What two facts did Newton need to be able to calculate the acceleration of the Moon?

To calculate the acceleration of the Moon, Newton needed two key facts:

1. The gravitational force between the Moon and the Earth: Newton's law of universal gravitation states that the force of attraction between two objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. In this case, Newton needed to know the masses of the Moon and the Earth, as well as the distance between them.

2. The Moon's orbital period: Newton also needed to know the time it takes for the Moon to complete one orbit around the Earth. This information is necessary to determine the Moon's speed and, subsequently, its acceleration. The orbital period can be determined through astronomical observations or historical data on lunar movements.

With these two facts, Newton could apply his laws of motion to calculate the acceleration of the Moon.