What is the shape of the Earth?

The Earth is not a mere sphere but an oblate spheroid i.e., a sphere flattened slightly at the top and bottom (poles) and bulging at the central region. There is a little more flattening at the bottom than at the trop.

Why is the Earth an oblate spheroid rather than a sphere?

The Earth’s spinning motion causes the central region to bulge leading to flattened top and bottom.

Why is the study of the Earth significant for astronomers?

The Earth, the third planet from the Sun, is only planet that can be easily studied. A study of the Earth (as a planet) helps astronomers to understand the other planets better.