The Astro Lair Monthly
A different topic for every lunation, courtesy of the Astro Lair! |
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This Lunation's Topic:
The Joys of Lunar Observing
My Top 25 Targets on the Moon
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Over the years, the majority of amateur astronomers I have met are primarily interested in observing Deep Sky Objects (DSO’s). The allure of magnificent nebula, sparkling open clusters, faint ghost like galaxies, elusive planetary nebula, and mighty globular clusters keep these astronomers yearning for ever darker skies and ever larger apertures with which to enjoy them. This comes as no surprise, since these objects, so far removed from our own environs in space, spark imagination and wonderment like no other bodies in the heavens. They are challenging to find, observe, and comprehend. And once someone rises to the challenge, they often find themselves in a lifelong pursuit for better views and clearer understanding of what seems to be the essence of our universe.
To these amateurs, the Moon represents a major impediment. Our lone natural satellite is looked upon not with a discerning eye, but with disdain. For at least two weeks of every lunation, reflected sunlight, sailing a quarter million miles through space, sends the deep sky enthusiast into retreat, leaving them cursing every clear night wasted on a full moon. And they would be quick to tell you that the best weather always takes place between day 7 and 21 of each lunation! For the enthusiast who must retreat to remote observing locations to enjoy dark skies free from man made light pollution, the window of opportunity is even narrower. Many serious DSO hunters would not waste a long trip on a night when they will be greeted in the early morning hours by a rising third quarter moon. Their observing window, more realistically, is reduced to perhaps10 days for optimum observing. If the astronomy gods are truly on their side, this might bridge two weekends!
This is indeed a shame. Our partner in space is such a wonderful target for the earth bound observer. There is nothing boring or routine about this body. Having now had the opportunity to get a good look at many of the moons gracing the outer planets of our solar system, via robotic spacecraft, I would argue that our own moon ranks right up near the top of the list in terms interesting geology and pure esthetics. And what makes it most special of all, is that the amateur can study it in amazing detail, unlike any other object in our solar system.
Our moon is a demanding target. Detecting the most subtle features places demands upon the amateur’s telescope, and can stretch the capabilities of the observer and his instrument to the very limits of performance. Many amateurs (if not most) have not taken the time to study the significant changes in appearance that can occur due to changing angles of illumination; not only the difference between lunar sunrise (the most common view) and lunar sunset (when only the lunar enthusiasts venture out), but minute by minute, as the blackest of lunar shadows race across the depths of craters and sinuous rilles, and specks of sunlight dance from the highest lunar mountain tops majestically rising above the razor sharp line between night and day. Some say that the moon always looks the same. But these words are clearly spoken by those who have never taken the time and effort to appreciate and study it.
Now, I want to be clear that I am not talking about observing programs that have some scientific research goal in mind. My advice is geared towards the enthusiast who is primarily seeking challenge and pleasure from observation of the moon. Gaining a better understanding of the moon, through the power of observation, carries with it great personal rewards and satisfaction; not the least of which is that the lunar observer enjoys a year long show, and has at least a solid 22 consecutive day observing window during each lunation to make quality observations, weather and seeing conditions permitting. While your observing buddies are studying star charts in preparation for the next star party, you’re out under the night sky, soaking in moonbeams! An extra perk is that your observing program can be pursued under the best of conditions; all of the comforts of home observing can be utilized, since light pollution, and even dark adaptation, is of no consequence.
So.... have I wet your appetite for the lunar show now playing in a sky near you? I hope so. And to get you started, here is the main feature of this month’s article: 25 lunar targets that will get you off and running. In fact, you may find that these become some of your favorites, and you will return to them again and again.
The AstroLair Top 25 Lunar Targets
2. On the third day of the lunation, Mare Crisium steals the show. It measures approximately 280 miles north to south, and 350 miles east to west. It doesn’t appear that way due to foreshortening, however. In fact, it looks just the reverse. i.e., longer from north to south. This is one of the best lunar objects for understanding the effect of foreshortening. Most of the interesting detail in Mare Crisium is nestled along the western portion, where there are some nice craterlets and mountains. 3. On day 3 and 4, the crater Petavius is well placed for viewing. This 100 mile diameter crater is located south of Mare Crisium. There are some great examples of lunar rilles on the floor of this crater, one of which is prominent even in very small telescopes during sunrise illumination.
