Annular Solar Eclipses 

Eclipse path on 14 Oct 23 confined to the Americas

I had read all I could about solar eclipses, but I was quite unprepared for the experience of totality. It was electrifying, sublime, awesome and humbling all at the same time.

- Fred Espenak

 

 

Path of annularity

Prelude

A spectacular annular solar eclipse is due next Saturday (14th October 2023).  It will be confined solely to the western hemisphere and visible in large parts of the American continents as can be seen in the graphic above.

The excitement expressed by Fred Espenak, the great eclipse chaser and inveterate ‘computer’ of eclipses for NASA, is applicable to a total solar eclipse, not as much to an annular eclipse like the one due on the 14th of this month.  It will still be a memorable experience if one is located anywhere on the path of annularity.  In any case, it will have to be ignored by everyone in India, and indeed in most parts of the world, because the entire path, let alone the much narrower and crucial path of annularity, covers a different part of the globe. 

Apart from describing the forthcoming annular eclipse in the context of solar eclipses in general, and two eclipses due within a short span of each other in the USA in particular, I take this opportunity to recount my earlier experience with two annular eclipses that I have viewed, both in India.

Solar Eclipses

First, let me review what solar eclipses are. The following text is adapted from one of my earliest blog articles on eclipses (see here).

Eclipses of the Sun and the Moon as viewed from any place on Earth are possible only because of a fortuitous and accidental circumstance associated with the Sun and the Moon. While the Sun is about four hundred times bigger than the Moon, it is also nearly as many times farther away from the Earth as is the Moon. Therefore, they appear to be of nearly the same apparent size (about 0.5 degree in angular diameter) as seen from the Earth. On the occasions when these three bodies are nearly in a line, solar or lunar eclipses, which may be partial or total, are possible. A partial solar eclipse results when the lunar disk hides only a portion of the solar disk on a new moon day. A total solar eclipse happens when the lunar disk is slightly larger than the solar disk and blots it out of sight from the earth at the viewing site, revealing the spectacular sight of the solar corona, which can be viewed with the naked eye. An Annular Eclipse results if the lunar disk is slightly smaller than the solar disk and a thin peripheral ring of the Sun can still be seen at maximum eclipse. 

Total and annular solar eclipses are extremely rare events at any specific place on earth and last only a few minutes at most.  For the duration of a total solar eclipse, day turns nearly into night and produces some breathtakingly beautiful effects, justifying Espenak’s exhilaration cited above. In contrast, a part of the sunlight gets through at all times of an annular eclipse, even at the peak of annularity, and to that extent it is still daylight. However, the brightness of the sunlight getting through depends on the fraction of the sun’s disc obscured, and it will be a minimum during the peak of the annularity phase. In any case, it would be dangerous to look at an annular solar eclipse with the naked eye, as also a total one, except during the very brief period of totality when the Sun is completely obscured.

With reference to the diagram below, total and annular eclipses are possible at locations in the umbral and antumbral shadow regions, and partial ones outside of them, in the penumbral shadow regions. 

[From nineplanets.org]

Annular Eclipse of 14 Oct 23

The really significant part of the progression of this annular eclipse can be followed live on Saturday, 14th October 2023 from 9:00 PM to 11.30 PM (approximate times), with the maximum occurring around 10:24 PM, on several online channels, including:

https://www.timeanddate.com/live/eclipse-solar-2023-october-14

Below is a map of the USA showing the path of annularity in relation to some of the prominent geographical locations. The map also shows the appearance of the Sun at maximum eclipse at locations outside the path of annularity where the eclipse is only partial, and nowhere as attractive to observe as within the path of annularity. 

Path of annularity of 14Oct23 Eclipse

Below is a simulation of how the ‘ring of fire’ produced by the visible part of the Sun around the lunar disc will appear at a place like San Antonio in Texas.

Two recent annular eclipses

Besides a few total solar eclipses, I have had the opportunity to view two annular solar eclipses, both of them in recent times and within India. The first one, on 15 Jan 2010, viewed from Dhanushkodi in Tamilnadu, has been described in detail in one of my blog articles (see here). Here is a sequence of pictures taken at that time: 

During the peak of the annularity phase that lasted over ten minutes (the longest this millennium!), the ‘ring of fire’ was a nearly perfect ring alright, but such a large fraction of the solar disc was still visible that the resulting drop in brightness was barely noticeable!

