Moon Phases & Lunar Eclipses
Everything you need to know β the science, the mythology, how to photograph them, and when to watch the next one.
What Are Moon Phases?
The Moon generates no light of its own. Every crescent, gibbous, and full moon you've ever seen is nothing but reflected sunlight β the same sunlight that lights your day, bouncing off 38 million kmΒ² of ancient lunar rock, then travelling 384,400 km to reach your eyes.
As the Moon orbits Earth over roughly 29.5 days (a synodic month), we see different portions of its sunlit half. The geometry shifts constantly, producing the familiar cycle of eight primary phases that humans have tracked for 50,000 years.
The Eight Primary Phases
Why Doesn't the Cycle Match the Calendar Month?
A calendar month is 30β31 days; a synodic month is 29.53 days. The mismatch means full moons slowly drift through the calendar β some months see two full moons. The second is called a Blue Moon, occurring roughly every 2.5 years. The Islamic calendar is still purely lunar today, which is why Ramadan rotates through every season over a 33-year cycle.
Why Do Moon Phases Change?
The changing phases are purely a geometry problem β nothing about the Moon itself changes. No shadow from Earth darkens it during normal phases (that only happens during an eclipse). It's entirely about which part of the sunlit half faces Earth as the Moon orbits us.
The SunβEarthβMoon Geometry
The Sun illuminates exactly half the Moon at all times. From Earth, we see that half from constantly shifting angles as the Moon orbits us every 29.5 days:
- New Moon: Moon is between Earth and Sun. We see only the dark, un-illuminated side.
- Full Moon: Earth is between Moon and Sun. We see the entire sunlit face head-on.
- Quarter phases: Moon is 90Β° from the Sun as seen from Earth. Exactly half the lit side faces us.
The Terminator: The Moon's Most Dramatic Feature
The boundary between the lit and dark sides of the Moon is called the terminator. At quarter phases, the terminator runs straight down the middle and craters cast dramatically long shadows β making this the best time for telescopic observation. The full moon is the worst time for lunar detail: without shadows, the surface looks flat and washed out.
Why Do We Always See the Same Side?
The Moon is tidally locked β it rotates on its axis in exactly the same time it takes to orbit Earth. The same hemisphere always faces us. The "dark side of the Moon" isn't always dark (it receives sunlight half the time), but it is always facing away from Earth. The tidal forces that caused this locking also gradually slow Earth's rotation β billions of years ago a day was only 6 hours long.
Interactive Moon Phase Diagram
Click any Moon in the diagram below to learn about that phase. The orbit ring shows the Moon's position relative to Earth (centre) with sunlight arriving from the top.
What Is a Lunar Eclipse?
A lunar eclipse occurs when Earth moves directly between the Sun and the full Moon, casting its shadow across the lunar surface. For a few hours, the Moon darkens β and during a total eclipse, it glows an otherworldly coppery red that has terrified and fascinated humans for millennia.
The key advantage of lunar eclipses over solar ones: they're visible from anywhere on Earth where it's nighttime. No narrow path of totality to chase. If the Moon is above your horizon, you can watch it.
Earth's Two Shadows
- Umbra: The innermost, darkest cone where Earth completely blocks the Sun. The Moon turns dramatically dark and often red when it enters here.
- Penumbra: The outer shadow where Earth only partially blocks the Sun. The Moon is dimmed but not dramatically darkened β the effect is subtle.
- The entire Moon passes through Earth's umbra.
- Turns deep red, orange, or copper β the exact shade depends on atmospheric conditions. Heavy volcanic dust produces darker, brownish eclipses.
- The red colour comes from Rayleigh scattering: Earth's atmosphere filters blue light and bends red wavelengths around the planet's curvature β projecting the light of every simultaneous sunrise and sunset onto the Moon.
- Totality lasts up to 1 hour 47 minutes. The full event including partial phases spans 3β4 hours.
- Visible from the entire hemisphere of Earth facing the Moon.
- Part of the Moon enters the umbra while the rest stays in the penumbra or full sunlight.
- A distinct dark "bite" is visible on the Moon's edge β unmistakable even without optical aid.
