around the moon in 28 days: lunar observing for beginners · section 7 - lunar day 2 tonight...

Around the Moon in 28 Days: Lunar Observing for Beginners

Course Notes

Section 6 - Lunar Day 1 (New Moon)

Section 7 - Lunar Day 2





Section 12 - Lunar Day 7 (First Quarter)

Copyright © 2010 Mintaka Publishing Inc.


Because the Moon is seen mostly at night, the time of sleep and dreams, our ancestors often endowed it with magical properties. Its repeating cycle symbolized birth and death – and measured time. Its return to the sky gave order to the seasons as it measured itself against the planets and stars.

At 24 to 36 hours old, tonight's Moon is going to be a huge challenge just to see in twilight sky with the unaided eye. To meet this challenge, you'll need to be well away from any horizon obstructions and begin looking just before the Sun is officially set (check your local sunrise and sunset times). If you are lucky, you'll find the Moon’s pencil-slim smile in the western sky that is the very beginning of “The Old Moon In The New Moon's Arms”. Don't worry if you can't catch it tonight, because the challenge lasts until the Moon is about 72 hours old (that is, past New). Because the sky will still be very bright, you may need your binoculars to assist you in finding it during the first few days of its cycle. Look for the most slender crescent that you can imagine and you'll see the illuminated curve is pointed exactly in the same direction as the setting Sun. Don’t worry about seeing any surface features. If you can find the Moon at all in the first 32 hours after New, you have done well!

As we wait for the Moon to reveal itself, a word first about directions on the face of the Moon...

At one time, the limb of the Moon facing west was called the “west” side, the limb of the Moon pointing north was the “north side”, and so on. This changed at the dawn of the space age, because this convention meant astronauts of the Moon would see the sun rise in the lunar west and set in the east. It also meant the dividing line between day and night on the Moon-- the terminator-- progresses from west to east, which is opposite that of Earth.

So astronomers switched it up in the 1960’s. North and south on the Moon still refer to the limbs that point north and south in our sky. But east and west are reversed. So if you look at the Moon at first quarter, the bright half on the western side of our sky is the east side of the moon. And vice versa. Confusing? Not really. You will become accustomed to it very quickly if you just remember the terminator always moves from east to west and the north section of the Moon is far more devoid of features than the heavily cratered south.

And one more thing... a telescope may flip the Moon’s image to make it even more confusing. A Newtonian reflector (or a Dobsonian) will flip north and south, east and west. Same story if you are using a refractor without a 90 degree star diagonal. But with a star diagonal, a refractor preserves north and south, but flips east and west. Don’t worry, a little experience will

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help you keep this straight. And binoculars? They keep the image the same way you see it with your unaided eye, which is one reason they are easy to use.

Figure 6-1: The crescent moon near sunset.

Just like on Earth, the lunar terminator – the dividing line of night and day - always progresses from east to west. This is fact, no matter how Moon appears oriented in the sky. Lunar north and south is the same as our cardinal directions, but not quite so easy to distinguish in a telescope. For binoculars and refractor telescopes, the view is presented correctly, but a reflector telescope produces a mirror image. This means what you are viewing is reversed from left-to-right and upside down. Confusing? Not really. You will become accustomed to it very quickly if you just remember the terminator always moves from east to west and the north section of the Moon is far more devoid of features than the heavily cratered south.

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Tonight we'll start with our eyes only looking for a very slender crescent Moon which sets as the sky darkens. Looking like a pair of bright horns bearing a dark disk, such a vision may have given rise to the ancient symbol associated with fertility goddesses originating in Egypt and Mesopotamia. Tonight we are looking for the “da Vinci Effect” - brilliantly lit along one edge and softly illuminated over the rest of the disc. Today we more commonly refer to monthly occurrence as "Earthshine". No special equipment is needed to see this phenomenon. Leonardo da Vinci was the first to correctly theorize that this ghostly light was sunlight was reflecting off the Earth and illuminating the portion of the Moon not lit by the Sun. Said Leonardo:

"Some have believed that the Moon has some light of its own, but this opinion is false, for they

have based it upon that glimmer visible in the middle between the horns of the New Moon...this brightness at such a time being derived from our ocean and the other inland seas -- for they are

at that time illuminated by the Sun, which is then on the point of setting, in such a way that the

sea then performs the same office for the dark side of the Moon as the Moon when at the full

does for us when the Sun is set...."

Figure 7-1:- da Vinci's sketch of Earthshine

Now, let's begin learning some features!

