Why does a day have 24 hours?  Is it based on an angular measure of the sun?
470281
The History of Analog Clocks (SEE FIRST LINK BELOW) provides an explanation of the origin of the 24-hour day. The system dates back 4,000 years, to ancient Egypt and Babylon. \n\nEgyptian astronomers divided the night hours into 12 distinct sets of star patterns, which emerged over the horizon at roughly hour-long intervals. They divided the day into 12 hours to match, and because they lived near the equator, the days and nights were of roughly equal length throughout the year. \n\nThroughout the rest of the world, the 12 "hours" of the day and night were flexible depending upon the season. It wasn't until the 13th century A.D. that an Arab scientist named Abul-Hassan suggested the idea of clearly defined hours. \n\nIt's also worth noting that the number 12 is special in many cultures. For example, Egyptians counted in base 12. Dividing the day into two sets of 12 was a simple and elegant way of condensing the annual calendar into a day. \n\n*Repost*
611229
Due to the direction of rotation of the earth, remember the sun is not actually moving at all we are rotation and rotating around the sun (days, years).  Galilao got into a lot of trouble with the vatican to teach us this :)
1001671
So earth will complete a complete rotation on its axis in 6 hrs instead of 24 hrs. So we have on average 3 hrs days & nights.It will also affect the distance of earth from sun. In nutshell the life on earth will be in danger.
582503
A day is the length of time that it takes for the earth to rotate once. There is a slight difference depending on whether you use the sun for the reference point or a star. The solar day (when the sun is used) is 24 hours. The siderial day (when a star is used) is 23 hours 56 minutes. The difference is because the earth also orbits the sun and so it takes a bit longer to realign with the sun than it does with a star.
432119
It takes about 365.2422 days to orbit the sun (i.e. a solar year). If we have a year be 366 days every four years, that averages out to 365.25 daysper year. This is still a bit large, so we declare 3 of the four century marks to *not* be leap years. That then gives an average of 365.2425, which is close enough for most purposes.\n\nSpecifics: Every year that is divisible by 4 is a leap year *except* those ending in 00. These are leap years only if divisible by 400.
626709
Four hours.  The earth rotates through a full 360 degree circle in 24 hours, this means it rotates at the rate of 15 degrees and hour (360 divided by 24).  So it will take 4 hours to rotate through 60 degrees.
445983
It doesnt have years or days like we do.  For us a day is one rotation of the earth buit the sun doesnt spin.  For us a year is one revolution around the sun, but the sun cant revolve around itself
17260
The hour was originally defined in ancient civilisations (including those of Egypt, Sumeria, India and China) as either one twelfth of the time between sunrise and sunset or one twenty-fourth of a full day. In either case the division reflected the widespread use of a duodecimal numbering system (counting with each thumb the spaces between the joints of the other finger on the same hand, i.e. 3 x 4 = 12) and the equally widespread tendency to make analogies among sets of data (12 months, 12 zodiacal signs, 12 main compass points, 12 hours, a dozen).
392165
Because it takes the earth 24 hours to orbit, . I know what you mean though, i wish there were more hours in the day.