The more recent annular eclipse that I viewed, along with a group of associates and friends, was on the morning of 26th December 2019 at Bekal Beach near Kasargod in Kerala state.  Here is a set of unedited pictures sent over WhatsApp and headlined by the local ‘Star of Mysore’ newspaper the same evening: 

Apart from photography, we made it possible for a large number of onlookers to view different phases of the eclipse by projecting an image of the eclipsed Sun on a white screen using a small telescope.  Here is a treasured picture of my colleague Mr Krishnamurthy focusing the image at the peak of the annularity phase:

The fraction of solar disc visible in the above picture is much smaller than the one in the annular eclipse of 15 Jan 10, yet the surroundings are bright* enough for shadows to be visible clearly, as also the onlookers.  This is the reason why an annual eclipse is almost always much less impressive visually than a total one.

[*Note:  An important parameter associated with eclipses is its magnitude, which is the fraction of the angular diameter of the celestial body being eclipsed, in this case the Sun.  For the annular eclipses of 15Jan10, 26Dec19 and 14Oct23, the magnitudes are 0.919, 0.970, and 0.952 respectively.  Clearly, the forthcoming eclipse promises to be no more spectacular than the one in 2019.

On the other hand, the annular eclipse of 21Jun20, visible in parts of northern India, had a magnitude of 0.994. A small group of us were to have witnessed it in Suratgarh, Rajasthan, but unlucky to miss out the trip because of travel restrictions due to the Covid pandemic. From descriptions of those who did view it, I understand it was pretty much like a total eclipse lasting just a few seconds.]

 USA – Eclipses in Quick Succession

The USA is the rich ‘beneficiary’ of as many as three great solar eclipses within a short period of seven years, from 2017 to 2024. All three of them touch vast areas of continental USA as the respective maps indicate. The first one, on 21 Aug 2017, was a total solar eclipse that could be seen over a vast stretch of land spanning from the northwest to central east (see map below).  The second is the forthcoming annular eclipse that is the topic of this article. 

Total Solar Eclipse of 21 Aug 2017

The third is another great total solar eclipse that is due next year on 8th April, again covering a vast stretch of the country, and beyond, as the following map indicates: 

Total Solar Eclipse of 08 Apr 2024

If the two previous maps are superposed, we end up getting the following composite map showing both the paths, and very interestingly, their intersection as well.

The intersection, shown magnified in the following map, tells its own story: 

The huge state of Texas finds large parts of its territory covered by both eclipse paths, which means anyone in such a location (in the large city of San Antonio for example) can see both eclipses within a span of six months.  Probabilistically, the waiting period for any specific location on earth experiencing such consecutive eclipses is estimated to be around 375 years!

Personal regrets

Three great solar eclipses within a span of less than seven years meant both an opportunity and a challenge for me, challenge because any place in USA is as far away from my home as it can get, with the consequent drain on my resources. It is pointless to go to a far-off place just to see an eclipse however unique it may be. To get the best out of the visit, one has to make it part of a much longer tourist trip.  I did that in 2017, making a successful visit to Nashville, Tennessee, to view the total eclipse as a part of a long trip to USA and then on to Europe. 

Now, I find myself unable to visit USA twice within a span of six months and needing to settle for only one visit.  For this reason, I am regrettably opting out of the forthcoming annular eclipse in favour of a more spectacular total one on 8th April next year, somewhere north of Austin, Texas.  Naturally, I intend to make it part of a longer trip, including Mexico and Canada apart from USA.

The bottom line

Apart from the generally very short duration, the rarity of total or annular solar eclipses at or near any particular location on earth means that we may be lucky to see one in an entire lifetime.  The rarity is compounded by the vagaries of weather, especially cloud cover, at the time of totality or annularity, which may spoil the best part of the show completely and make the journey almost worthless.  However carefully the observing location on the central path of the eclipse may have been chosen, luck also plays a significant role in one’s success. I have been particularly lucky in having been able to see all six of the events I have observed so far in different countries, including two in India, totally successfully. I hope that not only my opportunity but also my luck continues unabated.