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Observing the Moon, Sweating it out with an 8" Refractor

Posted by Jim Phillips   08/20/2005 00:00:AM

Observing the Moon, Sweating it out with an 8" Refractor
Editor's Note: The author, Jim Phillips, is a member of the GLR (Geologic Lunar Researches Group) an international organization based in Italy, devoted to the study of the Moon. You can visit their site at

Stepping out of the cool air-conditioned house, the air envelops me. It is thick, very warm and muggy, almost 80 degrees, and the humidity is sky high. There is a slight haze out, a signal, sometimes, for good seeing. You might think that after growing up and living in the South all my life, where the summers are long, hot, and very humid, it wouldn’t bother me any more. But, that is certainly not the case. I have become addicted to the A/C, moving from the cool dry house into my air conditioned car and, once parked, into my office with the thermostat set at a cool 70 degrees. No time to get use to anything. Once outside, things get sticky during the short walk to the observatory. My shirt clings to me, my hat is uncomfortable. Inside the observatory with the roof rolled back, I throw my hat aside, take off my shirt, wipe my face and the back of my neck with it, and then slip on a lightweight t-shirt. The final insult, the ritual oil down with mosquito repellent, always put on down wind of the observatory, is next. Walking back inside, I wipe my hands off with one of those alcohol soaked paper towels and I’m all set.

The Moon is high overhead. The observatory has been open since sunset with the dew remover on to ensure the lens has not fogged. Turning the telescope, my TMB 8” F/9 apochromatic refractor, on the Moon I realize the tube is wet. I am not the only thing that has been sweating. As I focus in on the rugged lunar surface any uncomfortable feelings vanish. The view is spectacular. Although for many years I observed with one eyepiece I have become a fan of the binoviewer. I can understand the logic surrounding loss of light when using a binoviewer on deep sky objects, but for the Moon and planets any loss of light is insignificant. I believe I can see more with my telescope, more faint detail, with a binoviewer than without. And, of course, observing with two eyes is more natural. To add to the comfort of observing, I have an adjustable seat. As the height of the telescope changes, the seat height can be modified as well so that I am always in a comfortable seated position when observing. The Feathertouch focuser allows precise focusing although the image produced by the 8” LZ0S lens snaps into focus without the need of the micro focuser. Still, it is a nice feature.

Seated comfortably at the eyepiece of my 8” refractor, the rugged lunar surface clearly defined, seemingly within arms reach below, I feel close somehow to my 19th century counterparts. Those observers were describing and mapping the Moon in fine detail. I, on the other hand, am just trying to See as much fine detail as my telescope, my eyes and the atmosphere will allow. They were looking for some evidence of lunar change, of volcanic activity still present, while I am amazed at the unchanged nature of the lunar surface, of a natural museum detailing the formation of planets and moons in our solar system. And, even though seeing the Moon in the smallest telescope will reveal enough detail to truly understand the big picture of meteoroid impact and crater formation with secondary change based on lava flows, the more detail seen, the more spectacular the view. Tiny craterlets and rilles, lunar domes and other detail more visible in larger aperture scopes, add to the overall picture. The lunar surface is an alien world very much unlike our own although both were formed in a similar fashion. On the earth, water, wind and geologic forces have, over millions of years, all but erased the surface detail related to the earth’s formation. Yet, the lunar surface, so close and so easily examined in minute detail, has remained virtually uncharged for millions of years. Trying to accurately describe the view of the lunar surface is nearly impossible, like trying to describe some famous work of art, Michelangelo’s David or Van Gogh’s Starry Night. You must view it first hand. Only then, after having a basis for interpretation, is there a chance of understanding, perhaps even visualizing, the written description.

As I scan the lunar surface at low power I am reminded of various theories of lunar crater formation. Lunar craters were, in the 19th and part of the 20th century, felt to be volcanic in origin. We now know they were formed by the explosive impact of meteoroids, asteroids, and comets, celestial debris swept up in the early millennia of our solar system as it formed. But we also now know that the large lunar seas and the floor of many craters were modified by the flow of volcanic magma. And so, as I sit and observe the Moon, I see great formations of both meteoric and volcanic origin. If the seeing will allow, my 8” refractor will show intricate detail. Perhaps, not as much as some other larger aperture telescopes, but quite an amazing amount none-the-less. When the seeing is good and the image is sharp and crisp at high magnification the view is truly spacecraft like. Although some may talk about eyepieces with a spacecraft view, it is this high power view that most seems like the view from a spacecraft to me.

Lunar domes are low blister-like swellings on the lunar surface found usually on mare plains or the floors of flat, magma flooded, craters. Sometimes the dome-like swelling has a central crater pit. North of Hortensuis is a group of six domes. These are very prominent tonight and the good seeing, along with the fine quality lens, allows me to boost magnification. The view under the slowly rising sun and lengthy shadows is spectacular. The reason for referring to these volcanic features as domes is obvious. The crater pits on their summits are easily seen. These gentle swellings, of volcanic origin, are made prominent by the stark lunar shadows merging to form the black lunar night beyond the terminator. A lunar domes characteristic blister-like shape is easily recognizable after studying classic examples like these next to Hortensius. Moving North and West there is another classic example of a dome, Milichius Pi. Tonight it is very prominent, located as it is, even close to the lunar terminator. Although lunar domes as a specific category do not appear to have been separated out until the late 19th or early 20th century, Milichius Pi is clearly represented on Johann Schroeter’s early drawings made in the late 18th century. As far as I have been able to find, Schroeter was the first to draw and publish an image of a lunar dome. Leaving Milichius Pi behind and continuing to the North there is a complex array of lunar domes many of which do not contain central crater pits. They are of varying sizes but all have that low blister-like appearance. This is a very interesting area to study using various eyepieces, highest power to look for tiny crater pits or to study other intricate detail, and lower powers to get an overall view and feel for this vast volcanic field.

