I think his Japanese has improved quite a bit, hasn't it?

I am busy with work during the daytime.

He learned the movements of the solar system using an orrery.

Pluto is classified as a dwarf planet.

Pluto is classified as a dwarf planet.

He is an expert in planetary science.

We installed solar batteries on the roof of our house.

Solar wind affects the Earth's magnetic field.

He was reading a book about the ancient Egyptian sun god.

A solar day is the time it takes for the Earth to orbit around the Sun.