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The Lunar 100: Your Complete Field Guide to the Moon's Greatest Features
There is a whole cosmos of detail hidden on the surface of the Moon — and most observers never see it. The Lunar 100 is the definitive observing list for anyone ready to go beyond simply tracking moon phases. Created by planetary scientist Charles Wood for Sky & Telescope magazine, it is often called "the Moon's answer to the Messier List" — a curated challenge of 100 increasingly difficult targets, from the Moon itself (L1) to the barely-visible magnetic swirls of Mare Marginis (L100).
This interactive map and field guide gives you everything you need: real-time phase data, feature-by-feature spotlights, a phase-by-phase observing planner, and expert tips to get the most out of every clear night. Use the interactive map above to highlight any feature on a live lunar surface, then use this guide to know exactly what you are looking for and when.
What Is the Lunar 100?
The Lunar 100 is a structured observing challenge covering the 100 most scientifically significant and visually compelling features on the lunar surface. Unlike casual Moon-gazing, working through the Lunar 100 teaches you to read the Moon as a landscape — understanding how impact basins formed the maria, how rilles trace ancient lava channels, and how mountains on an airless world cast crisp geometric shadows you can measure with a ruler.
Each entry is assigned a number from L1 to L100, ordered roughly by observational difficulty. L1 is the Moon itself — visible to the naked eye. L100 is the Mare Marginis swirls, requiring a large aperture, maximum eastern libration, and ideal illumination. Even experienced observers only tick it off once or twice a year. The journey between those two extremes is a semester's worth of genuine lunar science.
The original list was published by Charles A. Wood, a former NASA scientist and one of the world's foremost lunar geologists. Wood designed it deliberately: each feature was chosen not just for visual impressiveness, but for what it reveals about the Moon's geological history. When you find Theophilus, Cyrillus, and Catharina (L8) lined up across Mare Nectaris, you are reading three craters at different stages of degradation — a geological timeline laid out in one field of view.
"The Lunar 100 teaches you to read the Moon as a geologist reads a rock face — every crater, every rille, every ray system is a chapter in a 4.5-billion-year story written in silence."
The Three Difficulty Tiers
Think of the Lunar 100 in three broad tiers. These are not official divisions but a practical framework used by experienced observers worldwide.
L1 – L30 · Naked Eye & Small Scopes
The Moon's headline features. Every item here is achievable with binoculars or a modest 60–80mm refractor on your first few outings.
- L1 – The Moon (naked eye)
- L2 – Earthshine (naked eye)
- L4 – Apennine Mountains
- L6 – Tycho
- L10 – Mare Crisium
- L15 – Straight Wall (Rupes Recta)
- L17 – Schröter's Valley
- L25 – Messier & Messier A
L31 – L70 · 4–8" Telescopes
This tier rewards a 100–200mm telescope and careful timing with the terminator. Many features only reveal themselves under very low-angle lighting.
- L34 – Lacus Mortis
- L42 – Marius Hills (volcanic domes)
- L47 – Alphonsus Dark Spots
- L51 – Davy Crater Chain
- L57 – Reiner Gamma (swirl)
- L66 – Hadley Rille (Apollo 15)
L71 – L100 · Large Aperture & Libration
The toughest targets demand 8"+ aperture, exceptional atmospheric seeing, and precise timing with libration. Each one is a genuine achievement.
- L75 – Ptolemaeus B
- L80 – Orientale Basin
- L83 – Plato Craterlets
- L87 – Humboldt
- L91 – De Gasparis Rilles
- L100 – Mare Marginis Swirls
How to Use the Lunar 100: A Phase-by-Phase Observing Planner
The most important rule of Lunar 100 observing is this: the phase determines everything. The Moon you see on a waxing crescent night is a completely different world from the Moon at full phase — different features are lit, different shadows appear, and different targets become accessible.
Check the current moon phase before each session, then use the interactive map above to confirm which features are currently near the terminator — the line between lunar day and night is where all the contrast lives.
Waxing Crescent (Days 1–6)
The terminator sweeps across the eastern limb. Mare Crisium and the eastern highlands emerge first under extreme shadow contrast.
- L2 – Earthshine (most vivid days 2–4)
- L3 – Mare/Highland Dichotomy
- L10 – Mare Crisium (isolated eastern sea)
- L16 – Petavius (central peak & rille)
- L25 – Messier & Messier A (ricochet pair)
First Quarter (Days 7–9)
The terminator bisects the disk. Maximum shadow contrast on the Apennines and Mare Serenitatis — the single best night for mountain ranges.
