December 13, 2019

Astro-Challenge: Spotting Two-Faced Iapetus.

As the majestic planet Saturn approaches opposition on March 21st, I’d like to turn your telescopic attention to one of the most bizarre moons in the solar system; Iapetus. It was way back when in the 17th century that Italian astronomer Giovanni Cassini noted that he could only see Iapetus when it was to the west of the ringed planet, but never to the east. He correctly deduced that Iapetus must not only be tidally locked, that is, holding one face towards Saturn, but must be correspondingly dark on one hemisphere and brighter on the other. In fact, Iapetus is known to vary from magnitude +10 to magnitude +12 over its 79 day orbit, a variation of 6 times in terms of brightness. the Cassini space probe has confirmed the duality of Iapetus, showing us a dark leading hemisphere with an albedo of 5% (think fresh asphalt) and a trailing hemisphere with an albedo of about 50% (think dirty snow). The third largest of the Saturnian moons, Iapetus is a “walnut shaped” world, with a large ridge running the equator of this twisted moon. Discovered by Cassini on New Year’s Eve 2004, no satisfactory explanation for the ridge is known, but the little world must have had a tumultuous history.

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16.10.09:A Moscow UFO?

What is it? Earlier this week, the above image and obligatory YouTube video flew around ye ‘ole Internet, purportedly showing an “Independence Day”-like spacecraft seemingly descending through the clouds over Moscow. The video was shaky, and the perspective of the light poles moving in the foreground all lent themselves to an eerie look and feel…a classic UFO, right?

Semi-unfortunately, this phenomena has a slightly more prosaic explanation, although its still pretty cool. Many naysayers are simply claiming that the video was “Photo-shopped” although we here at Astroguyz HQ don’t necessarily believe so. The patterns look to be consistent with low altitude, mammatus-type clouds. Of course, the hoaxer might have been a meteorologist…what your looking at is known as a parahelic arc, a breed of sun-dog shining through low-altitude clouds seen under somewhat unusual conditions. Many folks on the ‘Net have stated that the glowing ring is the cloud, but if you look closely, the entire sky is overcast. Meteorologists confirm that a converging front was over Moscow at the time, and that the sun was indeed at a low angle, i.e. prime sun-dog conditions. To explore near-sky phenomena complete with explanations, I refer you to Les Cowley’s excellent site on Atmospheric Optics. Stare at the sky long enough, and you’ll see all sorts of bizarre things. Incidentally, pilots are much more familiar with this sort of reflection phenomenon, as they frequently fly above low cloud banks. I would suspect that there is also an inversion source, like say, a heat belching factory right below the halo. Alas, no ET…but isn’t UFO debunking fun?