Is the earth a perfect sphere?

No, the Earth is a bit wider than it is "high". The shape is often called a geoid (Earth-like) or an ellipsoid. The rotation of the Earth causes a slight bulge toward the equator. The circumference of the Earth at the equator (24,901.55) is about 41 miles greater than the circumference through the poles (24,859.82 miles. If you were standing on the moon, looking at the Earth, it would be virtually impossible to see the bulge and the Earth would appear to be a perfect sphere. The mathematical name for the shape of the earth is an 'Oblate spheroid'.