The correct option is (a) 1 only.
Explanation
The "Circle of Illumination" is a geometric boundary resulting from the spherical shape of the Earth and its position relative to the Sun. It defines the division between the hemisphere receiving sunlight and the hemisphere in shadow.Statement-wise Analysis:
- Statement 1 is Correct: The Circle of Illumination is the imaginary line or circle on the globe that separates the day (illuminated portion) from the night (dark portion). Due to the spherical shape of the Earth, only one half is illuminated by the Sun at any given time.
- Statement 2 is Incorrect: The Earth's axis of rotation is tilted at an angle of 23.5° from the vertical (or 66.5° from the orbital plane). The Circle of Illumination is always perpendicular to the Sun's rays. Consequently, the Circle of Illumination does not coincide with the axis of the Earth, except during the equinoxes (March 21 and September 23). At all other times, the axis and the circle intersect at an angle, causing variations in the length of day and night.
Key Takeaway: The Circle of Illumination is perpendicular to the orbital plane, whereas the Earth's axis is tilted. This divergence is the primary reason for the unequal length of days and nights across different latitudes.