Most people know a total lunar eclipse turns the Moon blood red. Far fewer know that a complete eclipse event unfolds across six distinct contact points spanning three to six hours — and that the blood moon is just one act in a much longer sequence. Whether you are preparing to observe an upcoming eclipse or simply want to understand what the timing numbers in a prediction table actually mean, this guide covers every phase in the sequence, from the first whisper of Earth's shadow to the last.
Why Lunar Eclipses Unfold in Phases
Earth does not cast a single clean shadow into space. It casts two nested zones: the umbra, a dark inner cone where Earth completely blocks the Sun's light, and the penumbra, a much larger outer cone where Earth only partially blocks the Sun. The Moon's path through these zones — which differ in darkness, size, and depth — is what creates the distinct phases of a lunar eclipse.
As the Moon moves through its orbit at roughly 1.03 km per second, it crosses each shadow boundary at a measurable moment. Astronomers call these moments contact points, and they define the beginning and end of each eclipse phase with precision. Every lunar eclipse prediction table you will ever read is built around these contacts.
The two shadow zones also explain why not every full moon produces an eclipse. The Moon's orbit is tilted about 5° relative to Earth's orbital plane, so most full moons pass above or below both shadows entirely. An eclipse only occurs when the full moon falls close enough to a lunar node — one of the two points where the Moon's orbit intersects Earth's orbital plane — for the shadows to align.
The Six Contact Points: P1, U1, U2, U3, U4, P4
A total lunar eclipse has six contact points. Partial eclipses have four. Penumbral eclipses have just two. Each contact point marks a precise geometric moment: the instant the Moon's limb becomes tangent to a shadow boundary. Here is what each one means and what observers can expect to see.
Earth's outer shadow first touches the Moon's limb. This is the official start of the eclipse event, but it is nearly impossible to detect by eye. The penumbra is a diffuse, partial shadow — the Moon loses only a small fraction of its brightness, and the effect is invisible without careful comparison to pre-eclipse brightness. Casual observers have no reason to go outside yet.
Earth's dark inner shadow first touches the Moon's eastern limb. This is the moment most observers notice something is happening. A distinct, curved dark bite begins to appear on the Moon's edge — unmistakable even to the naked eye. The contrast between the umbral shadow and the sunlit portion is sharp and dramatic. This is the moment to step outside.
The Moon's entire disk is now within Earth's umbra. The last sliver of direct sunlight vanishes from the lunar limb, and the blood moon colour fully emerges across the whole surface. The exact shade — from pale copper to deep brick red to near-black — depends on the state of Earth's atmosphere at that moment. U2 only exists in total eclipses; partial eclipses never reach this contact.
Not a contact point per se, but the midpoint of totality. The Moon is at its closest to the centre of Earth's umbral shadow cone. Colour and darkness are at their most intense. This is when the Danjon scale rating is assessed, when astrophotographers typically take their headline shot, and when the eclipse is most visually striking. The time of greatest eclipse is always listed in prediction tables.
The mirror image of U2. The Moon's western limb begins to re-enter direct sunlight. A bright arc returns on one side while the rest of the disk remains deep red. The transition from total back to partial eclipse is one of the most dramatic visual moments in the sequence — the reappearing bright limb is dazzling against the still-darkened surface.
Earth's umbra leaves the Moon's surface entirely. The dark bite disappears and the Moon returns to its full brightness, though still within the penumbra. The dramatic portion of the eclipse is over. Only the subtle penumbral dimming remains, and for most observers this is effectively the end of the show.
Earth's outer shadow fully clears the Moon. The eclipse is officially over and the Moon returns to its normal full brightness. Like P1, this contact is not visually detectable without instrumentation. Its primary value is in calculating total eclipse duration and in establishing the complete geometric record of the event.
Which Contact Points Are Present in Each Eclipse Type
Not every eclipse has all six contacts. The table below shows which contacts apply to each eclipse type — a quick reference when reading a prediction table.
| Contact Point | Penumbral Eclipse | Partial Eclipse | Total Eclipse |
|---|---|---|---|
| P1 — Penumbral begins | ✓ | ✓ | ✓ |
| U1 — Partial begins | — | ✓ | ✓ |
| U2 — Totality begins | — | — | ✓ |
| Greatest eclipse | ✓ | ✓ | ✓ |
| U3 — Totality ends | — | — | ✓ |
| U4 — Partial ends | — | ✓ | ✓ |
| P4 — Penumbral ends | ✓ | ✓ | ✓ |
The Three Eclipse Types and Their Phase Sequences
Penumbral Lunar Eclipse
Only P1 and P4. The Moon passes through Earth's outer shadow only, never touching the umbra. The effect is a subtle dimming — often invisible without a direct comparison to a previous night. Penumbral eclipses where less than 60% of the Moon's diameter enters the penumbra are essentially undetectable to the naked eye.
