Astronomy - Ch. 17: The Nature of Stars (28 of 37) Determining a Star's Luminosity

[@LithiumHydroxide]

Sir, this is your best video! Helped me a lot! I was trying to derive an equation and I couldn't just because of I didn't know relation of luminosity! Thank you so much...

[@MichelvanBiezen]

You are welcome. Glad you found our videos. 🙂

[@joneslu1377]

Therefore, spectral analysis enables positioning of a star on the Main Sequence, which in turn allows use of the equations to determine the luminosity of the star in question with its known mass relative to Sun! Is this correct understanding?

[@jaideep_rankawat]

Sir, how to we derive these equations?

[@MichelvanBiezen]

These relationships are experimentally derived. For the hotter stars, a greater portion of the emitted light is in the UV range, so they appear less bright than you would expect for their size.

[@LithiumHydroxide]

I am stuck on a problem, it goes like - Consider a molecular cloud with a uniform density p=1x10^-20 gcm^-3 and a temperature of 15K.Calculate the Bonnor-Ebert mass (M(be)) for this molecular cloud. Determine whether the cloud is gravitationally bound or not by comparing its total mass to the Bonnor-Ebert mass. Additionally, calculate the free-fall time (T(ff)) for the cloud. Please make a video to solve it. TYSM

[@MichelvanBiezen]

That is indeed an interesting problem, but they did not give you the size of the cloud, which means you cannot find the mass of the cloud to compare to the Bonnor-Ebert mass. First find the velocity of sound = sqrt (kT/mu m) = sqrt (1.38x10^-23 x 15 / 1.67x10^-27 kg) = about 350 m/sec. Then plug that into the mass equation. Not sure if we'll have time to make a video on it soon, but we'll put it on the list of requests.

[@Physics-Learner-fs8xd]

michel i was using my calculator to figure out the real max limit and i dont know how you did it to find those limits

[@MichelvanBiezen]

For the first example take 0.43 and raise it to the 2.3 power. Your calculator should be able to do that.

[@HosseinShahbazi-g6f]

Were good 🎉

[@MichelvanBiezen]

Thank you.