A note by Shri Narottam Sahoo, Scientist, Gujarat Science City
Ahmedabad

‘Astronomy teaches us to look upwards.’ It is the study and understanding of the universe beyond the planet Earth. It is impossible for anyone to rival the magnificence of universe. The astronomical bodies viz., Planets, Comets, Asteroids, Meteors, Nebulae, Stars and celestial manifestations like eclipses, occultations, transits, oppositions and planetary conjunctions absolutely reveal the magnanimity of astronomy.

Come 9th May this year, It’s a Monday and it’s the day of Transit of Mercury over the Sun. It would be a rare celestial spectacular event to be seen on our sky that will definitely create excitement and curiosity to explore more.

A ‘Transit’ is principally the passage of a celestial object (usually this presents a smaller angular size) in front of another object, presents a much larger angular size, as seen from Earth. In other words, a small celestial object will pass in front of a huge celestial object. On 9th May, it is possible to witness the planet ‘Mercury’ passing in front of the massive and dazzling heavenly object ‘Sun.’

India, Gujarat and Transit had a long association… actually first use of telescope in India is said to be used by Jermiah Shakerley in 1651 at Surat to observe the Transit of Mercury.

Passages of Mercury in front of the Sun, or “Mercury Transits” in astronomical terminology, are comparatively rare events, due to the different orbital inclinations of the Earth and Mercury as they move around the Sun.

On Monday, May 9, 2016 Mercury will transit the Sun for the first time since 2006. The transit or passage of a planet across the face of the Sun is a relatively rare occurrence. As seen from Earth, only transits of Mercury and Venus are possible.

During a transit, Mercury is seen as a tiny black dot moving slowly in an East-to-West direction across the Sun. The 2016 transit commences on 9th May at 4.30 pm and ends later during the midnight. The total duration is therefore about 7½ hours.

As per our sky, the transit of Mercury will be visible from 4.30 pm till the Sun set at 7.11 pm. Till 6.30 pm, we can see the 1/4th of the transit process.

The planet Mercury crosses the Sun in a North-east to South-west direction, as opposed to a South-east to North-west direction at the previous transit in November 2006. This is because May and November transits of Mercury are viewed from opposite sides of the Earth’s orbit, Mercury being seen descending (moving North to South) during May transits and ascending (moving South to North) during November transits.

There are about 13 Mercury transits each century and they follow in time intervals of approximately 13, 7, 10 and 3 years. The most recent one took place in November 8, 2006. After 2016, the next two Mercury transits will take place on 11th November 2019 and 13th November 2032. The 11th November 2019 transit will not be visible to India.

The disk of Mercury is very small and will be very difficult to see. Bathed in intense sunlight, this small, hot planet moves around the Sun in an elliptical orbit at a mean distance of only 58 million km, much closer to the Sun than other inner planet, Venus (108 million km) and the Earth (150 million km).

In order for a Mercury transit to happen, the planet must be located directly between the Earth and the Sun and also near one of the two points in its orbit where Mercury’s orbital plane intersects that of the Earth. We then face the dark side of Mercury – the hemisphere that is not illuminated by the Sun – and see it as a small dark spot moving across the bright solar disk.

A powerful telescope is needed to observe this event and to show clearly how Mercury moves across the solar disk. During the transit, Mercury will only block 1/20,000th of the Sun’s light.

The German astronomer Johannes Kepler (1571-1630) was the first person to predict a Mercury transit event, although he did not observe one himself. His prediction of a transit on November 7th 1631 enabled the French astronomer Pierre Gassendi (1592-1655) to observe it, in the year following Kepler’s death.

Observations of the Transit

The Transit of Mercury cannot be observed with naked eye – this would also be extremely dangerous because the enormous brightness of the Sun will cause total blindness in a fraction of a second.

Observations can only be made by means of telescopes which project the solar image onto a white screen. Solar filters can be used to have a glimpse of the transit. Other hands on projects including pin-hole camera can be used to project the transit picture for observation.

Gujarat Science City has been organizing special outreach programmes and activities on 9th May 2016 for students, teachers and the visitors. Gujarat Council on Science & Technology (GUJCOST) has also arranges public viewing programmes at its Community Science Centers and Science Club Schools at each districts in the State.

As the programme doesn’t happen often, the Science City and Community Science Centres across the State will guide you to “spot the spot” — Mercury’s silhouette — as the innermost planet crosses the Sun’s disk.

GUJCOST is organizing training workshops for science educators, communicators and amateur astronomers to orient them about the upcoming Transit of Mercury. Special activity modules have been designed to explore and understanding the inner planet and its behaviour.

Celestial event like this are a great opportunity for the science educators and communicators to reinforce their efforts to inculcate scientific temper among the people.

Happy Mercury Transit!

Outreach activities at Science City

1. Large size telescopes with solar filter for direct viewing the transit
2. Projected images of Sun with Transit by Binoculars and Smaller telescopes
3. Special live webcast from NASA Sun-Earth website
4. Hands-on activities by students from kg to pg classes
5. Interaction with experts and scientists
6. Demonstration by pin-hole camera and ball-mirror experiment
7. Illustrative poster exhibition on Mercury: the first and smallest planet
8. Arrangement for live telecast by different media channels
9. Coordination with all Community Science Centers in the state
10 Mercury Test, quiz, puzzle, drawing competition and many more.