Partial Lunar Eclipse
P1, U1, U4, P4. Part of the Moon enters the umbra but it never fully crosses inside. A distinct dark arc bites into the lunar surface — the most immediately recognisable visual of all eclipse types. The darkened region may show a reddish tint near the umbra's edge but no full blood moon develops.
Total Lunar Eclipse
All six contacts: P1, U1, U2, Greatest, U3, U4, P4. The Moon passes fully through Earth's umbra. The blood moon colour develops completely during U2–U3 totality. The rarest of the three types but by far the most dramatic. Every total eclipse begins and ends as a partial and penumbral eclipse along the way.
How Long Does Each Phase Last?
Eclipse duration varies considerably depending on the Moon's path through Earth's shadow. The key variable is gamma — the minimum distance between the Moon's centre and the axis of Earth's umbral shadow cone, measured in Earth equatorial radii. A gamma value near zero means the Moon passes through the shadow's centre, producing longer totality. A gamma value closer to 1 means the Moon grazes the shadow edge, producing shorter or shallower events.
| Eclipse Phase | Calculated As | Typical Range | Maximum Possible |
|---|---|---|---|
| Total penumbral duration | P4 − P1 | 2–4 hours | ~6 hours |
| Partial (umbral) duration | U4 − U1 | 1–3 hours | ~4 hours |
| Totality duration | U3 − U2 | 30–80 minutes | 107 minutes |
The longest totality recorded in the 21st century was the lunar eclipse of July 27, 2018 — 1 hour, 42 minutes and 57 seconds, very close to the theoretical maximum of 1 hour and 47 minutes. The overall event including all penumbral phases lasted nearly 4 hours.
Why is lunar totality so much longer than solar totality? Earth's umbral shadow at the Moon's distance is roughly 2.5 times the Moon's diameter. The Moon therefore has a lot of shadow to cross. Compare this to a solar eclipse, where the Moon's shadow cone barely reaches Earth's surface — totality there lasts a maximum of 7.5 minutes. The Moon's slower apparent movement through a wide shadow is the reason a lunar total eclipse is a multi-hour event rather than a minutes-long one.
Eclipse Magnitude and Gamma: Reading the Numbers Before the Event
Any serious eclipse prediction table will include two numbers that tell you how dramatic the event will be before it happens: umbral magnitude and gamma.
Umbral Magnitude
This is the fraction of the Moon's diameter immersed in Earth's umbral shadow at the moment of greatest eclipse. The scale works as follows:
- Below 0 — Penumbral eclipse. The Moon does not touch the umbra at all.
- 0 to 1 — Partial eclipse. The Moon partially enters the umbra.
- Above 1 — Total eclipse. The Moon is fully within the umbra. The higher the value above 1, the more centrally the Moon passes through the shadow, and generally the darker and more visually dramatic the totality.
Gamma
Gamma measures the minimum distance from the Moon's centre to the axis of Earth's umbral shadow, in units of Earth's equatorial radius. A gamma value near zero means the Moon passes almost exactly through the shadow centre — these are the deep, dark, long-totality eclipses. A gamma value approaching 1.0 means the Moon barely clips the umbra, producing a shallow partial eclipse. Negative gamma values indicate the Moon passes south of the shadow axis; positive values indicate north.
Quick rule of thumb: When you look up an upcoming eclipse, check the umbral magnitude first to know the type, then check gamma to gauge depth. An umbral magnitude of 1.4 with a gamma of 0.1 means a deep, central total eclipse with long totality. An umbral magnitude of 0.6 with a gamma of 0.8 means a partial eclipse where only a modest arc will darken.
The Danjon Scale: Rating Eclipse Darkness
During a total lunar eclipse, the Moon's colour and brightness during totality can vary enormously from one event to the next. The amount of refracted red light reaching the Moon depends heavily on the clarity of Earth's atmosphere — particularly the presence of volcanic aerosols, dust, and cloud cover at the terminator. The Danjon scale, devised by French astronomer André Danjon, provides a standardised way to rate this.
