A solar eclipse is an astronomical phenomenon in which the sun is obscured by the moon. In a total solar eclipse, the moon precisely covers the sun's bright orb, leaving the normally invisible solar corona glowing all around it, as if the sun had turned to pitchblende, coldly radiant in a twilight sky. It's a wonderful natural spectacle, worth travelling a long way to witness - as you may have to. It's only visible for a couple of fleeting minutes along a very narrow track, so you have to be in precisely the right place at precisely the right time, and be lucky with the weather. So the travel arrangements are the key to success.
The moon orbits the earth and so at "new moon", when its dark side is towards us, it lies between earth and sun - but seldom exactly. The moon is a relatively small object and its orbit tilts at a 5° angle to earth's, so most months its shadow isn't cast onto the earth's surface, it misses to the north or south. All that usually happens is that the dark moon can't be seen in the sun's glare, until a day or two goes by, it moves further from the direct line and more of its earth-facing surface returns into sunlight, and we see the first slender crescent of the waxing moon.
But once or twice a year, it does line up, and casts a shadow onto earth. Seen from earth, it's as if a dark bite has been taken out of the sun - a partial eclipse. Indeed the ancient Chinese believed that a dragon was trying to eat the sun, and so they beat gongs and drums to try to scare off the dragon. (To date this remedy has never failed.) The zone over which the shadow is cast and the eclipse can be seen might be several hundred miles wide and many thousand miles long. At the edge of this zone, the "bite" is marginal and the eclipse is short, while towards the centre, the bite extends until a high proportion of the sun is covered then reverses, with the whole event taking 2-3 hours. A partial eclipse looks odd but not wonderful. It's not in itself worth travelling far to see, unless -
In about half of these eclipses, there is a much narrower band - just as long but maybe only 50 miles wide - where the sun becomes completely covered, a total eclipse. This really is something special. The combination of the moon's movement around the earth, and the earth's surface rotating on axis, means that the "zone of totality" races west to east along a sinusoidal curving track at over 1000 mph (with some odd-shaped tracks in polar regions, where it may go east to west). Observers on the edge of the zone will see totality for only a few seconds, so you want to be as near as possible to the centre of the track. Here it might be total for a couple of minutes, bracketted by a partial eclipse for an hour or so either side. It may take months of planning and considerable expense and inconvenience to position yourself on that track, then the clouds roll in and all you get is an unusually dark gloomy day: a total eclipse is entirely capable of generating its own bad weather, as described below. Deciding which eclipse to aim for and which to pass by is a crucial first planning step.
The total eclipse is brief and spectacular because the sun is 400 times the diameter of the moon, yet is 400 times further away, so they're the same size as viewed from earth - the match is precise. But the moon's orbit, as well as being at a tilt, is also slightly off-centre of earth, so an eclipse sometimes happens when the moon is around its furthest out. Then the sun shines around all sides with the dark moon in the middle, it's not quite total, but an annular eclipse. This looks very odd . . . but wonderful? Not really, because you don't get the corona and other sights of totality, described below. And the track is as narrow as for a total eclipse, so the travel planning needs to be just as precise; arguably you get the worst of it all round. Sometimes the moon teeters on the edge, creating an annular eclipse on part of its shadow track and a total eclipse elsewhere, and this is called a hybrid eclipse.
At "full moon" the line-up is reversed, and the earth lies between sun and moon. Again, it's seldom a precise line-up. But the earth casts a much bigger shadow, so generally at least twice a year there is a lunar eclipse, which in some years is total. The moon then looks red, illuminated only by light refracted through earth's atmosphere. Lunar eclipses last for a couple of hours and can be seen from anywhere on earth where the moon is risen and the skies are clear. You don't need to travel to see one, just wait for one visible from your neighbourhood and in good weather; so they're not considered further on this page.
Within the solar system, no other planet has eclipses as beautiful as Earth's. On most, the occluding body is either too near/big, so it simply creates night, or too small/far out. We have the lucky coincidence of a sun and moon that look roughly the same size to a viewer on the surface. The only other planet in our solar system with similar eclipses is Saturn, and due to the shapes and orbits of its moons, the eclipses there wouldn't be as spectacular as they are on Earth. The moons of Mars orbit in the same plane as that planet, so they frequently appear to cross the sun, eg as visualised by the NASA rover Opportunity. But Deimos just appears as a small dot, while Phobos creates an annular eclipse lasting 20 seconds. Not worth travelling for.
