April 6, 2012

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Domical Profiles

image by Peter Oberc, Ljubljana, Slovenia

Here is a great example of the complementarity of grazing illumination telescopic views and spacecraft data. Peter recently acquired this image of Arago and its two domes, Alpha (above) and Beta (left). These domes are known to be relatively tall and rough textured, the latter characteristic showing up in the image. I created some profiles using the LOLA altimetry data from the LRO QuickMap website to explore their heights and shapes, and found some unanticipated surprises. The top profile at upper left covers the area shown by the light grey line which crosses the barely visible dome from about west to east. The surprise is that the mare surface the dome erupted onto slopes significantly toward the east – the center of the Tranquillitatis Basin – over just the 43 km of the traverse. The dome rises about 230 m above the adjacent mare to the west, but nearly 450 m above the mare to the east. This factor of two could account for differences in telescopically measured values, although the GLR group value of 330 m falls in the middle, a good average value. A similar west to east profile across the Beta dome (middle graph) reveals a similar regional tilt to the east so that the dome’s height differs depending on which side is measured. A north to south profile (bottom) goes more along a constant contour so that the dome's height does not vary as strongly. Beta is about 225 m high on the north and 300 m on the south, generally confirming the GLR value of 270 m. Peter's image reveals topograpic features just barely visible in the higher Sun LRO mosaic, giving guidance to where topo profiles should be investigated.
Chuck Wood

Technical Details
28 March 2012, 18:25UT. Scope: C11 @ 6000mm, 0,13"/px, IR filter + Camera: Basler Ace ACA1300-30GM (mono) + Processing: AutoStakkert
2 + Astra Image + Photoshop

Related Links
Rükl plate 35
Slovenia astronomy website

Yesterday's LPOD: What a Difference a Day Makes, 24 Little Hours

Tomorrow's LPOD: Learning To See From Lunar Orbit


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