Chasing the South American ECLIPSE
Will Gater looks ahead to one year from now, when the Moon’s shadow will sweep across Chile and Argentina
The finale of a total solar eclipse can be a funny thing. In a single moment, at the end of the eclipse the world around you that was so dramatically transformed by the Moon’s shadow returns to normal, as if nothing of import had happened in the skies above. That instant often prompts a swirling mix of emotions, from relief – if the eclipse chase has been successful – to overwhelming awe and even serenity. But observe enough of these unique celestial spectacles and there’s one phrase you’ll hear uttered again and again following their conclusion: When’s the next one? Following last year’s historic US eclipse it’s a safe bet that many will have been bitten by the eclipsechasing bug, whether they attended in person or simply saw the coverage. And if you, too, are one of those people wondering where and when it’ll all happen again, the answer is South America, a year from now on 2 July.
The swathe of the planet from where the 2019 total solar eclipse can be seen lies mostly across the open ocean of the South Pacific, though it does cover the uninhabited Oeno Island, in the remote Pitcairn Islands. However, it’s the thin strip of Chile and Argentina that the Moon’s shadow crosses where most eclipse chasers will head to. The Moon’s shadow will make landfall on the Chilean coast, close to the city of La Serena, before crossing the spectacular Andes Mountains and heading into Argentina, just skirting through southern Buenos Aires, before ending its journey across the globe 150km southeast of the city.
Heart of darkness
The eclipse path is defined by the dark core of the lunar shadow sweeping across our planet as the Moon passes between the Earth and the Sun. We say ‘dark core’ because the Moon’s shadow is, in fact, composed of two parts: a lighter, outer region called the ‘penumbra’ and a darker, inner region known as the ‘umbra’. To observe the breath-taking phenomenon of ‘totality’ – where the disc of the Sun is completely hidden by the silhouetted disc of
the Moon – you have to be located within the path of the ‘umbral’ shadow. This is the reason why the narrow ribbon of the Earth’s surface along which the Moon’s umbra will travel during a solar eclipse is commonly referred to as the ‘path of totality’.
If you’ve never seen a total eclipse before you can expect a celestial show that is completely without parallel. If you want to see the 2019 South American eclipse for yourself, there are several companies in the UK and abroad offering guided tours. If you’re considering travelling under your own steam, then as a rough guide flights to Santiago, Chile from London for late June and early July of this year start from around £950 at the time of writing. As Santiago is around 350km south of the path of totality, you’ll need to arrange local accommodation and transport to a suitable viewing site within the eclipse path.
When you do finally make it to your viewing site in 2019 there are some important safety precautions that you’ll need to take to prevent damaging your eyes. In order to view and photograph the partial phases of a total solar eclipse you will need to use a correctly-fitted, certified, solar filter on any optics you’re using. If you intend to observe the event just by eye you will still need to wear a pair of certified eclipse glasses to view the partially eclipsed Sun.
Each total solar eclipse begins with a moment known as ‘first contact’; the instant the Moon’s disc first appears to ‘touch’ the disc of the Sun. In practice it can sometimes be difficult to see that the Moon has taken a ‘bite’ out of the Sun at this point – especially if poor daytime seeing is causing the Sun’s limb to shimmer or ripple – so you may have to wait a minute or so from the official moment of first contact to see that the eclipse is underway.
First contact marks the beginning of the first ‘partial’ phase of a total solar eclipse when the Moon gradually covers more and more of the Sun, which becomes an ever-thinner crescent. It comes to an end with the start of totality, then a second partial phase begins when the Sun’s disc starts to re-emerge. This is essentially the first partial phase in reverse with the Sun’s crescent becoming wider until the instant when the Moon slips off the solar disc completely – what is known as ‘fourth contact’.
During both of the partial phases, either side of totality, the changing appearance of the Sun’s disc
isn’t the only thing you’ll want to monitor. Indeed, some of the most intriguing phenomena associated with total solar eclipses occur during these periods; oddly enough, one of the easiest to spot requires you to look not up at the sky but down to the ground.