First decision is which eclipse to try for and which to leave alone. It needs to be a total eclipse, in a locality that you can physically travel to, and with decent amenities and good viewing prospects. It may involve intercontinental travel, in which case you're committing to a trip of a week or two - is there enough else to see and do there for a satisfactory trip? For instance, the last eclipse visible from Europe, on 20 March 2015, was only partial on the mainland. It was total across the Atlantic but made landfall in the Faroe Islands. These do have transport, accommodation etc which is limited and expensive, yet logistically practical - but the Faroes in March?? Viewing prospects were poor, lots of people went regardless, but the sky was heavily clouded that day and all they experienced was an extra dose of winter night. As it happened, the sky was clear in Jan Mayen Island way up in the Arctic Circle, so a few hardy souls there saw a good eclipse, but no-one could have planned on that basis.
Because total eclipses, especially those viewable easily from land, are fairly rare, there are two problems with getting in: to find transport to the location at all and then to book it before everyone else does. Solar eclipses can attract hundreds of thousands of viewers, overwhelming the local transport and accommodation. For a well-resourced tourist area (like the 2012 eclipse in Cairns, Queensland Australia), you should book many months in advance but there may be some availability close to the event. If the eclipse is off the beaten track, make arrangements a year or more ahead. Expect at least peak season pricing. Hotels and car rental companies may not accept bookings just for one or two nights but impose a longer minimum period. If you waited too long and everything seems to be booked up, there may be work-around solutions, eg people may hire buses or rent out their backyards to campers. But the event may also encourage flaky providers, who dishonour bookings when someone else offers them better money.
Sometimes transport companies offer special trips by plane, boat or land to reach the path of totality. Cruise ships may have special itineraries, and some flexibility to sail into a cloud-free viewing area - for polar regions they're the only realistic option. Aviation can get you to the right area but is not a good platform for viewing the eclipse: aircraft climb above the clouds but then you're behind windows, which in airliners are small and thick, with few seats getting any view. Light aircraft and helicopters are likely to be booked out to Celebs and VIPs (with their entourage all in impressive sunglasses) and those that aren't booked out don't have a licence to fly passengers, probably for a reason. Ballooning sounds cool but they can't climb above the clouds, they're highly weather-dependent, and have less manoevrability for the view than you would on a bicycle.
Plan lots of extra time to get in and out. Especially in small towns that are good viewing locations, you can expect horrible traffic jams and crowded trains and buses. There will be lots of road accidents caused by extra vehicles, fraught drivers, and shunts into tailbacks. Aim to arrive at your viewing location extra early and leave late. Make contingency plans in case you're unable to get back to base. Carry extra food and water, and be topped up on fuel. Expect long lines to use toilets that may be squalid. Don't rely on your cell phone for communication or navigation, the local cell towers may be overwhelmed, if indeed the area has coverage at all. That extra clothing, just for the eclipse, may turn out to be your bedding as you're forced to sleep in the car.
The next total eclipse
The next total solar eclipse is on Monday 14 Dec 2020. It starts out in the Pacific at around 11° South, 131° West and tracks southeast. It crosses the island groups of Kiribati and Polynesia, but in the midst of their wet season, so it's unlikely to be visible there. Its continental landfall is near Puerta Saavedra in Chile at 13:00 local time. It continues east-south-east across Patagonia in Argentina, reaching the Atlantic Coast between Las Grutas and La Loberia at 13:23. Totality is just over two minutes along the central track. It moves east then northeast across the Atlantic to be terminated by sunset before reaching the Namibia coastline at around 24° 30 South, 11° East: see the NASA chart.
That part of southern Chile has 50% cloud cover in December whereas Patagonia in Argentina has 30-35% cover. But this underestimates the viewing chances, as the timing means the sun will be at its height, to burn away any cloud or mist. There remains a chance that any location you choose may be socked in, but with a clear view within a few miles: a rental car will be a good investment. The main choice of base is:
- Neuquen in Patagonia, then drive south 100 km on Highway 6 / 8 from General Roca to the junction where those highways divide (totality starts 13:13): that gives you a little east-west and a lot of north-south flexibility. The junction is an utterly deserted spot in semi-arid scrubland with no other roads; expect horrible traffic congestion getting through General Roca. Perhaps some entrepreneur will organise pop-up facilities, as Argentina’s total eclipse of 2019 showed the money to be made, but chances are there’ll just be a burger van.
- Beach resorts in Rio Negro Province in Patagonia around the Golfo San Mathias, such as Las Grutas, Bahia Creek and La Loberia. These have accommodation and other amenities and are central on the path of totality, starting at 13:22. Highways from Las Grutas give lots of east-west and north-south flexibility. Probably a flotilla of small craft will head out into the gulf for viewing.
- Cruise ships will be in the area as this is the South American summer cruising season, but the only one that advertises the total eclipse is Princess Cruises. They sail from Santiago on 3 Dec 2020, round Cape Horn and the Falklands to view the eclipse off Puerto Madryn, then continuing via Montevideo to end at Buenos Aires on 18 Dec. Other ships will at best see a partial eclipse, eg Celebrity Cruises trip to Cape Horn that month.
