June 6, 2020

Astro-Challenge: Exploring Reiner Gamma.

Finding Reiner Gamma…note that the shot through the Astroguyz 8″ SCT is flipped and inverted!

(Credit: Wide shot by Author, closeup from Lunar Orbiter 4 in 1967/NASA).

The waning gibbous Moon may provide a good cause to do some early AM astronomy this week. Amidst the familiar features such as craters, rays, and lunar mountains are more mysterious anomalies, one of which we’d like to bring to your observing attention this week. Reiner Gamma is a curious feature located at 7.5°N 59°W on the edge of the Oceanus Procellarum. Often mis-identified as a crater on early Moon maps, this feature is one of the finest examples of what is known as a Lunar Swirl on the nearside of the Moon. The area generally reaches an optimal illumination angle around three days past Full Moon, which occurred on the 15th. This means that Reiner Gamma may be within reach of a backyard telescope this week. Look for Reiner Gamma to appear as a splotchy oval about 35 km in diameter, with a 200 km tail, much brighter than the surrounding maria.

Other events to watch out for this week include a fine occultation of a +6.5 magnitude star by the asteroid 90 Antiope spanning the Pacific Northwest early on the morning of the 19th; also, Mercury reaches a greatest eastern elongation of 27° degrees from the Sun in the dusk skies on the 20th.  The space shuttle Atlantis has also been extended for an additional day in Low Earth Orbit as this goes to press… landing at the Kennedy Space Center is now slated for 5:56AM EDT on the morning of the 21st. This means that the Southeastern United States might just get to see an orbiter in space one last time the morning prior… follow @Astroguyz on Twitter for all the updates.

Finally… have you ever spotted the planet Jupiter…in the daytime? I once accomplished this feat of visual athletics while working Arm-End-Of-Runway in Kuwait in my USAF days… on the mornings of July 23rd-24th, the waning crescent Moon will be about a hands’ width at arm’s length from the giant planet. Note the position before sunrise and/or aim a polar-aligned scope equipped with a tracking motor at Jupiter, and YOU may be able to follow the gas-gaint into the daytime skies!

The astro-term for this week is Lunar Swirl. While reading the above, did you happen to wonder what Reiner gamma is? Lots of theories have been proposed over previous years to explain these curious features, from cometary impacts to electro-statically charged lunar dust particles as seen by the Surveyor spacecraft during lunar sunset… let’s look at what we know lunar swirls aren’t; Doppler measurements taken from low lunar orbit using the laser altimeter aboard NASA’s LRO spacecraft do not detect any corresponding elevation or depression in the area of indentified lunar swirls. What the Apollo and Lunar Prospector missions do pick up in the vicinity of the swirls is increased magnetic activity; our Moon doesn’t have an overall magnetic field like the Earth, but instead has pockets of “lumpy” magnetic activity scattered over the surface, and the area of Reiner Gamma is one of the strongest. Probably one of the leading theories for the origins of lunar swirls was proposed by L.L. Hood and C.R. Williams of the University of Arizona in 1989. The idea is that while most of the lunar surface allows for solar wind ions to bombard it unimpeded for eons, the magnetic field around Reiner Gamma streamlines and shapes the incoming solar wind, causing alternating dark and light stripes. Whatever the cause, this is but one more region of the lunar surface that begs for further exploration… does a mother lode of magnetic ore sit under Reiner Gamma? We won’t know until some space prospector gets there, “laser-pick” in hand to check it out!

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