Launched decentralized Bluetooth communication in early JulySocial platform "Bitchat", after touting itself as a social service that allows people to chat without using the internet, Twitter founder Jack Dorsey recently launchedNamed "Sun Day", which focuses on application services that can track sunlight and UV exposure data, thereby entering the personal health and lifestyle market.
"Sun Day" is now available through Apple's TestFlight platformConduct beta testing, which focuses on tracking and analyzing daily sun exposure. By combining the user's location, clothing type and skin color information, it estimates the individual's daily exposure to ultraviolet (UV) rays and the amount of vitamin D that may be absorbed.
The operation is quite simple. Users need to first provide their current location information and select the type of clothing to wear on that day from the system. They can also choose from 6 options that suit their skin color type to facilitate a more accurate estimate of exposure time and sun safety.
Based on this information, the system displays the current UV index, the highest UV value for the day, sunrise and sunset times, and an additional "burn limit" value, which indicates the maximum amount of time you can safely spend in the sun. If you're interested in tracking your daily vitamin D absorption, you can also click the "Track UV exposure" option to estimate your daily cumulative vitamin D levels.
The emergence of this app demonstrates Jack Dorsey's continued emphasis on decentralization and autonomy. Unlike "Bitchat," which focuses on peer-to-peer messaging even when the internet is offline, "Sun Day" is more closely aligned with health and wellness needs, particularly as people increasingly prioritize sunlight intake and outdoor activity management.
Currently, "Sun Day" is still in beta, available only to a limited number of iOS users via TestFlight. It has not yet been officially released on the App Store, and there are no plans for an Android version. However, the successive releases of "Bitchat" and "Sun Day" demonstrate that Jack Dorsey is actively exploring new possibilities in social and personal apps, and is attempting to create a digital lifestyle that is independent of mainstream social networks or platforms.
Whether "Sun Day" will integrate more health sensor data, or even import information from wearable devices, will be one of the key areas of observation in the future.
