Table of Contents

Sunclock Concept

Spiral Clock




Location and Time zone

Culture and Religion

For Photographers

Azimuthal equidistant projection of the earth (aka Flat Earth)



Preference Options Menu

Sunclock home page

Sunclock Concept

Sunclock is a classic analogue clock with a 12-hour dial, an hour hand and a minute hand.

Sunclock becomes an astronomical clock if an astronomical dial is added. It has a scale of 0 to 24 and is divided into a day and a night section. It rotates once per day, because we want to reuse the hour hand from the 12-hour dial on the 24-hour dial. The ratio of the sections change with the seasons similar to the changes of day length and night length. The day is separated from the night by the twilight. One speaks of the civil twilight for the time when the sun has set up to 6 degrees below the horizon. The nautical twilight goes to 12 degrees and the astronomical twilight goes to 18 degrees.

12-hour dial 24-hour dial with day/night sectors
Two small yellow dots near 12 and 24 o'clock show true noon and midnight. They change their position up to 15 minutes per year according to the equation of time and jump one hour with daylight saving time.

If both dials are combined, we get a unique 24-hour clock with the normal hour hand angle like on a classic 12-hour dial. The hour hand is still horizontal for three o'clock and nine o'clock and vertical for six o'clock and twelve o'clock. The 12-hour hand rotates twice per day and the 24-hour dial rotates once per day. As a result, the hour hand shows the time on both dials.

It is 8 past 10 at night It is 8 past 10 at day
Sunclock can also display the time on a classic 24-hour dial. The 24-hour dial is turned 30 minutes because the real noon shall be displayed vertically on top. It is also twisted by an hour because of daylight saving time. The Northern, Southern and both Hemispheres can be shown with sun symbol, analemma (equation of time), users location and latitude.

By dragging over the app, the time and date can be simulated for any time of day and every day of the year. The upper half of the screen is reserved for time simulation and the lower half for date simulation. Press the stop button "X" to finish the animation and to switch back to normal time and date display.

This button starts an automatic animation. It changes time (first tap) or change date (second tap) or stops animation (third tap).

Sunclock can be used as desktop clock or wall clock and permanently show the time in full screen mode. In this case, a back button is located in the left top corner of the screen. After a short time, it is made transparent. You still can touch it to finish full screen mode. If the phone or tablet is connected to a charger, the light will not go off.

Spiral Clock

The spiral clock gets its name from the four-part spiral. It is divided into day, night, dawn and dusk. The jump back from the inner to the outer curve is not in the civil middle of the night at 12 PM or midnight, but in the astronomical middle of the night. This is halfway between sunset and sunrise. The hour hand changes its length so that its tip is always on the spiral. A special minute ring has a 15-minute division, so that the respective times can be read on the dial with an accuracy of about five minutes using the small arrows

Eight o'clock in the summer. It is already day. Eight o'clock in winter. It's still night.


The moon in Sunclock can be visualized in three different ways.
  1. The well-known moon phase shows what the moon looks like.
  2. The moon circular arc shows when the moon rises and sets (similar to sunrise and sunset times)
  3. The moon culmination spheres shows the time when the moon is at its highest point. At the same time, the sun culmination is shown. The combination of both show the moon phase in a new way.

New moon four days ago First quarter Full moon in four days


Two widgets can be placed on the home screen, one for home location and one for abroad location.

Home widget and abroad widget Sample widget from the gallery with moon and golden hour

To add a clock widget:
Go to home screen -> tap and hold on an empty space -> select "Widgets" -> find and tap on one of the "Sunclock" versions Abroad or Home -> tap and hold the widget -> drag the widget to a preferred position on the home screen.

You can scale the widget by long pressing it and dragging the handles.

The second hand cannot be displayed in the widget. The reason is that widgets cannot be updated every second (Android limitation).

