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Rising Signs

Inside Co—Star, the app that’s feeding millennials’ astrological fascinations with mystical algorithms and an old-school approach to the zodiac

Photography by Amelia Holowaty Krales / The Verge

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Illustration by Alex Castro / The Verge

In a white-walled, cement-floored room on the sixth floor of an office building in Chinatown, a handful of young content creators and engineers gather each day to put thousands of years of astrological knowledge into an algorithm. The workers are mostly women and non-binary people who speak in low voices and wear cool shoes. On the early summer day I visit their office, everyone is wearing black casual wear and staring intently at more than one computer monitor around a long, white conference table in the middle of the room. A couple of them huddle near a wooden bookshelf that has been artfully stacked with titles like Identifying Planetary Triggers; Sex Signs: Every Woman’s Astrological and Psychological Guide to Love, Health, Men and More!; and Maslow’s Toward a Psychology of Being that rest comfortably atop Marianne Williamson’s A Return to Love

The workers refer to these and other related tomes as they develop Co—Star, one of the many new-ish astrology apps currently capitalizing on the renewed millennial interest in the ancient practice of reading the stars. The app asks users for detailed biographical information to develop an accurate natal chart, which is an “astronomical snapshot of the sky based on the exact day, time, and place you were born,” according to the copy on the app’s website. Co—Star sets itself apart from its competitors by using “data from NASA” and a proprietary algorithm that spits out unique, slightly robotic horoscopes for users each day, delivered in the form of push notifications. The style of the missives — direct, a little witchy, sometimes straight-up rude — has spawned countless memes and continues to drive users to the app almost two years after its founding. Since downloading Co—Star earlier this year, I have received notifications like “Check your ego” and “Do you play well with others?” and “Look in the mirror and ask yourself ‘who’s the boss?’” 

It is the perfect app for the current moment: spare and stylish, more than occasionally nihilistic in tone, and made to be shared on social media. That it is about astrology is almost incidental, but has obviously contributed to its popularity. Because astrology, as you have probably heard, is trending.

“The crux of feeling like a human is being able to talk about your reality”

In the last five years, the practice has grown from a niche, New-Age pursuit to one of the main pillars of the millennial internet. What was once mainly a topic of discussion in female and queer spaces has permeated almost every corner of social media. Conversations about planetary transits and memes about what Virgos may be apt to do when presented with conflict are everywhere on Instagram and Twitter. (Co—Star itself has over 800,000 followers on Instagram.) It has been easier to remember friends’ birthdays over the last couple of years, because they will start posting on Instagram about “Taurus season” or “Pisces vibes” in advance of their special days. Horoscopes are so popular that even David Brooks is talking about them.

The “mystical services” market, which includes astrology as well as services like aura reading and mediumship, is now a $2.2 billion industry. Naturally, these kinds of services are moving online, and several app developers have stepped in to monetize the trend. Sanctuary, which launched earlier this year, charges users $19.99 a month for “live, on-demand personalized readings with professional astrologers.” The Pattern, a “personality” app that uses natal charts to determine users’, well, patterns, went viral in July after Channing Tatum posted an Instagram video accusing it of being too accurate. (The attention caused the app to briefly crash.) Co—Star is free to download, but users can pay $2.99 to enter friends’ or partners’ birth information in the app. As of this summer, Co—Star had over 5 million registered accounts.

Many have attributed the current astrology frenzy to millennials’ desire to talk about themselves at every turn. As Amanda Hess wrote at The New York Times last year, “Astrology checks several boxes for viral-happy content: It provides an easy framework for endlessly personalized material, targets women, and accesses ’90s nostalgia. It’s the cosmic BuzzFeed quiz.”

CEO Banu Guler sits for a portrait in the New York office of the Co-Star astrology app.
CEO Banu Guler sits for a portrait in the New York office

But according to Banu Guler, the 31-year-old co-founder and CEO of Co—Star, there is nothing silly about using astrology to explain yourself to your friends and followers. “The crux of feeling like a human is being able to talk about your reality,” she tells me on the morning of my office visit, in between bites of an everything bagel with cream cheese. “And I think the reason astrology has stuck around for 2,500 years is because it’s remarkably good at that.”

Guler is wearing a black turtleneck, black paper-bag style pants, and she is carrying a Juul, which she uses occasionally. She has a gold septum ring, a perfectly pointy mauve manicure, and speaks with seriousness about her work. A former employee of the fashion startup VFiles, she launched Co—Star in 2017 with co-founders Ben Weitzman and Anna Kopp partly because she wanted to focus her career on something more meaningful after President Trump was elected in 2016.

Astrology, she argues, “is a form of self care. I think it’s also a way of, sort of, collective care. Right? Maybe ‘collective self care’ is the word … this idea of building relationships with each other and taking care of each other.” 

Whatever kind of care astrology provides, VCs have determined that it is very valuable. In April, Co—Star raised $5.2 million in seed funding to continue growing the app and develop an Android version of it. “By positioning human experience against a backdrop of a vast universe, Co-Star creates a shortcut to real talk in a sea of small talk: a way to talk about who we are and how we relate to each other,” said the company in its funding announcement. “It doesn’t reduce complexity. It doesn’t judge. It understands.”

The New York office of Co-Star
The New York office of Co-Star
Reading materials
Reading materials
The New York offices of the Co-Star astrology app.
Signs, defined

Caring is not the first word that comes to mind when you open Co—Star, which has a sparse, black-and-white design. The feel of the app makes it stand out from the cozy, millennial-pink aesthetic of so many other current startups — and that is on purpose, Guler says. “We live in this moment where all the startups can look the same, feel the same, kind of talk to people like they’re toddlers,” she said. “Everything’s cartoon and curvy edges. But that’s not real.” 

