So what's on the Moon

There is more on the moon than just craters and mountains. The moon is most likely the first thing you will look at through your scope. It is also very easy to see detail on the moon with a good pair of binoculars although most of the features below require at least a small to medium size scope.

Most amateur astronomers dislike the moon for part of the month because from the first quarter until after the third quarter it makes viewing of deep sky objects more difficult. However after a recent lunar workshop given by one of our members many of us in the group have a new respect for our closest neighbour.

This group is very lucky to have as a member Simon Hanmer, a prominent canadian geologist. His work in geology and his love of astronomy has led him to study the rocky planets in our solar system and to become somewhat of an expert on the geology of the moon. The information below was compiled by Simon and is here to assist you in developing an interest in that big bright light of the night.

If you are new to the hobby then this information will give you something interesting to look at as you learn your new scope. As for the more experienced observers these features should be easy to locate but there are many more of these same features in other locations that should be a little more challenging to find.

Remember that all of these features will stand out better only when they are close to the terminator, (line between light and dark during any phase other then full). So that means that even from one night to the next different features will visible.

The darker numbers correspond to one of the 14 features listed below. You will find a list of definitions at the bottom of the page. 

Click on a number to jump to that feature

Definitions of common terms









 

Altai Scarp

Located in section 57

This scarp is up to a kilometre high in places. It is the remnant of one of the multiple rings generated during the great impact that formed the Mare Nectaris impact basin.

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Archimedes Platform

Located in Section 22

Within the box are several cracks (rilles)
parallel to the rim of the Mare Imbrium impact basin, including Hadley Rille, site of an Apollo landing. The Rilles likely represent
flexing and cracking of the Mare margins due to the weight of the basalt lavas that fill the ~12 km deep impact basin.

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Rupes (ridge) and Rima (valley) Cauchy

Located in Section 36

These straight, segmented features in Mare Tranquillitatis are probably associated with tectonic faults. They are probably rift-type feature where the "keystone" between two close-spaced faults have either dropped down (valley) or pushed up (ridge). Alternatively, the ridge could be associated with lava extruded at the surface along a fault/crack.

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Copernicus Domes

Located in Section 30

A field of wide spaced, relatively large volcanic domes (volcanoes - looking like small blisters) WNW of Copernicus crater.

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Gruithuisen Domes

Located in Section 9

These two "pimples" just SSW of Sinus Iridum (W side of mare Imbrium) are two of the largest volcanoes visible on the Moon. Think Hawaii !!

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Hyginus & Ariadaeus Rima (valley)

Located in Section 34

Hyginus to the left: a wandering valley made of segments, with a prominent small crater in one of its bends. This is a valley created by a string of volcanic collapse structures guided by a tectonic fault.

Ariadaeus to the right: a straight valley associated with a segmented tectonic fault. Given the lack of classical erosion (by water or ice) on the Moon, the valley may be a narrow rift whose floor has dropped between two fault, or the roof of a sheet of magma - guided by a fault - that collapsed when the magma was drawn back into the interior of the Moon (yes, these things are known to happen).

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Marius Hills

Located in Section 29

These pimples, West of Marius crater (West of Kepler crater) are the most spectacular field of volcanic domes anywhere on the near-side of the Moon.

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Plato & Alpine Rima (valley)

Located in Section 4

Plato (left): ENE of Plato crater, on the N side of Mare Imbrium, this squiggly valley is a giant lava tube whose roof has collapsed along most - but not all - of its length. The lava in the tube was flowing from the highlands down to fill the Mare Frigoris North of the Mare Imbrium.

Alpine (right): The most cassical valley on the Moon, this rift is a lunar equivalent of the Ottawa Valley. In a really big scope, there is a second squiggly valley (an ancient lava river) running along its length. To picture this - think of looking from the Champlain Lookout at the top of the Eardley escarpment overlooking the Ottawa Valley and the Ottawa River.

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Unnamed Catena (crater chain)

Located in Section 44

This extraordinary feature, tangent to Ptolemaeus crater formed as an incoming meteor broke up in flight and
struck the lunar surface in an "instantaneous" series of impacts. This is probably the best example of this phenomenon on the near-side of the Moon.

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Reiner Gamma

Located in Section 28

This light coloured patch and associated strands in Oceanus Procellarum is a puzzlle. No-one's quite sure what it is, but it is pretty well unique on the near side of the Moon.