- L4 – Apennine Mountains (razor shadows)
- L7 – Altai Scarp (basin rim cliff)
- L8 – Theophilus, Cyrillus, Catharina
- L20 – Posidonius (floor-fractured crater)
- L29 – Ariadaeus Rille (linear graben)
Waxing Gibbous (Days 10–13)
The terminator crosses the central nearside. Best nights for rilles, the Straight Wall, and the great southern craters.
- L6 – Tycho (rays beginning to emerge)
- L9 – Clavius (arc of decreasing craters)
- L15 – Straight Wall (Rupes Recta)
- L19 – Alpine Valley (linear graben)
- L24 – Hyginus Rille (collapse chain)
Full Moon (Days 14–15)
Shadow depth vanishes but ray systems and albedo features explode into visibility. The best night for swirls, rays, and colour contrasts.
- L5 – Copernicus (full ray system)
- L11 – Aristarchus (brightest point on Moon)
- L17 – Schröter's Valley
- L22 – Aristarchus Plateau
- L57 – Reiner Gamma (bright magnetic swirl)
Waning Gibbous (Days 16–19)
The western features gain shadow in reverse. Gassendi, Schiller, and the limb basins come into their best relief.
- L13 – Gassendi (floor-fractured, rilles)
- L30 – Schiller (elongated oblique crater)
- L36 – Grimaldi Basin (very dark floor)
- L43 – Wargentin (lava-filled plateau)
- L80 – Orientale Basin (if libration favors)
Last Quarter & Waning Crescent (Days 20–28)
The pre-dawn sky belongs to advanced observers. Western limb features are perfectly lit and seldom-studied craters reward the patient.
- L66 – Hadley Rille (Apollo 15 site)
- L77 – Sirsalis Rille (longest rille on Moon)
- L87 – Humboldt (radial floor fractures)
- L91 – De Gasparis Rilles (complex system)
- L100 – Mare Marginis Swirls (final target)
6 Must-See Lunar 100 Features — And What Makes Them Special
With 100 features to explore, knowing where to start matters. These six entries span the full difficulty range and represent six completely different types of lunar geology.
Tycho
Only 108 million years old — a geological infant. Tycho's ray system stretches over 1,500 km in every direction, a frozen snapshot of a catastrophic collision during the age of the dinosaurs. The central peak is visible in binoculars at full Moon.
Straight Wall (Rupes Recta)
One of the Moon's great geological illusions. This 110 km fault scarp drops only ~400 m — a slope gentle enough to walk up — yet appears razor-sharp under a low sun as a fine dark line slicing across Mare Nubium.
Hyginus Rille
A rille unlike any other — it contains a chain of rimless collapse pits rather than a smooth channel. Those missing rims are strong evidence of a volcanic origin: the pits collapsed inward rather than being blasted outward by impacts.
Reiner Gamma
A ghostly bright swirl on the floor of Oceanus Procellarum with no topographic relief — just brightness. It sits above a magnetic anomaly that deflects the solar wind, preventing the surface darkening that affects the surrounding mare. Its origin remains debated.
Orientale Basin
The youngest large impact basin on the Moon and the finest example of a multi-ring structure in the solar system. Seen nearly edge-on from Earth, its three concentric rings spanning 930 km are only fully accessible when western libration is at maximum.
Mare Marginis Swirls
The final target. High-albedo swirl patterns on the eastern limb caused by magnetic anomalies that deflected the solar wind and prevented the usual surface darkening. Requires 8"+ aperture, excellent seeing, and maximum eastern libration — conditions that align only a few times per year.
What Equipment Do You Need for the Lunar 100?
One of the Lunar 100's great strengths is its accessibility. You can start tonight with nothing but your eyes and still log your first entry.
Naked Eye & Binoculars
The first 30 targets require no telescope. A good pair of 10×50 binoculars reveals far more than most people expect from a hand-held instrument.
- 10×50 or 7×50 binoculars
- Stable surface or tripod adapter
- Dark-adapted eyes (20 min)
- This interactive map as your guide
60–150mm Refractor or Reflector
A modest 60–150mm telescope is the workhorse of Lunar 100 observing. A quality 4" refractor handles the majority of this tier under good skies.
- 60–150mm aperture scope
- Eyepieces: 25mm + 9mm + 4mm
- Barlow lens (2×) for high power
- Stable equatorial or alt-az mount
- Neutral density lunar filter
200mm+ Reflector or SCT
The final 30 targets demand aperture, excellent optics, and patience to wait for exceptional seeing. An 8" Dobsonian is the classic entry point.
