<P> For a person or object touching the surface where the shadow is projected (e.g. a person standing on the ground, or a pole in the ground) the shadows converge at the point of contact . </P> <P> A shadow shows, apart from distortion, the same image as the silhouette when looking at the object from the sun - side, hence the mirror image of the silhouette seen from the other side . </P> <P> The names umbra, penumbra and antumbra are often used for the shadows cast by astronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots . An astronomical object casts human - visible shadows when its apparent magnitude is equal or lower than - 4 . Currently the only astronomical objects able to produce visible shadows on Earth are the sun, the moon and, in the right conditions, Venus or Jupiter . </P> <P> A shadow cast by the Earth on the Moon is a lunar eclipse . Conversely, a shadow cast by the Moon on the Earth is a solar eclipse . </P>

What conditions are necessary for the formation of shadow