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

this means that the temperature of both substances will be equal

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia