Solar Eclipse Explained

Time & Astronomy

A total solar eclipse is the only astronomical event that people cross oceans to stand under. For two or three minutes the Sun is switched off in the middle of the day, the temperature falls, the horizon glows orange in every direction at once, and a pearl-white halo appears where the Sun used to be. Everything about it — the rarity, the narrow strip of ground it covers, the strict rules about looking at it — follows from the shape of a single shadow.

Key takeaways

A solar eclipse happens at new moon, when the Moon passes between the Earth and the Sun and casts its shadow onto the surface.
There are four kinds: total, annular, partial and hybrid. Only a total eclipse turns day into twilight.
The path of totality is at most about 270 km wide and races across the ground at well over 1,500 km/h.
Totality typically lasts two to four minutes and can never exceed about seven and a half.
A given spot on Earth sees one roughly every 375 years on average, which is why people travel to the path instead of waiting.
Never look at a partly covered Sun without certified filters. The only safe moment for the naked eye is totality itself.
Contact times are published in UTC and differ from place to place, because the shadow sweeps across the globe rather than arriving everywhere at once.

The Shape of the Shadow

The Moon casts two shadows at once. The umbra is the dark inner cone where the solar disc is hidden completely; the penumbra is the much wider, weaker shadow around it where only part of the Sun is blocked. What you see depends entirely on which one you are standing in.

The umbra is barely long enough to reach us. Averaged over its orbit, the tip of the cone falls close to the surface of the Earth, so small changes in the distance of the Moon decide whether the cone lands on the ground or runs out just short of it. When it lands, you get totality. When it falls short, the extension beyond the tip — the antumbra — sweeps the surface instead, and an observer there sees the Moon surrounded by an unbroken ring of Sun. That is the whole difference between a total and an annular eclipse: a few thousand kilometres in the distance to the Moon. The size coincidence that makes both possible is described in What Is an Eclipse?

The Four Types

Type	What you see	Why it happens	Does it go dark?
Total	The disc vanishes; the corona appears	The Moon is near enough to look slightly larger than the Sun	Yes, to deep twilight
Annular	A bright ring of Sun around a black Moon	The Moon is far enough away to look slightly smaller	No, only a strange dimming
Partial	A bite taken out of the Sun	You are in the penumbra, off to one side of the main path	No
Hybrid	Annular at each end of the path, total in the middle	The curve of the Earth brings the middle of the path closer to the Moon	Only in the total stretch

Hybrid eclipses are genuinely rare, making up only a few per cent of the total. Partial eclipses, by contrast, are what almost everybody actually experiences: the penumbra is thousands of kilometres across, so each total eclipse delivers a partial one to a continent-sized region either side of the path.

It is worth being blunt about the difference in the experience, because the numbers are misleading. A 95 per cent partial eclipse is not 95 per cent of totality. It is not even close. The remaining sliver of photosphere is still blindingly bright, the corona stays invisible, and daylight looks merely a little flat. Totality is a different event, not a stronger version of the same one.

The Path of Totality

Because the umbra is a narrow cone and the Earth is turning underneath it, totality is confined to a strip. Its dimensions are unforgiving:

Width: up to about 270 km at the very best, and often 100 km or less. Step outside it, even by a kilometre, and you get a deep partial eclipse instead.
Speed: the shadow crosses the ground at roughly 1,700 km/h where the Sun is overhead, and far faster near the ends of the track, where it can exceed 5,000 km/h. No airliner can keep up with it; Concorde once could.
Duration: two to four minutes is normal. The theoretical ceiling is about 7 minutes 32 seconds, and the longest eclipse of this century, in July 2009, managed 6 minutes 39 seconds.
Length of the track: often 10,000 km or more, curving across the globe as the Earth rotates beneath the shadow.

Somewhere on Earth a total solar eclipse happens roughly every 18 months, and only ever during one of the two eclipse seasons that punctuate the year. Any particular town, though, waits an average of about 375 years between them, because the paths are so thin that they take centuries to cover the same ground twice. That statistic is the reason a whole culture of eclipse chasing exists, and why the practical question is never when but where and how do I get there.

What Actually Happens, Minute by Minute

Astronomers label four moments, called contacts, and the drama is compressed into the seconds around the middle two:

Moment	What happens
First contact	The Moon touches the edge of the Sun. Nothing is visible without a filter.
The next hour	The crescent narrows. Light turns metallic, shadows sharpen, the temperature starts to fall.
Second contact	The last sliver breaks into Baily’s beads, then a single diamond ring. Totality begins.
Totality	The corona is visible, planets appear, the horizon glows on all sides. Filters can come off.
Third contact	The diamond ring returns on the other side. Filters go back on immediately.
Fourth contact	The Moon leaves the solar disc, an hour or so later.

Baily’s beads are sunlight streaming through valleys on the edge of the Moon, and they last only a few seconds. The corona that follows is the outer atmosphere of the Sun, a million degrees hot and about as bright overall as a full moon — permanently there, but drowned out by the disc except during these few minutes. Observers also report shadow bands, faint ripples of light that slide across pale surfaces just before and after totality, and a temperature drop of 5 to 10 degrees Celsius. Birds go quiet, and livestock frequently head for shelter as though night had fallen.

How to Watch Without Damaging Your Eyes

This is the one part of eclipse-watching where the rules are not negotiable. Looking at even a thin crescent of uncovered Sun can burn the retina, and because the retina has no pain receptors the damage is completely painless and may only become obvious hours later.