1012693
I'm not sure what he means by his explanation, but he's not totally off to think there would at least be a possibility of the longest 'day' not being adjacent to the shortest 'night'.\n\nAs measured from the Sun's local zenith to the next local zenith, solar days are not the same length of time (24 hours is just the average amount of time to get from noon to noon).  It takes longer to get from local noon to the next local noon at the solstices when the Earth is tilted directly toward or directly away from the Sun.  The shortest solar days (noon to noon) should be at the equinoxes.  (In other words, if there are more total seconds in the solar day at the solstice, then having the most daylight seconds doesn't necessarily mean having the shortest night time seconds).\n\nAdditionally, the Earth's orbit is slightly elliptical.  At perihelion (closest point to the Sun), the Earth is traveling faster and sweeping out a bigger angle per second.  That means the Earth has to rotate further to get back to noon the next day.  Solar days near perihelion are longer while solar days near apohelion (furthest from Sun) are shorter.  This is where your dad's argument starts to break down.  The Earth is at apohelion around the first week of July and at perihelion the first week of January.  In other words, there are more seconds in a solar day in the winter than there are in the summer.  The tilt of the Earth is more significant, so there are still more seconds in a solar day near the summer solstice than either equinox, even if the longest solar day (noon to noon) isn't in the summer.\n\nThe biggest reason his argument breaks down is sheer magnitude.  The variation in the length of a solar day is in seconds/day while the difference in the amount of daylight/darkness can be minutes/day (the amount of variation depends on a person's latitude)\n\nFor 2006, the longest daytime period will be on Jun 21, with the shortest nightime period being Jun 20 or 21 (the Naval Observatory's charts only list hours and minutes).
185180
The earth's shape and rotation make it imposible to have the same amount of light throughout the globe at any particular time, it is day on one side of the world while it's night on the opposing side. Time zoning is meant to give us a reasonably standard method to measure time OF DAY throughout the globe.
425853
You can learn that something is moving.  Either the earth is rotating (true), or the sky is revolving around the earth (once thought to be true).  You can also measure the length of the siderial day.  That is the length of time it take for the earth to rotate reletive to the stars.  Our "day" of 24 hours is based on the sun's motion.  If we were to measure time based on the stars we would have a day of 23hours and 56 minutes.  You can measure the length of the day with star trails, although to really get the timing down might be hard.
634373
I think he meant to ask why a day is divided into 24 and not 36 or 48.  The actual time would be the same but there would be short intervals.  A half hour would end up being an hour.  Why divide a circle into 360 or an hour into 60.  \n\nHour :- "a traditional unit of time, equal to 60 minutes, or 3600 seconds, or 1/24 day. The custom of dividing the daylight into 12 hours goes back at least as far as the Babylonians, who liked to divide units by 12 because groups of 12 are easily divided into halves, thirds, or fourths. Originally an hour was 1/12 of the time between sunrise and sunset, so summer hours were longer than winter hours. Later, when people wanted to express times at night, it was natural to divide the night into 12 hours as well, making 24 hours in the day. Only after the invention of mechanical clocks, around 1300, did hours became equal intervals marked by clocks. The word comes from an ancient Greek word hora which originally meant a season, especially a religious season, and hence a "defined" period of time. In the Christian church hora came to mean one of the services held at seven specific times during the day, thus establishing the word as marking subdivisions of the day." \n\n\nhttp://mathforum.org/library/drmath/view/58460.html
1107632
There's Greenwich Mean Time, which was measured from the 0 degree meridian in Greenwich, UTC (Universal Time co-ordinate) which is measured from an atomic clock in france somewhere (UTC doesn't have summer time, GMT does) and there's standard time which works on the premise that 1 rotation of the earth is 24 hrs, so 360 degrees in 24 hrs = 15 degrees every hour, so every 15 degrees of longitude is 1 hr of time difference
174227
The sun rotates on its axis about once every 27 days.\n\n"enables" is not quite the work I would use to describe it, but the sun rotates due to the law of conservation of angular momentum.\n\nWhen the sun way forming out of a giant cloud of dust millions of years ago, that dust was very slowly moving.  When the dust started to condense, the roation sped up.  The more it condenses, the faster it rotations due to the law of conservation of [angular] momentum.
435661
The week based on the 6 days it took God to make the universe and rested on the seventh day. Thats the week but the week is composed of the 24 hour periods where we spin fully. The year where we revolve around the sun in 365 days.\n\nI hope that answers your question
520978
Because it's not a solid body, different areas of the Sun rotate at different speeds.\n\nEQUATOR - 25 days per revolution\nPOLES   - 36 days per revolution\n30-degrees above/below equator - 28 days