FAQ

What are the “light seasons” and how does the moon calendar work?

Sun Clock divides the year into eight phases of increasing and decreasing daylight. These “light seasons” are calculated astronomically and shift slightly from year to year.

The moon calendar counts nights instead of days and follows the actual lunar cycle. For details see:

• Four Light Seasons
• Lunar Structure

What are temporal hours?

Temporal hours divide daylight and night into twelve equal parts each. Because the length of day and night changes throughout the year, the length of these hours changes as well.

This was a common way of measuring time before mechanical clocks standardized the hour.

Why do temporal hours appear as “6.2ἡ ≈ ¼7”?

Temporal hours in Sun Clock are counted from 0.0 to 11.9. Historically, hours were usually announced after they had begun. If people said “we meet at the sixth hour”, the meeting actually took place at the beginning of that hour, not after it had finished.

To avoid this ambiguity, Sun Clock counts the temporal hour internally from 0.0 upward. The sixth hour therefore begins shortly after 5.9 and is announced at 6.0.

For orientation, the display also shows an approximate familiar expression. For example: 6.2ἡ ≈ ¼7 . This means: a quarter after the beginning of the sixth temporal hour. A similar counting logic still exists in some German dialects (and in Russian): “half three” means 14:30, “quarter three” means 14:15, and “three quarters three” means 14:45. These expressions describe the approach toward the completion of the next hour rather than the hour just passed.

See also: Temporal Hours

Why is the app so large?

Gordon’s Sun Clock is designed to work completely offline.

The app contains:

• the Python runtime and the Kivy framework (via Python-for-Android)
• astronomical calculation libraries (Skyfield, NumPy, jplephem)
• the JPL planetary ephemeris DE440s excerpt
• global timezone geometry data (timezonefinder)
• high-resolution images of the planets
• several font sets

Because of this, the app does not depend on external servers or internet access once installed and runs completely offline (except for additional functionality like local weather).

Can I use Sun Clock to observe the real sky?

Yes. If you face south (on the northern hemisphere) and hold the device in front of you, the sky on the dial corresponds to the real sky.

Objects that appear higher on the screen are higher above the horizon. Objects on the left are to the left of you, and objects on the right are to the right of you.

The dial shows the sky as a cylindrical silhouette. Because a 3-D sky is mapped onto a flat screen, distances near the left and right edges appear compressed compared to reality.