To do this, it is useful to identify edges, and surface markings.

Gilbert made the first attempt to map the surface markings on the Moon in the 1590s.

The common name of this species is derived from the darker surface markings that sometimes resemble letters.

Dawes presumed that the atmosphere of Mars was thin because surface markings on the planet could easily be seen.

That same year, he used observations of the surface markings on Mars to determine a rotation period of 24 40.

The surprising conclusion seems to be that the big surface markings on Io have hardly changed at all.

Mariner 9 was to study the enigmatic seasonal and secular changes of surface markings.

It was a belted world, without clearly defined continents or surface markings.

This area includes an array of linear dark surface markings that appear to criss-cross.

Today, the surface markings taken to be canals are regarded as an optical illusion.