere.
Effects on life and human activity: Seasons affect agriculture (which crops are grown and when — e.g., kharif and rabi crops in India), animal behaviour (migration, hibernation), festivals (Holi in spring, Diwali/Makar Sankranti around harvest/winter), clothing, energy use and school calendars.
- India: Summer in India (hot and dry in many parts) peaks in May–June; monsoon (wet season) arrives mostly in June–September bringing heavy rains; winter is generally from December–February with cooler temperatures in northern India.
- Opposite seasons in hemispheres: When it is summer in the Northern Hemisphere (June–August), it is winter in the Southern Hemisphere (June–August) — e.g., July is summer in India and winter in Australia.
- Equinox effect: Around March 21 and September 23 the Sun is overhead at the equator and day and night are about equal everywhere.
- Polar phenomena: Above the Arctic Circle (e.g., northern parts of Norway) the Sun does not set for several weeks around the summer solstice (Midnight Sun) and does not rise for several weeks around the winter solstice (Polar Night).
- Agriculture: Rabi crops (wheat) are sown in winter and harvested in spring; kharif crops (rice, maize) are sown with the monsoon (summer) and harvested in autumn.
- \[Earth's axial tilt: 23.5° (approx).\]
- \[Time for one revolution around Sun: ≈ 365.25 days\]\[Time for one rotation on axis: ≈ 24 hours.\]
- \[Solar intensity (approximation): I = I0 × cos θ\]\[where θ is the angle between the Sun's rays and the perpendicular to the surface\]\[Smaller θ (more direct rays) → larger I → warmer.\]
- \[Relative day length concept (qualitative): When a hemisphere tilts toward the Sun its day length > 12 hours\]\[when tilting away day length < 12 hours. (Accurate day-length formulas use latitude and solar declination — for Class 6 the qualitative rule is sufficient.)\]
Key Terms and Summary Concepts
Key Terms and Summary Concepts
Key Point: Rotation period: T_rot ≈ 24 hours (one day).
The motions of the Earth — rotation (spin on its axis) and revolution (movement around the Sun) — explain day and night, the year, seasons, changes in day length, and time zones. Below are short definitions of essential terms followed by core summary concepts that link the terms to real observations.
Key terms
- Rotation: Earth turning once around its axis. One rotation ≈ 24 hours = one day.
- Axis: The imaginary line through the North and South Poles about which Earth rotates. It is tilted ~23.5° to the plane of Earth's orbit.
- Revolution: Earth’s orbiting motion around the Sun. One revolution ≈ 365.25 days = one year.
- Tilt (Obliquity): The 23.5° tilt of Earth’s axis; causes seasons by changing the Sun’s directness on different hemispheres.
- Solstice: Two days (around June 21 and December 21) when one hemisphere gets maximum or minimum sunlight (longest/shortest day).
- Equinox: Two days (around March 21 and September 23) when day and night are about equal worldwide.
- Circle of illumination: The dividing line between day and night on Earth’s surface at any moment.
- Perihelion and Aphelion: Perihelion = Earth closest to Sun (~early January). Aphelion = Earth farthest from Sun (~early July). Not the cause of seasons.
- Longitude and Time Zones: Longitude measures east–west position. Every 15° of longitude ≈ 1 hour difference in local solar time.
- Leap year: Because a year is ~365.25 days, an extra day (Feb 29) is added roughly every 4 years to keep calendars aligned.
Summary concepts
- Rotation causes day and night: the surface turned toward the Sun is in daylight; the opposite side is in night. The circle of illumination moves with rotation.
- Because the axis is tilted (23.5°) while Earth revolves, different hemispheres receive varying sunlight angles during the year — this produces seasons. When the Northern Hemisphere tilts toward the Sun, it experiences summer while the Southern Hemisphere has winter, and vice versa.
- Solstices mark the extremes of sunlight (longest and shortest days); equinoxes mark when day and night are nearly equal.
- Earth’s distance from the Sun (perihelion/aphelion) changes slightly through the year but does not cause seasons — tilt does.
- Time zones are based on longitude: every 15° corresponds to one hour. Local solar time differs with longitude; standard time zones make civil time uniform across regions.
- Day length varies with latitude and season: near the equator day length stays near 12 hours year-round; at higher latitudes day length changes strongly and polar regions can have continuous daylight or darkness for part of the year.
- Leap years correct the calendar so seasons and months stay aligned with Earth’s position in orbit.
- Sunrise and sunset: As Earth rotates eastward, places move into and out of sunlight — explaining daily sunrise and sunset times.
- Seasons in India vs Australia: When India (Northern Hemisphere) has summer (June–August), Australia (Southern Hemisphere) has winter because of Earth’s tilt.
- Equinox observation: Around March 21 and September 23, most places experience roughly 12 hours of daylight and 12 hours of night.
- Midnight sun and polar night: Above the Arctic Circle in June there can be 24 hours of daylight; in December there can be continuous night — a result of tilt and revolution.
