Elementary Ideas of Astronomy

Explain how Newton arrived at his law of gravitation from Kepler’s third law.

Explain how geocentric theory is replaced by heliocentric theory using the idea of retrograde motion of planets.

Explain in detail the Eratosthenes method of finding the radius of Earth.

Describe the measurement of Earth’s shadow (umbra) radius during the total lunar eclipse

The following photographs are taken from the recent lunar eclipse which occurred on January 31, 2018. Is it possible to prove that Earth is a sphere from these photographs?

A student was asked a question ‘why are there summer and winter for us? He replied as ‘since Earth is orbiting in an elliptical orbit, when the Earth is very far away from the Sun (aphelion) there will be winter, when the Earth is nearer to the Sun (perihelion) there will be winter’. Is this answer correct? If not, what is the correct explanation for the occurrence of summer and winter?

The Moon I_o orbits Jupiter once in 1.769 days. The orbital radius of the Moon I_o is 421700 km. Calculate the mass of Jupiter?