Variations in the length of daytime and
nighttime from season to season are due to
revolution of the earth on a tilted axis
Understanding Seasonal Day and Night Length Variations
The question asks about the primary cause for the changes in the length of daytime and nighttime throughout the different seasons of the year. Let's break down the factors involved in Earth's movement and orientation in space.
Earth's Movements and Their Effects
- Earth's Rotation: The Earth spins on its axis, completing one rotation approximately every 24 hours. This rotation is what causes the cycle of day and night. As a point on Earth rotates towards the sun, it experiences sunrise and daytime; as it rotates away, it experiences sunset and nighttime. While rotation causes day and night, it does not explain why the *length* of the day changes from season to season.
- Earth's Revolution: The Earth orbits the sun, completing one revolution in about 365.25 days. This journey around the sun is crucial for the occurrence of seasons, but it's not just the revolution itself that causes the seasonal changes in day and night length.
- Earth's Axial Tilt: The Earth's axis of rotation is not perpendicular to its orbital plane around the sun. Instead, it is tilted at an angle of approximately $\text{23.5}^\circ$. This tilt is constant relative to the stars as Earth orbits the sun.
How Axial Tilt and Revolution Cause Seasonal Variations
The combination of Earth's revolution around the sun and its constant axial tilt is the key to understanding seasonal changes in day and night length. As the Earth orbits the sun, the hemisphere (Northern or Southern) tilted towards the sun changes:
- When the Northern Hemisphere is tilted towards the sun (around June), it receives more direct sunlight and experiences summer. During this time, the sun appears higher in the sky, and the period it is above the horizon (daytime) is longer. Conversely, the Southern Hemisphere is tilted away, experiencing winter with shorter days.
- When the Southern Hemisphere is tilted towards the sun (around December), it experiences summer with longer days. The Northern Hemisphere is tilted away, experiencing winter with shorter days.
- Around March and September, neither hemisphere is significantly tilted towards or away from the sun. This results in roughly equal lengths of day and night across most latitudes (equinoxes).
Therefore, the revolution of the Earth *while its axis is tilted* is the phenomenon that causes different parts of the Earth to receive varying amounts of sunlight duration throughout the year, leading to seasonal variations in the length of day and night.
Analyzing the Options
Let's look at the given options:
the earth’s rotation on its axis:
This causes day and night, but not the *variation* in their length seasonally. Incorrect.the earth’s revolution round the sun in an elliptical manner:
Revolution around the sun is necessary for seasons, but the elliptical shape is not the primary cause of seasonal day/night length variation. The tilt is far more significant. Incorrect.latitudinal position of the place:
Latitude affects *how much* the day/night length varies (variation is minimal near the equator and extreme near the poles), but it doesn't explain *why* there is a seasonal variation in the first place. Incorrect.revolution of the earth on a tilted axis:
This correctly identifies the combination of Earth's orbit around the sun and its constant axial tilt as the cause for the seasonal changes in the length of day and night. Correct.
Based on the analysis, the variation in the length of daytime and nighttime from season to season is due to the revolution of the Earth on a tilted axis.
| Motion | Description | Primary Effect |
|---|---|---|
| Rotation | Spinning on axis (approx. 24h) | Day and Night cycle |
| Revolution | Orbiting the sun (approx. 365.25 days) | Part of cause for seasons (combined with tilt) |
| Axial Tilt ($\text{23.5}^\circ$) | Axis is tilted relative to orbit plane | Uneven distribution of sunlight over the year; cause of seasonal day/night length variation and seasons (combined with revolution) |
Revision Table: Earth's Tilt, Revolution, and Seasons
Here's a quick summary table to review the key concepts related to Earth's motion and its impact on seasons and day/night length.
| Concept | Explanation | Relation to Day/Night Length Variation |
|---|---|---|
| Earth's Axial Tilt | Axis is tilted about $\text{23.5}^\circ$. | Crucial factor. Determines which hemisphere leans towards the sun. |
| Earth's Revolution | Orbit around the Sun. | Provides the yearly cycle during which the tilt's effect changes. |
| Combined Effect | Revolution + Constant Tilt | Causes varying angles of sunlight and duration of daylight throughout the year, leading to seasons and different day/night lengths. |
Additional Information: Solstices and Equinoxes
The seasonal variations in day and night length are most pronounced at specific points in Earth's orbit:
- Summer Solstice: Occurs around June 20-21 in the Northern Hemisphere (longest day) and December 21-22 in the Southern Hemisphere (longest day). The hemisphere is maximally tilted towards the sun.
- Winter Solstice: Occurs around December 21-22 in the Northern Hemisphere (shortest day) and June 20-21 in the Southern Hemisphere (shortest day). The hemisphere is maximally tilted away from the sun.
- Equinoxes: Occur around March 20-21 (Vernal or Spring Equinox) and September 22-23 (Autumnal Equinox). At these times, neither hemisphere is significantly tilted towards or away from the sun, resulting in approximately 12 hours of daylight and 12 hours of nighttime across most latitudes.
The degree of variation in day and night length increases as you move away from the equator towards the poles. At the poles, there can be periods of 24-hour daylight or 24-hour darkness.
Important Questions from Climate of India
With reference to 'Indian Ocean Dipole (IOD)' sometimes mentioned in the news while forecasting Indian monsoon, which of the following statements is/are correct?
1. IOD phenomenon is characterised by a difference in sea surface temperature between tropical Western Indian Ocean and tropical Eastern Pacific Ocean.
2. An IOD phenomenon can influence an El Nino's impact on the monsoon.
Select the correct answer using the code given below:
The seasonal reversal of winds is the typical characteristic of:
“Climate is extreme, rainfall is scanty and the people used to be nomadic herders.” The above statement best describes which of the following regions?
During a thunderstorm, the thunder in the skies is produced by the
1. Meeting of cumulonimbus clouds in the sky.
2. Lightning that separates the nimbus clouds.
3. Violent upward movement of air and water particles.
Select the correct answer using the codes given below:
Which one of the following is the characteristic climate of the Tropical Savannah Region?
