Chandra Grahan is a scientific astronomical phenomenon which is more commonly known as the lunar eclipse, when the planet Earth shadows its satellite the Moon completely.
Hindu mythology has its own explanation of Chandra Grahan. However, unlike Surya Grahan or Solar Eclipe, Chandra Grahan is not of much significance until and unless the Lunar Eclipse is visible to the naked eye. Hindu pundits have not considered lunar eclipse to be influential on normal lives.
Chandra or the Moon, according to Hindu mythology is a God and also a Graha or a Planet. Chandra is also known as Soma, which signifies the sap of a plant and thus Chandra is also considered to be the God of all kinds of Vegetation.
The mythology related to Chandra Grahan-
Chandra in Hindu Mythology has been described as a beautiful in demeanor, has two arms bearing a club and a lotus. His chariot is pulled by ten white horses or an antelope and he rides across the night sky in the chariot is what mythology tells us.
When the ocean was being churned for the nectar for immortality or Amrita, the demon Rahu got inside the line of Gods waiting for Amrita. Vishnu, being alerted beheaded him, but since he had already consumed Amrita; he could not be killed but became two namely Rahu and Ketu. Rahu and Ketu nurtured grudges against Sun, Surya and Moon, Chandra, as they were the ones who had alerted Lord Vishnu. Thus they out of sheer grudge come and swallow these planets occasionally. When the Moon or Chandra is swallowed up partially or completely, we call it Chandra Grahan.
As mentioned earlier that if the lunar eclipse or Chandra Grahan is not visible then it is unimportant to be observed according to Hindu astrological guidelines. People posts the Chandra Grahan have a holy bath to erase the negative effects, if any from the Grahan.