Both ancient and medieval records help modern scientists investigate the long-term variations in the length of a day. In 1675 Danish astronomer Ole Romer observed lunar eclipses of Jupiter's moons. Such observations provided an early proof of the finite speed of light. Lunar eclipses today provide information about how the Moon's soil cools when the Sun's radiation is suddenly removed, enabling scientists to draw conclusions about the soil's conductivity of heat and its structure. Ancient records provide hundreds of accounts of solar and lunar eclipses, most coming from Babylonia, China, and Greece.
Records are also available from Medieval European and Islamic countries.
Solar and lunar eclipses were considered omens of bad things to come in the ancient world. In many cultures, the moon is depicted as being a goddess, and a lunar eclipse was viewed as the death of the goddess. Ancient historical records often associate an eclipse with some unfortunate event that followed soon afterward, such as the death of a king or a wide famine. Greek poet Pindar presents a solar eclipse as an omen, and prays that the portent will become a painless blessing. Greek author Plutarch was very interested in eclipses and often referred to them in his dialogues.