A
solar eclipse occurs when the
Moon passes between the
Earth and the
Sun, casting a shadow on Earth that temporarily obscures part or all of the Sun's disc. Eclipses can occur only when all three bodies are properly aligned. Partial eclipses, in which only a portion of the Sun's surface is obscured, are relatively common due to the width of the Moon's outer shadow, or penumbra, which may be several hundred miles wide. Total eclipses occur when the Moon's inner shadow, or umbra, reaches the surface of the Earth, completely obscuring the Sun over a much narrower portion of the ground. If the Moon is too far away at the time of an eclipse, its umbra may not reach the Earth's surface, and only a partial eclipse will be visible. Before the advent of modern science, solar eclipses were often viewed with superstitious dread. However, eclipses are also of interest to science due to the various phenomena that can be observed when they occur. The Sun's outer atmosphere, or
corona, is normally invisible due to the brightness of the solar disc, but becomes visible from Earth during a total eclipse. Until the twentieth century, solar eclipses provided the only opportunity for scientists to observe and study the Sun's corona. With the development of photography during the first half of the nineteenth century, it became theoretically possible to record a still image of the Sun during a total eclipse. A variety of processes were used for early photographs, of which the most successful was the
daguerreotype. ==Observations==