“Aristarchus Rising”
In my early years of exploring the night sky with binoculars, I was frequently amazed by a brilliant feature on the Moon, to the left of Mare Imbrium. I wondered, “What could be so bright?”. After a little reading, and consultation with a local wizard (Herbert Z. Lund, MD, avid amateur astronomer, and mentor/friend to both my wife and I), I learned that the bright spot was the crater Aristarchus. I learned that it is among the very brightest features on the Moon, due to the unusual reflectivity of the material within and around the crater. It sits on the edge of a plateau with a history of intense volcanic activity, including immense channels through which lava rivers once flowed, contributing to the vast lava plains (maria) that surround the plateau. I learned that Neil Armstrong reported an unusual brightness, with some fluorescence, from the area of Aristarchus during the Apollo 11 Mission. Could the fires of Aristarchus still be active? I was hooked. Aristarchus became a favorite observing target for me.
Last Thursday night, at the Pop-Up Telescopes event, I noticed Aristarchus being illuminated by the first rays of sunlight, a bright point on the day-night terminator line of the Moon. As I seldom capture this Moon phase photographically, I decided to do so after I returned home. Below is the photo I captured.
The photo shows a region of the Moon where the huge lava plains of Mare Imbrium merge with the gargantuan lava plain of Oceanus Procellarum, below the Jura Mountain range that defines the western and northwestern rim of Mare Imbrium. Aristarchus occupies the bottom center in this photo, next to the line dividing bright daylight from the deep night darkness. Its raised rampart and interior western crater walls are illuminated, but its depths are still deeply shadowed. Some of the edge of the surrounding plateau can be seen, as can a piece of the rim of adjacent Hesiodus crater, which otherwise is cloaked by night. The area of the lower right portion of the photo shows streaks of lighter-toned material that generally radiate away from Aristarchus crater. These are the ray system that surrounds Aristarchus, composed of material that was blasted upward and outward when an asteroid gouged the crater into the Moon. Ray features, over eons of time, are darkened by constant bombardment by solar radiation and they become indistinguishable from the older lunar surface materials. Their presence declares that Aristarchus is one of the young lunar craters. It can’t be more than half a billion years old! Alas, my photo reveals no sign that the fires are still burning.
To the right and upward from Aristarchus there is a horseshoe shaped feature, surrounded by a few mountains. The horseshoe is Prinz crater; long ago flood basalt surges overtopped the southern rim of Prinz crater and filled its interior. The mountains surrounding Prinz crater are called the Montes Harbinger, the “Harbinger Mountains”, for they become visible a day before dawn comes to Aristarchus. Inspection of the valleys between the mountains and the area between the mountains and Aristarchus shows several squiggly features, like streambeds, flowing away from the mountains. These are ancient lava channels; each originates in a dormant volcanic vent and marks a path the lava flows took to the plains below. They are collectively named Rimae Prinz. The similar features originating on the edge of the Aristarchus Plateau are called Rimae Aristarchus.
Above and left of the Harbinger Mountains is a medium-sized crater, with a deeply shadowed interior. This is Krieger crater. On its bottom-side rim is another small crater, which shows due to its brightly-lit western rim. This is Van Biesbroeck crater. Take a moment to appreciate the long triangular shadows cast by the craters and mountains in this area. To the left of Krieger crater are two tiny craters, with the rather cute names, first names really, Rocco (upper) and Ruth (lower). Rocco is 4.37 km in diameter, and Ruth only 3.0 km. I discovered during preparation of this writeup that the middle region of this photo is dotted with tiny craters with first names. Names like Gaston, Linda, Boris, Samir, Louise, Isabel, Walter, and Ivan. These are not just informal names: they are official designations assigned by the International Astronomical Union. And they are truly tiny. The smallest I have identified in this photo is Samir, at 1.87 km. I am puzzled as to the Why? behind giving these features official names. It seems they were given names during the preparation for NASA of the highly-detailed Apollo-imagery related maps known as the Topophotomap series. The legends at the bottom of the maps say the names were intended as “informal” names, to be used only in describing that particular map. However, in 1976, most of them were formally adopted into the official IAU Nomenclature. So why are they named? Because that they happened to fall in one of the very few portions of the Moon covered by a Topophotomap. I hope the names are significant for someone, maybe honoring loved ones, friends, or pets. They are examples of fun things one finds when rummaging through science, like when I found out that there is a dinosaur named after Mark Knopfler.
Back to the image. Near the right middle edge of the photo is another medium-sized crater with a partially shaded interior and surrounded by what appears to be a rubble field. This is Delisle crater. To its left is a lamb chop shaped mountain called Mons Delisle, and to its upper right is what seems to be a tiny chain of craters (catena) called Rupes Boris. The word “rupes” means cliff or escarpment, and yes, it’s named after the previously mentioned Boris crater. The area around Rupes Boris is home to the previously mentioned Boris, Linda and Gaston craters. If you squint, you might detect one or two. Below Delisle crater is a smaller bowl-shaped crater called Diophantus. Between Delisle and Diophantus you can see a light-shaded patch. At the center is a tiny crater. This is Samir. Its bottom is only 1 km across, so maybe this is my break into the club of astrophotographers that can claim to have resolved 1 km. If not, give me a break and let me enjoy my moment. Resolving a one km feature (or even a 1.87 km feature) from a distance of 380,000 km is a pretty cool feat.
Now for the final stretch on this essay. In the upper left corner of the photo the terrain becomes very broken and mountainous. These are the Jura Mountains of the Mare Imbrium rim. Amidst these mountains is the prominent crater Mairan. At the lower end of these mountains are two larger mounds. These are the lunar volcanoes Gruithuisen Gamma (left) and Gruithuisen Delta (right). Gruithuisen Gamma even has an obvious summit crater. They are unusual among lunar volcanoes for their heights (1,500 and 1,800 meters, respectively). This is the first time I can recall capturing them in a close-up photo. Lastly, at the upper center of the photo there is a projection of mountains into the plains of Mare Imbrium. This is Promontorium Heraclides, marking the southern end of the popular lunar feature, Sinus Iridum.
Best 12% of 19,399 video frames processed with PIPP and stacked with AutoStakkert!3. Wavelets processing performed with Registax 6. Post-processing with Photoshop CC 2024.
Celestron Edge HD8 telescope
ZWO ASI 290MM camera
Celestron Advanced VX Mount
Seeing: below average, 2/5
