Of course, as any astrology aficionado knows, you can actually learn a lot just from someone's birthday, namely their sign. Sure, your baby probably won't be born on the exact day they're due, but even a ballpark date can help you determine which sign the sun will be traveling through when your child enters the world. And, when it comes to having either a breezy Gemini or a sensitive Cancer, knowing what you're in for ahead of time really can help.