Properties Of Nearby Stars

Question 1

Distinguish between a star’s apparent brightness and its luminosity

Answer 1

Luminosity is an instrinsic property of the star - total amount of power (energy per second) the star radiates into space
Apparent brightness: the amount of starlight reaching earth
◦ Two lights could be the same brightness at different distances, or different brightness at different distances etc, but just because they look the same doesnt mean they actually are the same

Question 2

Draw a diagram illustrating how to use the parallax method to measure the distance to a nearby star

Question 3

Define the term light year and use it correctly, distinguishing it clearly from measures of time

Answer 3

• a unit of astronomical distance equivalent to the distance that light travels in one year
• the distance light travels in a year - 6 trillion miles

Question 4

Explain how the inverse square law of light relates a star’s luminosity to its apparent brightness

Answer 4

• the amount of light received from a star falls off with the square of the distance from the star

So if you’re 2AU away from the sun, its 2^2 = 4

So compared to the amount of light received by a solar panel orbiting the sun at 1AU, the exact same solar panel would receive how much light is it were orbiting at 3AU = 9

What is the relationship?
- apparent brightness depends on the luminosity and distance = so you can find the apparent brightness as equivalent to L/4(pi)d^2

Question 5

Explain how we can measure a star’s luminosity

Answer 5

In solar units - 4x 10^26 W