at night,  we do not observe much light coming from the sun because the earth's other part is enough to cover the sunlight. except the fact that the moon reflects the sunlight. 
solar eclipse means that the moon obstructs some part of the sunlight and makes it not clear i.e, the sun looks black. but it does not mean that it blocks all the light coming from the sun. moon is smaller than the sun. so it cannot block all the sunlight. some of the light comes from beyond the moon and reaches the earth in the area where we cannot see the sun. 
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