Question

How are the perihelion and aphelion of a planet determined?

Answer 1

Where G is the universal gravitational constant, M is the mass of the Sun, and a is the planet's semimajor axis. At perihelion, Earth's distance from the Sun is r=a(1-e) and at aphelion, it's r=a(1+e). So plugging in the numbers, the speed at perihelion is 30,300 m/s and at aphelion it's 29,300 m/s.