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A deep partial lunar eclipse will cover 96.3% of the Moon’s visible disk as seen from Earth, creating a spectacle that may closely resemble a total “blood moon.” But the event is more than a skywatching show: it is a natural experiment in orbital mechanics, atmospheric optics and even the techniques astronomers use to study distant exoplanets.

On the night of Aug. 27 into Aug. 28, skywatchers across the Americas will watch almost the entire full Moon slip into Earth’s shadow. At the deepest point of the eclipse, around 04:13 UTC on Aug. 28, 96.3% of the Moon’s visible disk will lie inside Earth’s umbra — the central region of shadow where our planet completely blocks the Sun. The eclipse will be particularly well placed for North and South America, while portions will also be visible from western Europe and western Africa.

It will look remarkably close to a total lunar eclipse. Most of the Moon may take on copper, orange or dark red tones while only a narrow bright segment remains directly illuminated by the Sun. Yet astronomically, the event remains a partial lunar eclipse because the Moon never becomes completely immersed in Earth’s umbra. That narrow distinction provides an unusually good opportunity to understand what a lunar eclipse actually is — and why the familiar phrase “blood moon” is ultimately a consequence of Earth’s atmosphere rather than anything happening on the Moon itself.

96.3% or 93%? Both Numbers Are Correct

Reports describing the eclipse have variously said that 93% or about 96% of the Moon will be covered. That apparent contradiction comes from two different ways astronomers measure an eclipse. NASA lists the Aug. 28 event with an umbral magnitude of 0.930. Eclipse magnitude measures how much of the Moon’s diameter enters Earth’s umbra. A magnitude of 0.930 therefore means that roughly 93% of the lunar diameter will be inside the dark central shadow at maximum eclipse. But diameter is not the same as area.

NASA’s Scientific Visualization Studio calculates an obscuration of 96.3%, meaning that 96.3% of the Moon’s visible circular disk by area will lie within the umbra. The difference results from the geometry of two overlapping circles — Earth’s shadow and the lunar disk. For ordinary observers, 96.3% is probably the more intuitive figure because it corresponds more closely to what the eye sees: almost the entire lunar surface darkened, with only a thin bright crescent remaining. This distinction also explains why calling the event “96% total” can be misleading. Lunar eclipses are not classified according to how dramatic they look. The definition is geometric: if any part of the Moon remains outside the umbra, the eclipse is partial.

What Is Actually Casting the Shadow?

A lunar eclipse occurs only at full Moon, when the Sun, Earth and Moon are arranged in approximately that order. Earth then casts two principal shadow regions into space. The outer region is the penumbra. From a point inside the penumbra, Earth blocks only part of the Sun. When the Moon enters this region, its brightness falls only slightly, and the change can be difficult to notice without careful comparison. Inside that lies the much darker umbra. From anywhere inside the umbra, the entire solar disk is hidden behind Earth. Once part of the Moon enters this region, the eclipse becomes visually obvious: a dark, curved boundary appears to move across the lunar surface.

The Aug. 27–28 event begins with a subtle penumbral phase before the Moon starts entering the umbra at about 02:34 UTC. Maximum eclipse occurs around 04:13 UTC, after which the Moon gradually emerges from the shadow. The partial umbral phase lasts about 3 hours and 18 minutes, while the entire event including the faint penumbral phases spans roughly 5 hours and 38 minutes. The curved edge of the shadow is itself a reminder of an ancient scientific insight. Aristotle noted more than two millennia ago that Earth’s shadow on the Moon during an eclipse is always curved — evidence consistent with a spherical Earth. NASA’s historical eclipse material notes that only a sphere casts a round shadow from every orientation.

If Earth Blocks the Sun, Why Does the Moon Not Become Completely Black?

