It was a fine, brisk Sunday morning, and Crowley and Aziraphale were still relaxing in bed, Aziraphale nibbling a pastry and reading the paper while Crowley sipped his coffee and watched him. It was quiet, comfortably so, until something caught the demon’s eye as Aziraphale flipped a page.
“Hey angel, what’s your sign?”
Aziraphale kept reading, unfazed. “My what?”
“Your sign," Crowley repeated, lifting the paper from his hands and turning it to display the horoscopes section.
Aziraphale stared blankly at the paper, his drowsy green eyes trying to understand, then he looked up at Crowley, and back down. “I don’t know what that means."
“Yeah you do, come on." Crowley met the angel's gaze, saw the complete lack of recognition in his eyes, and gave a disbelieving scoff. "You have to have heard of astrology.”
“It rings a vague bell, but I’ve never looked into it," Aziraphale replied. He frowned in thought for a moment, his brows knitted, and then straightened his back a bit triumphantly as he seemed to remember something. "Weren’t you involved in something a few years back? It was – I don’t recall, it was something to do with the occult.”
Wrinkling his nose, Crowley made a disgusted noise in the back of his throat, somewhere between a retch and a groan. “No. Wrong Crowley. No relation, no association, prefer to forget he ever happened." And then he did his best to do just that, gliding along in the conversation as if the subject hadn't come up. "I’m talking about real astrology.”
Aziraphale frowned again, hesitating. “Pardon my ignorance," he began, speaking in the tone of one who is treading lightly as an outsider in a foreign culture, "but I rather got the impression that none of it was real.”
“Well, this is real." Crowley sat up straighter, turning to face the angel fully, crossed his legs and dove into an explanation. "It’s the tropical zodiac, aligned with equinoctial points, alright. There are twelve star signs, corresponding to twelve constellations that cross the ecliptic. But their dates don't necessarily line up with the locations of the constellations."
Crowley took a breath, oblivious to the angel's struggle to keep up, and continued: "The ecliptic plane is divided into twelve sectors of thirty degrees, not directly based on the constellation boundaries. The measurements are fixed relative to the equator rather than the constellations themselves. Got it?"
Blinking several times, Aziraphale shook his head. “I understand all of those words individually, but I haven’t the foggiest clue what you’re talking about.”
Crowley sighed in a fond sort of mockery of exasperation, blowing a lock of hair out of his face as he did it. “The position of the stars at the moment of your birth, angel," he explained slowly. "It has an impact on your personality; your likes and dislikes, your strengths and weaknesses,” – he gave an exaggerate waggle of his dark eyebrows – “your sexual compatibility.”
“It most certainly does not," said the angel, folding his hands in his lap, finally getting his bearings enough to contribute to the conversation.
“How do you know?” Crowley teased, cocking his head.
“Well, because – I’d know, wouldn’t I?" Aziraphale almost looked worried for a fraction of a second, but then he set his jaw and spoke with certainty. "If that were true, then I would think it would be common knowledge in Heaven.”
“Maybe it’s a secret," Crowley shrugged. "Maybe only the highest angels on the ladder get to know the truth about it. Maybe it’s –”
“Don’t you dare –”
Shooting the demon an icy glare, Aziraphale chose not to rise to the bait. “Regardless, even if it were true for humans, which I don’t believe it is, it still wouldn’t apply to me.”
“Oh?" Crowley smiled smugly, lifted his brows. "And why’s that?”
“Well, I wasn’t born.”
Thrown just the slightest bit off his path, the demon bit his lips and looked away, pondering the issue. When he figured out how to answer, he put on a persuasive tone that bordered on tempting. “Maybe not in the same way a human is born, but –”
“Not in any way," Aziraphale interrupted him. "I simply was not born.” He paused until he saw Crowley take a breath, preparing to speak, and then added, “And neither were you.”
Crowley sighed. “No, angel, it’s like – it’s a looser definition of birth, see? Like the way stars are born. It just means – well, when you came into existence, you know?”
Aziraphale took a beat, considered this, and then said in his fondest you're wrong voice, “Crowley, when I came into existence, the stars hadn’t even been created yet.”
