How does an eclipse of the sun happens ?

As the moon goes around the earth, so the earth goes around the sun . An eclipse happens when the moon comes between the Earth and the sun, which gradually disappears. How long it takes depends on the positions of the Earth, the sun and the moon, and the distance of the moon from the earth. Total eclipses are visible only in some parts of the world, so although they are fairly frequent , one person may not see all of them.