Eclipses, both solar and lunar, have enthralled humans for thousands of years, but especially total solar eclipses. Few who see one ever forget it; it can be a tremendously moving experience. The Sun has a larger and larger bite taken out of it, until it is all gone, except that these amazing glowing forms appearing in a ring around the black disk where the Sun had been. That ring is the corona, the Sun's violent atmosphere, suddenly becoming visible because it is no longer drowned out by the brightness of the Sun itself. Having the Sun vanish in broad daylight, naturally would have been seen with wonder and fear. The Chinese used to bang pots to scare away the dragon eating the Sun, and it worked! The Sun came back. The meanings that people put on the event can vary, but it is easy for mayhem to break loose when day suddenly becomes night. Vikings were sailing to the Shetland Islands when the Sun became obscured and vanished, Norse mythology talks of Ragnarok, the end of all things in cold and dark, so they thought the end of the world had come. A battle between the Medes and the Lydians was stopped by a solar eclipse, which was seen as the gods giving a sign, and they made a truce. The eclipse worked out well there. The Babylonians realized there was an 18 year cycle of eclipses from the records they had kept, and the Greeks used that information to create a kind of mechanical 'computer' for astronomical phenomena including the eclipses. Once every 16 to 18 months somewhere on Earth you can expect an eclipse. In 2017 there will be one in American, and I had the opportunity to be just outside Salem, Oregon, to see it, and it truly was a memorable sight. The Moon and the Sun are vastly different in size, with the Sun four hundred times bigger in diameter than the Moon, but it is also 400 times further away, so the two appear almost exactly the same size. However, the Moon is slowly moving away from us, so it won't completely block the Sun in half a billion years. What a coincidence that the two fit so neatly right at the time when intelligent species emerged on Earth. Astronomers in the past used eclipses to prove the Earth was round, from observing the shadow of the Earth during lunar eclipses. Where you are when an eclipse occurs changes what you will see. There is a fairly narrow band marked out on the Earth from where you will see a total eclipse, and on either side of that are wider bands from where you could see a partial eclipse, with the Moon taking a bite out of the side of the Sun, but never fully covering it so the corona is not seen. The Penumbra is where you see a partial eclipse, and the Umbra (less than 100 miles wide) is where you see a total eclipse. Any specific spot on Earth can expect to see a total solar eclipse about once every 360 to 375 years, so you can understand how they are taken seriously when they occur.
A lunar eclipse occurs when the Moon passes through the Earth's shadow. Lunar eclipses foretold famine and disease in China, earthquakes in Japan (bigger or more frequent). There was a lunar eclipse on the winter solstice 2010, and a 7.4-magnitude earthquake in Japan at the same time – could the combined gravity of Sun and Moon have caused the earthquake? Not really – there is no correlation seen in long term statistics. You can see a blood-red moon in a total lunar eclipse due to the bending of the light through the dust of Earth's atmosphere. Columbus knew eclipses were predictable, and he used that knowledge to impress the natives, predicting a total lunar eclipse and consequently getting them to provide food and services. Alexander the Great used the observation of a total eclipse to encourage his army in Mesopotamia, turning it to a weapon of fear against the Persians, and he won the battle. So it was a good omen for Alexander, but an ominous one for the Persians.