iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
The Moon’s radius is decreasing by an estimated 6–11 centimeters per million years—about 0.1 micrometers (0.0001 millimeters) per year if the long-term average has remained constant. That is imperceptibly slow on a human timescale, but the contraction still compresses the lunar crust, activates faults and can produce shallow moonquakes.
How fast is the Moon shrinking?
The best current geological estimate is a loss of 6–11 centimeters of radius per million years. Expressed annually, that is approximately 0.1 micrometers per year, or 0.0001 millimeters. The figure is not a year-by-year measurement from a continuously shrinking ruler. It is an average inferred from the ages and dimensions of contractional landforms mapped on the Moon.
NASA gives a complementary cumulative perspective: the Moon’s diameter has decreased by about 50 meters (150 feet) over the last several hundred million years. Radius and diameter are different measurements, and the two figures describe different time intervals, so they should not be divided or compared without first aligning those units and periods.
| Measurement | Reported value | What it describes | Important qualification |
|---|---|---|---|
| Radius-loss estimate | 6–11 cm per million years | Long-term contraction rate | Inferred from mapped faults and their ages; assumes the average rate stayed constant |
| Annual equivalent | About 0.1 µm per year | Scale of the same radius estimate | A conversion of the geological average, not a direct annual observation |
| Cumulative diameter change | About 50 m (150 ft) | Total shrinkage over several hundred million years | NASA’s public summary; it measures diameter, not radius |
Is the Moon getting smaller right now?
The evidence indicates that lunar contraction is probably still occurring, but scientists cannot yet replace the geological estimate with a precise modern measurement of the Moon’s radius. The rate may have varied through lunar history as the interior cooled, so treating 6–11 cm per million years as a constant is an assumption that makes the estimate usable rather than a demonstrated present-day speed.
#1 Best Overall
- 【Excellent Optics】Astronomical telescope features 80mm aperture 600mm(f/6.7) focal length-The big aperture can capture more light; high transmission multi-fully coated optical lens can improve light transmittance, reduce the reflection of light. It will bring you more bright and clear images.
- 【Portable & Stable】Our refractor telescope has a backbag, an adjustable aluminum tripod and an upgraded phone adapter. All accessories can be packed into the bag, which is convenient for you to carry and storage for traveling. The tripod is stable and the height can adjust from 17.7" to 52", which is suitable for adults and kids. With the phone adapter, you can take amazing photos through your phone.
- 【Easy to Operate】 This telescope is easy to assemble even for astronomy beginners and kids. You can set up easily with the detail installation manual and video. No tools are required. It’s a great astronomy gift telescope for adults, astronomy enthusiasts, beginners and kids 8-12.
- 【Optimum Magnification】Our telescope for kids and adults is equipped with two replaceable excellent-quality eyepiecesa (20mm and 9mm) for 30X and 66X magnification. A moon filter transmits only 13 percent of the incoming light and improving contrast. Also with 5x24 finderscope, you can locate objects easily. A great option for astronomy lovers to explore the moon, Saturn and Jupiter.
- 【Satisfaction Service】We provide 3 years satisfaction service. If you have any questions about the product and service, please feel free to contact us to get 24-hour technical support from our expert team. Whether observing moon or viewing planets, our telescope can meet your all needs. It’s a great telescope for adults & 8-12 kids & astronomy beginners.
What is established is that the Moon has young contractional features and recent seismic activity. Those observations show that cooling-related deformation is not confined to the distant past.
What makes the Moon shrink?
Cooling reduces the interior’s volume
The Moon formed nearly 4.5 billion years ago. As its interior loses heat, the material inside contracts. The solid outer crust is brittle, so it cannot smoothly follow every change in volume. Instead, it is compressed, fractures and shifts in blocks.
Thrust faults shorten the crust
On a shrinking world, one crustal block can be pushed up and over another along a thrust fault. The resulting scarps and wrinkle ridges are surface evidence of shortening. These faults are the Moon’s visible response to the interior’s gradual loss of volume.
