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Through endless watching, ancient people could follow the course of the sun and tell where it would move. They had almost no idea of what the sun was like, however. True, it can be seen many hours of each day, shining brightly in the sky；but it is this brightness which makes it difficult to watch. The sun cannot be studied with the unprotected eye. Looking at it for a long time can cause total blindness and even a quick glance can make the eye hurt. But not even this great danger has stopped man from searching out the secrets of the sun.