+ - twilight refers to the dull light that can be seen near the horizon even though the Sun is
yet to rise or has set already Astronmical twilight refers to the moment when sun is about 18o below the horizon.
This usually is taken as the time when Sahr ends (and Fajr begins) in the mornings and
as the beginning of Isha in the evenings Nautical twilight refers to the moment when sun is about 12o below the horizon.
The morning light at this time has been historically taken to be enough for navigational purposes Civil twilight refers to the moment when sun is about 6o below the horizon.
The light at this time is usually taken by civic authorities in many countries to be the time to
turn off the street lights, head lights of vehicles etc
Transit refers to the time in which the Sun reach its highest point in its east-west movement
everyday. Luhr begins shortly thereafter