Solar eclipses

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.

Understand

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 very close. (In optical terms they both subtend about 30 arcminutes, or half a degree.) 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 remarkable as Earth's. On most, the occluding body is either too near/big, so it simply creates night, or is 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 moons of Mars orbit in the same plane as that planet, so they frequently appear to cross the sun, e.g. as visualised by the NASA rover Opportunity; but Deimos just appears as a small dot, while Phobos creates an annular eclipse lasting 20 seconds. Saturn occasionally has total eclipses from several of its moons, but the sun out there is only 3 arcminutes, a tenth of its apparent size from Earth. Altogether they're not worth travelling for.

Get in

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 eclipse is on Thursday 20 April 2023. Realistically the only place you can view it is from Exmouth in Western Australia.

This eclipse is hybrid: it’s annular over its early track across the Indian Ocean, and over its late track in the west Pacific. But in mid-track it’s total for about 75 seconds and makes three landfalls. The first, and the only one worth considering, is at 11:28 local time (03:28 UTC) in Exmouth. Viewing chances are maybe 80%, the area is well developed for tourism, and there’s lots else to see and do, such as Ningaloo Reef. But there are problems getting there, described below.

The second landfall is over East Timor (Timor-Leste) at 13:20 local time (04:20 UTC). The area is little developed, and April is their rainy season when the chance of good visibility is maybe 30%.

The third landfall is in West Papua, the Indonesian part of the island of New Guinea, at 13:48 local time (04:48 UT). This is not at all developed, bordering on expedition territory especially in the wet season, and viewing prospects are maybe 10%. Indeed that figure may be optimistic since in moisture-laden air the eclipse will generate its own cloud cover, as described earlier. So you’d only travel to the Timor or Papua landfalls if you were obliged to be there for some reason, or you’ve been thrown out of too many places in Exmouth and the police have circulated your mugshot.

It’s maddening that with a target the size of Australia, the track of totality just clips one corner like a bug ricocheting off a windscreen. There are three ways to experience it.

By sea: pricey but comfortable, and ships have some manoeuvrability to get into the best viewing spot. They can’t land along this notoriously shallow, reef-strewn coast, but they can put out small boats for shore excursions and snorkelling jaunts. Ships in this area will be:

• P&O on Pacific Explorer, out of Fremantle 17-22 April. Prices start at AU$1100 pp.
• Coral Discoverer is a small ship out of Broome 18-21 April and is already sold out with a waiting list.

As of Dec 2021, these are the only operators. Others advertising eclipse cruises are just selling onto these sailings and charging a mark-up for their trouble, though they may have late availability if they’ve block-booked berths. It’s possible that others will organise cruises but these are usually scheduled at least two years in advance, given the constraints of positioning large ships.

By air: the regular flights to Exmouth will sell out long in advance, but some package tours are either block-booking those flights or bringing in a charter. You need to check their arrangements after landing at Exmouth. The airport itself is a suitable but unlovely viewing spot. By land: independent but bumpy. There is just the one long ribbon of highway coming up from Perth via Geraldton and Caernarvon to Exmouth, a 750 mile / 1250 km / 13 hour drive. It’s reckoned some 50,000 visitors will come this way, meaning extreme congestion on the entire route, shunt-collisions and breakdowns, filling stations out of gas and with bad-tempered queues awaiting the next tanker delivery . . . and then you get to Exmouth and your problems start.

Anywhere along the highway between the airport at Learmonth and Exmouth town will get 60-75 seconds of totality. The tip of the northwest cape narrowly misses out, as does Coral Bay. You can also reach totality by going all the way round Cape Range to the dead-end at Yardie Creek in the national park, but that’s chancy – you could get stuck in traffic, and park access is likely to be restricted.

Exmouth council, police and park rangers have not (as of Dec 2021) announced any special measures, except to fulminate against illegal camping, which is understandable but doesn’t much advance the cause of a safe and enjoyable event. What’s needed is temporary campsites, toilets, viewing areas and parking lots to keep the highway open, plus a scattering of catering and first aid tents.

Totality misses the rest of the Australian mainland but passes over Barrow Island to the northeast. This is a private oil-gas company facility, so no doubt some company guests will get to see the eclipse, but there's no general public access.

