A solar eclipse occurs when the Moon moves between the Sun and the Earth,
blocking the Sun’s light either partially or totally for a short time.
Basic Alignment (Very Important)
Sun – Moon – Earth (in a straight line)
This alignment is called Syzygy.
When does a Solar Eclipse occur?
• Only on a New Moon day (Amavasya)
• When the Moon is near one of the lunar nodes
Why not every New Moon causes an eclipse?
• Moon’s orbit is tilted about 5° to Earth’s orbit
Types of Solar Eclipse
• Total Solar Eclipse → Moon completely covers the Sun (Umbra)
• Partial Solar Eclipse → Sun partly covered (Penumbra)
• Annular Solar Eclipse → Ring of fire appearance (Antumbra)
• Hybrid Solar Eclipse → Total at some places, annular at others
Shadow Regions
• Umbra → Total eclipse
• Penumbra → Partial eclipse
• Antumbra → Annular eclipse
Duration & Visibility
• Lasts only a few minutes
• Visible from limited areas of Earth
Solar vs Lunar Eclipse
Solar Eclipse → New Moon, unsafe to see directly
Lunar Eclipse → Full Moon, safe to view
• Mass is the amount of matter → does not change anywhere
• Weight = m × g → depends on gravitational acceleration (g)
• In a satellite, the astronaut and satellite are in continuous free fall around the Earth
• Normal reaction becomes zero → apparent weight = 0 (Weightlessness)
👉 Gravity is not zero in orbit; the astronaut only appears weightless
Key Concepts You Must Know
1. Mass vs Weight
• Mass → Independent of location, SI unit: kg
• Weight → Depends on gravity, SI unit: Newton (N)
• In space → Mass same, Weight zero (apparent)
2. What is Weightlessness?
• Condition when apparent weight becomes zero
• Occurs when no supporting force acts on the body
• Seen in satellites, free-falling lift, space stations
3. Why do astronauts float?
• Satellite has tangential (orbital) velocity
• Gravity provides centripetal force
• Astronaut and satellite fall together → no contact force → floating effect
4. Is gravity absent in space?
❌ No
• Gravity decreases with height but never becomes zero
• At satellite height, gravity is about 90% of Earth’s surface value
• Earth is an oblate spheroid (flattened at poles, bulged at equator)
• Radius of Earth is smaller at poles than at equator
• Gravitational acceleration (g) is inversely proportional to square of radius
• Smaller radius at poles → greater value of g → greater weight
Role of Earth’s Rotation
• Centrifugal force is maximum at the equator
• Centrifugal force is zero at the poles
• Centrifugal force reduces effective gravity at equator
Why other options are incorrect?
• Moon’s attraction is negligible compared to Earth’s gravity
• Sun’s attraction does not cause daily weight variation
• Gravitational pull being more at poles is an effect, not the root cause
Key Formula
• Weight (W) = m × g
• Mass remains constant; g varies with location
Comparison: Poles vs Equator
• Poles → Minimum radius, zero centrifugal force, maximum weight
• Equator → Maximum radius, maximum centrifugal force, minimum weight