Diurnal Time (DT) is calculated with respect to the sunrise in the place you are located. During the day, DT will be a positive number representing how long it has been since the sunrise. After the sun sets, DT will be a negative number representing how long before the sun rises again. These numbers are unique to each day and to every location.

If you find yourself thinking more about the ends of days rather than the beginnings, you can press the 'r' key on your keyboard or touch/click on the clock in order to display Diurnal Time with respect to sunset.

TL;DR: Maximize your daylight. Get home before dark.

What compromises do we make by governing our lives within Coordinated Universal Time (UTC)? Modern technologies have collapsed geographical distance and made it effortless to have a conversation with someone across the world at the cost of weakening our connections with the world immediately around us. The glow of our screens eclipses the rhythms of the earth and the light of the moon.

With the hope of reclaiming a sense of presence, I propose a time format that brings us back to a kind of sun-based simplicity while still relying on modern capabilities- precise geo-location and the ability to compute predictable astronomical motions. I’m not suggesting that we replace our current time system; UTC is invaluable for synchronizing life across distance. Instead, I want to supplement it with a local system grounded entirely in the moment the sun rises at our location.

In this format, time resets to 0:00 at sunrise. Positive time marks the hours that have passed since sunrise; negative time marks the hours remaining until the next sunrise. This time will differ slightly even between people living just tens of miles apart, yet that very localization encourages a deeper connection to daylight, more intuitive planning of rest, and a healthier alignment with natural cycles. Its uniqueness offers a shared rhythm across a town or region. Before the full adoption of Greenwich Mean Time, communities in the United Kingdom maintained local solar times that had guided daily life for generations. This idea is, in a way, a return to an emphasis on the local.

Here is how Diurnal Time works in practice based on November 3, 2014:

At Sunset: 5:08pm PST = -13:26 DT (as 13 hours and 26 minutes remain until the sun rises)
Night: 9:34pm PST = -9:00 DT (as 9 hours remain until the sun rises)
Night: 12:34am PST = -6:00 DT (as 6 hours remain until the sun rises)
Sunrise: 6:34am PST = 0:00 DT
Day: 9:34am PST = 3:00 DT (as it has been 3 hours since the sun rose)
Day: 12:34pm PST = 6:00 DT (as it has been 6 hours since the sun rose)
Just Before Sunset: 5:07 PST = 10:33 DT (as the day contained 10 hours and 33 minutes of sunlight)

Because sunrise and sunset shift each day, these numbers shift as well. The final daylight value is smaller in winter and larger in summer, and the nighttime negative values stretch longer or shorter depending on the season. These changes are simply reflections of the earth’s tilted axis as we move through the year.

For questions or comments contact Alex Barangan .

Special thanks to Andy and Sunspeck Labs for the really great sundial.