Nov 25, 2009

All About Lunar and Solar Eclipses

Even seen a lunar eclipse? Aren’t they’re awe-inspiring? While we now admire them this celestial event, before the telescope was invented, people were frightened by lunar eclipses and associated dramatic stories with this scientific phenomenon. But what exactly is a lunar eclipse, and how is it different from a solar eclipse? What are some cool facts about eclipses and what are the myths associated with such happenings?

What is a lunar eclipse
The moon orbits the earth in an elliptic path, while the earth orbits the sun. Sometimes, when the moon appears to be full, it so happens that the sun, earth and moon are aligned in a straight line. The moon (eclipsed object) is behind the earth (eclipsing object), therefore, the earth prevents some or all of the sun’s rays from reaching the moon. The moon, since it merely reflects sunlight, gradually grows smaller and begins to change colour as it passes through the shadow of the earth. Since the earth is round, the shadow cast upon the moon is curved as well.
What is a solar eclipse
A solar eclipse occurs when a new moon comes between the earth and the sun. It is dangerous for the eyes to look towards the sun at this moment because harmful filtered ultraviolet rays can burn vision cells. However, viewing a lunar eclipse without protection does no harm as its light is less intense.
How lunar eclipses happen
As the moon enters the umbra (complete shadow) or penumbra (partial shadow) of the earth, it begins to darken and a cloud seems to appear in front of it. The white area grows smaller and smaller, just as though the moon were completing its monthly cycle, but in a matter of a few minutes! Eventually, the moon crosses the umbra or penumbra, i.e. reaches the other side of the shadow, and it appears again as a new moon.

The entire moon is visible in a matter of just three hours.
Types of lunar eclipses
This simply depends on the position of the moon.
  • In total lunar eclipses, the moon passes directly behind the earth or through the centre of the earth’s umbra. The moon is almost invisible.
  • In partial lunar eclipses, some part of the moon passes behind the umbra, and a reddish-brownish or even orangish colour prevails on the moon.
  • Lastly, in a penumbral eclipse, the moon passes through the penumbra (outer part of the shadow) of the earth. The effect on the moon’s light is not too drastic to be noticed by you or I, because the slight dim in the illumination is only visible in very dark surroundings.
Why the funny colours?
Lunar eclipses are full of interesting facts! For instance, you may have wondered why the moon changes its colour to orange or brown at such moments. It’s simple. When the group of seven colours combined (violet, indigo, blue, yellow, orange and red) to form white light reaches the earth, some of these rays scatter on the earth, while others bend around our planet and reach the moon. The bent rays comprise the orange, red and yellow rays made of longer wavelengths, and are displayed on the moon’s surface.
These changing colours are a source of many myths and folklore about lunar eclipses, which you can read here.

These same colours make the sky ever so pretty at sunset (the end colours of the prism) and dawn (the beginning colours of the prism)! This is because the respective light rays bend at those moments as well. I have only one thing to say; science is amazing.
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