This is where the most beautiful physics begins. If Earth had no atmosphere, the portion of the Moon inside the umbra would become extremely dark because Earth would block direct sunlight. But Earth has an atmosphere, and the atmosphere behaves like a vast optical filter and lens. Sunlight reaching the edge of Earth passes through a long path through the atmosphere. Shorter wavelengths — particularly blue and violet light — are scattered much more efficiently by atmospheric molecules. Longer wavelengths such as orange and red pass through more readily.

This phenomenon is known as Rayleigh scattering. It is the same reason the daytime sky appears blue and sunsets appear red. When the Sun is overhead, scattered blue light reaches us from all directions. Near sunrise or sunset, sunlight travels through a much longer path through the atmosphere, scattering much of the blue light away before it reaches an observer. What remains is enriched in red, orange and yellow wavelengths. During a lunar eclipse, something similar happens on a planetary scale. Sunlight skimming around Earth passes through its atmosphere, where the blue wavelengths are preferentially scattered. The remaining reddish light is also refracted — bent — by the atmosphere into Earth’s geometric shadow. That filtered light travels hundreds of thousands of kilometers farther to the Moon, strikes its surface and is reflected back toward Earth. So when we see a red eclipsed Moon, we are effectively seeing sunlight that has passed through the ring of Earth’s atmosphere. NASA describes the effect memorably: it is as though all of Earth’s sunrises and sunsets are being projected onto the Moon at once.

Why This Will Not Be a Full ‘Blood Moon’

“Blood moon” is a popular description rather than a formal astronomical classification and is most commonly associated with total lunar eclipses. During totality, every visible part of the Moon lies inside Earth’s umbra, so no portion of the lunar disk receives direct sunlight. The dim red and orange light filtered through Earth’s atmosphere can therefore dominate the Moon’s appearance.

The Aug. 27–28 eclipse is different. A thin portion of the Moon will remain directly illuminated even at maximum eclipse. That small area will be dramatically brighter than the reddish portion inside the shadow, producing a high-contrast appearance. NASA notes that as the illuminated portion becomes very small, observers’ eyes can adapt enough to perceive the copper-colored light on the rest of the Moon. This means the eclipse may visually resemble a total blood moon even though it technically falls just short. The phrase “almost blood moon” is therefore a useful shorthand — as long as the distinction is understood.

Why the Moon Does Not Turn Exactly the Same Color in Every Eclipse

The color of an eclipsed Moon is not fixed. One eclipse may produce a bright copper Moon. Another can appear deep red, brown or unusually dark. That variation occurs because the light reaching the Moon must travel through Earth’s atmosphere, and the atmosphere is constantly changing. Clouds can block part of the refracted light. Aerosols and dust can alter how different wavelengths are scattered or absorbed. Large volcanic eruptions that inject material into the stratosphere can make subsequent lunar eclipses significantly darker. NASA notes that the amount of dust and cloud along the atmospheric limb can strongly influence the color and brightness of an eclipse. In that sense, the Moon during an eclipse becomes a giant screen displaying information about Earth’s atmosphere. The color is not produced by lunar geology. It is a filtered optical fingerprint of our own planet.

Why Did This Lunar Eclipse Arrive Just Two Weeks After a Total Solar Eclipse?

On Aug. 12, a total solar eclipse crossed parts of Greenland, Iceland, northern Russia, Spain and a small corner of Portugal. Now, roughly two weeks later, Earth is producing a lunar eclipse. This is not coincidence. The Moon’s orbit around Earth is tilted by about 5 degrees relative to the plane in which Earth travels around the Sun, known as the ecliptic plane. If the two orbital planes were identical, Earth would experience solar and lunar eclipses every month. But because of the tilt, the Moon usually passes slightly above or below the perfect Sun-Earth-Moon alignment. There are only two points in the lunar orbit where it crosses the ecliptic plane. These are called nodes. When the Sun is positioned near one of these nodes, the geometry becomes favorable for eclipses. This period is known as an eclipse season. An eclipse season lasts long enough for both a new Moon and the following full Moon to occur near the alignment zone.