The following total eclipse (see below) is in West Antarctica in Dec 2021, with only limited, expensive access by cruise ship. After that it's April 2023 in parts of Indonesia that have few amenities and are often cloud-wraithed. So if you give Patagonia a miss, your next good chance is April 2024 across North America. That's how far ahead you need to plan for these events.
- 2019, December 26 (annular). The pathway is at a maximum over Sumatra (Indonesia) and Singapore, but the path starts in Saudi Arabia, and passes through Qatar, the United Arab Emirates, Oman, southern India, Sri Lanka, Malaysia, and touches Borneo and Guam. (NASA chart)
- 2020, June 21 (annular). The pathway passes through Congo-Brazzaville, Congo-Kinshasa, South Sudan, Ethiopia, Eritrea, Yemen, Saudi Arabia, Oman, Pakistan, India, China, and Taiwan. The greatest eclipse is over parts of the Himalayan North of India and Tibet in China. (NASA chart)
- 2020, December 14 (total) - see section above.
- 2021, June 10 (annular). Mostly over remote regions, with the path crossing parts of Canada, Russia, and Greenland. (NASA chart)
- 2021, December 4 (total). The path of totality crosses West Antarctica, with a partial eclipse visible from elsewhere in Antarctica. (NASA chart)
- 2022 has no annular or total solar eclipses. There are two partial eclipses:
- April 30, mostly over the South Pacific, but also visible in Chile. (NASA chart)
- October 25, visible in most of Europe, European Russia and the Urals, Central Asia, the Middle East as well as large areas of North and East Africa. (NASA chart)
- 2023, April 20 (hybrid). Over Indonesia, with the path of totality/annularity crossing Papua and Nusa Tenggara. A partial eclipse will be visible from elsewhere in Indonesia as well as Papua New Guinea and Australia. (NASA chart)
- 2023, October 14 (annular). Crosses a significant portion of the Americas, including parts of the United States, Mexico, Belize, Honduras, Nicaragua, Panama, Colombia, and Brazil. The greatest eclipse will be in Central America, around Nicaragua and Costa Rica. (NASA chart)
- 2024, April 8 (total). The pathway crosses Mexico, the United States of America and Canada, directly south of the beaten-path Windsor-Quebec Corridor and continuing into New Brunswick. In or near the path of totality are Windsor-Detroit, Cleveland, Toronto-Buffalo, Montréal-Burlington, Boston and much of New England, with the greatest eclipse over Northern Mexico. (NASA chart)
- 2024, October 2 (annular). Mostly over the Pacific Ocean, but the path also crosses Argentinian and Chilean Patagonia. (NASA chart)
- First contact: the first little nick taken out of the sun. Until this point, you've been planning and travelling and spending all for the sake of a mathematical prediction. Now here's the first physical proof that it's really going to happen.
- Partial eclipse: this is where you need eclipse-rated glasses or other protection, as described below. The eyes have a strong natural reflex to avoid being blinded by the sun. Your iris constricts, your eyelids close, you flinch and turn away. As the eclipse deepens, there's less light and the reflex can be overcome. You can gaze directly at the sun but at your peril, because damaging amounts of visible light, infra-red and ultra-violet are being focussed onto your retina. The damage may be permanent and severe.
- The weather: what's it doing? With perhaps 20 minutes to go, is the sun in a clear sky, are the clouds dragging over, does it look like you could realistically improve your viewing chances by moving a few miles? You are searching (probably along with several thousand frantic fellow-observers) for a good big hole in the cloud cover. A little chink is not worth chasing, it will close up. In a damp climate, the eclipse creates its own bad weather because the shadow and loss of sunlight cools the air, and clouds form; these further shade and cool the air beneath, so the cloud layer thickens. This gloom approaches from the west, regardless of the direction of the wind and pre-existing cloud. You'll feel cold, even if the day remains clear, and want an extra layer of clothing.
- The dark tower: with a minute or so to go, the shadow of totality is a great dark column hurtling towards you, especially if there's mist and cloud. It's spooky, almost scary. It always approaches from the west so if you're looking east at a morning eclipse, it will come from behind like an ambushing dark genie.
- Totality: wow! Now and only now you look directly at the sun. Its orb is completely dark but surrounded by the cold glow of the corona. So cold that until 1724, observers thought the glow was from the moon not the sun; yet paradoxically it's the hottest thing in view. The sun's visible surface is a mere 5500oC; the corona is at 1-3 millionoC, yet being so tenuous it emits far less light. Just how it gets to be so hot is complex and still a matter of debate. The size of the corona varies with the 11-year solar cycle, but even during a "minimum" it's an impressive sight. You may be exceptionally super-lucky and see a solar flare or prominence within the corona, but these are brief phenomena that rarely coincide with a total eclipse.