You don’t have to observe just along the terminator, but, it is along the terminator that the lowest hills, slopes and, of course, lunar domes stand out. Stark black shadows stretch for miles across the maria from the smallest mountain peaks. Crater walls stand out in sharp relief. It is the alien surface of the Moon at its very best. And, tonight, with steady seeing allowing my telescope to deliver the type high quality image it is capable of producing, I could not be more pleased, as I sit viewing the rugged lunar surface in intricate detail. I adjust the speed of my hand controller for my AP 1200 mount so that I can smoothly move the telescope at high power in every direction across the surface of the Moon. As I slip along the terminator I see the bright white peaks of mountains and outcroppings from crater ruins reflecting the sunlight, surrounded by the pitch-black lunar night. These are the first manifestation of some massive crater or mountain range. Just along the terminator the lunar surface takes on a soft dark shade, a combination, no doubt, of the reflected light and shade of the smallest rocks sitting on the lunar surface. In this area the smallest relief is accentuated. Incredible surface detail now stands out beautifully. I change from medium to higher to highest magnification studying the area, mesmerized by the view. I am not really sure of the size of the smallest craterlets that flicker in and out of view. At times everything sharpens with all the tiny craterlets snapping into focus and remaining clearly in direct view for tens of seconds at a time. For me, at my location, this is excellent seeing. Continuing along the terminator I come upon a crater filled with shadow. The night seems like liquid pitch, which has run into the crater, filling the floor and extending into every tiny crack in the crater wall, through any breech merging with the surrounding night. The crater rim itself, a pure and white dazzling white thread of light, forms an oval above the black abyss below. I imagine the view from the very top of the brilliant star-like central mountain peak, the only visible feature within the wall, surrounded by the black lunar night. There, I imagine being in the brilliant sunlight, alone, with black below and in all directions, truly the meaning of “alone”. I decide to break this train of thought and move on.

Forty years ago I sat down at a library table filled with astronomy books. My earliest recollection of the Moon through a telescope was from this time. A neighbor had a small reflecting telescope aimed at the Moon and I was invited to take a look. The view was a low power one with the entire Gibbons Moon visible. I was shocked at how impressive the Moon appeared. Far more detail could be seen than I thought possible with such a small telescope. That was it. Between the fascinating discussions I read in many library books from many different libraries, combined with this view of the Moon though a small astronomical telescope, I wanted to observe the Moon, planets, comets, stars, galaxies, you name it. If a telescope could show it I wanted to see it. And from the very start the Moon has held a special fascination for me. For this, I am very lucky as most of the locations from which I have observed have been significantly light polluted. While light pollution can destroy the beauty and detail of many Deep Sky objects; it does not really interfere with lunar, planetary and other high-resolution observing. What is needed, of course, is steady seeing. And, perhaps equally lucky, many of my light polluted observing sites have had fair numbers of nights of good seeing each year.

The tangential light from the rising sun also accentuates the next object, a wrinkled ridge, which catches my attention. Just as with domes the name fits. Thin and not so viscous, lunar lava flowed across and filled the floors of gigantic impact basis, covering forever craters, mountains and all in its path to form large Mare or seas. Lava may have flowed from many different locations and there may have been over time, a number of eruptions as well. Sometimes, the last flow formed, what appear to be, waves on the mare, frozen in place, the wrinkled ridges. Tonight, a wrinkled ridge is near the terminator, the soft edges of which rise slowly from the surrounding lunar sea. The surface of the ridge is not entirely smooth, having a braded appearance, the wrinkles, with the ridge extending for hundreds of miles across the mare.

The smooth surface of the mare is everywhere pitted with craterlets of varying size. Small hills, ridges and gentle bulges, related perhaps to some distant lava flow, all become more prominent along the terminator. The image is extremely sharp and the faintest sparkling of craterlets is easily held with direct vision. I actually prefer the high-resolution view of the Moon through a telescope to spacecraft views, particularly images from the surface of the Moon. The telescopic view appears crisp with, under good seeing conditions, surface detail sharply defined, and exhibiting little evidence of weathering. This view led to early drawings showing the lunar surface consisting of tall mountains with rugged, sharp peaks and an unweathered surface. Lunar landing crafts have shown us that, instead, the surface has a very worn appearance due to micrometeoroid impact, extreme temperature change from day to night as well as long-term effects of the solar wind. On the surface, the Moon looks her age.

By now I suppose I have become somewhat adapted to the heat and humidity. Covered in a thin layer of perspiration, the mosquito repellant has been amazingly effective. There is iced tea in a thermos jug, welcome refreshment. Moving away from the telescope I sit in a large winged back chair in the corner of the observatory, my feet propped upon a short step stool. It’s been a very good night of lunar observing. The detail has been extraordinary. After quickly checking Rukl’s Atlas to insure that I have not missed some particularly interesting feature, I decide to take a last tour at low and medium power traveling along the terminator from pole to pole. I then call it a night, roll the roof back on the observatory, turn on the A/C, and fall asleep in my observatory chair, content.

Jim Phillips