I would like to study a topic in astronomy , an interesting topic ?

Meteoritics is fascinating. Calculating orbital motion is tough, but rewarding. Astronomy is a hobby that never gets old. You could learn something new every day for life. Enjoy.

Try going to http://www.jpl.nasa.gov/ you can find all sorts of things to study there. Personally, I started within our own solar system, and after i got to know it, I started studying our galaxy.

Once I got to know our own galaxy, I stared studying other galaxies. There are many interesting topics you could study, almost an infinite amount since space is infinite.

Only YOU know what you find interesting.

http://en.wikipedia.org/wiki/Helioseismology

http://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System

http://library.thinkquest.org/27930/planet_formation.htm

http://en.wikipedia.org/wiki/Active_galactic_nucleus

http://heasarc.gsfc.nasa.gov/docs/objects/agn/agntext.html

http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html

http://www.brown.edu/Departments/Geology/research/geochem.html

Stellar Evolutions , Star birth!

galaxies...yeahhhh

http://curious.astro.cornell.edu/galaxies.php