What is a civil day?
A civil day is the day of 24 hours used routinely on Earth for setting clocks i.e., 24 hours divided into two portions- day time and night time- depending on whether the Sun Shines in the sky or not.
Does the difference between the civil and astronomical days have any significance in astronomical 
observations?
Since the civil day is 3 minutes and 56 seconds longer than the astronomical day, any star in the sky will rise 3 minutes and 56 seconds earlier every day compared to the previous day.
