the total rotation period of earth is 23hrs n 56 mins,then why is a day considered to be of 24 hrs?

Answer 1

So that us "normal" people can easily spot you obsessive-compulsive disordered types when you ask these kinds of questions.

It's easier to round it off to 24 hours. I suppose we could have 24 hours of 59.833333 hours each but 60 minute hours are just more convenient.

Answer 2

Humanity has a need to measure time in a practical fashion.
Now, first, let's consider that the time base for a day is set to be 240,000 "something", say -- 240,000 bobs.
When one asks you what time it is, you would have to give hard-to-remember and hard-to-pronounce, non practical big numbers like: "it's 190,000 bobs."
On the other hand, if we take a very small number as a day time merit like the number 1, we would have a hard time calculating time. I mean, it would be 0.5 bobs at noon and there will still be a hard thing to track time.
The best way to track time is if we can have an easy-to-remember and easy-to-track number any time we can. So, the more integer numbers denote time, the more practical time system we will have. That is why we begin with 0 hours and get to 12 (or 24, EU tracking of time).

Now, someone could say that it's better if we had 20 hours in a day not 24. That way, you would measure 0-10 am and 0-10 pm instead 0-12. 0-10 seems an easier system.
But there is one benefit when "bobs" are mesured in a 12 "bob" system. This way, we have more divisors. For instance, 10 can get an integer if divided by 1,2,5 and 10. That means that we will be correctly in time for work, only if the work lasts 10/1 hours (10 hrs), or 10/2 hrs (5 hrs) or 10/5 hrs (2 hr). Or, for instance, if you need a break that is equal to a third of your working time, you can't determine the exact longitude of the break, because it would be 3,333333... hours. With the 10 hr system, you can have exactly timed breaks only if you take a 2 hr or 5 hr break (yor working time is 8 hrs)

But 12 has more divisors, they are: 1, 2, 3, 4, 6, 12. This means that you can have a bigger number of exactly timed breaks: 12/2=6hr break, 12/3=4hr break, 12/4=3hr break, 12/6=2hr break.

Having exact timing for breaks is very important :-)

Hope it helps, Goran.

Answer 3

Historical legacy...for example, sundial clocks were among the first clocks used by mankind. By noting shadows when the sun set versus when it rose, early mankind was able to determine the span of time between sunset and sunrise. They simply noted the half-way point and put some marks in between the two extremes.

Because the sundial is circular, they decided time traveled 360 degrees between sunrise and the next sunrise. So whatever the smaller intervals between sunset and rise were to be, they had to fit into 360 degrees. 12 does that fine; so twelve intervals were marked on the sundial or its equivalent like, maybe, Stonehenge. These 12 intervals became the earlier hours, very imprecise but good enough for government work...you know, for slaying dragons and rescuing fair damsels in distress.

If more precision is needed, say for fixing star positions, the precise sidereal time is used; not the 24 hour clock. Check this out:

"A mean sidereal day is equal to 23 hours, 56 minutes, and 4.091 seconds of mean solar time" [See source.] Because the Earth's rotation is slowing down, this measure has to be adjusted from time to time by adding on a few seconds.

Earth is about 24,000 miles circumference at the equator. So we can use that to say, approximately, we rotate at about v = 1,000 mph tangential velocity on the surface of the Earth at the equator. That useful result comes from S/t = v; where S = 24,000 miles and t = 24 hours.

Answer 4

The Earth rotates once every 23h 56m, but during that time it has also revolved slightly in its orbit around the sun. So in order for the Sun to return to where it was the previous day, the Earth must rotate a bit MORE than exactly once around, and it is that period--- the SOLAR day (not the Sidereal day) that we base our clocks on.

You've gotten some bad answers here. The difference between solar and sidereal days has NOTHING to do with leap years.

Answer 5

In the time it takes for the earth to complete one rotation it has also moved some in its solar orbit.

Thus, if you ignore the time factor, when the earth rotates exactly 360 degrees the stellar alignment will not be exactly the same (especially when you calculate the angle between the star, the earth and the sun.)
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Answer 6

Because a solar day is precisely 24 hours. And solar days are easier to measure and work with - they are the time between successive noontime suns.

But the Earth also moves a little around the sun each day, so the solar day is actually a little shorter than the sidereal day - the time for one 360 degree revolution.

However, the solar day is still the more useful.

Answer 7

Because duration of one day is not equal to rotation period of the Earth with respect to the Universe. One day is one apparent rotation of the Sun in the sky.

The rotation of the Earth around the Sun makes the number of days (sunrises if you wish) per year to appear to be 1 day less than true number of revolutions of Earth. Thus duration of one day is

23h 56min x (365.25 +1) / 365.25 = 24h even.

Answer 8

i suppose it is the same as to why it takes the earth 365.25 days to orbit the sun even though our year is 365 days long, every four years we have a leap year, and catch up once the .25 adds up for times to get a whole day, so i guess logically that would explain your quesion as well

Answer 9

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Because it's a nice, round number. Everyone knows it's not exact, and this is why we have leap years. Throw in an extra day ever four years and everything pretty much catches up with itself.

Because even THAT is not exact, there are other "leap" rules, like, for example, the only "00" year that is a leap year is when the year is divisible by 400. So, for example, the year 2000 was a leap year, but 2100 won't be.

Interesting, huh?
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Answer 10

It's just rounded off to 24 hours and you just answered the question as to why my sleep cycle keeps getting messed up. I'll blame it on that since I need my 8 hours every night.