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"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!

As the Earth rotates it turns away from the sun’s light, and the sky becomes dark. However, if you think about the millions and millions of bright stars all around the sky at night, you might start to wonder why it isn’t just as bright as it was when we were facing the sun!

The planet is one of the brightest objects in the night sky, and even a small telescope can reveal its multicolored stripes. These stripes are bands of clouds being pushed around the planet by strong east-west winds. Jupiter is a world of complex weather patterns. Its most prominent feature is an orange-red oval called the Great Red Spot. The oval is a storm system that has lasted at least 300 years and is bigger across than Earth and Mars combined.

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).

Nightmares tend to occur after several hours of sleep, screaming or moving about is very uncommon, the dream is

usually elaborate and intense, and the dreamer realizes soon after wakening that he or she has had a dream.

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.

In the night sky (and to some extent during the day) the moon, planets and stars are visible in the sky.

We experience some deep, quiet sleep and some active sleep, which is when dreams happen. You might think sleepwalking would happen during active sleep, but a person isn't physically active during active sleep. Sleepwalking usually happens in the first few hours of sleep in the stage called slow-wave or deep sleep.

Sleepwalking may run in families and sometimes occurs when a person is sick, has a fever, is not getting enough sleep, or is stressed.

For starters, cats’ visual fields are broader than ours, spanning roughly 200 degrees instead of 180 degrees, and their visual acuity isn’t as good. So, the things humans can sharply resolve at distances of 100-200 feet look blurry to cats, which can see these objects at distances of up to 20 feet. That might not sound so great, but there’s a trade-off: Because of the various photoreceptors parked in cats’ retinas, they kick our asses at seeing in dim light. Instead of the color-resolving, detail-loving cone cells that populate the center of human retinas, cats (and dogs) have many more rod cells, which excel in dim light and are responsible for night-vision capability. The rod cells also refresh more quickly, which lets cats pick up very rapid movements — like, for example, the quickly shifting path a marauding laser dot might trace. Lastly, cats see colors differently than we do, which is why the cat-versions of these images look less vibrant than the people-versions. Scientists used to think cats were dichromats — able to only see two colors — but they’re not, exactly. While feline photoreceptors are most sensitive to wavelengths in the blue-violet and greenish-yellow ranges, it appears they might be able to see a little bit of green as well. In other words, cats are mostly red-green color blind, as are many of us, with a little bit of green creeping in.

Cats and dogs are just like color blind humans, seeing some colors but not all of them. For the bright daytime light, cells known as cones are needed. Humans have three kinds of cones, enabling them to see blue, red and green.

Cats and dogs, on the other hand, have just two kinds of cone cells (blue and green sensitive), allowing them to see only partial color.

cats, missing out on seeing life in glorious full color is really no big deal. Brightness and motion are far more important aspects of what our pets see.