Jews who at dawn on Wednesday observe the once-in-28-year Birkat Hahama or 'Solar Blessing' should not look directly at the sun, as gazing directly for even a few seconds at a sliver of the brilliant star can cause irreversible damage to the retina. The blessing is traditionally said when looking at the dawning sun when, according to Jewish tradition, the sun, Earth and the other stars and planets are positioned in the exact same place as they were at the Creation of the world and the Exodus from Egypt. Asked to comment on whether there are any health dangers, Prof. Anat Loewenstein, chairman of the ophthalmology department at Tel Aviv Sourasky Medical Center considered the matter and said gazing directly at the sun - even a small piece of it - can lead to permanent harm. "The rays won't burn the retina in the eye but it can cause a chemical change and hurt the center of vision, resulting in solar retinopathy. This can happen during a solar eclipse as well. The deepest layer of photoreceptors can be harmed." She told The Jerusalem Post that people who do expose their eyes even for a few seconds to the sun's rays may not be aware of any changes at first. But when they are asked about it, they will notice changes in pigment of what they see. Only then will they understand that they suffered damage," she said. "It is not known exactly how much time one sungazes before damage sets in. It is also probably a variable thing according to the individual. But even when the sun sets and a reddish sun appears on the horizon, it is very advisable not to look at it. The rays still reach the eye," said the senior ophthalmologist. She advises using the same tool that is used to view a solar eclipse: Put your back to the Sun and use an empty box with a pinhole facing the sun to indirectly see its shadow inside the box.