Bright Stars + Physics = No Girlfriend

                                 

A conversation of me and my girlfriend a couple of years ago in Hawaii:

Me:  This night is perfect! (Trying to sneak a kiss)

My Girlfriend: Yes, it is the best!! (We kissed)

Me: You are the best kisser ever. (She laughs)

My Girlfriend: (Looking through the telescope) Wow, the stars really look bright tonight.

Me: Yes they sure are. That is called the Alpha Centauri. It’s almost impossible to see it from where we lived, but here we can see part of it.

My Girlfriend: Really? They are so bright… but it’s not brighter than the sun though.

Me: (I laugh) No honey, Alpha Centauri is actually brighter than the sun.

My Girlfriend: No I don’t believe you. It’s not like you can measure its brightness.

Me: Oh yes I can.

The brightness of any star is measured in terms of the radiant flux that the star emits. The radiant flux is the total amount of light energy of all wavelengths that crosses a unit area oriented perpendicular to the direction of the light’s travel in time.  The radiant flux also received and depends on the object luminosity, energy being emits per second, and also the distance being observe.

The equation to measure radiant flux is…

F - Radiant Flux

L - Luminosity

r - radius

So if a star is surrounded by a spherical shell and assuming that no light is absorbed when it exits the shell, the radiant flux can be measure in relation of the radius of the shell and the luminosity by the shown equation. A Greek astronomer named Hipparchus is actually one of the first one to notice this and he catalogs the stars. (My girlfriend is giving me the look like she wants me to “shut up.”) He assigns something called the apparent magnitude where m = 1 is the brightest and the scale goes up from there, so the higher the apparent magnitude, the dimmer it gets. Photometers can be used to measure these apparent magnitudes.  

I then proceeds to calculate the radiant flux, but not before finding the luminosity and radius values on my iphone. I also looked up the calculated valued  of the sun and show my girlfriend the two radiant flux and explains to her that Alpha Centauri appears less brighter because it is farther away whereas our sun is closer. (She stands up as I also rose, and she proceeds to smack me and say “We are through you Physics Nerd.” It was a really awkward trip back to California when she tries to make me jealous by flirting with another guy on the plane. Never saw her again.) TRUE STORY OR IS IT? :D