The region SW of Encke

The ruined walled-plain called Maestlin R presents a somewhat brief but dramatic scene soon after sunrise by reason of the fine spires of shadow thrown by its eastern rampart. It would seem that the region is comparatively little known, but there are a number of interesting minor features in the form of crater chains and delicate rilles on the eastern side.

The failure of an observer to find delicate detail shown on maps is sometimes to be explained by the time at which the observation is made. The two observations shown are morning aspects made 4 hours apart and quite independently of each other. They show the rapid retreat of shadow and the emergence of fine features not visible under the lower light, even though it was not necessarily hidden – for instance, the afore-mentioned crater chains and rilles which are not revealed in their true character until surface brightening enhances the contrast. Such features are often best looked for some distance from the terminator when the Sun's local altitude is about 4° or 5°.

The Delisle–Diophantus Region

Whenever there is a good prospect of a long session at the telescope together with excellent seeing conditions, then undivided attention paid to a selected region resulting in the making of sequential drawings can very often yield a good deal of useful information not otherwise obtainable.