Starting with a simulation of the August 21, 2017, total solar eclipse as seen from southern Illinois, we examine what eclipses are and how to safely view them.
Three recent eclipses are reviewed, showing the movement of the Moon's shadow across Earth's surface. One eclipse was a total solar eclipse, another was an annular solar eclipse, and the last was a partial solar eclipse.
From a perspective in space, the motions of the Earth, Sun, Moon system are discussed, including Earth's revolution around the Sun, Earth's rotation on its axis as the cause of day and night, and the revolution of the Moon around Earth as the cause of the lunar phase cycle.
The path of the Sun and Moon are shown to be tilted to one another, crossing at two points called nodes, and the relationship between the nodes and eclipses is explained.
Lunar eclipses occur as the Moon interacts with Earth's shadow. Penumbral lunar eclipses happen as the Moon passes through the Earth's outer shadow. Partial lunar eclipses happen when the Moon grazes across the inner umbral shadow, and total lunar eclipses happen when the whole Moon passes through Earth's umbral shadow.
The distance between the Sun and Earth varies throughout the year, so sometimes the Sun appears larger or smaller. The same is true as the Moon orbits Earth. The change in the Moon's apparent size causes some solar eclipses to be total and others, when the Moon appears smaller than the Sun, to be annular.
Caution must be observed when viewing solar eclipses. Safe ways to view an eclipse are described, including visual filters and projection techniques for the partial phases of a solar eclipse.
There are many things to watch for during a total solar eclipse. The first observation is the moment the dark Moon blocks a small notch in the edge of the Sun. As more of the Sun is covered, the appearance of your surroundings changes, including the colors of the sky, the temperature, and winds. Near the time the eclipse becomes total, animals begin reacting to the lower light levels, and the brightest planets fade into view. As the eclipse becomes total, the brightest stars become visible, and the solar corona and prominences are revealed. The total eclipse comes to an end with the Diamond Ring, when the first bit of sunlight appears from behind the Moon.
Planning travel to a total eclipse involves locating a place to view the eclipse based on the duration of the eclipse and the probability of clear weather. Other considerations include ability to relocate if clouds move in, and other activities if the eclipse is clouded out. Tools for observing and comfort during the eclipse are described.