Sun, Moon, and Earth: Capitals or Not

These are important celestial objects, but do they need a capital letter?

In the case of Earth, I just capitalized it. That’s because I used it the way I would use a person’s name, without putting “the” in front of it. If I were speaking of the earth, I would not use a capital letter.

So:

I live on Earth, and I love the earth. 

There are a few oddities to note.

In an idiom, such as “move heaven and earth” or “down to earth” or “Where on earth have you been?” there is no capital. But when you use it as the proper name it is spelled with a capital.

The sun and the moon are not capitalized in non-technical usage. They are always in lower case when used in the plural.

How many moons does Jupiter have? 

Could any of the stars we see be suns with planets around them?

• While we are at it, here is a reminder that heaven and hell are not important enough to warrant capital letters.