Tonight's binocular challenge is to identify the partially disclosed Mare Crisium just lunar north of center along the terminator. Because you are looking along a curve, the emerging mare won't look large, but it's actually the size of the state of Washington. Mare Crisium is a unique

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feature because it isn't connected to other maria. If the lunar terminator has not advanced too far at your viewing time, scan the southeast shoreline of Mare Crisium for Agarum Promontorium - a bright, peninsula-like feature. Take mental note at how it invades northward across the dark plain before it disappears beneath the once-molten lava.. Great lunar observers of the past have noted a mist-like appearance in this area. These types of very rare occurrences still happen and are referred to as transient lunar phenomenon.

Figure 7-2: The Moon at two days old (left). A close- of Mare Crisum and Agarum (right).

Next up is a telescopic challenge - crater Langrenus. You'll find it located almost centrally on the terminator and very noticeable. Depending on your viewing location and time, it may be divided by the terminator. Named for Belgian engineer and mathematician Michel Florent van Langren, the crater floor stretches out over 132 kilometers in diameter with walls rising up to 1981 meters high. The deepest area reaches down 4937 meters below the lunar surface and could swallow Ecuador's Mount Cotacachi whole. Look for sunrise over its brilliant east wall to see if you can spot Langrenus' central mountain peak. Rising up 1950 meters, it's as high as the

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base elevation in Jackson Hole, Wyoming! While that might seem large, it's small for a crater this size and will present a challenge to spot.

Have a look with a larger telescope at high magnification. Formed in the Eratosthenian geological period, Langrenus could be anywhere from as much as 3.2 billion to as little as 1.1 billion years old. Its southern border is deformed by its C and E craters and the structure of Crater Lohse further south seems to help support its ancient walls and terraces. On the crater floor a 1000 meter high double mountain peak looms impressively, but look for additional small hills and craterlets. Another challege is to spot the bowl-like formation of 14 kilometer wide crater Acosta intruding on Lagreneus' northern slopes.

Figure 7-3: An extreme close-up of the crater Lagrenus (courtesy of Damian Peach)

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Tonight we'll start off with binoculars in the northeast quadrant of the Moon for a more detailed look at Mare Crisium - the "Sea of Crises" - home to a gravitational anomaly called a mascon. This "mass concentration" could possibly be fragments of the asteroid or comet whose impact with the lunar surface created the basin buried beneath the lava flow. How do we know it’s there? A mascon creates an area of high gravity and causes changes in the orbits of lunar probes. This excess gravity has even been known to cause low orbiting lunar satellites to either crash land or be flung out into space!

Now take a look at Mare Crisium in your telescope and identify the long frozen wave of lava along its west bank known as Dorsum Oppel. And the two small punctuations of crater Swift to the north and crater Pierce to its south. When you reach midway along the western shoreline, look for Promontoriums Olivium and Lavinium. Up the magnification and you'll see the small well of crater Picard resides in the east.

Figure 8-1: A closeup of Mare Crisium (courtesy of Virtual Moon Atlas); crater Picard is on the

lower-left of Mare Crisium in this image

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Figure 8-2: The major features of the Moon on Day 3.

Now look south of Mare Crisium near the center of the lunar terminator to identify more than 3 billion year old Mare Fecunditatis (the Sea of Fertility). Its expanse covers 1463 kilometers in diameter. The combined area of this mare is equal in size to the Great Sandy Desert in Australia - and almost as featureless. Here you will find glasses, pyroxenes, feldspars, oxides, olivines, troilite and metals in the lunar soil known as regolith. Studies show the basaltic flow inside of the Fecunditatis basin may have occurred all at once, making its lower titanium content and chemical composition different from other maria.

If you're into challenges and curiosities, then look north in the southern edge of the foothills which surround the Mare Fecunditatis for a very little known feature known as Sinus Successus - the "Bay of Success". This 104 kilometer wide, C-shaped feature will take you to points of

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success - the successful lunar landings of the Soviet Luna 16, Luna 18 and Luna 20 probes. Look for the ring of crater Webb between Sinus Successus and Langrenus.

Luna 16 was the first robotic probe to land on the Moon and return a soil sample back to Earth. On September 20, 1970, approximately 100 kilometers east of Webb crater, it set itself down and went to work. Panoramic television cameras surveyed the surface - relaying back data. An automatic drill collected a soil sample while radiation and temperature were recorded. Then... a successful lift off and return! On September 7, 1971 Luna 18 entered lunar orbit and successfully completed 85 communications sessions and 54 lunar orbits before it was directed to land in the same area. On September 11, Luna 18 began descent, but the order failed and it slammed into the mountains rimming Sinus Successus. Even though it crashed, it wasn't a failure. Luna 18’s continuous-wave radio altimeter still broadcast back the mean density of the lunar topsoil. Luna 20 fared even better. It touched down on the lunar surface on February 21, 1972 - an unbelievable 1.8 kilometers from the crash site of Luna 18. Its samples were safely collected and returned to be shared with American and French scientists alike. That makes Sinus Successus a very successful place indeed!

