My friend asked me the definitions of the all Zmanim shown on most Luchot, but i was not sure. i would like to know the meanings of the terms, such as Neitz Hachama, Plag Hamincha, Mincha Gedola, Shekiya, etc, and also how they are calculated. thank you for your time. kol tov.

 Zricha = sunrise – the first ray of sun  Shkia = sunset – as the sun ball disappears.  Alot Hashachar = dawn – an hour or 90 minutes before zricha.  Tzeit hakochavim = the appearance of three medium size stars – about 24 minutes after shkia – depends by season, place and Halachic opinion one follows.  Chatzot = mid day - the exact time between zricha and shkia.  Sha'a zmanit = a proportional hour – one twelfth of the time between zricha and shkia.  Plag hamincha – 10 3/4 proportional hours from zricha (1.25 before shkia)  Mincha gedola – half an hour after chatzot.  Moncha ketana – two and a half proportional hours before shkia  These times have numerous implications – from Tfilah through Tahara to brit milah – practically any Jewish aspect connected to time.