Night or nighttime (also spelled night-time or night time) is the period of ambient darkness from sunset to sunrise during each 24-hour day.
Consider the following statement of Vyasa from the Mahabharata
The house-holder should never sleep during the day, or during the first part of the night, or during the last part thereof.
Vyasa is mentioning the first and last parts of the night.
Into how many parts a night has been divided according to scriptures? How much time span does each part take and how to calculate the timings of those parts according to the location?