Figure 8-3: Luna 16 (courtesy NASA).

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Let’s continue exploring Mare Fecunditatis tonight. Stretching out across an area about equal in size to the state of California, the Sea of Fertility's western edge shares a tectonic formation we have here on Earth - grabens. These down-dropped areas of landscape between parallel fault lines happen where the crust is stretched to the breaking point. On Earth, grabens occur along tectonic plates, but on the Moon they are located around basins. The forces once created by lava flow weighted down the inside of the basin caused tension along the border. Look closely along the western shore of Fecunditatis where many graben features are located. They are also bordered by parallel fault lines similar to Death Valley in the western United States.


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For our telescopic challenge tonight, aim towards the earthen shore of Mare Fecunditatus and identify the flat, bright oval of of our previous study, Langrenus. Identify two small craters just slightly northwest of the mare's center - Messier and Messier A. This twin pair was named for the famous French comet hunter, Charles Messier. The easternmost crater is somewhat oval in shape with dimensions of 9 by 11 kilometers. At high power, Messier A to the west appears to have overlapped a smaller crater during its formation and it is slightly larger at 11 by 13 kilometers. For a challenging telescopic note, you'll find another point of interest to the northwest. Rima Messier is a long surface crack which runs diagonally across Mare Fecunditatis' northwestern flank and reaches a length of 100 kilometers. Keep the Messiers in mind, for in a few days you will see a pair of "rays" extending out from them.

Figure 9-2: Mare Fecunditatus, with craters Messier and Messier A.

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Figure 9-3: A closeup of the craters Messier (right) and Messier A (left) in Mare Fecunditatus

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On the lunar surface tonight, let's begin with a binocular look at Mare Serenitatus – the “Serene Sea”. On its northeast shore, you'll have no trouble spotting the shallow ring of crater Posidonius. As flat as a pancake from eons of lava flows, this crater displays different textures along its floor when viewed in a telescope. This huge, old, mountain-walled plain is a class V crater and could be as much as 3 billion years old. Measuring 84 by 98 kilometers, shallow Posidonius drops only 2590 meters below the surface. Power up to observe the stepped, stadium-like wall structure and many mountain peaks joining its small, central interior crater. Posidonius also displays an interior rim that's especially prominent to the east. Also look for smaller craters Posidonius A inside the greater Posidinius, and Posidinius B on the northeast edge of the rim of Posidonius.


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Figure 10-2: A closeup of the crater Posidonius, with inlying crater Posidonius A and

Posidonius B on the northern (upper) rim.

Now look a bit south of and east of Posidonius and almost parallel to the terminator for a curious feature known as the Serpentine Ridge, or properly as Dorsa Smirnov and the accompanying Dorsa Lister. This thin, white line meanders across the western section of Mare Serenitatus for a distance of at least 134 kilometers and raises up as high as 305 meters above the smooth sands. This lunar "wrinkle" is an amazing 10 kilometers wide! Power up in a telescope. The northern section of the Serpentine Ridge is called Dorsa Smirnov until it branches west and becomes Dorsa Lister. If the shadow play is good at your time, you might be lucky enough to resolve Dorsum Nicol, which connects the two. Only about 51 kilometers long, Dorsum Nichol will appear almost as a circular, crater-like feature - but it isn't. As part of the Mare Serenitatis / Mare Tranquilitatis border, it's not much more than a just an area where the two distinct lava flows cooled and contracted, causing the surface to buckle upwards.

It is where these two vast lava plains merge that we will set out on a historic and challenging telescopic journey. Power up and you will see a bright "peninsula" westward from where the two mares conjoin and look toward the east: for bright and small crater Pliny (Plinius) – a 44 kilometer wide ring with a prominent central peak. It is near this rather ordinary crater that the remains of Ranger 6 lie forever entombed on the lunar surface where it crashed on February 2, 1964. Unfortunately, technical errors occurred and Ranger 6 was never able to transmit lunar

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pictures. Not so Ranger 8! On a very successful mission to the same relative area, the spunky little probe delivered 7137 "postcards from the Moon" in the last 23 minutes before hard landing. On the "softer side," Surveyor 5 safely touched down after two days of malfunctions nearby Pliny on September 10, 1967. Incredibly, tiny Surveyor 5 endured temperatures of up to 139° C and was able to spectrographically analyze the area's soil. And by the way, it also managed to televise an incredible 18,006 frames of "home movies" from its distant lunar locale!

