Janssen and Vlacq


Daniel McGlashin
  Frosses, County Donegal, Ireland
Photo Title
  Janssen and Vlacq
Time and Date taken
  30th November 2004 2126UT
Equipment used
  Helios EQ 114, 2x Barlow lens
Capturing device used
  Logitech 4000 with mogg adaptor
Technical details
  60 second AVI @ 10 frames per sec, AVI was processed in registax and slight adjustment made to contrast.

Daniel has captured a lovely image here showing the Janssen crater and rille with Pitiscus, Vlacq and Rosenberger craters in clear view. The moon was at it's waning gibbous phase so the craters are "backlit" so to speak.

South of the Nectaris Basin, the Moon has a sameness of flat-floored craters that makes identification of particular features difficult and it took the expertise and experience of John McConnell to correctly identify this image. One crater stands out as unique in this area of uniformity. Janssen is huge (190 km diameter) and weird. First, its northern end is confused by an overlapping crater, Fabricus (very top edge of view), and an "underlapping" one that has no designation. When seen from directly above, the northern rim of Janssen is clearly the ridge that arcs into Fabricus. The southern portion of Janssen's floor contains smooth material which the 140Km long Janssen rille arcs through. What's interesting about this rille is that it cannot be explained how it got there by natural processes. Most rilles occur on maria lavas, but the Janssen patch of smoothness is not dark at full Moon and doesn't have the spectral properties of maria. The various linear valleys to the East of the rille are radial to Nectaris, so are expected ejecta from the formation of Nectaris.

The grain around the edge of the frame is due to the stacking process within Registax. The telescope was drifting slightly as can also be seen at the top left. Daniel was able to extend the view of his capture using the "expand image" feature within Registax.


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