# How long does it take a photon to escape from the center of a star? **URL:** \ **Category:** Factual Questions\ **Created:** [August 8, 2002, 8:41pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021 "2002-08-08T20:41:35Z")\ **Posts on this page:** 5\ **Page:** 3
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [August 12, 2002, 8:41pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021/41 "2002-08-12T20:41:37Z")
**rsa** , the Time-Independent Schrondinger Equation does not apply to the entire problem because we have propagation of a system (our photons) through time. The advantage of solving the time-independent formulation is that you can actually see the quanta as the static solutions give you the eigenstates of your wavefunction (or system of wavefunctions). The quanta are still there in the Time-Dependent solutions, but they get mixed up depending on the probabilities associated with each state. Of course, the minute an observation is made, one of the eigenstates is spit out probabilisticly. This is where you get a connection between the configuration space (that deals in probabilities of a photon being in a given state) and physical state (that is all about what properties of the photon we actually _observe_). If the above paragraph is as clear as mud, keep pestering and we’ll try to arrive at some meaningful explanation for ya. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [August 12, 2002, 8:50pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021/42 "2002-08-12T20:50:35Z")
> [@](#): > > Of course, Andromeda has a lot more than that. Two major factors get in the way. First, not all of the light emitted by a star is visible. I think the average is around 0.1%. So, we’d have to multiply the number by 1000, to get 10 Billion. Also, Andromeda is a lot brighter than the minimum threshold. I think it’s around 3 mags, or16 times brighter. We’d have to multiply again, this time by 16, to get 160 Billion Suns. That sounds right to me, but my numbers in this paragraph may well be way off. Indeed, the numbers are off… The light we see is quite a bit more than 0.1%; the only sources of obfuscation are basically stuff (that’s given the portentious name of “dust”) that gets in our way. It’s actually not a bad approximation to say that we actually see ALL the light that heads out in our direction from Andromeda, so you can get rid of any kind of correction there. Multiplying by 16 for the fact that it IS brighter than the minimum threshhold gives you 160 million stars. Indeed, your average Spiral galaxy like Andromeda or the Milky Way contains just about 100 million stars. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [August 12, 2002, 8:59pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021/43 "2002-08-12T20:59:55Z")
After rereading, I see that I wasn’t clear as to why 0.1% should not be taken into consideration. Basically, we are dealing with only visible magnitude stuff here and don’t have to worry about the other part of the spectrum. Since the assumptions were already made within the confines of visible light the fact that we don’t see the entire E-M spectrum does not matter. The only thing that matters is whether there’s a bit of dust in our sightline. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [August 12, 2002, 9:03pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021/44 "2002-08-12T21:03:12Z")
[Carl Sagan on] **Billions** of stars. The Andromeda or the Milky Way contains just about 100 **billion** stars. [Carl Sagan off] ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [August 12, 2002, 9:54pm UTC](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021/45 "2002-08-12T21:54:00Z")
Indeed, you are right, **Exapno** , knock me over with a wet noodle… The 0.1% figure does come into play due to the 20 photons per second value given as the observed number of photons, which is not the same as the TOTAL flux from the sun. Since it is not the OBSERVED flux from the sun, we have our discrepency. Okay, I’ll go slink away now with my tail between my legs. Good work **Achernar**. You were right, I was wrong! [Previous page](https://boards.straightdope.com/t/how-long-does-it-take-a-photon-to-escape-from-the-center-of-a-star/123021.md?page=2)