Sidereal Sky

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  Sales page

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  Today's sky

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  Birth chart form

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  Birth Chart Example

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  App Icon

Inspiration

Most astrology apps use the tropical zodiac, locked in place over 2,000 years ago. The actual sky has shifted since then, planets aren't where tropical astrology says they are anymore. Sidereal Sky shows you where they really are.

What it does

Sidereal Sky calculates real-time sidereal planetary positions using JPL ephemeris data, shows daily moon phases and sign changes, and lets users unlock their full sidereal birth chart with Sun, Moon, and planetary placements, plus a personalized reading based on their Sun and Moon signs.

How we built it

Built using Flutter, pulling planetary position data from the JPL API. Monetization is handled through RevenueCat with a one-time non-consumable purchase to unlock the full birth chart feature.

Challenges we ran into

Getting accurate sidereal calculations right (correcting for the ayanamsa offset from tropical positions), and building a complete paywall-gated feature under hackathon time constraints.

What we learned

How much of astrology's modern framing comes from tropical convention rather than the actual sky! And also it was really cool that JPL has this API available. This was also my first time using Flutter which was great

What's next

Adding rising sign calculation, deeper AI-generated chart readings, and app store launch.

Built With

• api
• flutter
• jpl