Crowley pressed his lips together in a line, offering a thoughtful nod. “That’s true," he agreed reluctantly, "but we can retroactively calculate it based on observed patterns, if you know exactly how long it was before they were created.”
Narrowing his eyes, the angel studied Crowley for a long moment, trying to determine whether he was joking, as well as giving him some time to understand how stupid his statement had been. When he saw neither mirth nor realization in the demon's expression, he rolled his eyes. “How could I possibly know that?”
“So, you don’t?”
“No, I don’t.”
“You’re making this very difficult for me, you know.”
Aziraphale let out a good-natured, open laugh, a bright spark in his eyes. “Believe me, it’s not on purpose," he assured the demon, rubbing his back affectionately through his shirt with one broad, flat palm. "I’m still not following exactly what it is you’re trying to figure out.”
“Your sign, angel, your star sign, keep up.” He closed his eyes briefly, as if thinking hard enough about it might bring him some insight regarding the angel's natal chart. “Isn’t there any moment you can pinpoint as a figurative birth?"
"I suppose there's the day this body was created," Aziraphale offered helpfully.
"That could be something. It’d be… October 21st, yeah? That'd make you a Libra." Crowley tilted his head, his dark eyes narrowed, scrutinizing the angel's face for a long moment. "I wouldn't have pegged you for a Libra."
Not having vocabulary or knowledge enough to agree or disagree, Aziraphale hesitated until something occurred to him. "Hold on a minute. What's your sign? Do you have a figurative birth date?"
"Yeah,” Crowley answered easily, as if it should have been obvious, and began to elaborate in the same patient tone he'd been using to explain the whole thing to Aziraphale. “Once you account for the non-linear passage of time in Heaven and Hell, as well as the lack of any concept of time at all, I happen to know that I was kicking about for exactly nine hundred thirty years, four months, nine days, fifteen hours, and seven minutes before I showed my snake face here on Earth.”
“I’m fairly sure you made that up,” Aziraphale replied without missing a beat.
“You’ll never know. Anyway, my birthday is June 2nd. I’m a Gemini.”
“If you say so –”
“You know what, you’re not a Libra, now that I think of it,” Crowley continued, shaking his head. “It doesn’t suit you. We’ve got to come up with something better.”
Aziraphale furrowed his brow, processing and attempting to recall an earlier bit of their conversation. “You can change it? I thought you said it was determined by the position of the stars –”
Crowley nodded, almost impatiently, his messy hair falling into his face once again. “At the time of your birth, yes,” he said. “So… I don’t know, pick a different birth.”
Looking at him as if he’d properly lost his mind, the angel became even more confused. “I think that’s cheating.”
Crowley rolled his eyes, giving Aziraphale essentially the same look in response. “The only way it wouldn’t be cheating would be if you knew when exactly you were created. Since you don’t know that, it’s entirely up in the air.” He paused, deep in thought for several long seconds, before brightening abruptly. “Maybe we could reverse-engineer it.”
Stars were one thing, he could handle talking about stars for a while, even if he didn’t quite understand it, but Aziraphale’s hair stood on end at the mention of engineering. “What are you on about now?”
“Oh, yes, that’s perfect!” Crowley shot up straight in bed, his face lit up with a ridiculous grin at the brilliance of his own idea. “You can read up on the signs and their traits and whatnot, and then just pick which one fits you best.”
“I – that sounds like a ridiculous amount of effort,” Aziraphale protested weakly.
Crowley simply shrugged. “So? Close the shop, we’ll make a day of it.”
“The shop’s not open, dear heart.”
“Force of habit,” the demon shrugged apologetically, then lit up with excitement for his planned activity. “Let’s get started, then.”
In a last-ditch effort to avoid doing whatever it was that Crowley wanted him to do, Aziraphale whined, pouting out his lower lip just a bit. “Why can’t I take the one you already gave me?”
“It just doesn’t work for you, angel. You can’t be a Libra. I could be a Libra, if I tried, but you can’t be a Libra.” Crowley waved his hand vaguely in the air, materializing a thin book, and flipped through it until he got to the page he was looking for. “Here, read this and pick the description that feels the most like you.”
