The Deep Sky Darkness (DSD) calculator gives possibility to see details for different events in the current or selected night. Maybe the most important feature of imaging night is time of complete darkness that can be used for collecting data for deep sky objects. This calculator is mainly focused on this and calls it - Deep Sky Darkness Time (DSD Time). To have DSD the Moon has to be below the horizon and the astronomical twilight should be already ended or not started yet. The calculator also allows searching for a night with desired DSD Time.
Note: You have to set your imaging / observing site coordinates in Location Settings in order to get correct times.
If narrow-band filters are used, it is possible to gather good signal even when the Moon is above the horizon. Narrow-Band (NB) section show how much time can be used for imaging between the evening and morning astronomical twilights.
Take a look on the free (yes, free - no ads or marketing) Androind and iOS versions of the Deep Sky Darkness Calculator - Darkness Clock
Night dates
The dates of the night that is currently displayed. It can be the current or selected night.
In the left column are the selected evening events - time of the sunset, the end of the nautical twilight and the end of the astronomical twilight which is the actual start of the night.
In the right column are the selected morning events - the start of the astronomical twilight which is the actual end of the night, the start of the nautical twilight and the time of sunrise.
Shows when the when starts/ends the time suitable for imaging of deep sky objects - Deep Sky Darkness (DSD) in the selected night. DSD = No Moon and twilight.
Shows how long Deep Sky Darkness (DSD) time will be in the selected night. DSD = No Moon and twilight. When the current night is selected will show the remaining time if the night is already started.
Shows when the when starts/ends the time suitable for imaging of deep sky objects using narrow-band filters - Narrow-Band (NB) in the selected night. NB = No twilight (the Moon is ignored).
Shows how long Narrow-Band (NB) time will be in the selected night. NB = No twilight (the Moon is ignored). When the current night is selected will show the remaining time if the night is already started.
Allows to change the night which events are loaded. The Prev/Next buttons change the date with one day. You can also enter particular date and press the Enter key to recalculate.
If you press the Enter key on empty edit box, APT will use the current date.
You can search for the closest night which has Deep Sky Darkness (DSD) Time equal or more to the entered one. The value is in hours and accepts decimal numbers like 6.5
To open the Deep Sky Darkness calculator double click on 
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