Getting Started with the CelNav 360 app (Android version)
Celestial navigation exploits the principle that every measurement taken with a sextant (a `sight') converts to a line of position on a chart, the intersections of two or more such lines providing a position fix.
With the app you enter sights and inspect the resulting lines of position calculated for you under the hood.
It is possible to use your device camera in place of a sextant if you do not have one. See here
Tap AP in the action bar
Tap MODE in the action bar to toggle a view of the computed horizon at the assumed position
Open the Sights Table by tapping the icon at the bottom right of the screen.
Tap the sextant icon and select from Sun/Star/Planet/Moon
The dip correction at the bottom left of the dialog may be adjusted by tapping on it
The line of position derived from each sight is represented in the table by its intercept and azimuth.
Tap MODE in the action bar to toggle a graphical view of all the lines of position in the table
Select a table entry and tap altitude
A standard reference work for sight reduction and other techniques of celestial navigation is
Bowditch's American Practical Navigator
https://msi.nga.mil/Publications/APN