Question

Distances to local galaxies are determined by measuring the brightness of stars, called Cepheid variables, that can be observed individually and that have absolute brightnesses at a standard distance that are well known. Explain how the measured brightness would vary with distance as compared with the absolute brightness.

a) Measured brightness increases with distance
b) Measured brightness decreases with distance
c) Measured brightness remains constant with distance
d) Measured brightness has an inverse relation to distance

Answer 1

Measured brightness of Cepheid variable stars decreases with distance due to the inverse square law, allowing astronomers to calculate the distance of galaxies from Earth.

Step-by-step explanation:

Distances to local galaxies are determined by measuring the brightness of Cepheid variable stars. The measured brightness of a Cepheid variable star will decrease with distance when compared with the absolute brightness. This is described by the inverse square law; as the distance of the star from the observer increases, the apparent brightness diminishes proportionally with the square of the distance.

If a Cepheid star is measured as being less bright than its known absolute brightness, it implies that the star is farther away. The relationship between brightness and distance is used to calculate how far a Cepheid variable star, and consequently the galaxy it resides in, is from Earth.

The measured brightness of Cepheid variable stars would decrease with distance as compared to the absolute brightness. This is because as the distance between the observer and the star increases, the light from the star spreads out over a larger area, making it appear dimmer. The inverse square law states that the intensity of light decreases with the square of the distance from the source.