Astronomy Problem: How to Find Apparent and Absolute Magnitude of a Cepheid

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To find the apparent magnitude of a Cepheid variable star, direct measurement is required, while the absolute magnitude can be determined from its period using established relationships. A period of 2.5 days, for example, allows for the calculation of absolute magnitude based on Cepheid properties. Additionally, the discussion briefly touches on the differences between active and normal galaxies, suggesting that a simple Google search can provide comprehensive information. A suggested resource for understanding active galaxies is a Wikipedia link. The conversation emphasizes the importance of utilizing available online resources for astronomy-related queries.
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I didnt find an astronomy subforum on the Homework section so I decided to post here.

If I have the period of a cepheid (2.5 for instance), how to find apparent and absolute magnitude ?
 
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Apparent magnitude you have to measure - the absolute magnitude you get from the period see:
http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html
 
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Ok, thanks. One more question.
What are some differences between active and normal galaxies ?
 
Ivan91 said:
Ok, thanks. One more question.
What are some differences between active and normal galaxies ?

did you try googling... active galaxies ?

the first hit is a wikipedia link explaining the difference :)

Dave
 

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UC Berkely, December 16, 2025 https://news.berkeley.edu/2025/12/16/whats-powering-these-mysterious-bright-blue-cosmic-flashes-astronomers-find-a-clue/ AT 2024wpp, a luminous fast blue optical transient, or LFBOT, is the bright blue spot at the upper right edge of its host galaxy, which is 1.1 billion light-years from Earth in (or near) a galaxy far, far away. Such objects are very bright (obiously) and very energetic. The article indicates that AT 2024wpp had a peak luminosity of 2-4 x...
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