For Muslims it is obligatory to perform five prayers throughout the day and the night.
These are: Fajr, Dhuhr, Asr, Maghrib, Isha.
The times of the prayer are determined by the position of the sun.

Time
Dawn Prayer (before sunrise)
Beginning time for morning prayers
1.Fajr Angle of the sun under the horizon
Islamic Society of North America: 15°
University Of Karachi, Muslim World League: 18°
Umm Al-Qura University: 19°
Sunrise
end time for morning prayers
Shuruq  

 

 

Noon Prayer 2.Dhuhr, Zhuhr The time of Zuhr starts when sun passes its zenith.
Afternoon Prayer 3.Asr  

begins when the length of the shadow of a vertical rod
Hanafi:
 is equal to its shadow at noon plus twice the length of the rod.
Shafi: is equal to the length of the rod plus its shadow at noon.
It ends about 10 minutes before sunset.

Sunset Prayer 4.Maghrib begins immediately after sunset
Evening (Night) Prayer 5.Isha  

begins, at moderate latitudes, when the sky is completely dark and ends just before the Dawn Prayer.
Angle of the sun under the horizon
Islamic Society of North America: 15°
Muslim World League: 17°
University Of Karachi: 18°
Umm Al-Qura University: 90 minutes after the Sunset

Source: Islam Prayer Times