Your Co-Star is not your kundli

Co-Star and AstroSage Kundli sit on the same shelf of the same app store under the same word, and they are not two versions of one product. Give each of them the same person: the same birth date, the same hour and minute, the same town. Then wait for both to finish.

The first phone answers in three short lines. Sun in Leo. Moon in Aquarius. Leo rising. Underneath there is a paragraph about how you behave when people are watching you.

The second phone answers with a diagram drawn as a square. Inside it the sun sits in Karka (कर्क, karka), which is Cancer, the moon sits in Makara (मकर, makara), which is Capricorn, and the moon's star is given as Shravana (श्रवण, śravaṇa). Below the diagram is a table of dated periods running past 2040. Below that is a button offering to put you on a call with somebody who will talk you through it, charged by the minute.

The details above are invented. I wanted two screens that could be set side by side.

One person, one minute of one day, two skies. The first time this happens it feels like a fault, and the sensible next thought is that one of these apps must be broken.

Neither is broken, and the reason is dull enough to state in two sentences. The two kinds of app start counting the zodiac from different points, one from the seasons and one from the fixed stars. That gap between starting points is real, old, and well documented. Meghnad has worked it out properly in why your moon sign changes between apps. If the arithmetic is what you came for, it is there and I am not going to redo it.

I am interested in what is left once the arithmetic is settled. You still have two phones in front of you, and what separates them is not a rounding error. It is a difference of purpose, and the place to see it is in what each app keeps ready for you before you ask.

Take the first phone. Its app most likely belongs to a wave of Western products that arrived in a tight few years. The Pattern reached Apple's store in May 2017, Co-Star that October, Sanctuary in October 2018, CHANI in December 2020. They differ from each other, but they were built to do a broadly similar thing.

You hand over a birth date, a birth time and a birth place. The software works out where the sun, the moon and the planets stood at that moment, which is what a natal chart is: a list of positions for one instant. Co-Star's own store listing says it uses "NASA data to chart the exact location of the stars in real-time", and that this is "then interpreted by real human astrologers who collaborate with AI". Then the app gives you back sentences. A daily reading. A push notification. A screen that compares your chart with a friend's. The paid items are documents: a monthly subscription, a report on the year ahead, a report on somebody you have a crush on.

Notice the vocabulary these products chose. The Pattern's listing describes what it produces as "a psychological blueprint of one's self", and names its sections Your Pattern, Your Transits and Bonds. The nouns are borrowed from therapy and from self-help. The question the product is built to answer is a question about character and about how you are with other people.

Notice also what is not on that list. There is no calendar in it. Nothing there tells you which day is fit for a house-warming, which morning a fast begins, or when the moon changes station. That is not an oversight. It was never the product.

Now the second phone. AstroSage Kundli has been on Apple's store since February 2014, Astrotalk since March 2017, Astroyogi since September 2019, InstaAstro since February 2021. Same three questions at the front: date, time, place. What comes back is a different object.

You get a kundli (कुण्डली, kuṇḍalī), the birth chart as jyotisha (ज्योतिष, jyotiṣa) draws it, and then a stack of things computed from it. Divisional charts, which re-divide each sign into smaller parts and redraw the chart from those. The moon's nakshatra (नक्षत्र, nakṣatra), the star it occupied, since Indian practice counts twenty-seven of those around the same circle. A dasha (दशा, daśā) table, which is the classical scheme for cutting a life into named periods with dates on them. A matching score for two charts, out of thirty-six. The apps advertise reports of more than fifty pages.

And a calendar. These apps carry the panchang (पञ्चाङ्ग, pañcāṅga), the daily almanac, which for a chosen city gives the lunar day, the day's nakshatra, sunrise and sunset, and the festivals coming up. Priya has been through that sheet column by column in how to read a panchang. It is worth saying plainly why it is there. A jyotisha app is not only a machine for describing you. It is also a machine for telling you what today is, which means it has to know where you are standing, because sunrise is a local fact.

There is one more thing on the second phone that the first one rarely has. The free chart is the front door of a directory of people. One app's listing claims more than 1,500 astrologers available to chat or call. Another claims more than 5,000. A third claims more than 600 and opens at one rupee. The billing is per minute, the way a phone call used to be. Whatever else these products are, they are marketplaces with a chart generator at the entrance, and what that arrangement does to the incentives is a subject of its own.

I want to be careful here, because the neat version of this contrast is not quite true. Sanctuary, an American app on the store since 2018, sells live per-minute readings with a human. Several of the Indian apps will happily print you a personality summary. The two shapes borrow from each other constantly. What stays different is the centre of gravity: one wave sells you a text about yourself, the other sells you a calendar, a set of computed tables, and access to a person.

Here is the smallest sign of how thoroughly that difference is hidden. In Apple's store, Co-Star, AstroSage Kundli, Astrotalk and Astroyogi are all filed under Lifestyle. The shelf does not distinguish them. Neither does the search box, because both waves answer to "astrology", and in an Indian home both will be called the horoscope app by whoever is holding the phone.

Lumping them together like this costs something on both sides. Someone who wants to know which day suits a ceremony downloads the app a friend recommended, finds no calendar in it, and decides the whole subject is thin. A person who wants one sentence about their morning downloads the app their aunt uses, is handed a fifty-page report, a stack of tables and a stranger's phone number, and concludes the whole subject is heavy machinery. Both have judged one product by the other product's job.

There is a detail I keep coming back to. AstroSage's chart page lets you choose its ayanamsha (अयनांश, ayanāṁśa), which is the setting that fixes where the zodiac begins. It offers Lahiri, Raman, three settings from the Krishnamurti school, and the tropical count as well. That is a settings screen with the whole argument printed on it. You can change one option and watch your own sun move a sign, which is an unusual thing for consumer software to allow, and an honest one. The apps on the first phone, as far as I have been able to find, do not offer that choice or mention that a choice exists. They made it once, for everybody, and the decision is somewhere behind the paragraph about how you behave when people are watching you.

So open whichever app is already on your phone. Go past the headline, into the settings, and look for the page where the software names its own conventions: which zodiac it counted from, which city it used for sunrise, whose table of periods it printed. On some apps that page exists. On others it does not, and its absence is itself a fact about the product you are holding.

Then, before you next open either one, settle what you are opening it for: to be told what you are like, or to be told what today is. The two shops have already chosen which of those they sell. Choose your half of it before you tap.