Question

The Earth’s equatorial and polar radius respectively are:

• A. 6357 km and 6378 km
• B. 6378 km and 6357 km
• C. 3189 km and 3178.5 km
• D. 3178.5 km and 3189 km

Hint:

Earth's equatorial radius>polar radius due to centrifugal bulging from rotation.

Answer 1

The Correct Option is B

To determine the correct values for Earth's equatorial and polar radii, let's analyze the Earth's shape and dimensions:

1. Earth's Shape:
The Earth is an oblate spheroid, meaning it's slightly flattened at the poles and bulging at the equator due to its rotation.

2. Key Measurements:
The standard reference ellipsoid (WGS84) defines:

• Equatorial radius: Longer due to centrifugal force from Earth's rotation
• Polar radius: Shorter because of the flattening at the poles

3. Correct Values:
According to NASA and international geodetic standards:

• Equatorial radius: 6,378 km (average)
• Polar radius: 6,357 km (average)

4. Why Other Options Are Incorrect:

• 6357 km and 6378 km: Reverses the correct values
• 3189 km and 3178.5 km: Approximately half the actual radii
• 3178.5 km and 3189 km: Both values are too small and reversed

5. Practical Significance:
This 21 km difference (6378-6357) affects:

• GPS accuracy
• Satellite orbits
• Gravity measurements

Final Answer:
The Earth's equatorial and polar radii are respectively 6378 km and 6357 km.