Figure 10-3: Pliny as seen from Ranger 8 courtesy of NASA

Figure 10-4: Serpentine Ridge” from the Consolidated Lunar Atlas courtesy of NASA

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Tonight on the lunar surface, all of Mare Serenitatis and Mare Tranquillitatis will be revealed, and so it is fitting we should take an even closer historic look at both the "Serene" and "Tranquil" seas. Formed some 3.8 billion years ago, these two areas of the Moon have been home to most of mankind's lunar exploration. Let's go to the southwest edge of Tranquillitatis and visit with the Apollo 11 landing area. Although we can never see the "Eagle" telescopically, we can find where it landed. For telescopes and binoculars the landing area will be found near the terminator along the southern edge of Mare Tranquillitatis.

No scope? No problem. Find the dark round area on the lunar northeastern limb - Mare Crisium. Then locate the dark area below that - Mare Fecundatatis. Now look mid-way along the terminator for the dark area that is Mare Tranquillitatis. The bright point west where it joins Mare Nectaris further south is the target for the first men on the Moon. We were there!


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Telescopically, start tracing the western wall of Tranquillitatis and looking for the small circles of craters Sabine and Ritter which are easily revealed tonight. Once located, switch to your highest magnification that conditions will allow. Look in the smooth sands to the east to see a parallel line of three tiny craters. From west to east, these are Aldrin, Collins, and Armstrong - the only craters to be named for living humans. It is here where Apollo 11 touched down, forever changing our perception of space exploration.

“That's one small step for [a] man, one giant leap for mankind.”

- Neil Armstrong, July 20, 1969

-Figure 11-2: The Sea of Tranquility, showing the Apollo 11 landing site near the craters Ritter

and Sabine.

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When you're ready, let's change our perception of the size of the things we see on the lunar surface by exploring the edges of Mare Serenitatus - a feature that's about the same size as the state of New Mexico. On its southwest shoreline stands the Haemus Mountains, whose bright peaks will continue on beyond the terminator. Look in their midst for the sharp punctuation of Class I Menelaus. This small crater has a brilliant west inner wall and deeply shadowed floor. While the Montes Haemus look pretty impressive, they are nothing more than foothills compared to the Apennines which have yet to emerge into the sunlight. Look at Serenitatus' northwest edge to view some real mountains! These are the Montes Caucasus, rising up to 5182 meters above the desolate lunar plains. Like its Earthly counterpart, the Caucasus Mountain Range has peaks that reach upwards of six kilometers - summits as high as Mount Elbrus! Nearby and slightly smaller than its terrestrial namesake, the lunar Apennine mountain range extends some 600 kilometers with peaks rising as high as five kilometers. Be sure to look for the summit of Mons Hadley, one of the tallest peaks you will see at the northern end of this chain. It rises above the surface to a height of 4.6 kilometers, making that single mountain about the size of asteroid Toutatis.

Figure 11-3: Major lunar mountain ranges surrounding Mare Serenitatus; the site of the Apollo

15 landing near Mons Hadley.

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For those seeking a bit of a telescopic and binocular challenge, look no further than the Valles Alpes. More commonly known as the "Alpine Valley" this deep gash cuts across the northern surface just south of Mare Frigoris. Lighting conditions on Day 6 will be just right to notice its 1.6 to 21 kilometer wide and 177 kilometer long expanse. Using it as your guide, start at the western point and drop south along the Montes Alpes where you will see three bright peaks - Mons Blanc, Promontorium DeVille and Promontorium Agassiz. Can you see lonely Mons Piton in the gray sands of Mare Imbrium? It stands 2250 meters above the lunar surface – about the average height of the Sierra Madres – but as a single, lonely peak.

Figure 11-4: The Alpine Valley, just south of Mare Frigoris.

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By now the Moon has began to rise in skies around the noon hour. As the Sun begins to set, you'll notice its distinctive “half” shape high along the ecliptic plane. But why is it called the First Quarter Moon? While it appears appears half-lit to us, we need to remember that we really are only seeing one fourth of the Moon's surface. If we could see it in orbit around the Earth from above, it would be at a right angle. As it grows more and more each night, the Moon is said to be “waxing” toward Full.

