Radius, Temperature, and Size.


In our cosmology, the stars we see with the eye alone on a dark night are located at very different distances from us, from several light years to over 1,000 light-years. Telescopes show the light of stars millions or billions of light-years away.

A star’s luminosity depends on two things: Radius Measure and Surface Temperature.

Radius measure- Let’s presume a star has the same surface temperature as the sun, but sports a larger radius. In that scenario, the star with the larger radius claims the greater luminosity. In the example below, we’ll say the star’s radius is 4 solar (4 times the sun’s radius) but has the same surface temperature as our sun. We can calculate the star’s luminosity – relative to the sun’s – with the following equation, whereby L = luminosity and R = radius:

L = R2
L = 42 = 4 x 4 = 16 times the sun’s luminosity

Also, if a star has the same radius as the sun but a higher surface temperature, the hotter star exceeds the sun in luminosity.

We use the equation below to solve for the star’s luminosity, relative to the sun’s, where L = luminosity and T = surface temperature, and the surface temperature equals 2 solar.

L = T4
L = 24 = 2 x 2 x 2 x 2 = 16 times the sun’s luminosity

The luminosity of any star is the product of the radius squared times the surface temperature raised to the fourth power. A star whose radius is 3 solar and a surface temperature that’s 2 solar, we can figure that star’s luminosity with the equation below, whereby L = luminosity, R = radius and T = surface temperature:

In class we also talked about the different equations. We learned how to calculate them and look at them. We did lecture tutorials on them which helped understand it better. The lecture tutorials where we worked on equations helped me understand the concept very well. We also did clicker questions to test our selves which I also thought was very helpful.

I like to learn about these types of things because usually people don’t pay attention to it. No one really cares about these types of things. But when you look into it they are very very interesting. It’s very cool to know how to calculate the different characteristics of the stars. I really like the fact that there is so much behind a star. Also it;s very amusing how astronauts have found these things out.


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