The Nature of the Sun and the Stars

9. The Sun and the fixed stars shine with their own light.

For example, the Sun has the light within itself that dazzles our eyes.

It cannot borrow so much light from all the fixed stars combined, since they do not send us so much light, nor are they more distant from us than from the Sun, and no other body appears more radiant from which it might receive that light; if there were such a body, it would undoubtedly be apparent.

The same can easily be believed about all the fixed stars by those who consider how vivid the rays they emit are and how distant they are from us and the Sun.

If we were as close to any fixed star as we are to the Sun, it is credible that it would appear no smaller or less bright than the Sun itself.

10. The Moon and other planets borrow their light from the Sun.

On the contrary, the Moon shines only on the part that faces the Sun. It means that it lacks its own light and only reflects towards our eyes the rays it receives from the Sun.

The same is observed from Venus with the help of telescopes, and from Mercury, Mars, Jupiter, and Saturn with telescopes.

Their light is duller or more subdued than that of the fixed stars.

They are not so far from the Sun that they cannot be illuminated by it.

11. The Earth does not differ from the planets in terms of light.

The Earth is the same as those planets.

• It is made of opaque bodies that receive the Sun’s rays and reflect them no less strongly than the Moon.
• It is also covered with clouds which are much less opaque. When the clouds are illuminated by the Sun, they appear as white as the Moon.

So in terms of light, the Earth does not differ from the Moon, Venus, Mercury, and the other planets.

12. The New Moon is illuminated by the Earth

When the Moon is between the Sun and the Earth, its face that is not illuminated by the Sun.

It shows a certain faint light, which we can easily infer reaches it from the Earth, which then reflects the rays it has received from the Sun towards it.

It gradually diminishes as the part of the Earth illuminated by the Sun turns away from it.

13. The Sun can be counted among the fixed stars and the Earth among the planets

If we were to look at the Earth from Jupiter, it would appear smaller but perhaps not less bright than Jupiter does from here; from the nearer planets, it would appear larger.

But from the fixed stars, due to their excessive distance, it would escape all sight. From this, it follows that it can be counted among the planets, and the Sun among the fixed stars.

14. The fixed stars always maintain the same distance from each other, but the planets do not.

Planets are also called wandering stars. These continually change their position among themselves.