- Leap year example: Year 2020 was a leap year (Feb 29 added); 1900 was not (century not divisible by 400), but 2000 was (divisible by 400).
- Time difference: When it is noon at the Prime Meridian (0° longitude), it is 5:30 pm in India (approx. 82.5°E) because 82.5°/15° = 5.5 hours ahead.
- \[Rotation period: T_rot ≈ 24 hours (one day).\]
- \[Angular speed of rotation: ω_rot = 360° / T_rot = 15° per hour.\]
- \[Linear speed at equator (approx): v_eq = 2πR / T_rot\]\[where R ≈ 6371 km\]\[So v_eq ≈ 2 × π × 6371 km / 24 h ≈ 1670 km/h.\]
- \[Revolution period: T_rev ≈ 365.25 days (one year).\]
- \[Angular speed of revolution: ω_rev = 360° / T_rev ≈ 0.9856° per day.\]
- \[Orbital speed (approx): v_orb = 2πa / T_rev\]\[with a ≈ 149,600,000 km (1 AU)\]\[So v_orb ≈ 107,000 km/h.\]
Key Concepts
- Rotation
- The spinning of the Earth around its imaginary axis; one rotation takes about 24 hours.
- Revolution
- The movement of the Earth around the Sun along its orbit; one revolution takes about 365¼ days.
- Axis
- An imaginary line through the Earth joining the North and South Poles about which the Earth spins.
- Axial tilt
- The angle (about 23.5°) that Earth's axis is tilted relative to its orbital plane; this tilt affects seasons.
- Equator
- An imaginary line at 0° latitude that divides the Earth into the Northern and Southern Hemispheres.
- Poles
- The two points where the Earth's axis meets its surface: the North Pole and the South Pole.
- Latitude
- The angular distance of a place north or south of the Equator measured in degrees (°).
- Longitude
- The angular distance of a place east or west of the Prime Meridian measured in degrees (°).
- Prime Meridian
- The meridian at 0° longitude passing through Greenwich, London; used as the reference for longitude and time.
- International Date Line
- An imaginary line roughly along the 180° meridian where the calendar date changes when crossed.
- Tropic of Cancer
- A circle of latitude at about 23.5°N marking the northernmost position of the Sun at noon (June solstice).
- Tropic of Capricorn
- A circle of latitude at about 23.5°S marking the southernmost position of the Sun at noon (December solstice).
- Arctic Circle
- A circle of latitude at about 66.5°N; areas inside it experience at least one day of continuous daylight and one day of continuous night each year.
- Antarctic Circle
- A circle of latitude at about 66.5°S; regions inside it have at least one day of continuous daylight and one day of continuous night annually.
- Day and Night
- Alternating periods of light and darkness on Earth caused by its rotation; the side facing the Sun has day, the opposite side has night.
- Seasons
- Regular changes in climate and daylight during the year caused mainly by the Earth's axial tilt and its revolution around the Sun.
- Solstice
- A point in Earth's orbit when the Sun reaches its greatest distance north or south of the Equator (two times a year).
- Equinox
- Either of the two times in the year when day and night are approximately equal in length worldwide (around 21 March and 23 September).
- Time zones
- Regions of the Earth that have the same standard time, usually differing by whole hours from neighboring zones based on longitude.
- Perihelion
- The point in Earth's orbit when it is closest to the Sun (occurs in early January).
Practice Questions
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Earth's rotation causes: / पृथ्वी के घूर्णन के कारण होता है: (a) Seasons / ऋतुएँ (b) Day and night / दिन और रात (c) The leap year / अधिवर्ष (d) The phases of the Moon / चंद्रमा की कलाएँ
Show answer
(b) Day and night / दिन और रात — As Earth rotates on its axis from west to east, half of the Earth faces the Sun (day) while the other half faces away (night). / जब पृथ्वी अपनी धुरी पर पश्चिम से पूर्व की ओर घूमती है, तो आधी पृथ्वी सूर्य की ओर होती है (दिन) जबकि दूसरी आधी दूर होती है (रात)।
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The Earth's axis is tilted at approximately: / पृथ्वी की धुरी लगभग कितने डिग्री झुकी है? (a) 10° / 10 डिग्री (b) 45° / 45 डिग्री (c) 23.5° / 23.5 डिग्री (d) 66.5° / 66.5 डिग्री
Show answer
(c) 23.5° / 23.5 डिग्री — The axial tilt of about 23.5° is the primary reason why seasons occur as Earth revolves around the Sun, causing different hemispheres to receive varying amounts of sunlight. / लगभग 23.5° का अक्षीय झुकाव ऋतुओं के होने का मुख्य कारण है, क्योंकि जब पृथ्वी सूर्य के चारों ओर परिक्रमा करती है, तो अलग-अलग गोलार्धों को सूर्य का प्रकाश अलग-अलग मात्रा में मिलता है।
