Understanding a Day

Definition

• A day is a unit of time, equivalent to 24 hours
• It is the period of time it takes the Earth to rotate once on its axis

Structure

• A day is divided into 24 equal periods, called hours
• Each hour is divided into 60 minutes
• Each minute is divided into 60 seconds

Types of Days

• Solar day: the period of time it takes the Earth to rotate once relative to the Sun
• Sidereal day: the period of time it takes the Earth to rotate once relative to the fixed stars (23 hours 56 minutes 4.09 seconds)

Daylight and Night

• Daylight: the period of time when the Sun is above the horizon
• Night: the period of time when the Sun is below the horizon
• Twilight: the period of time when the Sun is between 6 and 12 degrees below the horizon

Day in Different Cultures

• In some cultures, the day begins at sunrise or sunset
• In others, the day begins at midnight or noon
• The international standard is to begin the day at midnight (00:00)

Take this quiz to learn about the definition, structure, and types of days, including solar and sidereal days. Test your knowledge on daylight, night, and twilight, as well as how different cultures define a day.