Astronomy 2 (short answer questions)

What is the importance of Cepheid variables in astronomy?

Cepheid variables have a period-luminosity relationship that allows us to determine their luminosity from measuring their periodic variations in brightness. Comparing the luminosity with the apparent brightness then gives us the distance to the star. In this way, we can determine distances to not just Cepheid stars but the clusters and even galaxies that they are associated with.

Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located five times Earth's distance from the Sun

The Sun would appear 1/25 times as bright. So the apparent brightness would be 1,300 ÷ 25 = 52 watts per square meter.

Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located half Earth's distance from the Sun.

The Sun would appear four times brighter. So the apparent brightness would be 4 × 1,300 watts per square meter = 5,200 watts per square meter.

Earth is about 150 million km from the Sun, and the apparent brightness of the Sun in our sky is about 1,300 watts per square meter. Determine the apparent brightness we would measure for the Sun if we were located one-third of Earth's distance from the Sun.

The Sun would appear nine times brighter. So the apparent brightness would be 9 × 1,300 watts per square meter = 11,700 watts per square meter

Process of Science: How do scientists estimate stellar luminosities?

They must find both the brightness of the star from Earth and its distance, and then use the inverse-square law

Process of Science: What is a basic assumption that is made when we measure stellar masses by observing their orbits?

We assume that the stars move around each other under the force of gravity in exactly the same way as planets move around the Sun in our Solar System. That is, Newton's laws are equally valid in these distant stellar systems.