He is the One who rendered the sun to emit light and the moon a light, and He
determined its phases that you may know the count of years, and for calculation.

These glorious Quranic words give us quite interesting pieces of information.

It may be common knowledge today that planets do not emit any light of their own, but only reflect light, however this information was not common knowledge in the seventh century when the Quran was revealed. The difference between natural light and reflected light is pointed out in the words "emit light" that describes the sun as opposed to the words "a light" that describe the moon.

The same reference is given elsewhere in the Quran:

Blessed is the One who placed constellations in the sky and placed in it a lamp and an illuminating moon. 25:61

The words in 10:5 also refer to the role that is played by the sun and the moon in our calculation of time (days, months and years). What is particularly interesting is that the words above refer to the phases of the moon (which result from its positional appearance round its orbit) and does not refer to the sun's orbit or appearance. This is consistent with the fact that it is the Earth and moon that spin around the sun and not the opposite. The sun's orbit, which is around the galaxy, is not a factor that we can use to calculate time on Earth.