Skyclock Company was founded in 1986 by John Rosevear and is based in Ann Arbor, Michigan.

The corporate mission of Skyclock is to promote and enhance the study and understanding of the sciences involving time, time keeping, astronomy, and geography.

The clock on the Ann Arbor Chronicle front page is powered by Skyclock.

In the news

The Ann Arbor-based Skyclock Co. has developed the first analog clock that, in addition to telling time, shows hours of daylight, nighttime, and twilight. Skyclock’s intent is that people use this extra information to better plan their time.

Despite financial setbacks, on June 2, 1987, he received US Patent #4669891 for an Area Code Twilight Clock, an early version of Skyclock. More recent refinements -- Skyclock V5.1 -- resulted in a 12-hour clock face showing daylight hours in blue, twilight in orange and night in black. Formatted for PCs, it's available for purchase on the Skyclock web site for $10. Mac and handheld-device versions are under development. Skyclock may be viewed for free on the web site and on the home page of The Ann Arbor Chronicle, one of the most steady sources of click-throughs to the Skyclock web site, Rosevear says.

John Rosevear's opus, 40 years in the making, can be seen projected on a wall at the Slusser Gallery on the University of Michigan North Campus.


A method and apparatus for displaying time, the day sequence for the beginning and ending of twilight, sunrise and sunset in pie-shaped section on a circular clock face. A corresponding day sequence is retrieved from a memory and presented on a circular clock face in pie-shaped sections that represent twilight, day and night for a particular coordinate position and calendar date.