The Flammarion Domes

The coordinates of this walled-plain are 3° S 4° W and it is, therefore, placed quite near to the centre of the mean disc. Formerly known as Herschel F, Flammarion is a large, rather open formation, irregular in shape with broken ramparts and having a mean diameter of 47 miles.

At the time of the observation, only a portion of the floor was visible, the remainder being heavily shadowed both to the north and south, but at this stage the extremely oblique illumination shows to advantage the low dome-like features on the interior. Both grouping and alignment seems preferential – the latter being in a NNE–SSW direction. Doubts have been expressed in some quarters as to the real nature of these low-relief features and whether they meet with the characteristics of categorised domes, but it is not clear upon what grounds these objections are based bearing in mind what was seen and depicted on this occasion under a solar altitude of only 1½°–2°.

It seems rather remarkable that there is no mention in early literature, or even as recently as the mid-1950s, of the Flammarion domes, as they are not difficult to descry under the right circumstances. Some, if not all, have been charted and incorporated in the ALPO dome surveys carried out in more recent years. The most likely explanation for their omission from earlier maps may lie in their essentially evanescent appearance.