Diameters of minor planets

The paper discusses the tremendous improvements in measurements of the asteroids since 1970, when polarimetric and radiometric methods began to replace the visual methods. A table is given which gives the sizes and albedos of 187 of the larger asteroids. When the asteroids are sorted according to albedo, they are seen to fall into two distinct groups: C-type, or carbonaceous, asteroids, with albedos of 2-5%, and a group of primarily stony or silicate bodies, the S asteroids, clustered around an albedo of 15%. The majority of the asteroids are seen to be very dark, and the maximum density in the asteroid belt must lie somewhere beyond 3.0 astronomical units.