This shadow has two parts: the umbra where the Sun is completely blocked and the penumbra where the Sun is partially obscured. Solar eclipses are only visible within this shadow (only about 300 miles or 480 km wide) and therefore cover a small area of Earth, often over the ocean, making it rarer to observe one unless you schedule it ahead of time. However, when the orbits line up exactly, the moon crosses directly across the Sun, covering it and casting a shadow across the Earth, blocking or partially blocking our view of the Sun. Normally, during the New Moon phase, the moon simply disappears as we “see” its nighttime side. Solar eclipses happen at the New Moon phase when the Moon is directly between the Sun and the Earth, but doubly so. In about 600 million years, it will move far enough away that it will be too small from the perspective of Earth to cover the Sun. It started much closer to the Earth and has been slowly drifting outward at about 1.5 inches (3.8 cm) per year. In fact, the Moon did not always eclipse the Sun and will not always continue to do so. This is not always the case, meaning that not every moon in the solar system eclipses the Sun like ours does. While the Moon’s diameter is 400 times smaller than the Sun’s, it is also roughly 400 times closer to Earth than the Sun, meaning they both appear about the same size in our sky. During a solar eclipse, the Moon appears to cover up the Sun. Let’s start with the one you are probably most familiar with: the solar eclipse. There are two types of eclipses: solar and lunar, determined by which body is being eclipsed. Anywhere from four to seven times a year, these three astronomical bodies line up just right to create these dramatic shadow shows. In this case, we see the Moon appear to cover the Sun from our perspective here on Earth or see the effect of the Earth covering the Sun on the Moon.ĭue to the Moon’s slight 5-degree tilt relative to its axis and the plane of orbit and the 23.5-degree axial tilt of the Earth, an eclipse does not occur each month as the Moon orbits the Earth. The motions of the Moon orbiting the Earth as it orbits the Sun create interesting interactions, the most dramatic of which are known as eclipses.Įclipses occur when one astronomical body appears to cover another body from the observation of a third body. The Moon orbits the Earth at an average of 238,855 miles (384,399 km) away in an elliptical orbit once every 27.322 days, creating phases in our night sky as its illuminated side points toward us and away from us at different angles in different parts of its orbit.
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