UCSB Science Line
How does the sun reflect on the earth and how do the planets rotate around the sun? How does the earth rotate around the sun?
Question Date: 2020-09-08

The sun is a massive ball of very hot gas. Just like the flame of a candle, the hot gas gives off energy in the form of heat and light. The heat and light energy from the sun reach all of the planets, including earth. We can see other planets and objects in space because light from the sun reflects off of them and reaches our eyes.

Earth (and the other planets) rotate on their own axes in addition to revolving around the sun. At this link, you can see an animation that shows how these two types of spinning (rotation and revolution) happen at the same time: (if the flash animation does not load, a similar video is found here ).

The rotation around the earth's axis is what causes night and day, because we can only see the sun's light when our side of the earth is facing towards the sun. If the earth did NOT rotate around its axis (but still orbited around the sun), nighttime and daytime would each last half a year, because it takes one year for the earth to complete one full orbit around the sun.

But the different planets have different speeds of rotation and revolution! The following table (taken from this website ) shows how long it takes each planet to complete one rotation about its axis, and how long it takes to complete one revolution around the sun.

Planets Time for 1 Full Rotation Time for 1 Full Revolution
Mercury 59 days 88 days
Venus 243 days 224.7 days
Earth 23 hr, 56 min, 4 sec 365.2 days
Mars 24 hr, 37 min 687 days
Jupiter 9 hr, 55 min, 30 sec 11.86 years
Saturn 10 hr, 40 min, 24 sec 29.46 years
Uranus 16.8 hours 84 years
Neptune 16 hr, 11 min 165 years

The Sun generates light energy because nuclear reactions occur in its core. There reactions generate light and this light spreads throughout the solar system.

The Earth intercepts a small portion of this light. Some is reflected off the clouds of the Earth into space. Some of this energy makes it to to surface where it is absorbed by rocks and soil and plants and people and the light becomes sensed as heat.

Meanwhile, the Earth revolves around the Sun due to gravity, one revolution in its orbit each year. At the same time the Earth spins on its axis, that points towards the North star once every 24 hours.

I hope this helps. The spin of the Earth and the orbit of the Earth are because when the Earth formed billions of years ago it had some spin and one of the laws of physics is related to the conservation of momentum … the original momentum plus the effects of gravity is why the Earth revolves around the Sun.