- The darkened section may show a reddish tint near the umbra's edge.
- The Moon passes only through Earth's penumbra β no part enters the dark umbra.
- The effect is a subtle dimming. Easy to miss in light-polluted skies without knowing it's happening.
- Deep penumbral eclipses show clearly darker shading to careful observers. The most common eclipse type overall.
The Saros Cycle: Predicting Eclipses Across Centuries
Ancient Babylonian astronomers discovered something extraordinary: eclipses repeat in a cycle of almost exactly 18 years, 11 days, and 8 hours. This is the Saros cycle β one of the most elegant patterns in all of astronomy.
After one Saros cycle, the Sun, Earth, and Moon return to nearly identical geometry. Any eclipse is followed, 18 years later, by a nearly identical eclipse. Families of eclipses β called Saros series β can contain 70+ eclipses spanning over 1,200 years.
Saros Series 131 β a sample of the eclipse sequence
Each dot = one eclipse in this Saros family, spanning centuries. Hover for type and approximate year.
Why 18 Years? Three Cycles in Near-Perfect Harmony
- 223 synodic months (full moon to full moon) = 6,585.32 days
- 242 draconic months (node to node, governing eclipse possibility) = 6,585.36 days
- 239 anomalistic months (perigee to perigee, governing Moon's distance) = 6,585.54 days
The three cycles match to within hours over 18 years β so the eclipse geometry nearly repeats exactly. The 8-hour offset means each successive eclipse occurs about 120Β° further west on Earth. It therefore takes three Saros cycles (54 years, 34 days β an "Exeligmos") for an eclipse to return to roughly the same geographic location.
Solar & Lunar Eclipse: Live Orbital Animation
Watch the Moon orbit Earth in real time. The animation automatically shows a lunar eclipse when the Moon reaches the full moon position β and a solar eclipse when it passes through new moon. Use the speed controls to explore the geometry.
When Do Eclipses Happen?
If every full moon produced a lunar eclipse, we'd have one every month. The reason we don't: the Moon's orbit is tilted 5.1Β° relative to Earth's orbital plane. Most full moons pass above or below Earth's shadow entirely. An eclipse only happens when a full moon occurs near one of two points where the Moon's orbit crosses the ecliptic β called lunar nodes.
Eclipse Seasons Explained
Twice a year β about 6 months apart β the Sun aligns with the Moon's nodes. During these roughly 34-day windows, any full moon close enough to a node will produce an eclipse. Each season can produce one or two lunar eclipses; in some years there are three, in others only subtle penumbral ones that most people miss entirely.
The Precessing Nodes
The lunar nodes aren't fixed. They slowly drift westward (precess) along the ecliptic, completing one full revolution every 18.6 years β the same nodal cycle that drives the Saros period. This cycle also causes a measurable wobble in Earth's axial tilt that affects long-term tidal patterns.
Who Can See It?
- Total lunar eclipses are visible from the entire hemisphere of Earth facing the Moon β roughly half the planet at once.
- Partial eclipses are equally widely visible, though partial phases may begin or end around moonrise/moonset for some locations.
- Duration: The penumbral phase begins and ends 2β3 hours before and after totality. Totality itself can range from a few minutes to nearly 2 hours.
- Weather is the real enemy: A perfectly placed observer under thick cloud sees nothing. Always check your local forecast.
Upcoming Lunar Eclipses
Here are the next significant lunar eclipses from today (April 2026). For a full schedule with exact local times, visit moonphase.today/eclipses.
A partial lunar eclipse where a portion of the Moon enters Earth's umbra. A clear dark shadow bites into the Moon's face β easily visible and photographable without any equipment. Maximum umbral depth around 35%.
A spectacular New Year's Eve total lunar eclipse. Visible across Europe, Africa, Asia, and Australia β the decade turns with a blood moon in the sky. One of the most geographically well-placed total eclipses of the decade.
A deep total lunar eclipse with a long totality window, well-placed for observers across the Americas, Europe, and Africa. One of the best-positioned total lunar eclipses of the coming decade.
