We get asked the same wonderful questions in the shop every week. Here are the answers, with the numbers that make people go quiet.
1,300,000+
The most complete modern survey of the Moon, built from Lunar Reconnaissance Orbiter data, catalogued over 1.3 million impact craters at least one kilometre across. Nobody has counted the smaller ones. Below a kilometre the number runs into the billions.
craters wider than 1 km
5,185
Twenty kilometres is about the size where a crater stops being a simple bowl and starts developing terraced walls and a central peak. There are a little over five thousand of those on the Moon.
craters wider than 20 km
99.8%
The International Astronomical Union has formally named roughly sixteen hundred lunar craters since Giovanni Riccioli began the modern naming convention in 1651. Set against 1.3 million catalogued craters, that means more than 99.8 percent of the Moon's craters have never been named by anyone.
of lunar craters are unnamed
Earth loses its craters to rain, wind, plate tectonics, and vegetation. The Moon has none of these. With no atmosphere and no water, the only thing that erodes a lunar crater is another impact. A crater formed three billion years ago can still have a sharp rim today.
2,500 km
The South Pole-Aitken basin on the far side spans about 2,500 kilometres and runs eight kilometres deep, making it one of the largest known impact structures anywhere in the solar system. It is so big that it was only properly recognised from orbit.
South Pole-Aitken basin
1,500 km
Tycho is only about 108 million years old, young enough that dinosaurs on Earth could have watched it form. Its bright ray system stretches more than 1,500 kilometres, and at full moon those rays are visible from a Joshua Tree driveway with no equipment at all.
of Tycho ray debris
Because impacts arrive at a roughly predictable rate, counting craters on a surface tells you how long that surface has been exposed. Crater counting is how planetary scientists date terrain on Mars, Mercury, and the moons of Jupiter.
3.8 cm
Tidal interaction is slowly pushing the Moon outward, about the rate your fingernails grow. In roughly 600 million years it will be too far away to fully cover the Sun, and total solar eclipses will end forever.
further away each year
29.5
The Moon rotates once per orbit, which is why the same face always points at us. Sunrise to sunrise at any point on the surface takes nearly a month, so a crater floor can bake at 120 degrees Celsius and then freeze to minus 170.
Earth days per lunar day
Apollo astronauts tracked regolith back into the lander and reported a distinct burnt smell once it hit the cabin air. Nobody has fully explained it. Samples returned to Earth lost the scent entirely.
With no wind and no water, the boot prints left in Mare Tranquillitatis in 1969 will remain legible for millions of years, disturbed only by the slow rain of micrometeorites.
The terminator is the line between lunar day and night. Along it the Sun sits low and every rim throws a long shadow, turning the surface three-dimensional. At full moon the light is straight on and the same craters flatten out and disappear.
Bortle 3-4
Joshua Tree National Park is one of the darkest accessible parks in Southern California, dark enough that the Milky Way casts a faint shadow on a moonless night. It became an International Dark Sky Park in 2017.
dark sky rating over the park
A pair of 10x50 binoculars, braced against a car roof on Park Boulevard, will show you the major maria, the Apennine mountains, and the ray system around Tycho. Most people are surprised how much of the Moon they can find without a telescope.
Giovanni Riccioli laid out the modern scheme in 1651, naming craters after philosophers and astronomers and christening the dark plains as seas. It was a beautiful system, and it was built for a Moon seen through a small refractor. Riccioli could resolve a few hundred features. He named what he could see.
Four centuries later, spacecraft have mapped the surface down to the metre. The International Astronomical Union has kept adding names, but deliberately slowly and only where science needs a label. The naming never caught up with the mapping, and it never will.
So the Moon sits there, fully charted and almost entirely anonymous. Well over a million craters, catalogued, measured, photographed from orbit, and nameless. That gap is where this company lives.
