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Two concentric craters and a strange transient

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Was out yesterday morning at 01.00 CEST with the 5.1" Heritage Flextube to get some moonlight. Sub-average seeing, but still usable for moments up to 130-150x. Started with Aristarch, Herodot and Schröter's Valley close to the terminator, went over to Prinz (spotted the western Rima shortly); the two Gruithuisen domes. Once again, a tiny ink-black shadow spot at Promontorium Laplace. Went southward to Schickard, Nasmyth and Wargentin. Close by was Palus Epidemiarum (appropriate to the earthly situation), with the bright crater Mercator A. Consulting LunarMap HD, I suddenly noticed in it the concentric crater Marth close by to the west - clearly depicted  in the LRO map, a pleasant view. At the eyepiece, the crater, very small, could be made out well, but not it's inner concentric crater wall. The same applied for the second concentric crater Hesiodus A a few degrees to the east (usually I gauge lunar seeing with the detectability of it's concentricity). I hauled out the 18" to get a better view of both craters, but to no avail, even with 250x mag (zoom 8 mmf). So I had a look at the nice crater Ramsden with Ramsden A and a bright spot in the NW crater wall. At 02.05, suddenly a tiny black speck came into view, that moved continuously to the west, visible for about  30-40 seconds. It was really small - smaller than Marth's size, and I twice lost it's view, having difficulties with finding and focusing again, but clearly visible, before it disappeared behind the terminator. No migrating bird (too slow), no plane, and no floater. Never seen anything similar during five decades of observing. I guess some satellite - but what species? Any ideas are appreciated. Slightly confused to bed at 02.20.

Attached a link to a Sky+Telescope article about concentric craters:


Thanks for reading


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I had a camcorder attached to my 150/600 refractor at that time hooked up to a 50" plasma tv (unfortunately not recording) and I think I spotted the same thing, I thought it was a bird but not 100% on that, it definately had shape to it.

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Posted (edited)

Hi Nyctimene,

If your object crossed a more or less full lunar disc in 30-40 seconds that's an apparent movement of, say 1 deg/minute which is much too slow for most satellites which are in low earth orbit. The ISS averages about 20 deg/min and about double that near the meridian where you were looking, so perhaps something in a higher orbit.

I used Previsat to find a satellite that fitted an object that I observed transitting the moon during a recent partial eclipse.  http://previsat.sourceforge.net/

Put in your time & location & see if anything crosses the moon.

Here is the thread on my observation.


Edited by lenscap
ISS speed correction
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