Cepheid Variable Stars - 13a - Intro to Astronomy Sessions
HTML-код
- Опубликовано: 16 июл 2024
- An overview of how Cepheid Variable Stars can be used to measure cosmic distances.
Full Series Playlist: • Intro to Astronomy Ses...
Please note that this was designed as an introductory survey of astronomy course, mostly for non-science majors, and does simplify many of the topics accordingly. I encourage people who are just getting into astronomy to use this as a jumping off point for more in depth studies. I've tried to edit out specific references to my course (regarding assignments, tests, etc.) but I might have missed some. Finally, scientific fields are constantly advancing, with new data and studies resulting in our ideas being continually improved. This means some of the ideas presented here may soon be out of date, so I again encourage people to continue to investigate whichever topics are of particular interest to you.
Opening Image Credit: www.nasa.gov/feature/goddard/...
I really enjoyed this video. Not a lot of videos explaining this in detail. Well done.
Thanks for the nice video, Michael.
Anton Petrov had an interesting video about Polaris, related to the video here.
Surely Leavitt's original Period-Luminosity relationship must have involved a relationship just with APPARENT luminosity? The actual or intrinsic luminosity was not in her data, was it? As I understand it, her formula initially produced an uncalibrated relative scale. Only when Hertzsprung and Shapley were able to independently determine the distance to a Cepheid star a year later did Leavitt's formula become useful for deriving the INTRINSIC brightness directly from the period, I thought. Or am I wrong? In general, the concept of luminosity IMHO creates a lot of confusion, when no systematic distinction is made between apparent and intrinsic brightness.
You're correct that what was originally being measured was apparent brightness rather than luminosity, but Leavitt was specifically looking at the Cepheid variables in the Small Magellanic Cloud (at least with the first paper) so if all those examples are at approximately the same distance, then the relative apparent brightness of each Cepheid would be directly proportional to their relative luminosity. So she was able to demonstrate almost everything about the period-luminosity relationship (that luminosity scales with pulsation period in a particular way) except the reference point of what luminosity that pattern starts from.
You're also correct that to calibrate the absolute scale, we needed to know the distance of at least one Cepheid. If we know distance and apparent brightness, we can calculate the luminosity, and that gave the last reference point needed to calibrate the scale (of course we've continued to make improvements to this pattern with better observations and larger data sets)
Thanks a lot. I just needed this nuanced explanation in order to accept that we may read off (intrinsic) luminosities directly from observed rates of the periods.👍🏻 @@PhysicistMichael
Do you have a Patreon account, Prof. Michael?
@@NalitaQubit Nope, and while I am flattered that anyone might think my material worth financially supporting, that's not my goal with this channel. If you know of anyone interested in science (laypeople, students, or teachers) and are willing to point them towards my channel, that would be wonderful.
If you do have disposable income and want to support the things that I try to do with my channel, maybe see if there are any science clubs, maybe through local schools, that could use some support. Or donate to local food banks, since people in food secure households are going to have more opportunities to direct their time and energy towards education. I'd value those above making a Patreon account for myself.
@@PhysicistMichael Thank you. The reason why I asked was to show interest in learning deeper from you and at the same time supporting your hard work. I find huge value in your work as I love Physics and QM and never want to stop learning. The way you present your material is conducive of not only learning, but also the love of learning. Thank you again, Prof. Michael.