The time taken for the Earth to make a full rotation about its axis with respect to the fixed stars; a sidereal day or stellar day. (informal or meteorology) A 24-hour period beginning at 6am or sunrise. The meaning of DAY is the time of light between one night and the next. How to use day in a sentence. Details about today's date with count of days, weeks, and months, Sun and Moon cycles, Zodiac signs and holidays. See the full list of today's national days, fun holidays, and awareness days to celebrate right now. It is daytime on the side of the Earth that is facing the Sun. When it is nighttime, that side of the Earth is facing away from the Sun. It takes 24 hours for the Earth to spin once, so that is one day, including the daytime and nighttime. This is mean solar time, measured relative to the Sun. Discover today's unique celebrations, holidays, and observances on National Today. Find out what makes this day special and worth celebrating! On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, and night. This daily cycle drives circadian rhythms in many organisms, which are vital to many life processes. Find a complete list of today's holidays, unique celebrations, and fun ways to celebrate every day of the year. July 30, 2026 - Today is National Father-in-Law Day, International Day of Friendship, National Chili Dog Day, National Cheesecake Day, National Oyster Day, National Talk in an Elevator Day, National Whistleblower Day, and National Get Gnarly Day. Find today's national days, explore what's coming up this week, and never miss a fun holiday again.