Both devices use the principles of celestial navigation to determine latitude and, in some cases, longitude.

Here's how they are similar and different:

Astrolabe:

* Purpose: Primarily used to determine latitude by measuring the altitude of stars.

* Method: Used a series of plates and scales to calculate angles.

* Limitations: Less precise than the sextant, could only be used at night, and was difficult to use in rough seas.

Sextant:

* Purpose: Also used for celestial navigation, measuring angles to determine latitude and longitude.

* Method: Uses mirrors and a telescope to measure angles more accurately.

* Advantages: More precise, can be used day or night, and more stable in rough seas.

While the sextant has largely been replaced by GPS, it remains a valuable tool for backup navigation and for learning celestial navigation principles.