The most famous low-Danjon eclipse occurred in December 1992, following the June 1991 eruption of Mount Pinatubo in the Philippines. The stratosphere was still loaded with volcanic aerosols, and the Moon became so dark during totality it was nearly invisible to the naked eye — an L=0 event. Most total eclipses under normal atmospheric conditions rate between L=2 and L=4.
What You Actually See: An Observer's Timeline
Reading about contact points is one thing. Here is how a complete total lunar eclipse actually unfolds for someone standing outside watching it.
Before P1: Normal full moon
The Moon is at its brightest. If you are planning to observe the eclipse, this is the time to get your eyes adapted to the dark, set up any equipment, and note the Moon's current brightness as a baseline for detecting the penumbral dimming later.
P1 to U1: The invisible opening act
Earth's penumbra is creeping across the lunar surface. You will likely notice nothing unless the eclipse is deep and you are consciously looking. Some experienced observers can detect a very faint shading on the limb entering the shadow during the last 20–30 minutes before U1, particularly if the penumbral magnitude exceeds 0.7. Otherwise, this phase is primarily of interest for timing purposes.
U1: The moment to pay attention
The dark bite appears on the Moon's eastern limb. This is visually unmistakable even without optical aid. Watch the terminator-like shadow edge — it is distinctly curved (the curvature of Earth's shadow was one of the earliest observational proofs of Earth's spherical shape). Over the next hour, this arc expands to cover more and more of the lunar surface.
U1 to U2: The partial phase
The dark arc deepens and expands. As more of the Moon enters the umbra, colour begins to emerge — a brownish-red tint appears in the fully shadowed portion, distinct from the still-bright limb still in direct sunlight. The contrast between the shadowed and sunlit portions during a deep partial eclipse is striking. Surface detail becomes visible in the shadowed region as the eye adjusts.
U2: Totality begins
The last sliver of direct sunlight disappears. The blood moon fully reveals itself. Depending on the Danjon rating, the Moon may be a vivid copper-orange, a dark brick red, or in extreme cases barely visible at all. Stars and the Milky Way become visible around the Moon as it darkens — a dramatic environmental change. The sky around a totally eclipsed Moon can be dark enough for deep-sky observing.
Greatest eclipse
The deepest, darkest moment. Colour saturation is at its peak. If you are photographing, this is your primary target. Note the colour as objectively as you can for a Danjon rating — this is also when to start checking whether the colour is closer to L=2 brick red or L=4 bright copper.
U3: Totality ends
A brilliant white arc blazes back onto the Moon's western limb. The contrast between the reappearing bright edge and the still-dark totality surface is one of the most visually dramatic moments of the entire event — many observers find U3 more striking than the onset of totality.
U3 to U4: Second partial phase
The reverse of U1–U2. The umbral shadow retreats across the surface, the dark bite shrinks, and the Moon's full brightness returns. The geometry is a mirror image of the first partial phase.
U4 to P4: Penumbral fade-out
The Moon is back to full brightness in terms of any obvious visual effect. The penumbra is still present but undetectable without comparison. For most observers the eclipse is over at U4. Stay out a few minutes longer if you want to experience the official end of the event at P4, but do not expect to see it happen.
Are Penumbral Eclipses Worth Watching?
This question comes up every time a penumbral eclipse is announced. The honest answer: it depends on depth.
A penumbral eclipse where less than 60% of the Moon's diameter enters the penumbra is essentially invisible — not a practical observing target. Many are barely mentioned even in astronomy publications because there is genuinely nothing to see without instruments.
A deep penumbral eclipse — where the Moon enters the inner penumbra and comes close to the umbral boundary — can show a distinct and obvious darkening on the limb nearest the umbra. The shading is subtle but real and satisfying to observe once you know what to look for. Check the penumbral magnitude in any prediction: if it exceeds 0.9 or so, the event is worth observing.
A total penumbral eclipse — where the Moon lies entirely within the penumbra without entering the umbra — is genuinely rare, representing only about 3% of all penumbral eclipses. These events produce a striking, uniform dimming across the entire lunar disk, distinctly different in character from a normal full moon. They are worth setting an alarm for.
How to Read a Lunar Eclipse Prediction Table
NASA, the US Naval Observatory, and Fred Espenak's EclipseWise all publish detailed contact time tables for every eclipse. Here is how to read them.
