Which of these was a contribution of Newton to astronomy?. Physics & Astronomy

Artificial satellites could be put into orbit about the Earth
The Sun's gravity is greatest on a planet at perihelion, so the planet must speed up
All of these were due to Newton's work
The Moon pulls as strongly on us as we do on it
His differential calculus lets us calculate planetary motions more accurately

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What is science? Lections

Philosophical problems in physics, biology, and psychology Lections