Physics

Calculating properties of stars

Useful equations

Wien’s Law Stefan-Boltzmann Intensity Doppler Shift distance in parsecs

parallax dcv

R

L IrTL

nmK T

sparK

1

4 4

103 sec2

24

max

6

 

 

 



 



TK = temperature in Kelvin max = peak emitted wavelength in nanometers

L= luminosity in watts =5.67 x 10 -8

W/m 2 K

4

I = intensity in Watts/ m 2 r = radius of star in meters

R = distance to star in meters d = distance to star in parsecs

 = Doppler shift in nanometers = wavelength in nanometers

H = 656 nm Ro, Mo, and Lo are solar units and can be found on the inside front cover of your text.

Using what you have learned about the stars and the above equations, find the color, temperature, luminosity,

distance, intensity, and radial speed of the following stars. Plot the 3 stars on an HR diagram. Points will be awarded

for correctness and work shown. Answers without any supporting math will receive 0 points. You may work in

groups, but the points will be divided among all team members. Remember to cite any sources that you used!

Remember to watch your units! Convert where necessary!

Sirius: Sirius has a mass of 2.02 Mo, a radius of 1.711 Ro, the H line is redshifted a distance of 0.028 nm, the peak

electromagnetic radiation emitted is of wavelength 301.8 nm, and the parallax angle measured from Earth is 379.21

milliarcseconds.

Polaris: Polaris has a mass of 4.5 Mo, a radius of 45 Ro, the H line is redshifted a distance of 0.037 nm, the peak

electromagnetic radiation emitted is of wavelength 434.8 nm, and the parallax angle measured from Earth is 7.54

milliarcseconds.

Thuban: Thuban has a mass of 3.85 Mo, a radius of 6.75 Ro, the H line is redshifted a distance of 0.0166 nm, the peak

electromagnetic radiation emitted is of wavelength 306 nm, and the parallax angle measured from Earth is 10.76

milliarcseconds.