Use eclipse glasses certified to ISO 12312-2. They are thousands of times darker than sunglasses. Through them you should see nothing at all except the Sun itself.
Sunglasses, smoked glass, exposed film and CDs are not filters. Neither is a phone camera held up to your eye.
Never look through binoculars, a telescope or a camera lens while wearing eclipse glasses. The optics concentrate the light and will burn straight through the filter. Any filter must be mounted on the front of the instrument.
Projection is the safest method for a group: a pinhole in card projects a small image of the crescent Sun onto a second sheet. A colander does the same trick several dozen times over.
During totality only, the filters come off. With the disc completely hidden, the corona is no brighter than the full moon and is meant to be viewed with the naked eye. Put the glasses back on at the very first hint of brightening.
Outside the path there is never a safe moment, because the Sun is never fully covered. Annular and partial eclipses require filters from beginning to end.

Why Everybody Sees It at a Different Clock Time

Eclipse tables are published in UTC, and for a solar eclipse the conversion is only half the job. Unlike a lunar eclipse, which is a single instant for the whole planet, a solar eclipse is a shadow in motion: the contact times belong to a place, not to the event. Two towns 400 km apart along the same path can be twenty minutes apart in local circumstances, quite apart from any difference in their time zone offset.

The total eclipse of 12 August 2026 is a clean illustration. Greatest eclipse falls at about 17:46 UTC out in the North Atlantic, after the shadow has crossed Greenland. Working outwards from that single UTC moment:

Where	Offset in August	Roughly when totality arrives
Reykjavik and western Iceland	UTC+0 all year	Shortly before 18:00 local, with the Sun still well up
Northern Spain: Oviedo, Bilbao, Zaragoza, Valencia	UTC+2 on summer time	Around 20:30 local, with the Sun only a few degrees above the horizon
Elsewhere in Europe, including Madrid	UTC+1 or UTC+2	A partial eclipse in the early evening

Iceland keeps UTC year-round and never puts its clocks forward, while Spain is two hours ahead of UTC in August because of daylight saving time. The same physical instant therefore carries two clock readings two hours apart, and the low Sun in Spain is a genuine planning problem: at that altitude a single ridge or bank of cloud on the western horizon takes the whole event away. The offsets that apply across the continent are set out in Time Zones in Europe Explained, and the abbreviations used in eclipse bulletins in Time Zone Abbreviations Explained. How low the Sun sits at a given hour, and how much the atmosphere lifts it above where it really is, is the subject of Sunrise, Sunset and Twilight Explained.

Approximate times are fine for planning a trip and useless at the roadside. Before the day, look up the contact times for the exact spot you intend to stand on, and check the current local offset on the city clock page for wherever you are travelling — especially if you cross a time zone on the way there, as described in Understanding Flight Times Across Time Zones. The conversion is set out step by step in How Astronomical Events Are Converted to Local Time.

The Next Solar Eclipses

Date (UTC)	Type	Path
12 August 2026	Total	Eastern Greenland, western Iceland, northern Spain
6 February 2027	Annular	Chile, Argentina and the South Atlantic
2 August 2027	Total	Southern Spain, Morocco, Algeria, Libya, Egypt, Saudi Arabia
26 January 2028	Annular	Ecuador, Peru, Brazil, then Spain and Portugal at sunset
22 July 2028	Total	Western and eastern Australia, including Sydney, then southern New Zealand
1 June 2030	Annular	North Africa, Greece, Turkey, Russia, China and northern Japan
25 November 2030	Total	Southern Africa and southern Australia

The 2027 event is the one to keep in mind. Its shadow lingers for just over six minutes near Luxor in Upper Egypt — among the longest stretches of totality anyone now alive will see from dry land — and it crosses a belt of desert with some of the most dependable August skies on the planet. Cairo lies just outside the path. Australia, meanwhile, is extraordinarily lucky in the late 2020s: 2028 puts totality directly over Sydney, and Auckland is close enough to make the trip trivial.

Frequently Asked Questions

What is a solar eclipse?

It is the Moon passing between the Earth and the Sun at new moon, throwing its shadow onto part of the surface. Inside the narrow umbral shadow the Sun disappears entirely; in the far wider penumbra around it, only part of the Sun is covered.

What is the difference between a total and an annular eclipse?

Distance. When the Moon is closer to the Earth it looks slightly larger than the Sun and hides it completely, giving a total eclipse. When it is further away it looks slightly smaller, leaving a brilliant ring of sunlight around it. An annular eclipse never gets dark and never becomes safe to view without a filter.

How long does a total solar eclipse last?

Totality usually runs for two to four minutes and can never exceed about seven and a half. The partial phases either side add roughly an hour each, so the complete event takes two to three hours from first to last contact.

Is it ever safe to look at a solar eclipse without glasses?

Only during totality, when the disc of the Sun is completely covered, and only if you are inside the path of totality. At every other moment, and everywhere outside that path, you need filters certified to ISO 12312-2 or a projection method. Sunglasses are never sufficient.

How often does a total solar eclipse happen in the same place?

On average about once every 375 years for any given location, even though one occurs somewhere on Earth roughly every 18 months. The path of totality is only a couple of hundred kilometres wide, so it takes centuries to sweep over the same ground again.

Why do eclipse tables use UTC instead of local time?

Because a solar eclipse crosses many countries and time zones within a couple of hours, and no local clock could describe it for everyone. Published contact times are given in UTC for each point on the path, and you convert them to the offset of the place you will be watching from.