If widget doesn't update properly try to turn off battery optimization: Apps and notifications - special app accesses - battery optimization, drop down menu: not optimized -> all apps, find "Sunclock", select "don't optimize". You find a button in Sunclock Preferences / Function / Widget that guides you directly to the "Power-saving exceptions" screen from the phone. Make Sunclock being shown in the list of exception. This way, Sunclock is allowed to run every minute to update the clock. Some vendors add additional power saving features. For Samsung phones you find a helpful article here which describes in chapter 1, 3,4 and 5 how to keep Sunclock widget running: Top 8 Fix­es for Sam­sung Phone...


You can set Sunclock as your home screen and lock screen wallpaper.

Sunclock shown on lock screen Sunclock used as background for the home screen

Sunclock is what is known as an active wallpaper. Such a wallpaper can be used for the home screen or the home screen and lock screen. It cannot be used for the lock screen without using it for the home screen.

To set Sunclock as wallpaper:
1.: Start Sunclock, select options (three dots right top), select "Set Wallpaper"
2.: Go to home screen -> tap and hold on an empty space -> select "Wallpapers" -> find and tap on "Sunclock" -> tap "Set Wallpaper".

A few words about the second hand in the wallpaper: The second hand can be shown in the wallpaper if wanted. Even a "linear" second hand which updates every 16 milliseconds (60 times per second!) can be shown. Such a second hand is not recommended for the wallpaper, as the large number of redraws may use too much power.

Location and Time zone

Sunclock needs location and time zone to calculate sunrise, sunset and prayer times for any place on earth. The location is used to calculate sunrise and sunset relative to Greenwich Mean Time (GMT). The time zone is used to add or subtract an offset to the calculated GMT. The time zone and the current date are used to add an hour automatically if the date is in daylight saving time. .

All calculations are based on the date, time and time zone of the phone being set correctly.

This is the only way to calculate the current GMT time, the basis for further calculations in Sunclock.

The location for the app is set at the very first start. Then the setting of the locations for app, widget and wallpaper can be reached from the Preferences.

Automatic Location Manual Location

Automatic Location
Latitude and Longitude are received from the phones built in GPS or from the network. The time zone is taken from the phone settings.

Manual Location
The location can be entered directly in the latitude and longitude fields. Alternatively, one of over 1000 cities can be selected from the city list. The city list is filtered when text is entered. Selecting a country in the country list filters the cities for that country. The time zone is initialized with the time zone of the phone. If a city is selected, the time zone of this city is set. If the location is entered via the coordinates, the time zone must also be selected manually.

Culture and Religion

Equinoctial hours
The modern clock shows equal or equinoctial hours, which, by definition, were of equal length. They are the twenty-fourth part of the full day, made up of day and night.

Read more: Hour

Temporal hours
In many cultures and religions, day and night were (separately) divided into 12 equal parts. Daytime hours were counted from sunrise to sunset and nighttime hours, from sunset to sunrise. As the length of daytime and nighttime change throughout the year, the temporal hours varied in length accordingly. You will find this old hour system in many of the clocks in this chapter.

Read more: Roman Timekeeping
Ancient Arabs clock, Ottoman timekeeping, Alaturka Hour System
Hebrew Hour
Eretz Yisrael Clock

Roman Catholic Liturgy of the Hours
The Roman Catholic Liturgy of the Hours is the official set of prayers marking the hours of each day and sanctifying the day with prayer.

Japanese clock (和時計, Wadokei)
The traditional Japanese clock Wadokei has six daytime units from sunrise to sunset and six night units from sunset to sunrise.
The six numbers 九 八 七 六 五 四 (9 8 7 6 5 4) were used for the day and the night. The numbers 1 to 3 were reserved for the bells of the monks (to put it simply).

