The morning of October 14, 2023, presented a unique opportunity to watch a spectacular celestial show — the annular solar eclipse.
Popularly known as the “Ring of Fire”, annular eclipses occur when the Moon comes in between the Sun and the Earth without completely blocking its view, leaving a thin rim of the solar disc visible all around.
This is in contrast to a total solar eclipse where the entire disc of the Sun gets blocked by the Moon. The specific occurrences depend on the relative distances between the Moon and the Earth, making the Moon appear bigger in a total eclipse and slightly smaller during the annular(L-r
(L-R) First contact, Eclipse in progress, Annularity = Ring of Fire, Beginning of the exit
On October 14, the shadow of the Moon swept across the US starting from Oregon on the West coast and passing over Utah and New Mexico and exiting through Texas before going over Central and upper part of South America.
To watch an eclipse one must be in the path of the Moon shadow and preferably close to the centre line of the shadow band or eclipse path, as it is technically called.
Weather often plays spoilsport in eclipse viewing. The most detailed planning can just go to waste. To maximise our chances of viewing, we chose to go to Albuquerque, New Mexico, based on the weather and cloud cover predictions.
We were lucky to have an ideal weather — a crisp and sunny morning with cloudless sky offered us perfect viewing throughout the duration of eclipse.
The beginning of the eclipse, known as first contact (C1) between the edges of the Sun and the Moon, was visible around 9.14am.
About 80 minutes later, at 10.35am, was the second contact (C2), marking the beginning of annularity, which lasted slightly more than four minutes.
Then came the third contact (C3), which signifies the end of annularity and the beginning of the exit of the Moon from the solar disc. Fourth contact (C4) was observed around 12.10pm when the edges of the Sun and the Moon met for the last time, marking the end of the eclipse.
Solar eclipses, total as well as annular, must be watched through solar filters.
Even during the annular phase, the ring of fire is so intensely bright that it can burn the retina (and even camera sensors), causing permanent visual impairment. Solar filter cuts light by 99.9 per cent (more than 16 stops) and makes the sky look totally black. It also imparts a yellow orange colour to the Sun which can be seen in photographs.
As the eclipse progresses in the sky, one interesting phenomenon can be simultaneously observed on the ground. The round patterns of sunlight seen under any tree take the shape of the partially eclipsed Sun. In effect, each blob of sunlight is an image of the Sun caused by a gap in overlapping leaves, acting like a pin hole camera lens.
At the moment of annularity, these look like a host of circular rings. It is possible to observe the progression of the eclipse without looking directly at the Sun.
There is good news for sky watchers. Next year, two major solar eclipses will take place.
On April 8, a total solar eclipse will be visible from large parts of Mexico, the US and Canada. Later in the year, on October 2, people in South America will be able to observe another annular solar eclipse.
Arup Ratan Dutta is the director of Nephrology and Transplantation, Fortis Hospital and Kidney Institute Fortis Hospital, Anandapur, Calcutta