Solar and Lunar Eclipses
The first eclipses on earth were recorded by the Irish Neolithics, the Babylonian scholars, the Chinese astronomers, and the Greek philosophers. Some of the eclipses were recorded as far back as over 3000 years before the birth of Christ. These ancient scientists and wise men did not know what the eclipses meant, and often took them as omens or signs that trouble was on its way. After all, it must have been frightening to see day turn to night or for the moon to disappear then come back red instead of white and not know the reason why.
An eclipse occurs when one celestial body moves into the shadow of another. Most of us are familiar with this phenomenon from solar and lunar eclipses that often get announced on the news. When an eclipse happens within our solar system (a stellar system), three of the celestial bodies within the system's gravitation are in one straight line. This alignment is known as syzygy.
To understand what we see in an eclipse, we first have to understand syzygy. When this alignment occurs, one celestial body moves to block the sun from hitting the surface of the second celestial body. If the second celestial body is completely covered, it is in the umbra or full shadow of the first celestial body. However, if the second celestial body is only partially covered, it is in the penumbra or partial shadow ofthe first celestial body. Sometimes the second celestial body is completely covered, but a ring of light appears around it. This means it is in the antumbra or a considerable distance away in that the first celestial body refracts light from the sun towards the outer rim of the second body. If the second body was closer, it would be in the umbra and be completely covered or overshadowed.
A lunar eclipse happens when the moon moves into the shadow of the earth. This means that the earth is between the moon and sun. When we observe a lunar eclipse, it often looks like the moon is disappearing at a rapid speed. Sometimes only part of the moon disappears, meaning it is in the penumbra. If it passes through the earth's full shadow, it goes through the umbra. Usually, once the moon is in the full shadow of the earth, it appears again, but this time with a reddish glow. This reddish glow appears because the earth is refracting light towards the moon. Lunar eclipses can usually be seen by an entire hemisphere of our earth, this is because one whole hemisphere experiences night during the occurrence.
Solar eclipses on the other hand, cannot be seen by an entire hemisphere. At most favorable conditions, total solar eclipses can only be seen by a certain section of the earth. Partial solar eclipses, on the other hand can be seen by a wider audience. This is due to the distance of the earth from the sun. During the solar eclipse, the earth moves into the moon's shadow and in effect the sun is blocked.
Depending on the angle, the moon can appear to be the same size of the sun and sun appears to be completely blocked, meaning the earth is in the moon's umbra. In other angles when the sun is blocked but casts a large ring of light around the moon that partially illuminates the earth, the earth is in the moon's antumbra, this is also known as an annular eclipse. If the blocking of the sun is only partial, then the earth is in the moon's penumbra.
It is important to note that a solar eclipse is not really possible. It is simply conventionally called a solar eclipse. It is not possible because at no point does the earth or moon pass through the sun's shadow. It is in fact impossible, because the sun does not have a shadow. Other eclipses occur all throughout the solar system when planets and moons align with the sun or with other planets. Some of these eclipses can be observed with home telescopes, though most of them need specialized telescopes and equipment. When viewing a solar eclipse from the earth, it is important to use protective lenses to shield your eyes. Without the protective lenses, you risk damaging your eyes from the light of the sun.
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