The Moon in Mythology & Human Culture
Long before science explained it, humanity watched the Moon with wonder, fear, and reverence. Every civilisation developed stories to explain its phases and the terrifying spectacle of an eclipse. These weren't primitive superstitions β they were humanity's first attempts at astronomy, and many cultures produced remarkably accurate eclipse predictions centuries before the telescope.
How to Photograph the Moon & Lunar Eclipses
Lunar photography is one of the most accessible branches of astrophotography. A full moon is bright enough to capture with a smartphone; a blood moon during totality rewards a DSLR with careful exposure work and a tripod.
Use pro/manual mode. Lock focus and exposure on the Moon, reduce EV by 1.5β2 stops. Use a tripod or stable surface. Turn off Night Mode β it overexposes the Moon badly.
The Looney 11 Rule: at f/11, set shutter to 1/ISO. At ISO 100 β 1/100s at f/11. Use mirror lock-up and a remote shutter release to eliminate camera shake.
During totality the Moon is up to 10,000Γ dimmer. Open aperture wide, raise ISO significantly, and bracket exposures β totality colour ranges from bright orange to nearly invisible dark brown.
Use an intervalometer to capture a frame every 5β10 minutes across the full eclipse on a fixed tripod. Stack the images in post to show all stages in one dramatic composite.
The Moon appears largest near the horizon (the Moon illusion). Include a silhouetted foreground for scale. Use a telephoto lens for dramatic compression. Plan with The Photographer's Ephemeris.
Mount your phone at the telescope eyepiece. A phone adapter costs under $20 and can produce stunning surface shots showing craters only a few km across. Best at first or last quarter.
Post-Processing Tips
- Sharpening: Apply targeted sharpening β the Moon has extreme fine detail. Avoid over-sharpening which creates halos around crater rims.
- Hidden colour: Boost saturation 300β400% to reveal real mineral variation β blue-grey basalt seas, orange-gold highland regions, turquoise rays from young craters.
- Blood moon: Shoot RAW and adjust white balance in post. The reddish-orange cast is real β let it reflect the true colour of that specific eclipse.
- Stacking: Capture 30β50 frames and stack with free software (AutoStakkert, Registax) to dramatically reduce noise and increase sharpness.
Moon Phases vs. Lunar Eclipses at a Glance
Two related but entirely distinct phenomena, side by side:
| Feature | Moon Phases | Lunar Eclipses |
|---|---|---|
| Cause | Changing geometry β which part of the Moon's sunlit half faces Earth as it orbits | Earth passes directly between Sun and Moon, casting its shadow onto the lunar surface |
| Frequency | 8 phases every 29.5 days β completely regular, every month without exception | 0β3 per year; only when a full moon occurs near a lunar node |
| Alignment | None needed β happens continuously as a result of normal orbital motion | Precise SunβEarthβMoon alignment at a lunar node during eclipse season |
| Duration | Each phase lasts 3β4 days; transitions are continuous and gradual | Entire event 3β6 hours; totality up to 1h 47min |
| Appearance | Gradual cycle: invisible new moon β crescent β half β gibbous β full β back | Moon darkens and may turn red/orange/brown during umbral phases |
| Visibility | Anywhere on the nighttime side of Earth | Entire hemisphere facing the Moon β but only where Moon is above the horizon |
| Eye safety | Completely safe at all times | Completely safe β unlike solar eclipses, no special protection needed |
| Predictable? | Perfectly predictable centuries ahead | Predictable centuries ahead using Saros cycles |
Frequently Asked Questions
Staying in Sync with the Moon
The Moon is the most accessible object in the night sky β no equipment, no dark site, no special training required. Its phases mark time as reliably as any clock, and its eclipses offer some of the most dramatic free spectacles in nature.
Understanding the geometry behind phases transforms the Moon from a pretty light into a comprehensible, predictable, magnificent system. Knowing when the next blood moon rises over your horizon turns an ordinary Tuesday into an event worth staying up for.
Whether you're a first-time skywatcher or a seasoned astrophotographer, the Moon rewards attention. Every phase, every eclipse, every terminator line across a crater wall is part of a pattern humanity has watched, recorded, and marvelled at for 50,000 years.