Why is the planet sun's nickname Helios?

Answer 1

Helios is the Greek names for the sun. Early spectroscopic work on sunlight revealed a strong presence of an element that was not recognized yet, so the element was called "Helium". Later, when it have been identified and cataloged, it kept this name, as it does today.

Answer 2

The nickname "Helios" is derived from Greek mythology, where Helios was the personification of the sun. The planet is often associated with the sun due to its close proximity and solar-like characteristics, leading to the nickname "Helios."