4. Day 5 reveals the crater Posidonius, another fine crater resting along the west shore of Mare Sernitatis. 5. Throughout the first 7 days of the lunation (up until the first quarter phase), closely observe the floor of all the Mare for signs of the ribbon-like wrinkle ridges, many of which stretch for hundreds of miles. They show themselves best when near the terminator (the dividing line between night and day). 6. Theophilus, on the northwest shore of Mare Nectaris, is almost a perfect crater. It measures 65 miles across, and has multiple central peaks that are very interesting. Good detail can be observed inside the rim of the crater, on the inner slopes. 7. Inspect the prominent trio of craters Arzachel, Alphonsus, and Ptolemaeus, stretching adjacent to each other from south to north, respectively. It is most interesting to observe the difference in structure and apparent ages of the three craters.
8. The mighty crater Clavius, located to the extreme south. This crater contains a significant number of secondary craters and small craterlets. Try and count the number of craters within its walls each time you observe it. This exercise will keep you coming back to this terrific crater time and time again, both to better your count, and to better appreciate the battered beauty of this ancient lunar landmark. 9. The crater Tycho, just north of Clavius. Observe it near the terminator in order to pick up details within the crater itself. I find that it takes very favorable seeing to reveal the true textures within the crater; otherwise, it appears bland. As the lunation progresses, Tycho will reveal its most famous attribute: the marvelous ray system that it graces much of the lunar landscape. 10. Shifting gears to the north, the craters Aristotles and Exodus. These craters form a sort of gateway towards the more prominent crater Plato, to the west. But Aristotles and Exodus both deliver fine detail within their walls and immediate environs. 11. The Valles Alpes. Just west of Aristotles, it is the best example of a valley on the moon. There is a thin rille running along the base of the valley that is among the toughest telescopic challenges on the moon. I have only glanced it on one occasion, and revisit it at every opportunity to attempt a reconfirmation of the observation.
13. The Appenine mountains are perhaps the very best mountain range on the moon for observation. Make sure to check it out during sunset illumination. It is even better then, and worth getting up early to see.
16. Sinus Iridium, encircled by the Jura mountains. On day 10, the mountain ring often stands alone beyond the terminator, forming a coat hanger upon which the moon dangles in space.
17. Archimedes, a prominent crater south of Plato. This crater provides a classic example of variation in floor shading, with significant dark and light streaks racing across the floor.
18. Timocharis, a small crater west of Archimedes. It is worth high power observation, conditions permitting.
19. Aristarchus, the brightest crater on the moon. It can even be seen quite easily during the first few days of the lunation, as it reflects more than its share of earthsine. When illuminated, look for bright and dark radial markings on the interior walls.
20. Schroters Valley is a winding, complex system directly adjacent to Aristarchus.
21. The crater Kepler, just west of Copernicus. Like Tycho, it is the source of another mighty system of rays. It is a small crater, but worthy of higher magnification examination.
22. The ever-interesting crater Gassendi, on the north shore of Mare Humorum. This is one of my all-time favorites! Study the interior, which features prominent rilles, and observe the fractures in the rim.
23. If the seeing and transparency are good, return to Copernicus under high illumination (i.e., full moon conditions). Study the ray system, in particular. When seeing conditions are right, it is chock full of details and rich texture.
24. Throughout the lunation, study the lunar limb. Note the mountains in their profile view. Also, observe craters near the limb, as they will appear like you are looking at them more from a surface elevation. It is a really interesting effect, and it lets your imagination soar as you imagine the way it must look from a spacecraft in low lunar flight, peering towards the horizon.
25. And finally, if the libration is favorable, try to observe Mare Orientale on the western limb. Hunting it down provides the best case study for understanding the effects of libration.
Happy hunting, and steady skies
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