How long is a day?

Question

Every four years we add a day to february to balence the difference for how long a day should actually be.
I've also heard that every 100 years we take another day off to balence. Is this true?
And if it is, how would we calculate the true length of a day?

Answer 1

a day is 23 hours 56 minutes and 4 seconds explaining why we have a feburary 29th once every 4 years. So in 100 years that would actually take off an extra 25 days. to calculate the length of a day you divide the earths diameter (approx 23,962mi.) and divide by the speed of rotation 1000 mi. per/hour and you get 23.962hours per rotation

Answer 2

Every four years, we add a day to February to balance the length of a YEAR. This has nothing to due with the length of a day. The rule is this:

If the year number is evenly divisible by 4, then it is a leap year,
unless it is evenly divisible by 100, then it is not a leap year,
... except if it is evenly divisible by 400, then it is a leap year.

Counties that obeyed the Pope use the law of Pope Gregory XIII, from 1582. If you live in Britain, or a country that is or used to be a British colony, then this rule comes from a law passed in 1751. The rule is the same both ways.

These laws were made so that the first day of spring would always be on March 19, 20, 21, or 22.
The first day of spring is a physical thing, it doesn't care about what people do. There are 365.2425 days (about) between the start of one spring and the next. So the man-made calendar needs to do something about the extra 0.2425 days -- and leap years are the answer we use.

If you want to know about the exact length of a DAY, please ask another question.

Answer 3

A year is 365.2422 days long.
But a day has exactly 24hours.
It is due to the number of days in the year that we add a day to february.

The Gregorian calendar, the current standard calendar in most of the world, adds a 29th day to February in all years evenly divisible by 4, except for centennial years (those ending in -00), which receive the extra day only if they are evenly divisible by 400. Thus 1600, 2000 and 2400 are leap years but 1700, 1800, 1900 and 2100 are not.

Answer 4

An Earth Day is 23 hours, 56 minutes and 4 seconds as in that is how long the Earth takes to spin on its axis.

Answer 5

Every year the moon is moving away from our planet at 1.9cm.So it will get longer :-) eventually :-)

The gravitational interactions of Earth and Moon have been acting from the beginning to slow the rotation of the Earth and increase the distance from Earth to Moon. The changes depend on dissipation of tidal energy on the Earth, however, so the rate has varied as the configuration of continents and depth of the ocean have changed over geological time.

Check here http://www.jpl.nasa.gov/releases/99/lunarlaser.html

Answer 6

1- International System of Units (SI)
A day is defined as 86,400 seconds. Those are currently defined as:

The duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.

This makes the SI day last exactly 794,243,384,928,000 of those periods.


2- Astronomy

For a given planet, there are two types of day defined in astronomy:

1 apparent sidereal day:
A single rotation of a planet with respect to the distant stars
(for Earth it is 23.934 solar hours or 24 sidereal hours)

1 solar day:
A single rotation of a planet with respect to its Sun.

Answer 7

A day is 23 hours, 56 minutes, and 4 seconds long.

Answer 8

24 hours 2 minutes

Answer 9

The true length of day is predefined as 24 hours. We would have to redefine the word "day" if we re-calculated the length of it.

Answer 10

24 hours