Which phenomenon related to light allows scientists to measure the distance between a star and earth?

a) dark patches appear in the electromagnetic spectrum emitted by stars.
b) light waves spread out as they move farther from their source.
c) stars have different colors based on their temperature.
d) stars have unique elements that make up their atmospheres.

How are calculation for velocity and speed different

Ametal ring 4.20 cm in diameter is placed between the north and south poles of large magnets with the plane of its area perpendicular to the magnetic field. these magnets produce an initial uniform field of 1.12 t between them but are gradually pulled apart, causing this field to remain uniform but decrease steadily at 0.240 t/s . (a) what is the magnitude of the electric field induced in the ring? (b) in which direction (clockwise or counterclockwise) does the current flow as viewed by someone on the south pole of the magnet?

The amount of potential energy possessed by an elevated object is equal to what?