A transit of Mercury over the disc of the Sun will take place in the afternoon of May 9. This transit phenomenon will be visible from India.
This phenomenon takes place when Mercury will be seen as a small black dot travelling from one limb of the solar disc to the other. From Earth, this phenomenon is seen when the Mercury passes between the Sun and the Earth.
This happens only when the Sun, the planet Mercury and the Earth are lined up in one plane. The Mercury appears as a dot on the solar disc because its angular size is very small compared to that of the Sun as seen from the Earth.
The transit begins with Contact-I, the instant when the disc of the planet Mercury is externally tangent with the Sun (Ingress exterior) followed by Contact-II when the Mercury is internally tangent with the Sun (Ingress interior). The Mercury will be seen as a black spot, travelling several hours over the face of the disc, will reach the opposite limb of the Sun at Contact-III, when the disc of the planet Mercury is internally tangent with the Sun (Egress interior). Finally, the transit ends at Contact-IV when the disc of the planet Mercury is externally tangent with the Sun (Egress exterior).
The phenomenon is a relatively rare one which occurs 13 or 14 times in a century. It occurs in the month of May and November. The interval between one November transit and next November transit may be 7, 13 or 33 years whereas the interval between one May transit and the next May transit may be 13 or 33 years.
The transit of Mercury will be visible from most of Asia (except south eastern parts and Japan), Europe, Africa, Greenland, South America, North America, Arctic, North Atlantic Ocean and most of the Pacific Ocean. The entire transit, from beginning to end, will be visible from eastern North America, northern South America, the Arctic, Greenland, extreme north western Africa, western Europe, and the North Atlantic Ocean.
In India, the beginning of the event comprising of Ingress exterior (Contact-I) and Ingress interior (Contact-II) will be visible from all places. The duration of the entire transit event will be about 7 hour and 30 minutes. The observer in India will not see the ending of the event as the same will be in progress after sunset. Depending upon the sunset time of different places in India, the observer located in the extreme east of the country will see the event about 1 hour from the beginning and the observer located in the extreme west of the country will see the event about 2 hours and 45 minutes from the beginning.
In Delhi, the event can be seen for a duration of about 2 hours 20 minutes as it will start at 4:41p.m. and sunset will take place at 7: 01 p.m. Similarly, in Kolkata the event will start 4:41p.m and it can be seen for a duration of about 1 hour 26 minutes, in Mumbai the event will start at 4:41p.m and it can be seen for a duration of about 2 hours 24 minutes, in Chennai the event will start at 4:41p.m and it can be seen for a duration of about 1 hour 45minutes.
The last transit of Mercury occurred on November 6, 2006 when just end of the event was visible from the extreme north eastern parts of India at the time of sunrise. The next transit of Mercury will take place on November11, 2019 but the event will not be seen from India as the same will begin after the sunset time of all places in India. The transit of Mercury on November13, 2032 will be visible again from India.
The apparent diameter of Mercury will be nearly 12 arc-second which is 1/158 of Sun's apparent diameter. Thus, it will be difficult to see the Mercury at transit over the face of the Sun without optical magnification. This event can be viewed with the help of binocular or telescope attached with proper solar filter or by making projection of the Sun's image on a white board by telescope.
The Sun should never be viewed with the naked eye. Safe technique to observe is by using filter like aluminized mylar, black polymer or welding glass of shade number 14.
