Annular eclipse, special for India

The annular eclipse of January 15 is special in more than one sense for us in India.  Without spending much time and money, one can travel to the southern tip and enjoy the sight of the sun turning into a glowing bracelet. Also, an exactly similar eclipse ushered the dawn of astrophysics in independent India long ago.

Eclipses have a cycle of repeatability called the Saros. These are numbered in a specific sequence. The timing of Saros includes an eight-hour interval apart from 18 years and 10 days. This shifts the shadow to different parts on the globe.

On Dec 14, 1955, an annular eclipse of the longest duration belonging to the Saros 141 cycle occurred. The path was through the southern tip of Sri Lanka. At that time in India, a young astrophysicist, who had just returned from Harvard was working towards laying the foundation for astrophysics.

He led a team of people to the eclipse and carried out experiments in a tent. That was the first ever eclipse expedition of independent India. This young man, M K Vainu Bappu, later contributed to the development of observatories in India; the Institute of Astrophysics owes its origin to him.

Expeditions are not new to India. During the colonial days, several European teams visited India for eclipses. The discovery of helium in the sun during the 1868 eclipse was made when the moon’s shadow track passed through the fields of South India.
Annular eclipses are different from total eclipses only in geometry. The angular size of the moon is just not sufficient to block the sun, which shines like a band outside the dark orb of the moon. This is a simple consequence of their relative distances. For example on January 15, the moon is farthest at 406, 125 km (farther than the average distance of 3,84,000 km) and hence looks smaller than normal. The difference in size is barely noticeable.

The sun also displays a variation in size annually. On January 3, it was nearest and will be farthest on July 4. On January 15, it is at a distance of 148,006,650 km, which puts it nearer than normal. Again, this difference is not noticeable to the naked eye. This results in a slightly larger disc of the sun. The moon is not able to cover the sun completely which makes it an annular eclipse.

The shadow of the moon hits the earth at Africa at dawn. The shadows sweeps past the Arabian sea, turns north and passes through Sri Lanka, Kerala and Tamil Nadu. In fact, the best location is Dhanuskoti where it will last for almost 10 minutes. At other places like Kanyakumari, Tuticorin, it is slightly lesser. As you move inward, the duration of annularity decreases. For example, in Madurai and Thanjavur, it is just four minutes.
This is one of the best opportunities for us to enjoy the beautiful sight since the next total eclipse is due only on March 9, 2016.

There is a partial eclipse on January 4, 2011,  visible from North West India and another partial one on May 20, 2012, visible from North East India.

Since the January 15 eclipse is not total, it is dangerous to look at the sun even at the annular phase. Goggles are a must. Projection with telescopes and pinhole cameras are also safe. It would be safest to look at the shadows of trees for numerous pinhole crescent suns.