It is not an app, but a free mobile service. It gives you free text or email notifications whenever the International Space Station is visible. Bright enough to be seen even from a city, you’ll always know when to look up. https://spotthestation.nasa.gov
The Moon: Calendar Moon Phases
Lunar calendar is one of the oldest calendars in modern society. A lunar month can only be 29 or 30 days long. In other words, the length of a year…