The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Rank #2
- Superior Optics: 400mm(f/5.7) focal length and 70mm aperture, fully coated optics glass lens with high transmission coatings creates stunning images and protect your eyes. Perfect full positive telescope for astronomers to explore stars and moon.
- Magnification: Come with two replaceable eyepieces and one 3x Barlow lens.3x Barlow lens trebles the magnifying power of each eyepiece. 5x24 finder scope with mounting bracket and cross-hair lines inside make locating objects easily.
- Wireless Remote: This refractor telescope includes one smart phone adapter and one Wireless camera remote to explore the nature of the world easily through the screen and take amazing celestial images.
- Adjustable Tripod: This telescope allows for many different viewing positions with a adjustable aluminum alloy tripod and a carry bag, the telescope and tripod can fit inside the bag for easy traveling and storage.
- Satisfaction: Buy with confidence from a leading manufacturer.
Earth’s tides add stress
Earth’s gravity continually raises tides in the Moon. That tidal stress does not supply the primary heat-loss-driven contraction, but it can help orient faults or push an already stressed fault toward failure. The timing of some recorded quakes is consistent with that additional trigger.
What observations reveal the contraction?
Thousands of young fault scarps
Images from NASA’s Lunar Reconnaissance Orbiter and its camera have mapped thousands of young thrust-fault scarps. A 2019 NASA survey examined more than 12,000 images and identified young wrinkle ridges in Mare Frigoris. Some features formed within the last billion years; others may be no older than about 40 million years. Their young ages matter because they place contractional movement within relatively recent lunar history.
Apollo seismometers recorded shallow quakes
Four Apollo seismometers operated from 1969 through 1977 and recorded 28 shallow moonquakes. A later reanalysis located 8 of those 28 events within 30 kilometers of mapped faults. Six of those eight occurred near lunar apogee, when the Moon is farthest from Earth and the changing tidal stress associated with its orbit is greatest.
Rank #3
- SMARTPHONE-POWERED SKY TOUR: No experience needed! Just dock your phone, launch the StarSense Explorer app, and follow the on-screen arrows to locate stars, planets, nebulae, and more.
- PATENTED STARSENSE TECHNOLOGY: Unlike other astronomy apps, StarSense Explorer uses sky recognition technology to turn your phone into a celestial navigation system, analyzing star patterns overhead to pinpoint your telescope’s position.
- TONIGHT’S BEST TARGETS, INSTANTLY: The app generates a curated list of the top objects to see based on your time and location. See planets, bright nebulae, galaxies, and star clusters from the city—and even more from dark skies.
- SIMPLE SETUP, SMOOTH TRACKING: Features a manual altazimuth mount with altitude slow motion adjustment with a sliding rod. Follow the on-screen arrows to your target; when the bullseye turns green, you can view it clearly through the eyepiece.
- 114MM REFLECTOR WITH IMPRESSIVE VIEWS: The 4.5" Newtonian reflector with high-reflectivity coatings delivers sharp, vivid views of the Moon, planets like Jupiter and Saturn, and deep-sky favorites like the Orion Nebula and Andromeda Galaxy.
In 10,000 simulations, the chance of obtaining that degree of coincidence randomly was below 4 percent. That result supports a relationship between shallow quakes and fault activity, while not proving that every event had the same cause.
Recommended Free Tools
Can a shrinking Moon cause moonquakes?
Yes. Contraction loads the crust until existing thrust faults slip or new faults form. NASA describes shallow moonquakes reaching approximately magnitude 5 to 5.5; some can last more than 10 minutes because the dry, fractured lunar crust transmits seismic energy differently from Earth’s crust.
“The Moon is still quaking and shaking from its own internal processes,” said Nathan Williams of NASA’s Jet Propulsion Laboratory.
