Eclipse Control Center

Never look at any part of the Sun's bright surface without certified solar filters. That includes every moment of a partial eclipse, the whole of an annular eclipse, and both sides of totality. The only exception is totality itself, seen from inside the path of a total eclipse, and only for as long as the Sun is completely covered. A lunar eclipse needs no protection at all.

On this page

Your contact times

The five contacts are the spine of an eclipse, and they belong to a place rather than to a date. Your first contact can fall well over an hour from the moment of greatest eclipse quoted in headlines, which is why the clock at the top of the console counts to your next milestone and not to a single global instant.

Readiness board

The launch-control habit of polling every station in turn, applied to an eclipse. Each row answers for itself, and one of them can never be green.

Answers, right now

The questions people actually type during an eclipse, answered from the console's own state rather than from a fixed paragraph. These change as the clock moves.

The family it belongs to

Eclipses come in families. One Saros later, 18 years 11 days and about 8 hours, the Sun, Moon and node return to nearly the same arrangement and produce a very similar eclipse. The extra 8 hours is a third of a day, so Earth has turned an extra third of a turn and the path lands roughly 120 degrees of longitude further west.

Walk a whole series, member by member, with the Saros calculator.

How to read the console

The three views

All three are the same instant seen three ways, and they stay locked to one clock, so whichever you promote to the main stage the other two keep running beside it.

• Sky view shows what you would see from your own location: the Sun and Moon at their true apparent sizes and true separation, oriented so that up on the canvas is your zenith. The tick marked N points to celestial north, which is what a photograph through a telescope is lined up with instead. During totality the corona and the prominences are drawn rather than predicted, because their shape follows the Sun's magnetic field on the day and cannot be derived from orbital geometry; everything else in that view can.
• Shadow view shows where the shadow is landing. For a solar eclipse it is Earth as seen from the Sun, so the rim of the visible disk is exactly the sunrise and sunset line, with the penumbra, the umbra and the central track drawn on it. For a lunar eclipse it switches to Earth's shadow drawn out at the Moon's own distance, with the Moon's path across it, which is what a lunar eclipse physically is.
• System view answers why. It looks down on the ecliptic with the line of nodes at its true orientation and the Moon at its true elongation and ecliptic latitude. Distances and body sizes in that view are not to scale and say so; the angles are real, and the angles are the whole argument.

The clock

T minus counts down, flips its sign at the event and keeps counting as T plus, in the same notation a launch broadcast uses. It targets your next contact when you have set a location and the eclipse reaches you; otherwise it targets greatest eclipse, which is a global instant in UTC. The strip also carries the plain UTC and local wall clock, because knowing how long until something happens and knowing what time it is are two different questions.

Flying to an eclipse

Live is the default and pins the clock to the wall. Choosing an eclipse and pressing Fly to it moves the clock to just before first contact at your site and lets you play forward at a minute, ten minutes or an hour per second. Every panel is a function of the clock, so nothing is faked in simulation: it is the same computation, asked about a different instant. Scrubbing back after an event is over works exactly as well as scrubbing forward before one starts.

Conventions and limits

• Contact times are shown in your device's time zone. Event dates in the tracking line are UTC.
• Altitudes quoted for the Sun and Moon include atmospheric refraction. The geometry between the two bodies deliberately excludes it, because refraction lifts two bodies half a degree apart by slightly different amounts and would otherwise stretch their separation.
• Positions come from Astronomy Engine, vendored, and are reliable for roughly the years 1700 to 2200. Outside that span the console has nothing to say.
• Coverage is obscuration, the fraction of the disk's area that is hidden. Magnitude, quoted separately, is the fraction of its diameter. They are different numbers and almanacs use both.
• This console computes geometry. It does not know the weather, and it will not pretend to.

Common questions

Is 95 percent of a solar eclipse almost as good as totality?

No, and the gap is far larger than almost anyone expects. The Sun is about 400,000 times brighter than the full Moon, so at 95 percent obscuration the uncovered sliver still delivers roughly 20,000 full Moons of light. Even at 99.9 percent it is about 400 full Moons, which is bright enough to hide the corona completely. Totality is not the last step of a gradient, it is a different event with a hard edge. If you are anywhere near the path, travel into it.

When is it safe to look at a solar eclipse without a filter?

Only during totality, and only if you are inside the path of a total eclipse. From the moment any part of the Sun's bright surface is showing, certified solar filters are required. An annular eclipse never has a safe moment, because a ring of the Sun stays uncovered the whole way through, and neither does a partial eclipse seen from outside the path. The readiness board on this page states which of those three cases applies at your own location.

Do I need eye protection for a lunar eclipse?

No. A lunar eclipse is the full Moon passing into Earth's shadow, so it is dimmer than an ordinary full Moon and never brighter. It is completely safe to watch with your eyes, with binoculars or through a telescope. Unlike a solar eclipse it is also the same event for everyone: the whole night side of Earth sees it at the same moment.

Why is there not an eclipse every month?

Because the Moon's orbit is tilted about 5 degrees to Earth's, so at most new and full Moons it passes above or below the line to the Sun. An eclipse is only possible when the Sun is near one of the two points where the two orbital planes cross, the lunar nodes. That happens twice a year, in eclipse seasons roughly 34 days long. The system view on this page draws the line of nodes at its true orientation and states how far the Sun currently sits from it.

How dark does it actually get during a partial solar eclipse?

Much less than the percentage suggests, because the eye adapts and responds to light logarithmically. Below about 90 percent obscuration most people would not notice anything at all without being told. At 95 to 98 percent the light goes flat and oddly metallic and shadows sharpen, rather like an approaching storm with no clouds. Only inside the path of totality does it reach deep twilight, about as dark as half an hour after sunset, with the planets and the brightest stars visible.

Do eclipse glasses expire?

The three year expiry printed on older packaging is obsolete. It referred to filter materials that could degrade, and modern aluminized polymer filters do not. Glasses meeting the ISO 12312-2 standard stay good indefinitely provided they are not scratched, punctured, torn or coming away from the frame, so hold them up to a bright lamp and look for pinholes before you trust them. Be aware that the standard's logo is printed on counterfeits too, so the marking alone proves nothing: buy from a supplier on the American Astronomical Society's vetted list.

One test you can do at home in ten seconds: put the glasses on indoors and look around. Through a genuine filter you should see essentially nothing, not furniture, not a window, not a ceiling light. A bare lamp filament or a car headlight should be the only thing faintly visible. If you can make out the room, you are holding sunglasses.

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

It comes down to how far away the Moon happens to be. Its distance varies by about 13 percent over a month, and its apparent size varies with it. When the Moon looks larger than the Sun it covers the disk completely and the eclipse is total. When it looks smaller, a bright ring of the Sun remains all the way around it and the eclipse is annular, which is why an annular eclipse is never safe to view unfiltered. The size comparison instrument on this page draws the two disks against each other at true relative scale for whatever moment the clock is showing.

How accurate are the times on this page?

Positions come from Astronomy Engine, the same vendored library behind the rest of this site and its API, and the contact instants come from that library's own eclipse search rather than from a separate calculation here. Its root finder works to about one second, so treat the times as good to a few seconds. Two things it cannot cover: the Moon's edge is mountainous rather than smooth, which can move the start and end of totality by a few seconds, and nothing here knows anything at all about clouds.