The clock shows the solar day for your current location. 
White ticks indicate that the sun is up. 
The red marker shows solar noon. 
The grey pointer shows solar time and the white pointer local time. 
You can also see the hours and minutes until the next sunrise or sunset. For astronomy you can change the display to show astronomical twilight.
The compass shows the current heading as reported by the magnetometer. This magnetometer is very sensitive and reacts to metal and electrical current. 
The heading may not be accurate.
The yellow mark shows the current sun position. As the earth rotates around the sun this marker will rotate around the compass. 
The white ticks show the angles where the sun is up. 
The map shows the position of the sun at sunrise (yellow) and sunset (red). 
The white pointer shows the current position of the sun. When the sun in under the horizon, the pointer becomes grey. 
To get a detailed view enable Local Map in Settings.
Solar Data display

Astronomical Twilight changes the display of the clock to show astronomical dust and dawn. 
Lazy Updates refreshes the data every 30 seconds instead of every 5 seconds.
Local Map shows the Sun