After raising a skeptical eyebrow at the demon, Aziraphale took the book from his hands and started reading. “This is definitely not how this is supposed to work,” he mumbled petulantly.
“Which one of us is the expert, here?”
“Neither of us is an expert, as far as I can tell. I’m an unwilling participant and you’re a pain in my –”
“Read the book!”
Aziraphale breathed a soft laugh, returning his attention to the book. After a time spent reading, longer than Crowley thought he needed, the angel pointed to a paragraph on the page, turning it so Crowley could see. “I think it's this one.”
Marking the description with a pencil and setting the book aside, Crowley summoned a pamphlet to his hand next. “Alright, now read this and pick one.”
Aziraphale took the pamphlet with a long-suffering sigh and read it through. “This one,” he said, unquestioning. Crowley circled the one he’d picked and materialized another book and traded it for the angel’s pamphlet, pointing to the passage he needed to read; Aziraphale read it and gave his answer.
The process repeated so many times, Aziraphale lost count. It wasn’t too bothersome, though a bit tedious and repetitive; he hardly noticed how much time had passed by the time he properly tired of it, and even then it was only because he read a line about indulgent hedonism that prompted his mind to wander toward thoughts of gruyère and raclette fondue. He managed to finish reading the page and pick one of the descriptions before he got distracted enough to say something.
“Darling, don’t you think we’ve done quite enough of this? How much…” He hesitated, reluctant to use scientific verbiage and legitimize Crowley’s nonsense. “Experimentation is needed before you can analyze the results?”
Looking around at the piles and piles of papers, Crowley shrugged. “I suppose this’ll do.” He flipped through each book and pamphlet in rapid succession, taking mental note of the angel’s decisions, which he found shockingly simple due to the pattern that quickly emerged in the data. “Angel, this is uncanny.”
Aziraphale bit his lip, looking at Crowley and at the papers around them. “What? Did I do it wrong?”
“No, no, of course not. No.” Crowley laughed, running a hand through his dark hair and shaking his head in disbelief. “You just – you picked Taurus every single time, it’s – this is just. Wow.”
“Does that mean something?” Aziraphale still looked concerned, and Crowley reached up to smooth out the harsh lines of his forehead with a soothing hand.
“For our purposes,” he explained gently, “it means you have to pick a birthdate between April 20th and May 20th.”
Pursing his lips, Aziraphale tried to remember any important dates within those parameters, and came up blank. “You want me to just. Just pick one?”
“Yes, please,” Crowley replied, a sweet, innocent smile painted on his face.
“That hardly seems scientific.”
“I just need to know what day to celebrate with you, angel, it’s not that important.”
Aziraphale scoffed, gesturing to the sea of papers piled up around them on the bed. “This is an awful lot of research for something that isn’t that important.”
With a jerk of his head, Crowley vanished all of the books and brochures. “Pick a date,” he parroted. “Pick one. Pick one. Pick one.” He paused, searching the angel’s face for a hint of a break or a decision. “Please.”
For all he wished to get the ordeal over with, Aziraphale couldn’t resist being a bit of a bastard. He put on a slightly pained expression, as if he were trying his hardest to think of a date. “I really do think that October 21st is likely the best option,” he said eventually. “If you want it to be scientifically accurate, that is. There simply aren’t any other dates that could qualify as a birth in quite the same way.”
Crowley stared at him, his mouth open in exasperation. “Don’t be silly, angel. It's just not you. Besides, why would you want your birthday on the same day as our anniversary?”
“It would be easy to remember,” Aziraphale answered, bordering on defensive. “Isn’t that why we got married on the anniversary of the day we met? So it would be easy to remember?”
“Well, yeah,” the demon conceded, “but we can’t shove everything into one day. It would be like trying to celebrate all eight days of Chanukah at once.”
“There are too many dates being thrown about already,” Aziraphale groaned. “Please don’t bring more holidays into it. I’m completely lost.”
Crowley flashed a bright, teasing grin. “Have been all day.”
“And we didn’t even get into your other placements.”
