UPSC Mains General Studies Paper I

Topic: Geography of the World

Important Geophysical phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc.

 July 2018 Lunar Eclipse

  • Longest eclipse of the 21st century.
  • It occurred for around 1 hour 43 minutes.

What is a Lunar Eclipse?

  • A Lunar Eclipse (Chandra Grahan) is when one can’t see the moon at night because its position is relative to the sun and earth ensures that light doesn’t fall on the part of it we can see.
  • The moon has no light of its own and is only visible because it reflects the light of the sun.
  • We only see the part where light falls and thus as the earth and moon move through their orbits and different amounts of light falls on the moon, we see different phases of the moon.
  • A lunar eclipse can occur only when the Sun, Earth, and the Moon are aligned (in syzygy) exactly or very closely so, with the planet in between. Hence, a lunar eclipse can occur only on the night of a full moon. 
  • During a total lunar eclipse, Earth completely blocks direct sunlight from reaching the Moon. The only light reflected from the lunar surface has been refracted by Earth’s atmosphere.

What is Blood Moon?

  • When a lunar eclipse (Chandra Grahan) occurs, the Earth comes between the sun and moon, preventing light from falling on the moon.
  • When this happens, the moon appears to glow red and is thus called the blood moon.

Blood Moon

Why Moon apears to be red in colour?

  • This light appears reddish for the same reason that a sunset or sunrise does: the Rayleigh scattering of bluer light. Due to this reddish color, a totally eclipsed Moon is sometimes called a blood moon.
  • Sunlight is made of several colours and they all have different wavelengths. Depending on the way they travel through our atmosphere, we see different colours. That’s why the sun and sky have different colours during sunrise and sunset.
  • Blues and purples have shorter wavelengths and scatter in our atmosphere, giving the sky its inky colour, but reds and oranges have the highest wavelengths and pass through our atmosphere before it is bent or refracted around Earth, hitting the surface of the Moon and making it red.
  • The red colour is because of the way light travels through the Earth’s atmosphere. 

What is Danjon Scale?

L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality.
L=1: Dark eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.
L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.
L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.
L=4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a very bright rim.

What are the various Myths related to Lunar Eclipse?

  • Several cultures have myths related to lunar eclipses or allude to the lunar eclipse as being a good or bad omen.
  • The Egyptians saw the eclipse as a sow swallowing the moon for a short time; other cultures view the eclipse as the moon being swallowed by other animals, such as a jaguar in Mayan tradition, or a three legged toad in China.
  • Some Hindus believe in the importance of bathing in the Ganges River following an eclipse because it will help to achieve salvation.
  • The Incans believed that lunar eclipses occurred when a jaguar would eat the moon, which is why a blood moon looks red. The Incans also believed that once the jaguar finished eating the moon, it could come down and devour all the animals on Earth, so they would take spears and shout at the moon to keep it away.
  • The ancient Mesopotamians believed that a lunar eclipse was when the moon was being attacked by seven demons. The Mesopotamians linked what happened in the sky with what happened on the land, and because the king of Mesopotamia represented the land, the seven demons were thought to be also attacking the king. In order to prevent this attack on the king, the Mesopotamians made someone pretend to be the king so they would be attacked instead of the true king. After the lunar eclipse was over, the substitute king was made to disappear (possibly by poisoning).
  • In some Chinese cultures, people would ring bells to prevent a dragon or other wild animals from biting the moon.  In the nineteenth century, during a lunar eclipse, the Chinese navy fired its artillery because of this belief. During the Zhou Dynasty in the Book of Songs, the sight of a red moon engulfed in darkness was believed to foreshadow famine or disease.


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