for millions of years, light told the body what time it was. the circadian rhythm, the internal clock that regulates sleep, hormones, and temperature, calibrated itself on a single signal: the sun. cold, full light at midday, warm at sunset, darkness at night in one century we flipped it all. days indoors under artificial light, evenings in front of screens that never set. we live out of sync with our biological clock, and the body notices: tired eyes, sleep that drifts later, energy out of phase. your screen is one of those wrong signals. at 11pm it gives you the same cold light as at noon, and the body gets conflicting cues i built something about it it's called Circa, a macOS app that lives in the menu bar and keeps your screen in sync with the real sun, adjusting colors and brightness automatically based on where you actually are. during the day, full colors. at sunset it warms up gradually and at night it shifts to candle amber and lowers the brightness. free and open source: https://circa.watch