- 200mm+ aperture (8" Dob or SCT)
- High-quality ortho eyepieces
- Seeing forecast app (Meteoblue)
- Libration calculator (LTVT or PhotoPills)
- Camera adapter (optional)
10 Expert Tips for Completing the Lunar 100
Work the terminator. The line between lunar day and night creates maximum 3D shadow contrast. Plan every session around features currently within 5° of the terminator.
Track libration. The Moon wobbles slightly each month, revealing up to 59% of its surface. Limb features like L80 and L100 are only reachable during favorable librations — plan weeks ahead.
Keep an observing log. Record date, phase, equipment, seeing conditions, and a brief sketch. Revisiting notes is how you build genuine expertise and prove completion for ALPO certification.
Seeing beats aperture. A steady 4" telescope on a night of exceptional atmospheric seeing will outperform a 12" on a turbulent night for lunar detail.
Use a red flashlight. Your eyes need 20–30 minutes to fully dark-adapt. A red light lets you read your map without ruining sensitivity for faint rilles and low-contrast features.
Target clusters, not singles. Theophilus, Cyrillus, and Catharina (all L8) tell a complete impact-degradation story in one field of view. Plan sessions around connected feature groups.
Sketch, don't just photograph. Drawing forces slow, careful looking over 5–10 minutes. Observers who sketch consistently report noticing far more detail than those who only photograph.
Let your optics cool. A telescope moved from indoors to a cold night needs 20–45 minutes to reach thermal equilibrium. Blurry images are often a warm mirror, not bad seeing.
Use multiple maps. The Rukl Atlas of the Moon is the traditional gold standard. For digital use, the USGS Moon Nomenclature Tool offers pixel-accurate feature identification.
Submit your completion. The Association of Lunar & Planetary Observers (ALPO) accepts Lunar 100 completion logs and issues a formal certificate — a recognised milestone in amateur astronomy.
Lunar 100 Frequently Asked Questions
How long does it take to complete the Lunar 100?
Realistically, 6 months to 2 years for most observers. Targets L1–L40 can be checked off in a handful of good sessions, but the advanced targets (L71–L100) require specific phase windows, libration timing, and exceptional atmospheric seeing that only aligns a few times per year.
What telescope is best for the Lunar 100?
A quality 4–6" refractor or 6–8" reflector handles the vast majority of the list. For the final tier (L71–L100), an 8–10" Dobsonian delivers the aperture needed for features like Plato Craterlets (L83) and De Gasparis Rilles (L91). A few quality fixed-focal-length eyepieces make more difference than aperture at this level.
Can I observe the Lunar 100 from a city?
Yes — unlike deep-sky observing, lunar work is almost entirely unaffected by light pollution. The Moon is so bright that urban skies are no disadvantage. Atmospheric seeing (turbulence) matters far more than darkness, and many observers complete the entire list from suburban backyards.
What is the hardest Lunar 100 target?
By consensus, L100 — Mare Marginis Swirls. It requires the Moon near full phase for maximum albedo contrast, maximum eastern libration (+7°), exceptional atmospheric seeing, and a telescope of 8" or larger. All three conditions aligning simultaneously happens only a few times per year.
What is libration and why does it matter for the Lunar 100?
Libration is the slight wobbling of the Moon caused by its elliptical orbit and axial tilt. Over each month it reveals up to 59% of the total lunar surface. For limb targets like Orientale Basin (L80) and Mare Marginis Swirls (L100), a favorable libration is the difference between a clear, detailed view and a completely unusable one.
Is there an official certificate for completing the Lunar 100?
The list was created by Charles Wood for Sky & Telescope and is not tied to a single certifying body, but the Association of Lunar & Planetary Observers (ALPO) accepts completion logs and issues an official certificate. Submit an observing log covering all 100 features with dates, conditions, and descriptions to qualify.
Ready to Start Your Lunar 100 Journey?
Check the current moon phase to see exactly where the terminator falls tonight, then scroll up to the interactive map and select your first target. Start with L6 (Tycho) or L4 (Apennines) for a dramatic first impression — or go back to the very beginning with L1 and count it as your first tick. The Moon is out there every clear night, waiting to be read.
Browse our growing library of individual Lunar 100 feature guides linked from the interactive map above — each with finder charts, geological context, and observing tips.
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