Shatanand has not explained the reason for an eclipse, as documented in the Puranas but I feel it necessary to include. During the legendary churning of the Milky Ocean to obtain Amrit (Excelsior), God took the form of Mohini to get back the Amrit that was taken by the Asuras. Fooling the Asuras, she returned with the Amrit and began to offer the Amrit to all the Devas, as they sat in a line.
One Asura by the name of Rahu, realising that they had been fooled, sat in the line in the guise of a Deva, also to partake in the Amrit. As Mohini was about to approach Rahu, the Sun deity and the Moon deity, who were sat next to Rahu, revealed the true identity of Rahu and thus Mohini lifted her sword and severed Rahu's head.
The head continued to live but swore that it would avenge the outburst of the Sun and the Moon. For this reason Rahu is periodically engaged in battle with the Sun and Moon. Hence the eclipse to Hindus is considered as the time when Rahu ‘gobbles up’ either the Sun or the Moon and the subsequent fight of the Sun or Moon to free themselves from Rahu's jaws. During such time various acts and duties have to be observed.
Shatanand explains that just before the start of an eclipse (when the prohibition of touch is enforced - Sparsha Kala), one should suspend all work, purify themselves by bathing and begin to chant Shree Krishna's Astakshar Mantra or Naama Mantra. Shatanand says that one should not stay without bathing during such times, nor should they engage in any household duties.
Vashishta Muni explains ‘All caste members, when having sight of Rahu (eclipse) are affected by Sutaka (period of untouchability see Shloka 88). Therefore when an eclipse begins, one should bath and during the eclipse they shall chant Gods names, perform Homa (offerings) etc’. Purascharan Chandriko explains, ‘During the eclipse of the Sun or Moon, one should with pure mind, chant the Mantra of God, the Lord of the Universe’.
Markandeya Muni explains further about bathing water, ‘Bathing in cold water instead of warm water is better, deriving more Punya. One’s own water rather than somebody else’s, water from a small lake or pond (Tarav) rather than that from a well, running or flowing water rather than water from a Tarav, water from a large lake (Sarovar), water from a river (Nadi), water from the Ganges (Ghanga Jal) and the water from an Ocean or Sea (Samundra) are incrementally superior and Punya-Karak’.
Vashishta in Parashar Madhava explains that the Grahana or eclipse should be observed even if a person is observing Sutak (untouchability due to birth or death in the family). Brahmansiddhanta restricts viewing the eclipse, ‘One should look at an eclipse through a cloth or a reflection of it. A pregnant woman should never look directly at an eclipse’.
Gautama in Parashar Madhava explains the fasts to be observed, ‘All except the young, the old and the ill should stop eating four Prahars (12 hours) before a solar eclipse commences and three Prahars (9 hours) before a lunar eclipse commences. The young, the old and the ill should stop eating one Prahar (3 hours) before an eclipse.’
Nirnya Sindhu further explains, ‘If the sun sets whilst the solar eclipse is still in progress then one should fast the whole of that day and the rest of the night. Similarly if the Moon disappears (day breaks) whilst the eclipse is still in progress, then one should not eat that night nor the rest of the following day.’
The eclipse Vrata should be observed if any part of the eclipse is visible from the country that you are residing in. During the eclipse all cooked food becomes impure and not fit to be eaten afterwards. Clothes which are unclean or have been worn or touched are impure and to be washed after the eclipse.
The strict eating restrictions here mentioned is in accordance with Shastras and properly documented. There is no ‘phantom’ four-hour eating restriction before an eclipse that I know of. I presume that this is a misunderstanding in that people assume that a Prahar is the same as an hour when this is clearly not the case. This four hours problem is so wide spread that attention needs to be directed to rectify this and to get back to principles outlined by Shastras. Certainly in temples the true principle should be enforced and announced accordingly.
These restrictions are important and should be observed correctly if able. Loose attitudes in this regard will not yield the desired objectives of observing such a Vrata.