Co—Star, Guler says, is not afraid to give users the unvarnished truth about their lives. How to communicate that is a work in progress, however. On the day I visit, Guler gathers her team in a small conference room to go over the brand book for the app, which is currently evolving. Over the course of an hour-long meeting, slightly bored content writers decide that words like “energy” and “vibes” are not Co—Star, whereas “ego” and “attention” are much better. McBean Parkway, who runs the app’s social media accounts, describes the voice they channel on Instagram this way: Like a “cool, older punk sister. You can smoke weed with us, but we’ll read your letter to your crush.”

Guler says that the app’s edgy tone is central to its success. “You can’t grow without some negativity,” she tells me. “Negativity is the wrong word, because we’re not just like, ‘You’re a dick.’” 

She pauses for a moment. “I think we have actually said that. But, if you’re going to be self-reflexive and actually try to grow, you have to say, ‘I’m going to die, you’re going to die. I could be a dick in these ways. You could be a dick in these ways.’ But, if we start from there, and can just look at each other and be like, ‘Hey, we’re both humans,’ through all of that? Something really beautiful can happen.”

Sometimes not-so-beautiful things happen, too. It turns out people don’t like it when you talk about death too much. Guler acknowledges that the three-person content team is constantly working on finding the appropriate language to use in their horoscopes, and that sometimes the jokes they make in the office aren’t suitable for a wider audience. 

“There were some push notifications that were a little bit brutal… I think there were a handful about death,” she says. “And just kind of dragging people, which is actually how we kind of talk to each other: ‘Eh, we’re all going to die.’ But they don’t translate. I think especially given the context of, you get this push notification on your way to work and it’s just like, ‘We’re all going to die one day.’”

“So death is the line?” I ask.

“I think that’s a line we run up against,” she says.

“The content team is writing a textbook, not a blog,” she adds. “So it’s like there’s one corpus that gets fed.”

The carefully considered brand that Guler and her team are building is reaching enough millennials to make Silicon Valley take notice. The New York Times reported on Co—Star’s $5.2 million funding round when it happened and noted that VCs now see astrology as a way to reach female consumers. When I ask Guler her thoughts on this assessment, she somewhat rejects the question. “I think gender is on the way out,” she says.

She does mention two prominent women when I ask about careers she admires, though. “I think that that’s something that I think about a lot, because on the one hand, my reference points have been people like [fashion designer] Rei Kawakubo, who are effectively artists,” she says. “And on the other, people like [Glossier’s] Emily Weiss who are just bad bitches building huge companies, doing sick work and having this incredible impact on the world. I’m trying to find the halfway point between them that feels real and right.”

Guler is cagey about what exactly will come next in her personal career, however. “The future is unwritten,” she says. “Who knows what might happen?”

Perhaps that’s a question for the algorithm.

The New York offices of the Co-Star astrology app.

Oh yes, the algorithm. How does that work, anyway? No one on the team will say exactly, but the process of creating the app’s daily push notifications and horoscopes begins with lots of study. Ona Mirkinson, a lead content writer for the app, tells me that “studying astrology is a really big component to the production of content.”

“We’re always studying astrology,” she says. “So that means that we’re reading multiple books about astrology and also looking at how people are currently talking about astrology on social media, on different blogs, just on the street or whatever … And I think also we use a lot of varied references, too. So that’s one of the really fun things about working at Co—Star is being able to merge astrology with psychology and literature to create these different snippets that then get mapped to people’s natal chart.”

To be clear: Mirkinson and the rest of the content team are not creating personalized horoscopes for every user from scratch every day. Instead, they write “snippets that are mapped to various planets and houses and signs and combinations thereof, and they get assembled by the AI, and remixed by the AI,” Guler explains. 

“The content team is writing a textbook, not a blog,” she adds. “So it’s like there’s one corpus that gets fed.”

This process is extremely different from that of, say, famed astrologer Susan Miller, who has been a favorite of the fashion set for years. (Miller is admittedly technologically challenged; she is often late posting her monthly horoscopes for each sign to her site,

When I ask Guler about how Co—Star compares to “old-school” horoscopes like Miller’s, though, she stops me: Actually, she argues, the sun sign horoscopes Miller provides are a fairly recent tradition. A British astrologer named R.H. Naylor invented the sun sign horoscope — the kind you see in the back of a magazine — in the 1930s as a way to sell newspapers. Co—Star, with its use of the entire natal chart, provides a more traditional reading of the stars. 

She compared sun sign astrology to a scooped-out, diet bagel — all the good stuff gets taken out

“The point of full natal chart astrology is that people are complex,” she explains. “Maybe your ego is structured like this, but you communicate this way. You love in this way. You take action in this other way. And you have this really robust language for talking about personality. For talking about what’s happening to you, how you relate to others.” 

With sun sign astrology, astrologers ignore all that information in favor of traits that are associated with just your main sun sign. It is easier for both the astrologist and the reader to focus on just one element. But the Co—Star algorithm can handle the details. To really get the full picture of your personality, Guler says, you have to consider your rising sign, your moon sign, and so on. She compared sun sign astrology to a scooped-out, diet bagel — all the good stuff gets taken out. Co—Star provides a wealth of information about every aspect of your personality, pulling you deeper into the app each time.

Paradoxically, though, Guler says that people should spend less time on their phones and more time with each other. Before we met, I’d read that she disabled most notifications on her phone as a rule. Wasn’t Co—Star just one more app for people to check? Guler says that the team does not actually expect users to open the app when they get a notification. 

“I don’t open my Co—Star notifications, and I feel good about that,” she says. “It’s just like, you get your message and you keep going with your day.”