Rank #4
Sale
Dianfan Telescope, 90mm Aperture 800mm Telescope for Adults High Powered, Portable Professional Astronomy Refractor Telescopes for Beginners, with Stainless Steel Tripod & Phone Adapter, Carry Bag
- Superior Optics: Dianfan astronomy telescope features a focal length of 800 mm and a fully coated 90 mm objective lens. The large aperture gathers more light for brighter, clearer views, high-transmission coatings enhance contrast and color for sharp, vivid images for an enjoyable stargazing experience
- Powerful Magnification: With two eyepieces and a 3× Barlow lens, this telescope offers 32×–240× magnification. It allows you to observe craters and lunar seas on the surface of the Moon. With the 45° zenith mirror, images are upright and correctly oriented for terrestrial viewing, making distant targets details easier to observe. The telescope is ideal for beginners and astronomy enthusiasts
- Quick Setup & Beginner-Friendly: User-friendly design with clear instructions makes assembly simple—ready in about 15 minutes. Smooth focusing helps you quickly locate targets. Perfect for families to enjoy stargazing and explore the night sky together
- Portable & Versatile: Lightweight design with a sturdy stainless steel tripod ensures stable, steady viewing. Easy to carry in the included bag, making it perfect for travel and outdoor adventures. Suitable for stargazing, birdwatching, wildlife observation, and exploring cityscapes
- Professional Astronomical Telescope: The Dianfan 90x800 telescope combines quality , functionality and reliability. It delivers high-resolution views that bring the universe closer. Designed for adults high powered, it inspires interest in astronomy and science while encouraging exploration of the starry sky
The seismic evidence and young scarps reinforce each other: the landforms show where shortening has occurred, while the Apollo records show that faults in or near those structures can still move.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why the south polar region matters for exploration
Future lunar landing sites and outposts cannot be selected solely by mapping water ice, sunlight or terrain. NASA modeling indicates that shallow quakes in the south-polar region could produce strong ground shaking tens of kilometers from a fault scarp. Some slopes, including areas of interest for ice deposits, may also be vulnerable to landslides.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
“Our modeling suggests that shallow moonquakes capable of producing strong ground shaking in the south polar region are possible from slip events on existing faults or the formation of new thrust faults,” said Tom Watters of the Smithsonian Institution.
Best Value
Sale
Celestron Travel Scope 70mm Beginner Portable Telescope with Backpack | 70mm Refractor Telescope Kit, Bright Lunar & Planetary Views, Day & Night Use, Backpack Included, Quick No-Tool Setup
- BRIGHT, SHARP VIEWS ANYWHERE: Unlike many beginner telescopes, this quality refractor features fully coated glass lenses and a 70mm aperture for crisp, clear views of the Moon, planets, and daytime scenery—all in a lightweight, travel-ready design.
- PERFECT FIRST TELESCOPE FOR BEGINNERS: Designed for adults and kids to enjoy together, this beginner-friendly telescope sets up in minutes and delivers rewarding views with no prior experience required.
- EASY NO-TOOL SETUP: No complicated assembly or tools needed. The full-height tripod and telescope tube set up in seconds and pack neatly into the included backpack—so you’re always ready to observe on the go.
- DUAL EYEPIECES FOR VERSATILE VIEWS: Includes 20mm and 10mm eyepieces for wide and close-up views of celestial and terrestrial targets. Spot craters on the Moon at night or wildlife during the day.
- BONUS BACKPACK AND SOFTWARE: Includes a padded backpack with room for accessories, a finderscope, star diagonal, eyepieces, and a free download of Starry Night software to help you identify celestial objects and plan your next stargazing session.
Mission planners therefore need seismic-monitoring and slope-stability data alongside resource maps. A site that is attractive for communications, power or ice access may still carry geological hazards that change during an outpost’s operating life.
What the estimate does—and does not—tell us
- It gives the best available long-term average for radial contraction: 6–11 centimeters per million years.
- It does not mean the Moon visibly loses 0.1 micrometers on every calendar year; the annual figure is a conversion of an averaged geological rate.
- It does not predict the date or magnitude of a particular moonquake.
- It does show that cooling, crustal shortening and seismic activity are linked over geologically recent time.
Thomas Watters of the Smithsonian National Air and Space Museum summarized the significance of the fault study this way: “Our analysis gives the first evidence that these faults are still active and likely producing moonquakes today as the Moon continues to gradually cool and shrink.”
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
