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. See also:

• Temporal Hours

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

Temporal hours in Sun Clock are counted from 0.0 to 11.9. The full number shows the most recently completed (announced) hour, and the decimal part shows the progress toward the next one.

Historically, hours were announced only after completion. Thus “the sixth hour” corresponds to 6.0, while 6.1–6.9 describe the approach toward 7.0.

The notation (≈ ¼7, ½7, ¾7) expresses this progress: it names the next hour and indicates how far the current hour has advanced. This is the same counting logic still used in German dialects (and e.g. in Russian): “half three” means 14:30, “quarter three” means 14:15, and “three quarters three” means 14:45 — all referencing the approach towards completion of the next hour (“three”).

So 6.2ἡ ≈ ¼7 means you are shortly after 6.0, about a quarter of the way from 6 to 7.

How do I use Sun Clock as a wall clock?

Sun Clock works especially well as a living wall clock on an Android tablet. See Wall Clock for setup and recommendations.

What is the dashed area?

During major meteor showers, Sun Clock marks the part of the sky where meteors are especially likely to appear. Meteors can still appear elsewhere.

Red means good viewing conditions; grey means limited conditions. Below the horizon, the area is not visible from your position.

The small red square with a letter marks the radiant, the point from which the meteors appear to originate. The letter identifies the shower, such as [P] Perseids or [G] Geminids.

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 optional, additional functionality like local weather).

Can I use Sun Clock to observe the real sky?

Absolutely. 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.