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A day consists of two 12-hour periods, for a total of 24 hours. An hour consists of 60 minutes. A minute consists of 60 seconds. Seconds are subdivided on a decimal system into things like "hundredths of a second" or "millionths of a second."

hat's a pretty bizarre way to divide a day up. We divide it in half, then divide the halves by twelfths, then divide the twelfths into sixtieths, then divide by 60 again, and then convert to a decimal system for the smallest increments. It's no wonder children have trouble learning how to tell time.

How long is a day? It's the amount of time it takes for the Earth to rotate one time on its axis. But how long does it take the Earth to rotate? That is where things become completely arbitrary. The world has decided to standardize on the following increments:

in timekeeping

3,600 seconds, now defined in terms of radiation emitted from atoms of the element cesium under specified conditions. The hour was formerly defined as the 24th part of a mean solar day—i.e., of the average period of rotation of the Earth relative to the Sun. The hour of sidereal time, 1/24 of the Earth’s rotation period relative to the stars, was about 10 seconds shorter than the hour of mean solar time.

In even earlier systems of timekeeping, an hour was 1/12 of a period of daylight or darkness—hence, variable in length with seasonal changes in the length of day and night. The custom of dividing the cycle of day and night into 24 periods seems to have originated with the ancient Egyptians.

"The origin of our time system of 24 hours in a day with each hour subdivided into 60 minutes and then 60 seconds is complex and interesting," says Dr Nick Lomb, consultant curator of astronomy, from the Sydney Observatory.

Our 24-hour day comes from the ancient Egyptians who divided day-time into 10 hours they measured with devices such as shadow clocks, and added a twilight hour at the beginning and another one at the end of the day-time, says Lomb.

"Night-time was divided in 12 hours, based on the observations of stars. The Egyptians had a system of 36 star groups called 'decans' — chosen so that on any night one decan rose 40 minutes after the previous one.

Egyptians (who used base 12) developed a sundial which looked like a T-shaped bar placed in the ground with would divide the time between sunrise and sunset into 12 parts. Because of the seasonal change in the length of time between sunrise and sunset, summer hours were longer than winter hours! Historians theorize that the importance of 12 is based on the number of finger joints on each hand (not counting the thumb) or the number of lunar cycles in a year. The division of the night into 12 parts was achieved by Egyptian astronomers who observed the appearance of 12 key stars in the night sky. Out of these divisions was born the concept of a 24-hour day. However, seasonal hour length was used for many centuries, and fixed hours became common only after the appearance of mechanical clocks in 14th century Europe!

December 2003 answer: It appears that the Egyptians were responsible for the 24 hour day. The Eqyptians were fond of counting in base twelve (instead of base 10 which is commonly used today). This is thought to be because they counted finger joints instead of fingers. Each of your fingers has three joints, so if you count by pointing to finger joints with your thumb you can count to twelve on each hand. This might seem arbitrary, but is actually just a strange as counting in base ten simply because we have ten digits.

The Egyptians divided the clock into 12 hours of daytime and 12 hours of night-time (or alternatively 10 hours between sunrise and sunset, an hour for each twilight period and 12 hours of darkness). This is known because of various sundials from the period which have been found to be marked with hours. Interestingly this means that hours started out changing in length with the seasons (as the amount of daylight vs. darkness changes).

Marco Polo was a Venetian, but where he was actually born is not known with complete certainty. He was born in either the city of Venice or the city of Korcula, Croatia. In Polo’s day, the city was called Curzola, Venetian Dalmatia. Regardless of where he was born though, Marco was raised in Venice, and was Venetian by culture. Marco came from a family of explorers and traders, but it was his name that has become so famous because he took the time to write about all of his adventures.

His father, Nicolo, and his uncle, Maffio, moved around Eastern Europe searching for a place to safely do business trading Eastern goods to the West. Eventually, in 1264, Nicolo and Maffio were sent by Ilkhan Hulagu of Bukhara (one of the minor Khans of the Mongolian Empire) on a mission to visit his brother Kublai, the Great Khan. After traveling for two years, they finally reached Khanbaliq (modern-day Beijing). The Polos were sent back from the Khan with a Mongolian ambassador, Koeketei. The Khan wanted them to carry a message to the Pope, asking for a team of Westerners to come and teach Western culture and Christianity to those under his rule. They were unable to immediately fulfill this request because there was a three-year gap, from 1268 to 1271, during which there was no Pope to whom to carry this message. After Pope Gregory X was selected in 1271, the Polos left on their second journey.

An individual's unique sense of taste is partially inherited, but factors such as culture and familiarity can help determine why one person's favorite food made be hot and spicy while another just can't get enough chocolate.

Taste occurs when specific proteins in the food bind to receptors on the taste buds.

Taste buds for all four taste groups can be found throughout the mouth, but specific kinds of buds are clustered together in certain areas. Think about licking an ice cream cone; taste buds for sweetness are grouped on the tip of our tongue. The buds for sour tastes are on the sides of the tongue and saltyon the front.

Although Jupiter’s orbit, and therefore its year, is so much longer than the Earth’s, its day is much shorter.  The Earth turns on its own axis, turning away from the Sun and so giving us day and night, once every 24 hours.  Jupiter spins round much faster, turning on its axis once every 9.84 hours!