What is the exact distance between the sun and earth?
There isn't an exact distance as the Earth's orbit is not perfectly circular. The Astronomical Unit (AU) is based on the average distance 1 AU = 149,597,870.7 km exactly.
The Earth's orbit is approximately elliptical. The perihelion distance is about 147,098,000 km and the aphelion distance is about 152,098,000 km.
The Astronomical Unit has been defined which is based on the average distance between the Earth and the Sun. The AU is now an international standard and it is exactly 149,597,870.7 km.