Earth, Moon, and the Sun
1. Rotation of the Earth
- Earth spins on its axis (through North and South Poles) every 24 hours.
- Rotates anti-clockwise (West to East) when viewed from above the North Pole.
Effects:
- Causes day and night: Side facing the Sun has day; opposite side has night.
- Sun appears to rise in the East and set in the West.
- Stars and Moon also appear to move East to West; Pole Star stays nearly still.
2. Revolution of the Earth
- Earth revolves around the Sun in a nearly circular orbit, taking 365 days and 6 hours.
Effects:
- Changing Night Sky: Different stars are visible at sunset in different months.
- Seasons: Caused by Earth’s tilted axis and spherical shape.
- June: Northern Hemisphere tilts toward Sun (summer, longer days); Southern Hemisphere tilts away (winter).
- December: Opposite (winter in Northern Hemisphere, summer in Southern Hemisphere).
- Equinox (March 21, September 23): Equal day and night.
- Solstice (June 21: longest day; December 22: shortest day in Northern Hemisphere).
3. Eclipses
Solar Eclipse: Moon blocks Sun’s light from reaching Earth.
- Total: Moon fully covers Sun (small area, dark for minutes).
- Partial: Moon covers part of Sun.
- Safe Viewing: Use special goggles or project Sun’s image; never look directly.
Lunar Eclipse: Earth blocks sunlight from reaching Moon.
- Total: Moon fully in Earth’s shadow, looks dark red.
- Partial: Part of Moon in shadow.
- Safe Viewing: Can be watched with naked eye.
Moon’s apparent size matches Sun’s, allowing it to block Sun despite being smaller.
Key Points
- Earth’s rotation causes day/night and apparent motion of celestial bodies.
- Earth’s revolution and tilted axis cause changing night sky and seasons.
- Eclipses occur when Moon or Earth blocks sunlight; solar eclipses need safe viewing.
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