- The twilight world: take a few moments to look around at your strangely-lit surroundings. Birds and animals may react as if night has fallen. This is partly a quirk of the sudden totality, as eyes don't have time to fully adapt to the dark. The light intensity corresponds to mid-twilight on an ordinary evening, when if the sky is clear, you can still perceive colours, whilst if it's heavily overcast, it will be night. It's a downer if at this point the local streetlights and house driveway lights are triggered into life.
- Baily's beads are little bright dots around the moon's edge, where chinks of sunlight are passing through vast lunar canyons and craters. They're mostly seen near the beginning and end of totality. They may look red, like sunrise / sunset.
- The diamond ring is seen as a group of Bailey's beads suddenly coalesces and goes thermonuclear, a thin crescent of light cloaks the dark moon, and totality ends with a sunburst. Look away now while you put your eye protection back on. The same effect occurs in reverse at the start of totality, but is less spectacular as the sun is fading not rejuvenating.
- The tail-end partial eclipse is the least interesting, least observed part of the event. The main show is over, and there follows an anticlimactic hour or so as the sun returns to its full circle and strength. At this point you're thinking about how to spend the rest of the day and the trip. Keep an eye on the traffic and give it a chance to disperse. Anyone who's crocked his eyesight will be in denial, and will be trying to drive off while rubbing eyes and squirting the windscreen to make those dark floaty things go away.
- Citizen science: scientists have made all sorts of observations during eclipses. Most famously, Einstein's theory of relativity was tested during the 1919 eclipse over Príncipe, when the sun's gravity was observed to bend starlight. Present day travellers and amateurs may still be able to contribute: this is most likely where there's a strong tradition of public engagement in science, such as in the US eclipse of 2017, but other countries may appreciate volunteers. And there's much more than astronomy: what about animal behaviours? Do responses differ between daytime and nocturnal species? What about the business impact of eclipse tourism, the economic effects, the profile and sociology of travellers? Can we quantify the benefits and harms to the communities along the eclipse path? How should public services (such as traffic police or local schools) plan for such an event? Start looking months ahead for mass projects you can join in, and plan years ahead for any enquiry that you personally could lead.
- Photograph the eclipse, only if you are capable of taking a decent photo of the moon, and only if you have solar filters. Most efforts don't work, even on regular cameras let alone mobiles, as the moon is so small. Hold your hand at arm's length and move your little fingernail across the moon - it will easily cover it, that's how small your target is. Good shots mean high magnification, so a giant moon seems to roll above the trees and chimney-stacks. But high magnification of sunlight spells the instant obliteration of your eyesight and equipment, unless you have proper solar filters, available from an astronomy supplier.
- Look at the strange crescent-shaped shadows during a partial, total, or annular eclipse. You can project the eclipse through a pinhole camera or similar homespun device. Take two sheets of cardboard and make a small hole in one, so that sunlight projects through that hole onto the other sheet. The circle cast on the second sheet will change shape as the partial eclipse progresses. A similar trick is to bring a straw hat with a loose weave; each of the holes acts as a pinhole camera, so you can use it to produce dozens of the little crescents.
Never look at the sun with the unaided eye or with a camera or telescope, not even for a second and not even if only 1% of the sun is visible. This may seriously damage your eye and even make you blind. Always use an approved solar filter either directly over your eyes for unaided viewing, or over the lens of a camera or telescope. You can use:
- Eclipse glasses: These should be CE certified or conform to ISO 12312-2 or EN 1836 & AS/NZS 1338.1. They're usually simple cardboard glasses costing US$3-$5. Beware of fakes! Some unscrupulous manufacturers put the CE / ISO logo on glasses that are way below standard. Don't trust street vendors, buy from a reputable source. Glasses from science museums or astronomical organizations are almost certainly good to go; the American Astronomical Society also provides a partial list of reputable vendors. A single pair between two or three of you may suffice, as the partial eclipse takes an hour.
- Welder's goggles rated 12–14, the highest ratings for blocking radiation - nothing lower.
- Solar filters for cameras and telescopes, available from astronomy shops. The lens itself must be protected. It's not sufficient to use eclipse glasses to look through the viewfinder, as the lens has magnified the sun's power and you could still damage your eye. The sun will also destroy camera sensors if you haven't got a filter on the lens.
Do not use:
- anything designed for vision or photography in normal bright light, such as sunglasses or standard camera filters. These are far, far less protective than proper solar filters.
- lesser rated welder's goggles.
- any stacked lesser protections.
- any non-certified protections.
- eclipse glasses with damage such as scratches or tears.
As the moon fully obscures the sun during total eclipses it becomes safe to look without a filter and see the beautiful corona (the sun's atmosphere). Have your eye protection ready for the end of totality.