Isn't the alternative CE and BCE? Or common era and before common era. Honestly even my history nerd friends seem indifferent to the AD BC thing.
They shouldn't be. They don't understand what's really at stake. There are two forces at work in the world today. The Christian New Earth and the Roman Empire. Let's call that, even though it will seriously confuse you.
But you say, I'm an atheist, why do we need this stuff? Because, the words of Christ are for everyone, not Christians. It is the Year of Our Lord, because Christ died for all of us. Hindus, Jews (not sure about the Pharisees who had him strung up, but it seems he wanted them forgiven too for they didn't really understand what they were doing), people in remote parts of Africa, animals, faerie (there some old legend about cross-shaped stones as tears from when faeies cried over his death), whatever. Christians built a religion around Jesus, but he never meant to have a religion in the first place. Early Christian thought, before Paul and Romw got a hold of it, was probably much different. Anyway the theology doesn't actually matter. What matters is this.
Matthew 28:1-15
The story is still told this day. Some things of the Bible have become obsolete, like some valley was cursed, but now it's lush and green. But not this, why? Because, what Christianity is really about would shake this world. People aren't dying like they're supposed to? Let's punish them. What? People are still persisting in this dangerous belief? Let's get a high-ranking Pharisee and an Emperor of Rome to convert. Right... surely they won't have muddled a few key passages. That way future generations will think Christianity is about morality (nope that's Judaism).
Let's talk about Adam and Eve, but we're going to do so as originally intended. Long ago, a man sat alone in the Spirit World, a place where no Good or Evil existed. He was one with God, and yet after making a world for himself to see, and putting himself in it as a human (that's right, humans are the same substance as God, we've just chosen to forget). Like God, he is alone. So he splits himself in half, and wants to be male and female. Which is fine, he's not alone anymore. He/She are told by God not to eat from the tree of Good and Evil, but then told they will live if they do so. When human beings no longer accept that the world they live in has no Good nor Evil, they cease to live in the Spirit World (Eden). Judgement is the root of all suffering.
So now, humans live in a world of Earth, and they no longer understand that they and God are the same, that male and female are the same. They see the hand of God in their everyday life, those that follow God. But many don't, and have been trying to murder each other for years. This continues until a flood basically reboots everything.
Fast-forward some years, we have the Roman Empire. Everyone is citizens of Rome it says, all are equal it says, only it's not true. Rome has widespread slavery, it has taxation, it has opposition hung on crosses and nailed through the feet and hands. It is an instrument of fear and oppression, and it erases actual people from records who don't obey. This is the secular world, what it wants to do when it lobbies to disarm you. People dependent on the state, people living in fear. Pave over the ground so people don't feel the land beneath their feet, pave over the sky with falsehood (the firmament, in Genesis? It's not referring to any simple sky, these are ancient people talking about how the horizon shows us clear proof of our holographic universe, because we can't see more than 11 miles tops because of the horizon but apparently can see stars light years away) using doctored photography.
But there's another world out there. The world Christ showed us. It begins with families having time to spend with their kids. It begins with a nation being the first to do away with slavery. It begins with understanding that yes, even if you're personally an atheist, this is the Year of our Lord, and you have the right to be such and not crucified by the state authorities for not worshiping the state religion. Thanks be to God.