Astronomy - Ch. 17: The Nature of Stars (5 of 37) Distance=? given Absolute & Apparent Magnitude

[@PZK21]

This is the most informative video about astronomy I’ve watched. Bravo🎉

[@MichelvanBiezen]

Thank you.

[@adisakpirom]

You are great. Thank you very much for many clips about astronomy. My son is preparing for Thailand Astronomy Olympaid#16 end of this month. We mainly study from your clips. Excellent explanation, you made very difficult thing to be simple and fun.

[@MichelvanBiezen]

We wish your son good luck. It is all about having fun learning and discovering.

[@0219-n1e]

Beautiful subject. Please extend you work to Galaxy sciences and Galactic Halo. Thanks a lot

[@javeer1599]

thank you so much. that was way more helpful than my textbook

[@MichelvanBiezen]

You're welcome! Glad it helped.

[@filipspace24]

I have a problem. When I wanna calculate the distance between the Earth and the Sun I need app magnitude and abs magnitude, but when I know only app magnitude and I want calculate abs magnitude I need know distance, but I don't know that, cause distance is what I have to calculate. What should I do please?

[@MichelvanBiezen]

The absolute magnitude of the Sun is + 4.85

[@T83707]

Can I use the formula m-M=5log(d/10) to find the distance of the star away from the earth? d=214.78pc

[@T83707]

m-M is the ratio of the actual intensity of the star to the intensity if the star is at distance 10pc from the earth but not luminosity? Since i saw you write Delta L on the blackboard do you mean change of luminosity / change of intensity?

[@MichelvanBiezen]

Ken, Luminosity and intensity are often used interchangeably, but they are not the same. Intensity refers to the total energy output at all wavelengths. Luminosity refers to the light output. For many stars they are somewhat proportional.

[@T83707]

Michel van Biezen SO,WHY I USE m-M=5log(d/10) will give a different answer for the question?DO I use the wrong method ?

[@wastaggio]

It's the end of October and I can't wait for Orion to rise over the horizon later in the night, so I can see in my 70mm binoculars Betelgeuse's reddish glow.

[@MichelvanBiezen]

If you are willing to stay up late enough, you'll get a really good view of Orion.

[@lordlyamiga]

this distance is from that reference line or from earth?

[@MichelvanBiezen]

From Earth

[@juremadecarvalho2416]

Maybe in these sites the Absolute magnitude I found is -5.14 instead -6.0. What is the abs.mag of Betelgeuse?

[@MichelvanBiezen]

There is no exact number as it is a variable star and its exact distance is not know accurately. It is somewhere in the range you described.

[@juremadecarvalho2416]

I found the different distance for Betelgeuse in many sites (427 ly). Why?

[@MichelvanBiezen]

There is a lot of uncertainty as to the exact distance. The uncertainty is about 50 ly

[@soleilenvierge]

You just forgot to explain how you found the absolute magnitude. You just gave it a value of (-6.02) but where does that value come from?

[@MichelvanBiezen]

+cqwelkjncwfkjlcblkwfbveowkr The purpose of this video was to show you how to calculate the distance to the star when both the absolute and apparent magnitude are known. So we started with the two given values. Determining the absolute value is a different type of problem.

[@MichelvanBiezen]

+Michel van Biezen You can look up the absolute magnitude of various stars.

[@soleilenvierge]

+Michel van Biezen I'm confused -a lot- with the notion of absolute magnitude. I read everywhere that to get the absolute magnitude of a star, we need its distance. But to get its distance (in regards to the Distance Modulus equation), you need its absolute magnitude. So my question is this: how can we know the distance of any stars when the parallax method cannot be used ? regards,

[@MichelvanBiezen]

+cqwelkjncwfkjlcblkwfbveowkr OK, now I understand your question. There are other ways in which we can figure out the distance to stars, such as using the HR diagram and using the spectral class and spectral type information, along with the understanding of the Steffan-Boltzman law to figure out the the actual intensity of the star. Then coupled with the apparent magnitude of the star we can figure distance to the star, which then allows us to figure out the absolute magnitude. There are some videos in the playlist that explain the spectral type and spectral class of a star related to the HR diagram.

[@soleilenvierge]

+Michel van Biezen Thanks so much for taking the time to respond to my question, it's very appreciated. I'll check out your other videos.

[@emperor8716]

thank you!

[@MichelvanBiezen]

You're welcome! 🙂