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Rheita Valley

Located in Section 68

Due South of Nectaris basin and tangent to Rheita crater, this valley was carved out by a series of instantaneous multiple impacts by ejecta from the Imbrium impact basin, to which the valley axis is radial.

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Schroter's Valley

Located in Section 18

The most spectacular squiggly valley on the Moon rises on high ground in the Oceanus Procellarum, West of Imbrium Basin. It represents a large lava channel carved by magma flowing from the high ground to fill the Procellarum basin below. This is the best direct observation amateur astronomers can make to demonstrate
hat the flat fill of Mare basins is indeed lava.

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Serenity Cracks & Ridges

Located in Section 24

Rimae (valleys/cracks) Plinius (lower field): These fractures in southern mare Serenitatis represent stretching of the convex upward marginal Mare crust in response to sinking of the Mare centre under the load of the flood basalts that filled the impact basin.

Dorsae (ridges) Lister and Smirnov (upper field): These ridges represent shortening and folding of the concave upward interior Mare basalts also in response to the loading due to the weight of the basalt lava.

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Rupes recta, The Straight Wall

Located in Section 54

This tectonic fault in eastern Mare Nubium gives rise to a relatively low amplitude hill that is picked out by the light and shadow effects due to the low Sun angle. It looks like a sword with the handle and guard at the southern end. Although it is not a cliff, it is perhaps the most striking tectonic feature associated with faulting on the Moon's near side.

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Terms

Lunar mare
The lunar maria (singular: mare, two syllables) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and hence appear dark to the naked eye. The maria cover about 16 percent of the lunar surface, mostly on the near-side visible from Earth.

Impact crater
In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the hyper-velocity impact of a smaller body with the surface. This is in contrast to the pit crater which results from an internal collapse. Impact craters typically have raised rims, and they range from small, simple, bowl-shaped depressions to large, complex, multi-ringed, impact basins.

Domes
A variety of shield volcanos can be found in selected locations on the lunar surface, such as on Mons Rümker. These are believed to be formed by relatively viscous, possibly silica-rich lava, erupting from localized vents. The resulting lunar domes are wide, rounded, circular features with a gentle slope rising in elevation a few hundred meters to the mid-point. They are typically 8-12 km in diameter, but can be up to 20 km across. Some of the domes contain a small pit at their peak.

Highlands
The most distinctive aspect of the Moon is the contrast between its light and dark zones. Lighter surfaces are the lunar highlands, which receive the name of terrae (singular terra, from the Latin for Earth). The highlands are older than the visible maria, and hence are more heavily cratered.

Lava tubes
Lava tubes are natural conduits through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption. They can be actively draining lava from a source, or can be extinct, meaning the lava flow has ceased and the rock has cooled and left a long, cave-like channel.

Rilles
Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length.

Three types of rille are found on the lunar surface:

1. Sinuous rilles meander in a curved path like a mature river, and are commonly thought to be the remains of collapsed lava tubes or extinct lava flows. They usually begin at an extinct volcano, then meander and sometimes split as they are followed across the surface. Vallis Schröteri in Oceanus Procellarum is the largest sinuous rille.
    
2. Arcuate rilles have a smooth curve and are found on the edges of the dark lunar maria. They are believed to form when the lava flows that created a mare cool, contract, and sink. This are found all over the moon, examples can be seen near the south-western border of Mare Tranquillitatis and on the south-eastern border of Mare Humorum.
    
3. Straight rilles follow long, linear paths and are believed to be grabens, sections of the crust that have sunk between two parallel faults. These can be readily identified when they pass through craters or mountain ranges. Vallis Alpes is by far the largest graben rille, indeed it is regarded as too large to be called a rille and is itself bisected by a straight rille; Rupes Recta in Mare Nubium is a clearer example.
   
   Note:
   Rilles which show more than one structure are termed hybrid rilles. Rima Hyginus in Sinus Medii is an example, initially formed through a fault and subsequently subject to volcanic activity.
    

Wrinkle-ridges
Wrinkle ridges are features created by compressive tectonic forces within the mare. These features represent buckling of the surface and form long ridges across parts of the mare. Some of these ridges may outline buried craters or other features beneath the mares.

Graben
Graben are tectonic features that form under extension stresses. Structurally, they are composed of two normal faults, with a down-dropped block between them. Most graben are found within the lunar mare near the edges of large impact basins.