Is there any specific time period for morning, afternoon, evening and night?

morning is after midnight but is still dark and is night.9pm should be night but it could be still light so cant be night coz isn't night when its light? but even it there is a specific point of night - that is the opposite of day and day has many sub categories so is it in the same sense? plus in some places like iceland it doesn't get dark so what does that mean?