Art Tip #1

I remember writing a note about this a few years ago, so maybe the following notes are helpful, here goes....

1. Crater sizes: Besides the issue of randomly spacing the circles, there is the issue of the size of circles themselves. Asteroids, meteorites, and all broken fragments, and therefore the craters made by them, have a natural distribution of sizes. A rough rule of thumb, especially at sizes larger than 1 km (which is what you see from space) is that every time you go down by a factor of 2 in size, you must put in 4 times as many craters. Example: if you start with one 4 cm crater on your artwork, then at 2-cm size put in four craters, and at 1-cm size put in sixteen craters! If you take a small dirt clod or make a plaster ball or take any breakable object, and drop it or tap it and break it, you will see roughly this size distribution. One reason many early paintings of the moon looked unnatural is that people put in too many of the same sized craters. Incidentally, below the size of 1 km, this size distribution steepens noticeably, and when you go down by a factor 2 in size, you must put in more like 8 times as many craters! This is why there is so much softening and sandblasting of the lunar mountains by small impactors.

2. Overlap: The craters really formed in random order, but we usually see only small ones on top of big ones, not the other way around. You could imagine part of a small circle sticking out from behind the rim of the big one, but in reality, the bigger one throws out so much ejecta that it covers small ones in the area, and that's why you see only small ones overlapped on big ones. It's not that sizes got smaller.

3. Erosion/degradation: The hardest thing for me in painting cratered terrain is that old, large craters exist on any surface that are rounded, eroded, softened in profile, and they contrast with the fresher craters with their sharp rims. Sometimes you need to start with old shallow features and then build up to sharper, younger features, at the same time applying items 1 and 2 above.

Asteroid City  by Bryce Jacobs

Asteroids could be the perfect “vessels” for
interstellar generation ships or deep space habitats.

Copyright © 2001
International Association of Astronomical Artists