On Aug. 12, the Moon was near a node during new Moon, allowing it to pass between Earth and the Sun and produce a solar eclipse. About half a lunar cycle later, the Moon reaches full Moon on the opposite side of Earth. Because the geometry is still close to the same eclipse season, Earth can then cast its shadow onto the Moon. This is why solar and lunar eclipses often arrive in pairs — and occasionally even in groups of three. The August 2026 pair is essentially the same orbital alignment viewed from opposite sides of Earth.

Solar and Lunar Eclipses Are Mirror Images of the Same Geometry

A solar eclipse and a lunar eclipse can be understood as complementary events.

During a solar eclipse: Sun → Moon → Earth

The Moon casts its shadow onto Earth.

During a lunar eclipse: Sun → Earth → Moon

Earth casts its shadow onto the Moon.

The difference has a major consequence for visibility. The Moon’s umbral shadow reaching Earth during a total solar eclipse covers a relatively narrow path. That is why observers must travel to a specific corridor — the path of totality — to experience totality. Earth’s shadow at the Moon, however, is much larger than the Moon itself. And everyone located on Earth’s nighttime hemisphere who has the Moon above the horizon is effectively looking at the same eclipsed Moon. NASA therefore notes that a lunar eclipse can be visible from roughly half of Earth, making it accessible to vastly more people than any individual total solar eclipse.

Why the Americas Have the Best View This Time

The timing places the Americas particularly well. Maximum eclipse occurs near 04:13 UTC on Aug. 28, corresponding to roughly 12:13 a.m. EDT in New York and 9:13 p.m. PDT on Aug. 27 in Los Angeles. For the eastern United States and Canada, the Moon will be high in the nighttime sky around maximum eclipse. Across much of the western United States, the eclipse will already be underway near moonrise, producing the possibility of seeing a deeply eclipsed Moon low over the horizon.

South America also receives favorable visibility. Western Europe and parts of Africa can see portions of the event toward the morning of Aug. 28, but the Moon will be lower in the western sky as sunrise approaches. Much of East Asia, including Korea and Japan, will miss the event because the Moon will not be favorably positioned above the nighttime horizon during the eclipse. NASA lists the primary visibility region as the eastern Pacific, the Americas, Europe and Africa. Globally, billions of people could potentially see at least part of the eclipse if weather permits. AP reporting estimates that the Americas alone place close to a billion people in a particularly favorable viewing region.

Why Lunar Eclipses Are Safe to Watch

A lunar eclipse requires no protective glasses. Observers are looking at the Moon, which is reflecting sunlight rather than viewing the Sun directly. That makes lunar eclipses fundamentally different from solar eclipses. During most phases of a solar eclipse, looking directly at the Sun without certified solar filters can permanently damage the retina. No such hazard exists during a lunar eclipse. The event can be observed safely with the naked eye, binoculars or a telescope. NASA recommends binoculars or a small telescope mainly because magnification makes the moving edge of Earth’s shadow and the changing colors easier to see. Dark skies are helpful but not essential because the Moon itself is bright. However, moving away from strong city lighting can improve the eye’s dark adaptation and make the faint reddish regions more noticeable.

A Lunar Eclipse Is Also an Experiment on Earth’s Atmosphere

Astronomers have used lunar eclipses for much more than visual observation. Because sunlight reaching the eclipsed Moon has passed through Earth’s atmosphere, scientists can analyze its spectrum and determine which wavelengths were absorbed by atmospheric gases. This creates a remarkable analogy with the way astronomers study the atmospheres of exoplanets. When a distant planet passes in front of its star, a small amount of starlight passes through the planet’s atmosphere. Molecules in that atmosphere absorb specific wavelengths, creating spectral fingerprints that can reveal gases such as water vapor, methane or carbon dioxide. During a lunar eclipse, Earth itself effectively becomes the transiting planet.

