--(and planets, which are just called "stars")--
Why, then, were they called stars when they were planets?
Because until you invent a telescope and look through it, in about 1600, there is no difference between a planet and any other star, except that the planets are brighter stars because they are closer, and the planets are the special wandering stars, the five that are in close that move against the backdrop of the fixed stars (which aren't really fixed).
The difference between a fixed star and a moving star made the moving stars different and more interesting. But they're still stars. What makes a star a planet is looking through a telescope and realizing that it revolves around the sun.
The huge distinction we make between stars and planets in a heliocentric solar system causes us to see them as very different things.
But go out tonight and look up at the stars. Tell me which one is Saturn. And tell me, looking up at Saturn, what it is that makes Saturn not a star. It's your extrinsic learned knowledge that does. To the ancients, planets WERE stars. Fixed stars or moving stars. But stars, nevertheless.
That is why they were called "stars" when they were planets. Because a "star" in 1500 BC is a bright point of light in the firmament. A "star" in 2007 is a flaming ball of gas billions of miles away, as contrasted to a planet, which is a bright point of light that is a glob of dirt revolving around our sun. Take away that extrinsic knowledge, and the heavens consist - to the eye - of the sun, the moon, the clouds, the stars (moving and fixed), the milky way, the occasional comet, and the occasional meteor.
Some of the "stars" you see are actually galaxies. The bible doesn't mention them either, and you can't tell the difference when you look up.
That's why the difference isn't noted in the Bible. In 1500 BC, there is no difference between a planet and a star. They're both stars.