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When the Northern Hemisphere is tilted toward the Sun (around June 21), which season does India experience? / जब उत्तरी गोलार्ध सूर्य की ओर झुका होता है (लगभग 21 जून), तो भारत में कौन सी ऋतु होती है? (a) Winter / शीत ऋतु (b) Autumn / शरद ऋतु (c) Spring / वसंत ऋतु (d) Summer / ग्रीष्म ऋतु
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(d) Summer / ग्रीष्म ऋतु — When the Northern Hemisphere tilts toward the Sun, it receives more direct sunlight for longer periods, making it hotter (summer), while the Southern Hemisphere has winter at the same time. / जब उत्तरी गोलार्ध सूर्य की ओर झुकता है, तो उसे लंबे समय तक अधिक सीधी धूप मिलती है, जिससे गर्मी (ग्रीष्म ऋतु) होती है, जबकि उसी समय दक्षिणी गोलार्ध में शीत ऋतु होती है।
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On the days called equinoxes (around March 21 and September 23), the length of day and night is ___________. / अयनांत दिनों पर (लगभग 21 मार्च और 23 सितंबर), दिन और रात की अवधि ___________ होती है।
Show answer
Equal (approximately 12 hours each everywhere) / बराबर (लगभग हर जगह 12 घंटे) — On equinoxes, neither hemisphere is tilted toward or away from the Sun, so sunlight falls equally on both hemispheres. / अयनांत पर, न तो कोई गोलार्ध सूर्य की ओर झुका होता है और न ही दूर, इसलिए दोनों गोलार्धों पर समान धूप पड़ती है।
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Earth rotates ___________ degrees per hour because it completes 360° in 24 hours. / पृथ्वी एक घंटे में ___________ डिग्री घूमती है क्योंकि यह 24 घंटों में 360° पूरा करती है।
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15 degrees / 15 डिग्री — 360° ÷ 24 hours = 15° per hour. This is also the basis for time zones: every 15° of longitude corresponds to a 1-hour time difference. / 360° ÷ 24 घंटे = 15° प्रति घंटा। यह समय क्षेत्रों का आधार भी है: हर 15° देशांतर पर 1 घंटे का समय अंतर होता है।
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True or False: The seasons are caused by the Earth being closer to the Sun in summer and farther away in winter. / सत्य या असत्य: ऋतुएँ इसलिए होती हैं क्योंकि पृथ्वी गर्मियों में सूर्य के पास होती है और सर्दियों में दूर।
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False / असत्य — Seasons are caused by the tilt of Earth's axis, not by the distance from the Sun. In fact, Earth is slightly closer to the Sun in January (perihelion) when the Northern Hemisphere has winter. / ऋतुएँ पृथ्वी की धुरी के झुकाव के कारण होती हैं, न कि सूर्य से दूरी के कारण। वास्तव में, पृथ्वी जनवरी में सूर्य के थोड़ी करीब होती है (उपसौर) जब उत्तरी गोलार्ध में शीत ऋतु होती है।
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What is a 'leap year' and why does it occur? / 'अधिवर्ष' क्या होता है और यह क्यों होता है?
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A leap year has 366 days instead of 365, with February having 29 days instead of 28. / अधिवर्ष में 365 के बजाय 366 दिन होते हैं, जिसमें फरवरी में 28 के बजाय 29 दिन होते हैं। It occurs because Earth takes about 365.25 days to revolve around the Sun. The extra 0.25 days accumulate to make one full extra day every 4 years. / यह इसलिए होता है क्योंकि पृथ्वी को सूर्य के चारों ओर एक चक्कर लगाने में लगभग 365.25 दिन लगते हैं। अतिरिक्त 0.25 दिन जमा होते हैं और हर 4 साल में एक पूरा अतिरिक्त दिन बनता है।
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What is the 'Summer Solstice' in the Northern Hemisphere and on what approximate date does it occur? / उत्तरी गोलार्ध में 'ग्रीष्म अयनांत' क्या है और यह लगभग किस तिथि को होता है?
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The Summer Solstice in the Northern Hemisphere occurs around June 21. On this day, the Northern Hemisphere is tilted most toward the Sun, making it the longest day and shortest night of the year in the Northern Hemisphere. / उत्तरी गोलार्ध में ग्रीष्म अयनांत लगभग 21 जून को होता है। इस दिन उत्तरी गोलार्ध सूर्य की ओर सबसे अधिक झुका होता है, जिससे उत्तरी गोलार्ध में साल का सबसे लंबा दिन और सबसे छोटी रात होती है। The Sun is directly overhead at the Tropic of Cancer (23.5°N) on this day. / इस दिन सूर्य कर्क रेखा (23.5°N) पर सीधे ऊपर होता है।
Related Laws & Principles
Explore allFoundational laws & principles behind this chapter. Each one opens a full page — what it says, why it matters, five practice questions and the mistakes to avoid.