A Sphere is a perfectly round geometrical object in three-dimensional space. Every point on the surface is the exact same distance (radius) from the center.
The Shape of the World
For centuries, humans debated the shape of the Earth. Around 240 BC, the Greek mathematician Eratosthenes not only realized the Earth was a sphere but also calculated its circumference with surprising accuracy using shadows in different cities.
Why are planets spherical?
Gravity pulls matter inward equally from all directions. Over time, massive objects like planets and stars settle into a spherical shape because it is the most efficient way to pack matter together. Small asteroids, with less gravity, often have irregular "potato" shapes.
Properties
- No Edges or Vertices: A sphere is smooth.
- Surface Area: 4 × π × r²
- Volume: (4/3) × π × r³
Questions & Answers
Q: What is a Hemisphere?
A: A hemisphere is exactly half of a sphere. The Earth is divided into Northern and Southern hemispheres.
Q: Is a circle a sphere?
A: No. A circle is 2D (flat). A sphere is 3D (solid).