“You know, moon sign, rising sign, midheaven and all that,” Crowley answered. “Your sun sign is where the sun is at the moment of your birth, but there’s a lot of other bodies in the sky, and they rule different aspects of your personality.”
Aziraphale tried to look for at least a short moment as if he were considering it, which he wasn’t. “I will not be doing that, thank you,” he said, not unkindly. “I’ll pick a birthday later. Right now, you can take me out to dinner to make up for all the hardship and confusion you’ve put me through.”
“Of course, angel. Where do you want to go?”
“Perhaps we could do –”
Crowley said the end of the sentence in unison with the angel: “The Ritz?”
Turning to face the demon, Aziraphale wore a mask that betrayed a mixture of shock, confusion, and annoyance. Crowley laughed and shook his head, which only made it more irritating.
“You’re predictable,” the demon teased. “So set in all your patterns and habits. Classic Taurus.”
By now halfway across the room, having miracled himself into an appropriate outfit for dinner, Aziraphale began to walk out of the bedroom, barely turning his head to toss over his shoulder, “I’m leaving now.”
Crowley beamed with glee and called after him, “Coming, angel.” He took a quick moment to ensure that there would be a table open for them at the Ritz and then, hopping out of bed and getting dressed in one movement, followed his angel out the door.
 Sundays were the one day of the week that Crowley made a point to wake up early, to counteract the goodness of all the churchgoers, but he wasn't doing much work to that end because Aziraphale had brought him coffee in bed. Crowley figured with the combination of sloth and the whole married to an angel thing, he could probably write it off as a successful morning.
 Aziraphale had a whole repertoire of voices for telling people they were wrong. They ranged from the kind, sympathetic teaching tone that he often took with children to the saccharine way he condescended to particularly stupid customers to the disgusted, horrified manner in which he corrected strangers who felt the need to voice their rude assumptions in public. The tone he was using now was not reserved exclusively for Crowley, but it rarely came out for anyone else.
 June 2nd was also the birthday of Donatien Alphonse François, Marquis de Sade. Much like Aziraphale, we will never know if Crowley chose this birthday on purpose or if it was a complete coincidence that his Creation could actually be traced to that date.
 Despite being rather skilled in mathematics, hence his ability to keep impeccable records and inventory and his flawless taxes, Aziraphale did not enjoy it one bit. He did the things he needed to do in order to maintain his persona as a financially responsible human being, and otherwise avoided the stuff entirely. Anything to do with engineering was doubly nightmarish, as it involved not only doing maths, but also presumably building things, with his hands. Aziraphale had only a vague idea of what engineering meant, and he was distraught at the prospect of learning more about it.
 Crowley took a moment to miracle away the names of the astrological signs on the page, thinking they would get a much more accurate result if it was a blind test. He didn’t mention this fact aloud, lest Aziraphale choose to mock him for being so dedicated to his experiment. Not that he minded being mocked, but he very much wanted the angel to go through his trials without unnecessary distraction so he could get an answer to his question.
 It wasn’t how he would have chosen to spend his day, but Aziraphale’s protests and grumbling were mostly for show. He loved hearing about the ridiculous things Crowley was into; he was more than willing to endure the demon’s testing, and he wanted to do it right, so he took his time in reading each description carefully and making a serious decision.
 Crowley did not. In the course of nine and a half hours, he gave Aziraphale exactly 239 lists, blurbs, leaflets, textbooks, and articles to read, marking his choices in each one before setting it aside for later study.
 It took a few days, but Aziraphale eventually settled on April 23rd as his fake birthday, the day of Shakespeare’s birth and death. Crowley was impressed and entertained and not at all jealous of a centuries-dead blowhard who was good friends with Aziraphale back in the day.
 Partly to spite Crowley, and partly because it simply made more sense to him, Aziraphale made the decision to celebrate October 21st as his birthday as well. It soon became a tradition that each year, in the midst of their anniversary celebrations, the angel would purchase a cake for himself with extravagant letters reading Happy Birthday, Aziraphale! Crowley loved it so much, he couldn’t even pretend to complain, but he did take the opportunity to remind Aziraphale that his stubborn insistence upon that date was a typical Taurus thing to do.