Read more:, Wiki, JCWA, Seiko Museum

Traditional Chinese Hours (時辰, Earthly Branches)
In ancient China, a day and night were divided into twelve sections, and each section was called an hour. These hours were true hours of sunshine. That is, it is longer in summer and shorter in winter.
12 Chinese zodiac signs 卯 辰 巳 午 未 申 酉 戌 亥 子 丑 寅 can be translated to rabbit, dragon, snake, horse, goat, monkey, rooster, dog, pig, rat, ox and tiger.

Read more: Traditional Chinese timekeeping, Earthly Branches 時辰

Rahu Kalam
Rahu Kalam or the period of Rahu is a certain period of time every day that is considered inauspicious for any new venture according to Vedic astrology. The bezel is red if it's Rahu Kalam time.

Time since sunset
It shows the number of hours and minutes that have passed since sunset.

Read more: Byzantine time, Athonite time

Time since sunrise
It shows the number of hours and minutes that have passed since sunrise.

Shabbat Candle-Lighting Time
Sunclock can show candle-lighting time with a small hand on the dial.

Arabic hours
In Arabic, a day has 12 hours and each hour has a distinctive name. These names were mentioned by Abdulmalek bin Mohammad Ath-th’aleby (1038-961 AD) in his book “The doctrine of the Language and the Secret of Arabic”

Ṣalāh Prayer Times
Sunclock can show Ṣalāh with small markers on the 24-hour dial. They mark:

Eight calculation methods are implemented:

Spanish electric time periods
The Spanish government is seeking to encourage more efficient energy use with a tier-based model, featuring peak, low and average price periods depending on the time of the day.

For Photographers

Photographers can enable the blue hour. The term blue hour refers to the particular colouration of the sky during the time of dusk after sunset and before the night time darkness, while the sun is about 4 to 8 degrees below the horizon. The same colour is also seen at dawn.

Photographers can enable the golden hour. Golden hour is the time when the sun is plus minus 6 degree around sunrise and sunset. Daylight is redder and softer than when the Sun is higher in the sky.

Blue hour Golden hour

Azimuthal equidistant projection of the earth (aka Flat Earth)

Sunclock can show where on earth the sun is perpendicular and where day and night are. For this purpose, the earth is projected into the dial plane with a so-called azimuthal equidistant projection. The Northern Hemisphere, the Southern Hemisphere, or both hemispheres (the entire earth) can be displayed. In the latter case, the 30 degrees in the south (South Pole) are not shown because the geometry is too distorted. The entire earth can be represented as a topographical map or as a graphic inspired by the UN emblem. You can set the two colors of the graphic individually.

These earth projections are reminiscent of the myth of the flat Earth believed in by medieval European scholars and educated people. It is an archaic and scientifically debunked notion. Nevertheless, there are still supporters of this idea today.

The earth projections can be shown with sun symbol, analemma (equation of time) and users location (small yellow dot). If the analemma is enabled, the sun symbol location varies according to the seasons.

Projection of the Northern Hemisphere Projection of both hemispheres

The cosmic spectacle of the sun's movement is most impressively presented when the analemma and both hemispheres are turned on. Enjoy the dance of the shadow line and the rhythm of the sun on the analemma. Swipe the lower part of the screen or press the animation button twice.


Solar Compass Magnetic Compass

The solar compass shows Date and time can be changed by wiping the screen, compass sensor can be turned off and the location can be changed in the settings of the main screen.


Sunclock offers a wide range of options to configure the clock according to your wishes and needs. The preferences are grouped to three tabs Gallery, Function and Design plus options like described in next chapter. On the one hand, there are the functions of the watch that you can choose from. On the other hand, you can determine the design of the clock in detail. Last not least the first tab shows some sample clocks where you can get an overview and choose your starting point to configure your individual clock. As usual, you will see any changes immediately in the clock display in the upper half of the screen. Swipe the clock on top or on buttom to simulate time or date changes. Finally, you can save and exchange your settings with other users like described in next chapter.

Preference Options Menu

September 28, 2023
© Henning Benecke 2015 - 2023.
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