A magazine of lunar topographic studies Vol. 17 No. 2 December 2008

ment. Just east of Agatharchides A anothershallow rille runs south and is bisected bythe Rima Hippalus IV. This rille is alsofractured along its length, herringbonefashion (see Lunar Orbiter image IV-132at right).As the Rima Hippalus III strikes southwardsbeyond Agatharchides A, the rilleskirts a small hill, recorded sometimes ashaving a summit craterlet. Observationallyat least, the rille at this point has a pronouncedbend eastwards. It is interestingto note that this sharp ‘bendaround’ is notconfirmed by the overhead Lunar Orbiterimages, although many observers haverecorded it as such in the past. Rükl alsoshows no great curvature here, though forthe most part he based his charts on theLunar Orbiter photos. This apparent lunarillusion is shown well on my drawing of2004 March 1 (see p.12). Allowing for thisrille’s position on the lunar sphere, some30° west of the Moon’s central meridian,and the resultant distortion in its shape(curvature), we would expect the bend ofthe rille around the small hill to appear lessto the Earth bound observer, and not, as isapparently the case, much more. Furtherstudies by myself show that a section ofthe eastern half of the hill has fallen orslumped into the bottom of the rille.Whilst the extra shadow that this fallensection casts eastwards could explain anapparent increased curvature of the rille atAbove: Lunar Orbiter photo IV-132, at col. 48.66°. Credit: NASA.Below: Part of LAC 93 (featured on p.79-80 of The Times Atlas of the Moon) showingMare Humorum and Rimae Hippalus. North is at top. Credit: NASA.The New Moon December 2008Page 9