December 10, 2018

21.01.11: Earth Observations set for Glory.

Yesterday, NASA gave a sneak peek look at its latest tool in its arsenal in the quest for the understanding of global climate change. Glory arrived at Vandenberg Air force Base last week and is set for a pre-dawn launch atop a Taurus XL 3110 four-stage rocket on February 23rd.

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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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Astro Event: The Closest Full Moon of the Year.

(Editor’s note: Due to a flurry of astronomical events, February’s events of the week will be released on an accelerated schedule; hang on!)

Amid the opposition of Mars, two launches out of the KSC and the Cape next week, and an exceptionally fine elongation of Mercury in the early morning skies, this weekend brings us a special treat; the closest Full Moon of the year. This Moon, known also as the Full Wolf Moon, is technically full at precisely 06:00 Universal time on Saturday morning, the 30th of January. This comes only 3 hours prior to perigee, when the Moon is closest to Earth in its orbit. At this time, the Moon will be only 217,862 miles distant, and appear 34.1’ arc minutes in size, as opposed to 29.3’ arc minutes at apogee. An added plus is that this Full Moon occurs at a very northerly declination in the constellation Cancer, and hence will be riding high for northern hemisphere viewers all night. And don’t forget ruddy Mars, just 7° degrees north of the Moon!

The astro word for this week is albedo. Think that bright silvery Full Moon is bright? Science says otherwise. Albedo is the measure of the percentage of light reflected back by an astronomical object; 100% is a full mirror, optimal reflection, and 0% is pitch black. On Earth, fresh snow reflects about 85% of the light that falls on it, and the average albedo of Earth is about 30%, depending on the amount of cloud cover and the percentage of land versus ocean presented to the Sun. In fact, this phenomenon of reflectivity may play a key role in a lesser known effect impacting global climate; that of global dimming. Now for the real shocker; the average albedo for the Moon is about 10%, slightly less than worn asphalt! Ask the Apollo astronauts; the Moon is in fact, a very grey-to-black place! The reason that this weekend’s Full Moon looks bright is that you are seeing the sum of 5% of the Sun’s reflected light crammed into an area tinier than a fingernail at arm’s length. In fact, anyone who has stood under a 99% percent eclipsed Sun, as occurred earlier this month, will tell you that even 1% of the sun’s output is still pretty bright!

Spot the Lunar High- & Low-lands with the Naked Eye!

Did you happen to notice that the Moon was fat and nearly full Halloween night? The technical full Moon for November falls today, Monday the 2nd, at 2:14 PM EST (yes we’re back on standard time now; did you get to work an hour early this morning?) Of course, the full Moon, like all phases, only occurs at an instant in time. That instant is the time that the Moon is exactly 180 degrees, or 12 hours of right ascension opposite to the Sun.

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