Jack Dorsey Launches Sun Exposure Tracking App “Sun Day”
Block CEO and Twitter co-founder Jack Dorsey has launched a new beta app called “Sun Day” designed to quantify individual sun exposure.
The app is available for testing on Apple’s TestFlight platform. According to a white paper posted on GitHub, “Sun Day calculates vitamin D synthesis from UV exposure using a multifactor model based on scientific research.”
Key features include location-based sun tracking, user input on age, clothing type, and skin tone, plus integration with Apple’s Health app and HealthKit data.
“[…] doesn’t look for light. It’s a manual on/off toggle,” Dorsey clarified regarding the measurement method.
Sun Day Requires Manual Input
Users quantify exposure time manually, toggling the app on and off after sun and indoor sessions. Potential future updates cited in the white paper include more precise calculations using height, weight, seasonal data, and actual vitamin D blood tests.
Dorsey’s Second App in Two Weeks
Debuting the “Sun Day” launch over the weekend, Dorsey mentioned he “spends weekends reading up, sometimes even coding.” Previously, that same weekend saw him release the Bitchat peer-to-peer messaging beta.
Artificial Intelligence Assistance
Dorsey acknowledged using Block’s AI assistant, Goose, in developing these apps.
