This article has been updated to include some more trivia in the light of a total solar eclipse on August 21st, 2017 which can be viewed from several parts of the USA. One can view this animation to know the extent of this solar eclipse in their region.

Why are sun rays more harmful during a solar eclipse?

[Courtesy: wiki.answers.com]

Your eyes are at risk during a solar eclipse. You can burn your retinas at the back of your eyes. If you're looking at the sun normally, your pupils will contract and only allow a little bit of light in. Less radiation gets to your retinas. The intensity of the sun's light usually prevents you from looking at it directly anyway. During an eclipse, the direct sunlight is blocked by the moon, but not all of the radiation. Your pupils dilate because it gets darker, and strong radiation that does not affect the pupils is allowed to penetrate to the back of the eye. Therefore, never look directly at the sun during an eclipse. The safest methods are to use a pinhole projection onto a flat surface, or to use a certified filter made for the purpose of solar observations.

NASA ARTICLE - http://eclipse.gsfc.nasa.gov/SEhelp/safety2.html

Question

Why is it dangerous to look at the solar eclipse directly specially at that moment?

[Courtesy : Some forum]

Answer

You actually can safely look at a total solar eclipse while the sun is _totally_ blocked by the moon. It looks like the moon has a fiery white aura, and it is one of the more spectacular things I have ever seen. So why do people say it's dangerous to look at a solar eclipse? Well, in general (during non-eclipse times), you've probably been told not to stare at the sun. This is because the sun simply outputs more power than our eye is designed to handle, and exposing our eye to that kind of power can damage the retina. And in a nutshell, solar eclipses are dangerous because the sun can come out from behind the moon and "surprise you" before you have a chance to look away. And this is actually even worse than when you normally look away from the sun because during the total eclipse, it is dark out, and your pupil therefore dialates so that it can let in enough light to get a good picture. Then, when the sun reappears and starts flooding the area with really bright light, not only are you staring straight at it, but your eye is in a state where it is wide open, and actively trying to let in as much light as possible.
This explains why it is easy to damage your eye when watching a total solar eclipse, and why you should either be sure to time it very carefully (and allow for a good margin of error), or just view the thing through one of those sets of cheap "dark" glasses they sell for the express purpose of looking at the sun without getting hurt.

Answered by: Gregory Ogin, Physics Undergraduate Student, UST, St. Paul, MN

So, it is the nature of the eye that will make it dangerous to view eclipse and not the Sun-rays as such. The sun rays are still the same either during eclipse or during normal days.

Why one should avoid drinking stored water during Surya or Chandra Grahan?

During Surya Grahan or Chandra Grahan, one should not drink stored water. During a Sampoorn Surya Grahan (Total Solar Eclipse), Division of Environmental Biology of Vikram Sarabhai Research Centre with the association of S.N. Hospitals, proved that purity of the water was reduced after Grahan. They have researched it for few days and analyzed the results of water before Grahan and the same water after the Grahan.

Why Grass Blades or Durva are kept on food and water during Surya Grahan or Chandra Grahan?

Grass blades (Durva or Garika or Darbha) are kept on stored water and food during the time Grahan. It is not a blind ritual. It’s proven scientifically thatGrass blades purify the water more than Tulsi (Ocimum) leaves can during Grahanam. Grass blades have immense purifying power. This is the main reason why grass blades are kept on stored water and food like pickles.

This was relevant when people did not have UV-purified water. They probably depended on grass/tulsi for purification. Grass is a good oxidising agent (wheat grass is used to cure cancer). That might be the reason they used it to purify water and food items.

DHARBHA (KUSA GRASS) [Courtesy: Some forum]

It is necessary to mention on this occasion about Dharbha (Kusa Grass). Generally we observe usage of Dharbha in Hindu religious rituals while performing any Homa/Yaga or Pithru Karya. It is said that without this there is no sanctity for performing the rituals. Brahmins always keep some in their houses and it is used for purification in all kinds of ceremonies. The word Kusa is related to the Sanskrit Kushala meaning sharp in the sense of keen intelligence (because of the sharp tips of the grass). It is also ground up and the essence used for Kusha oil (to be used in Summer for it's cooling effects) and Kusha flavored sarbat also drunk for it's cooling effects.

Stories concerning the origin of Darbha/Kusha:

Pouranically it is said that Kusa grass was formed when the hairs on the Kurma Avatar of Lord Maha Vishnu got loosened during the churning of the ocean and got washed away to the shore of the ocean to form Kusa Grass. Later, when the amrita [nectar of immortality] was obtained as a result of the churning and distributed among the gods, some drops fell on the grass which further sanctified it imbuing it with healing properties. Therefore, in the traditional hair-cutting of Vaishnava toddlers, the hair is touched with kusha before it is cut.

Darbha Grass is identified with Lord Vishnu and is believed to possess the power to purify anything. It was used as a ritual seat as far back as the Vedas. Kusha, whose name signifies sharp in the sense of acute, is the root for the Sanskrit word for "expert," kosala. That is because the edges of the long leaves that grow in pairs along the tall stems are very sharp, so like the sword it is a symbol for discernment or "discriminating wisdom."

It is an age old tradition in Hindu families to cover the food items with Dharbha during eclipse to protect them from harmful ultra violet radiation. Usage of Dharbha (holy grass) is very celestial, sacred and also acts as a protector. (ref: http://www.khandro.net/nature%20plants_kusha.htm)

Thus eclipses are fascinating not only because they have astronomical and spiritual significance, but also because they give us insights into the culture, tradition and beliefs of people belonging to different periods. Next total solar eclipse is happening on July 22nd 2009 and is visible in India which is a total eclipse.

Is an eclipse harmful during pregnancy?

There is no evidence to suggest that an eclipse can harm a pregnant mum or her baby.

Eclipses are seen all over the world and in many countries there is no tradition of staying indoors during one. However, in many cultures, an eclipse is considered a bad omen.

There are some superstitions that an eclipse can cause deformities such as a cleft lip or unsightly birthmarks, but the scientific evidence does not support this belief.

If you or your family are concerned about the effects of an eclipse, there is no harm in following the customs. After all, it is just for a few hours and if it offers you and your family peace of mind, it is probably worth it.

But if you cannot stay indoors and abide by the usual dos and don'ts, or just don't want to, rest assured that this does not necessarily mean that your baby will come to harm or be born with a birthmark.

http://www.babycenter.in/x1011503/is-an-eclipse-harmful-during-pregnancy#ixzz4e2jSYdqU