Nightsky Astrolabe

Ancient or medieval people used astrolabes along with the stars to navigate for long distance or maritime travels. This app tries to replicate those experience in the modern world but with much easier approach, thanks to today's mobile technologies. And you will be able to navigate in the open air even if GPS or internet is not available.

Features in this app to achieve the experiences:
*Built-in offline database of 1200 stars that are visible to naked eyes.
*Built-in offline database of the coordinates of 20k most populated cities'.
*Virtual night sky, including showing the positions of the stars and planets, 88 constellations and some famous asterisms you may need to recognize the stars or navigate.
*Basic star information, long-press on the star in the virtual night sky will pop up the information of the stars near by.
*Allows you to measure a star/planet's horizontal altitude with the phone's gyroscope. And also allows you to lock a certain direction like a compass, this way you could avoid the background magnetic noise in some circumstances.
*AR feature is an alternative and experimental feature for you to measure the star/planet's horizontal altitude or to lock a certain direction.
*Calculates your possible current Latitude based on the altitude result you got from the gyroscope.
*Latitude and Longitude sliders allow you to adjust your current location and see how the night sky rotate/scroll. You could compare the virtual night sky and the night sky you see above to get your rough longitude after you have calculated your latitude from the feature above. If you could see stars rising above the horizon, it's easier to get your longitude by comparing the stars right above the horizon.

In-App Purchase features:
* Remove all ads(and thus no more data collection from us and Google)
*Full access to offline location database and be able to reset your default location at anytime you like
*Location service from GPS/internet to get your Latitude/Longitude within seconds.(Convenient but not necessary, you learn how to find your coordinates without the access to internet or GPS)
*Location service to get your coordinates within seconds.(In-App Purchase)

While getting your coordinates from internet or GPS is not the objective of this app. There're occasions that you need to access your current coordinates quick and precisely.
Furthermore, during the daytime. You c