The following total eclipse is on Monday 8 April 2024 across North America – this is a long eclipse of 4 minutes with many viewing spots. It starts in the Pacific crossing Socorro Island to come ashore at Mazatlán in Mexico. It tracks through Durango to the US border and crosses Texas, Oklahoma, Arkansas, Missouri, Illinois, Indiana, Ohio, New York, Vermont and Maine. In Canada it skims the south of Quebec Province, then crosses New Brunswick, Prince Edward Island and Newfoundland, to be ended by nightfall out in the Atlantic.

Then the next is on 12 Aug 2026 over the Arctic, Greenland, Iceland, north-east Portugal and Spain. That's how far ahead you need to plan for these events.

Future eclipses

• 2023, April 20 (hybrid). Total over Exmouth Western Australia, East Timor and West Papua, see above and NASA chart.
• 2023, Oct 14 (annular). Crosses a large swathe 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 northern Mexico, the United States of America and Canada, just south of Lake Erie and exiting in Newfoundland. In the path of totality are Dallas, Indianapolis, Cleveland, Buffalo, Rochester-Burlington, and much of northern New England, with the greatest eclipse over Northern Mexico. (NASA chart)
• 2024, Oct 2 (annular). Mostly over the Pacific Ocean, but the path also crosses Argentinian and Chilean Patagonia. (NASA chart)
• 2025 has no annular or total solar eclipses. There are partial eclipses on March 29 over NW Africa, Europe and Russia, and on Sept 21 over S Pacific, New Zealand and Antarctica.
• 2026, Feb 17 (annular) over Antarctica (NASA chart)
• 2026, Aug 12 (total) over the Arctic, Greenland, Iceland, north-east Portugal, and Spain (NASA chart)
• 2027, Feb 6 (annular) over Chile, Argentina and the Atlantic (NASA chart)
• 2027, Aug 2 (total) over Morocco, Spain, Algeria, Libya, Egypt, Saudi Arabia, Yemen and Somalia (NASA chart)
• 2028, Jan 26 (annular) over Ecuador, Peru, Brazil, Suriname, Spain and Portugal (NASA chart)
• 2028, July 2 (total) over Australia and New Zealand (NASA chart)
• 2029 has no annular or total eclipses. There are partial eclipses on Jan 14 over North and Central America, June 12 over the Arctic, Scandinavia, Alaska, and far north of Asia and Canada, July 11 over southern Chile and Argentina, and Dec 5 over Argentina, Chile and Antarctica.
• 2030, June 1 (annular) over Algeria, Tunisia, Libya, Greece, Turkey, south-eastern Bulgaria, south-eastern Ukraine, Russia, northern Kazakhstan, north-estern China and Japan. The path of annular eclipse was entire in Russia for about 2h 36 minutes!
• 2030, Nov 25 (total) over Botswana, South Africa and Australia. (NASA chart)
• 2031, May 21 (annular) over Angola, Zambia, Congo, Tanzania, south India, Malaysia and Indonesia.
• 2031, Nov 14 (hybrid). Total over the Pacific and Panama. (NASA chart)
• 2032, May 9 (annular) over the south Atlantic. (NASA chart)
• 2032, Nov 3 partial over Asia.

There are also NASA tables and maps of eclipses: table from 2021 to 2030, table from 2031 to 2040, and map from 2021 to 2040.

• The very last total eclipse might be in 620 million years. That's because the moon is speeding up as it draws tidal energy from the earth, moving into higher orbit and receding by 3.8 cm per year; meanwhile the earth's day gets longer as its spin is braked. Once the moon has receded by 23,000 km, it can no longer cover the sun when viewed from earth's suface. Total eclipses will be shorter, replaced by annular, until a last totality occurs for a split-second in an otherwise annular eclipse. Its time and position cannot yet be calculated even approximately, and perhaps it's a bit early to plan for. (Some calculations indicate eras with and without totality over twice that time span, until 1200 million years hence.) Still it's a prompt to seize the day, and view one of the examples above.

See

• 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 5500°C; the corona is at 1-3 _million_°C, 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 may look red, like sunrise or sunset. They're mostly seen near the beginning and end of totality, when the moon is only just covering the sun, and are especially numerous in the total phase of a hybrid eclipse.
• The diamond ring is seen as a group of Baily'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, and you'd still be wearing eye protection.
• 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.

Do

• 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.

Stay safe

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.

See also

• Astronomy
• Midnight sun