“The half Moon shows a face of plaintive sweetness

Ready and poised to wax or wane;

A fire of pale desire in incompleteness,

Tending to pleasure or to pain...” -- Christina Rossetti


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Tonight we will begin our lunar explorations as we look to the lunar far north with our eyes and identify the “Sea of Cold” - Mare Frigoris. This long, vast lava plain extends 1126 kilometers across the surface from east to west, yet never ranges more than 72 kilometers from north to south.

Now use binoculars to look for the unmistakable dark ellipse of landmark crater Plato caught on Frigoris' south-central shore. Named after the famous philosopher, this Class V crater spans approximately 101 kilometers but is a shallow one kilometer deep. The bright rim of Plato's enclosure is very worn and can rise as high as two kilometers above the surface, casting unusual shadows on the lava covered floor. At around 3.8 billion years old, Plato is even more ancient than Mare Imbrium to its south. For 300 years astronomers have been keeping a watchful eye on this crater. Noted lunar observer Hevelius called it the “Greater Black Lake,” due its low albedo (surface reflectivity). Despite its dark appearance, Plato is well known as a home for lunar transient phenomena such as flashes of light, unusual color patterns and areas that could be outgassing. A fun place to power up with a telescope and contemplate!

Figure 12-2: A closeup of the crater Plato, next to Mare Frigoris (courtesy of Damian Peach)

Are you ready for a challenge? Using your knowledge of Mare Serenitatis, look for a break along its western shoreline which divides the Caucasus and Apennine mountain ranges. Just south of this chink in the armor is the bright peak of Mons Hadley. If observing conditions are steady, high magnification with a mid-sized telescope will reveal a smooth floor, with a major fault line known as the Hadley Rille. It winds its way across 120 kilometers of lunar surface, in places spaning 1500 meters in width and dropping down 300 meters below the surface. This

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huge crack may have been formed by volcanic activity some 3.3 billion years ago. Geologically speaking, we can see the impact lower lunar gravity has on this type of formation. Earthly lava channels are usually less than 10 kilometers long and only around 100 meters wide!

Figure 12-3: Hadley Rille (courtesy of Damian Peach)

During the Apollo 15 mission, Hadley Rille was visited at a point where it is only 1.6 kilometers wide - still a considerable distance as seen in comparison to astronaut James Irwin and the lunar rover. Over a period of time, lava may have continued to flow through it, yet it remains forever buried beneath years of regolith. Hoping for fresh exposures from what were once thought to be stratified mare beds, astronauts scoured along tops of the rille walls collecting of samples of the region. Geologists would then be able to study the origin of lunar sinuous rilles and determine if they were caused by some sort of fluid flow mechanism-possible volcanic activity.

Now, let's head south for the huge, hexagonal walled plain of Albategnius - one of the most prominent craters. Located about one-third the way north from the southern pole near the terminator, Albategnius is one very old crater. Stretching 131 kilometers in diameter and 4390 meters deep, you'll see a brilliant inner west wall and - if the timing is right - a small central peak on its dark floor. Albategnius' walls are marred with many craters strikes, but one of the finest is crater Klein. You can spot it coming up from the southwest and almost touching the

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central mountain. Directly to its lunar east, and about the same distance as Albategnius' width, you may be able to distinguish a crater trio - small western Andel, larger eastern Descartes, and larger still southern Abulfeda. Power up! Between Andel and Descartes is the small pockmark of Dolland. North of Dolland is a ruined, unnamed crater with a pronounced set of rings on its northwestern shore. On the eastern edge of the relatively smooth floor, the remains of the Apollo 16 mission still shine on.

Figure 12-4: Apollo 15 astronaut Dave Scott at the edge of Hadley Rille (NASA)

Partially filled with lava after creation, Albategnius also holds a place in history. On May 9, 1962 Louis Smullin and Giorgio Fiocco of the Massachusetts Institute of Technology (MIT) aimed a ruby laser beam toward the Moon's surface and Albategnius became the first lunar feature to reflect laser light from Earth. On March 24, 1965 Ranger 9 took a "snapshot" of Albategnius from an altitude of approximately 2500 kilometers. Ranger 9 was designed by NASA for one purpose - to achieve lunar impact trajectory and send back high-resolution photographs and video images of the lunar surface. Ranger 9 carried no other science packages. Its destiny was to simply take pictures right up to the moment of impact.

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Figure 12-5: A closeup of the crater Albategnius and region (courtesy of Peter Lloyd)

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around the moon in 28 days: lunar observing for beginners · section 7 - lunar day 2 tonight...

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