How they named these features, I've got no idea.
Still, being three days after first 1/4 Moon, the Northern mountains forming Sinus Iridum shone out like a beacon. A really stunning feature this enourmous mountain range, Montes Jura, that rose out of the darkness of the terminator. Very striking indeed, with the arc of disconnected beads of light reaching out of the dark.
Sinus Iridum while seemingly featureless has a wealth of Lunar history to tell. It is the result of a very, very ancient massive impact that resulted in its floor being completely flooded by lava. BUT, it is much older than the neighbouring Mare Inbrium (Sea of showers). The hint to Iridum's antiquity comes from the Wrinkle Ridges that span its width. Wrinkle Ridges are the terminator line of lava flows. These lava flow stop-lines all run somewhat concentric from their origin within Mare Inbrium. As such, the floor of Sinus Iridum lies some 600m below that of the mean height of Mare Inbrium!
Volcanism within Iridum also didn't finish with its flooding. There are at least four "domes" or volcanos within it, one of which I've captured in my sketch, in the top left quadrant of Iridum, a tiny double lobed feature which is Heraclides 4 (the volcano, 3km dia.) and Heraclides E (4km dia.) [Promontorium Heraclides is the southern spur of the Montes Jura chain that surrounds Iridum]. The four main volcanic vents within Iridum all lie to the west of the line of wrinkle ridges that flow into it. Quite a story book of history this area.
While bereft of big impact craters, long examination of the area begins to reveal a patchwork of small ray craters. These are around the 3 to 5km mark in diameter, but their ray systems extends a little further out. These ray craters are all relatively new impacts.
I hope you enjoy this sketch.
Object: Sinus Iridum & Montes Jura (North is down)
Scope: C8, 8" SCT
Gear: 8mm Celestron Ultima LX, 250X
Date: 20th May, 2013
Location: Sydney, Oz
Duration: 1hr 50min
Media: White & grey soft pastel, black charcoal and white ink on A4 size black paper.
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Sinus Iridum is my favorite feature for only a single night or a few hours once a month. Every time I observe it at medium magnification, I think of sketching it. It's more so the lava flows and little rifts along those shadows that get my artistic desires going. You've rendered them quite well here.
