It's a bit tricky to say what Europeans "learned" about the astrolabe, because they didn't invent it! The astrolabe was a crucial tool for navigation, developed by the ancient Greeks and further refined by Islamic scholars and astronomers in the Middle Ages.

Here's what Europeans learned about the astrolabe, thanks to their interactions with the Islamic world:

* How to use it: Europeans adopted the astrolabe as a key tool for navigation. They learned from Islamic scholars and navigators how to use the astrolabe to determine latitude by measuring the angle of the sun or stars above the horizon.

* Its versatility: Europeans realized the astrolabe wasn't just for navigation. They learned about its use for telling time, determining the direction of prayer (Qibla) in Islam, and even making astronomical calculations.

* Its construction: Europeans studied and improved the astrolabe's design and construction. They introduced more detailed scales and features to make it more accurate and versatile.

In short, Europeans didn't discover or invent the astrolabe. Instead, they learned about it from the Islamic world and then adopted, adapted, and improved upon it. This exchange of knowledge was crucial for the development of European navigation and exploration during the Age of Discovery.