Astronomy problem. Need help

[Ivan91]

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 ?

[NobodySpecial]

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

[Ivan91]

Ok, thanks. One more question.
What are some differences between active and normal galaxies ?

[davenn]

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