What instrument did navigators use to calculate the positions of the sun and the stars?

a caravel

a carrack

an astrolabe

a compass

An Astrolabe

Explanation:

As we know that we need to find the positions of Sun and Stars

So here we will analyze the given options

1) A Caravel

2) A Carrack

above both are two different types of Sailing ships so they can not be the answers as we can not measure the positions of sun and star with the help of ship

4) Compass

It is magnetic needle placed in horizontal plane and it is used to find out the directions and worked on the magnetic field of Earth

3) An Astrolabe

This devise is used to find out the position of Sun and other Celestial bodies and used by astronomers in past time

so correct answer will be

An Astrolabe

luster is not a good characteristic to use by itself because luster is the property of minerals that indicates how much the surface of a mineral reflects light. the luster of a mineral is affected by the brilliance of the light used to observe the mineral surface.