How do scientists know when there will be an eclipse? Eclipses do not occur at random. They occur when the sun, moon and earth are aligned. When the earth is between the sun and the moon, we get a lunar eclipse. When the moon is between the sun and the earth, we get a solar eclipse.
The Chaldeans - an ancient people who lived in southern Babylonia from about 1,000 BC to 540 BC - discovered that every 18 years, 11 days and eight hours the series of eclipses of the sun and moon was repeated almost exactly. This cycle is called a saros.
Most saros cycles have about 72 eclipses.
Eclipses come in cycles because the motions of the earth and moon are predictable. Therefore, scientists are able to forecast when and where eclipses will occur.
In any one year, there can be a maximum of seven eclipses, either four solar and three lunar or five solar and two lunar.
However, at any one place on earth, more lunar eclipses are seen than solar eclipses. This is because a lunar eclipse can been seen by half the earth at the same time, while solar eclipses can only be seen along a narrow path on the earth's surface.
The solar eclipse which will occur on August 11 will only be seen by people within a narrow band running from Cornwall in southwest Britain, through continental Europe, Iran and finally India.
