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

Sky at Night Magazine - - SOUTH AMERICAN ECLIPSE -

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.

First con­tact

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

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