Researchers analyzing eclipsed moonlight have detected signatures associated with oxygen, ozone, water vapor, carbon dioxide and methane in Earth’s transmission spectrum. A landmark Nature study demonstrated that lunar-eclipse observations could reproduce the type of atmospheric spectrum astronomers would seek from a distant Earth-like planet. The Hubble Space Telescope has even used lunar eclipse observations to study Earth as though it were an exoplanet, detecting the spectral signature of ozone after sunlight had passed through our atmosphere and reflected from the Moon. In other words, watching a blood-red Moon is connected directly to one of modern astronomy’s biggest questions:

How could we recognize another Earth from light alone?

The Eclipse Can Also Reveal How Fast the Moon Cools

The rapid disappearance of sunlight during an eclipse creates another scientific experiment. The Moon has essentially no substantial atmosphere to redistribute heat. When a region of the lunar surface enters Earth’s shadow, solar heating suddenly drops, and the temperature of the surface can fall rapidly.

NASA’s Lunar Reconnaissance Orbiter uses its Diviner radiometer to study how different regions of the lunar surface respond to these abrupt temperature changes. NASA notes that lunar eclipses provide unique opportunities for Diviner measurements while most other instruments aboard the solar-powered spacecraft are shut down to conserve energy. Different rocks and soils cool at different rates, so thermal measurements can provide clues about material properties of the lunar surface. An eclipse that looks like a simple shadow to the human eye therefore becomes, for planetary scientists, a controlled experiment in lunar thermophysics.

This Eclipse Is Part of a Much Longer Orbital Cycle

The Aug. 27–28 eclipse belongs to Saros Series 138. A Saros is a repeating eclipse cycle of approximately 18 years, 11 days and eight hours. After that interval, the relative geometry of the Sun, Earth and Moon becomes sufficiently similar for another eclipse from the same series to occur. The previous lunar eclipse in Saros 138 occurred on Aug. 16, 2008. The next will occur on Sept. 7, 2044. The additional eight hours in the Saros period is important. Because Earth rotates by roughly one-third of a day during those eight hours, successive eclipses in a Saros tend to be visible from different longitudes. This is why eclipse cycles can be highly predictable without producing exactly the same experience from the same location every 18 years. Celestial mechanics is repetitive — but never completely static.

The Next Total Lunar Eclipse Is Still More Than Two Years Away

Because this eclipse narrowly misses totality, observers wanting to see the Moon completely immersed in Earth’s umbra will have to wait. NASA’s current eclipse catalog lists the next total lunar eclipse for Dec. 31, 2028, visible across large parts of Europe, Africa, Asia, Australia and the Pacific. That makes the August 2026 event especially notable: it is close enough to totality to produce many of the visual effects associated with a blood moon while preserving the bright sliver that reveals exactly where the line between partial and total eclipse lies.

More Than a Red Moon

For casual observers, the Aug. 27–28 eclipse will be an opportunity to watch most of the Moon turn dark copper beneath Earth’s shadow. But the event contains several layers of physics at once. The 5-degree tilt of the Moon’s orbit explains why eclipses are occasional rather than monthly. The geometry of the umbra explains why 96.3% coverage is still not totality. Rayleigh scattering explains why the eclipsed Moon becomes red. Atmospheric refraction allows sunlight to reach a Moon that sits geometrically inside Earth’s shadow. The timing of the eclipse after the Aug. 12 solar eclipse reveals the structure of an eclipse season. And the filtered light reaching the Moon can even be used to study Earth’s atmosphere in ways that resemble the search for habitable planets around distant stars. A lunar eclipse therefore is not simply the moment when Earth blocks sunlight from reaching the Moon. It is a visible demonstration of the geometry, optics and atmospheric physics connecting three worlds — the Sun, Earth and Moon. And on Aug. 27–28, almost the entire lunar surface will become the screen on which those laws of physics are displayed.

The lead image at the top of this article illustrates the Aug. 27–28 near-total lunar eclipse, highlighting its 96.3% obscuration, Earth’s umbra and penumbra, and the atmospheric scattering and refraction that give the Moon its reddish appearance. The lead image was generated using generative AI with ChatGPT.