That’s because any tiny gaps in dense tree or bush foliage can often act as pinhole projectors, throwing little ‘images’ of the Sun’s disc onto the ground. Where normally these small openings between the leaves create a dappled carpet of bright circles, during the partial phases of an eclipse these circles are transformed into a mass of small crescents.
A silvery twilight
As the first partial phase progresses and the Sun’s crescent shrinks away, the light levels around you slowly begin to drop. Under clear skies this change can be very subtle at first, and you have to be vigilant to notice the decrease; it might, for example, manifest itself early on as a change in the colour of the sky, from a milky white to a slightly deeper blue. As totality approaches, though, the drop is unmistakable. At 10-15 minutes before totality the illumination of the landscape can be very strange – somewhat like a de-saturated, even silvery-blue, twilight, but with a subtly different quality.
In the final minutes before totality keep an eye out on the ground for ‘shadow bands’. This elusive eclipse phenomenon is poorly understood in terms of what causes it, but manifests as very faint, fastmoving wavy dark lines that race and shimmer across the ground. If you can, take an ironed, white pillowcase or large piece of white card with you to place on the ground, as this can make shadow bands much easier to spot.
While checking for shadow bands, look also for the darkening of the western horizon and, if your observing site gives you a vantage over a very wide area, the rapidly approaching umbral shadow. At this point observing the Sun using a certified solar filter will reveal a razor-thin crescent – a sure sign that totality is imminent.
Totality arrives when the Sun’s disc is fully obscured by the Moon, and only during these moments when the Sun is completely hidden is it safe to remove your eclipse glasses. With totality the wispy ‘streamers’ of our star’s outer atmosphere – the ethereal, glowing ‘corona’ – are suddenly revealed, stretching away from the obsidian-black disc of the Moon into the deepest-blue sky. This is also the time to look for any ruby-red prominences leaping off the limb of the totally eclipsed Sun – a truly extraordinary sight to behold, if you’re fortunate enough for one to put in an appearance.
The length of totality
In 2019, the eclipse will last just over two-and-a-half minutes near the centre line on the western coast near La Serena, Chile. Further southeast along the
path of totality, in Argentina, that figure drops to around two minutes. What will make this eclipse feel different from last year’s in the US is that the totally eclipsed Sun will be lower in the sky – for example totality will begin at La Serena when the Sun is at an altitude of nearly 14° while at Venado Tuerto, in Argentina, it will only be around 4° above the horizon as the Sun is beginning to set.
This should enable some particularly striking astrophotography opportunities incorporating dramatic skylines and landscapes – especially in combination with the colours of the famous ‘360° sunset’ that appears all around the horizon during the totality of a solar eclipse. However, you will have to be careful when choosing your observing location to ensure that the eclipse isn’t hidden by large features in the surrounding landscape.
Ending on a low, then a high
Just prior to the end of totality be sure to reattach any solar filters you’re using, so that you aren’t caught out by the re-appearance of a thin sliver of the Sun’s blazing disc. At the instant when the Sun does re-emerge, the second partial phase begins, and a little over an hour later the Moon will have moved off the solar disc completely, bringing the eclipse to an end. By this point the Sun will have already set for observing sites towards the eastern end of the eclipse track. While on the Chilean coast – in La Serena, for example – the Sun will be very low near the horizon for the moment of fourth contact.
In the exhilarating minutes after the eclipse’s conclusion you’ll no doubt want to share stories and compare notes with your fellow eclipse chasers. But there’s also much to be said for taking a moment to drink in the atmosphere and absorb what has unfolded. And whether it was your first or fifth total solar eclipse, among all that emotion and excitement maybe it’ll be you who has that thought bubbling up inside them…
When’s the next one?
Uninhabited Oeno in the Pitcairn Islands would be a great place to see the 2019 eclipse, except that no planes fly there and the ferry from Mangareva to the Pitcairns only leaves four times a year
The path of totality for the 2019 solar eclipse across South America
The author’s own spectacular shot of totality during the American eclipse of 2107, showing the Sun’s corona
You’ll be able to see shadow bands much better if you have something large, white and flat handy
Totality enables you to see the Sun’s corona, and if you’re really lucky, you might witness some prominences too