Kolkata, May 09 (ANI): In a rare astronomical phenomenon that occurs only 13 times in a century, planet Mercury was seen as dot on the solar disc from several parts of India today. This phenomenon takes place when the planet, seen as a small black dot, travels from one limb of the solar disc to the other. This occurs only when the Sun, Mercury and the Earth are lined up in one plane. It appears as a dot on the disc because its angular size is very small compared to that of the Sun as seen from the Earth.