Properties of Stars §

We can measure the following properties of stars:

• Brightness/luminosity - some kind of light collecting/measuring device?
• Energy output - figuring out how much energy we get and considering that it is evenly distributed
• Distance - light travels over time

How do we measure stellar luminosities? §

Luminosity is the total amount of power (ENERGY PER SECOND = watts ) that a star radiates into space. Apparent brightness is the amount of starlight reaching reaching Earth (ENERGY PER SECOND PER SQ METER). The apparent brightness of a star depends on both distance and luminosity.

$$\begin{array}{rl}\text{Apparent Brightness}& =\frac{\text{Luminosity}}{4\pi \times (\text{Distance}{)}^2}\\ \text{Area of a sphere}:4\pi r^2& \end{array}$$

How do we measure stellar masses? §

We can only really measure mass if we look at a binary star pair.