The contact time columns
Tables list the UTC times for each contact point in order: P1, U1, U2, Greatest, U3, U4, P4. For penumbral-only eclipses, only P1, Greatest, and P4 will appear. For partial eclipses, U1, Greatest, and U4 will be listed without U2 and U3. Converting to your local timezone is straightforward: subtract 3.5 hours from UTC for NST, subtract 4 for EDT, subtract 5 for CDT, subtract 7 for MDT, subtract 8 for PDT.
The gamma column
As discussed above, gamma near zero means a deep, central eclipse with long totality. Gamma above 0.9 means the eclipse barely qualifies as total. Negative gamma means the Moon passes south of the shadow axis; this affects which limb enters the shadow first but does not change the overall character of the eclipse.
The magnitude columns
Most tables list both penumbral magnitude and umbral magnitude. For casual observers, the umbral magnitude is the number to check: above 1.0 means total, 0–1.0 means partial, below 0 means penumbral only.
Visibility
A contact time being listed does not mean you can see it. If U2 occurs at 14:00 UTC and the Moon is below your horizon at that time, you will miss totality regardless of how vivid the eclipse is. Always check whether the Moon is above the horizon at your location for each contact time. Eclipse maps from NASA show the geographic visibility zone for each phase.
Frequently Asked Questions
U1 marks the moment Earth's umbral shadow first touches the Moon's outer limb — the start of the partial eclipse, when a dark bite first appears. U2 marks the moment the Moon's entire disk is inside the umbra — the start of totality. U1 is the first umbral contact; U2 is when the last sliver of direct sunlight disappears and the blood moon colour is complete.
The total event from P1 to P4 typically spans 3–6 hours. Totality itself (U2 to U3) usually lasts 30 minutes to just over an hour, with an absolute maximum of 107 minutes. The partial phases on either side of totality each last roughly an hour. The penumbral phases at the start and end of the event add further time but are not visually significant.
Earth's atmosphere refracts (bends) sunlight around the planet's curvature, projecting it into the umbral shadow cone. The same Rayleigh scattering that produces red sunrises and sunsets strips blue wavelengths from this refracted light, leaving only red and orange. The light reaching the Moon during totality is essentially the combined glow of every sunrise and sunset happening simultaneously around Earth's circumference.
Eclipse magnitude is the fraction of the Moon's diameter immersed in Earth's shadow at greatest eclipse. For umbral magnitude: a value below 0 means penumbral only, 0 to 1 means partial, and above 1 means total. A value of 1.2 means 120% of the Moon's diameter is inside the umbra — the Moon is fully inside with room to spare on either side.
Gamma is the minimum distance from the Moon's centre to the axis of Earth's umbral shadow cone, measured in Earth equatorial radii. A value near zero means the Moon passes almost through the shadow's centre — producing deep, dark, long-totality eclipses. A value near 1 means the Moon grazes the shadow edge. Positive gamma means the Moon passes north of the shadow axis; negative means south.
Total lunar eclipses make up about 29% of all lunar eclipses. In a given century there are typically 85 total lunar eclipses, alongside roughly 57 partial and 86 penumbral events. From any fixed location on Earth, a total lunar eclipse is visible on average once every two to three years — considerably more often than a total solar eclipse, which repeats at the same location only once every few centuries.
No. Whether an eclipse is penumbral, partial, or total is determined entirely by the geometry of the Moon's path through Earth's shadow for that specific event. The classification is fixed before the eclipse begins. A partial eclipse with a gamma value of 0.5 will not suddenly become total — the Moon follows a fixed orbital path through the shadow, and it has been computed precisely centuries in advance.
A central lunar eclipse is a total eclipse in which the Moon passes through or very close to the centre of Earth's umbra — a gamma value near zero. These are the deepest, longest, and darkest total eclipses. Roughly 59.6% of all total lunar eclipses are central. Non-central total eclipses still produce the blood moon effect but with shorter totality and generally brighter appearance.
Related reading on MoonPhase.Today:
→ Moon Phases and Lunar Eclipses Explained — the science of why eclipses happen, Earth's shadow geometry, and the Saros cycle in depth
→ Lunar Eclipse Schedule — dates, contact times, and visibility maps for upcoming lunar eclipses
→ Current Moon Phase — live moon phase data, rise and set times, and illumination for your location
→ When Is the Next Full Moon? — lunar eclipses can only occur at full moon; use this to track upcoming full moons