Do Ostriches really stick their heads in sand?

This animal's reputation has little to do with reality.If the giant birds really did that,they wouldn't last long amid the predators of the African savanna and desert.When a lion or a jackal approaches,these flightless birds typically runaway from the danger-a smart choice considering they can sprint speeds of more than 40 miles an hour.

So where did the head hiding myth come from?When ostriches are reluctant to free-for instance,when guarding eggs or if they are unable to outrun a predator-they may flatten themselves against the ground and lie very still in hopes of not being discovered.They press their necks and heads right against the soil,and because their heads are not as dark as the rest of their body,they can blend in with the light-colored dirt.This may have given rise to the story that they stick their heads in the sand to hide

Why are there seven days in a week?

Our seven day week probably originated more than 3000 years ago in Mesopotamia,when the Babylonians first introduced a calendar that divided time into a year with months,weeks and days.Their week,like ours,was seven days long,but it's not entirely clear why they chose the number seven.It may be related to the phases of the moon,which last approximately seven days,or to the seven heavenly bodies(sun,moon and five planets)known to their astronomers.Each day in the Babylonian week was named after one of these celestial bodies,with one day set aside for recreation.

The Babylonian week may have been the source of the seven day week presented in the Old Testament.According to the book of Genesis,God rested on the seventh day,after creation the heavens and the Earth.The seventh day was therefor observed as a time for worship and rest.Some residents of ancient Rome used this biblical week,and in a A.D 321.Emperor Constantine made it official,designating the week as seven-day period with Sunday as a day of rest.As the Western world and other cultures adopted and refined the Roman calender,the week as we know it became the global standard.
Other systems for organizing time have been used through out ancient and more recent history.For example,the ancient Egyptian week was 10 days long,and the As-Syrian week only five.In 1793,the creators of the French Republican calendar abandoned weeks altogether,instead dividing months into three 10day periods called decodes.But the Nepoleonic regime discontinued the use ofthis calendar in 1806