Mapping is a time consuming occupation at best but I can’t ever begin to understand the hardship the early map makers on our planet had to endure.
Mapping is a time consuming occupation at best but I can’t ever begin to understand the hardship the early map makers on our planet had to endure. I suppose at the very least they were standing on their task not remote from it. The accuracy of the early Cartographers is really amazing. You know when I was in the R.A.N. (Royal Australian Navy) in the early sixties, 1963 or there about, one of our assignments was to travel up the east coast, mainly the Great Barrier Reef area and check out chart entries made by Captain James Cook and others of that early time. Now they didn’t have a lot to start with and the only entries that we could not verify were these pertaining to ‘Dirty Water’ or patches there of and a shifting sand quay or two. Now given the time lapse from the late 1700’s to 1963 I reckon that’s not a bad effort.
He (Captain Cook) even listed all the small bays, beaches, river mouths and islands etc. with pin-point accuracy using celestial navigation (sextant) magnetic compass and his chronometer. Now that is truly amazing and it brings me to my point – took awhile eh!!!
How in god’s name did those early astronomers in the early 1600’s even begin to make maps of the Moon? Oh, alright! I know about the invention of the telescope at that time but their target was 384,000 odd kilometres distant and we are talking ‘mapping’ not ‘viewing’. Now one of those fellows was Michael Florent Van Langren (a name like that should guarantee success, eh!) and he is credited with one of the first Moon Maps of the time with the then known features named. ‘Langrenus’ one of the craters we discussed on day 2-3 was named in his honour. Oh! By the way, map making on the Moon is called ‘Selenography’ not Topography as it is here on earth.
Others of course stepped up to the plate in future times and they and their efforts are no less noteworthy. Mayer’s Maps (that is Tobias Mayer 1723-1762) even had grid lines for longitude and latitude on them to make it easier for future uses. Satellites and probes have done extensive mapping in the last few decades with probably the most important work being done by ‘Clementine’ in 1994 and onward. I believe into the 2000’s.
About the Craters:
Most of the craters on the Moon are of a circular shape with only a few being different. Some may be slightly elongated, some even joined together to form ‘Schiller’ type craters but all were made by the impact of an object crashing into the Moons surface (or material from that impact) at high speed and with explosive force.
That is to say, that a large piece of asteroid material (a big rock travelling at about 20km/sec) impacted the Moons surface and created an explosion, with a force of around 50-60 thousand mega tonnes of high explosives. The result would be a crater some 18 or 20 kilometres wide. Of course, the harder the material the impacting object is made of the bigger the crater would be, to a point. Imagine the size of the asteroid that caused the crater we now know as ‘Mare Imbrium’, more on that soon.
So, to take stock we have an asteroid striking the Moon. The resulting explosion excavates huge quantities of material and flings it up and outward onto the surrounding surface (some times many 10’s of kilometres). In the case of ‘Tycho’ and similar events, ejecta rays travelled enormous distances from impact point and the bottom of a crater is shattered downward for kilometres. In some large impacts the crater bottom rebounds to form that central peak or mountain range. The outer walls can be extremely rough terrain depending on what the excavated material was and how old the particular crater is. Remember there is no water or wind erosion to assist in the levelling out process only time and very minimal gravity. The inner crater walls can slowly (over long periods) slip and settle down in some cases to create terraced plateau’s such as those shown in close up images of ‘Copernicus’ for instance. If every crater on the Moon over 2-3km was tallied up, the number could be around the 250,000 mark (but who’s counting, eh!)
OK, so much for that stuff! Let’s get into our trip down the Terminator for Days 9½ -12. We’ll stat off mid-way down the moon at a crater known as ‘Copernicus’. This crater is one of the Moon’s show pieces and shares pride of place with craters like ‘Tycho’, ‘Clavius’, ‘Gassendi’ and ‘Plato’, etc.. It is without a doubt one of the best preserved crater examples on the Moon’s surface and to watch it appear over the Terminator and grow over a couple of days is really something of an experience. First views show very steep walls and a rugged untamed beauty (which I feel is unmatched on earth) that seems to flatten out a little over the period until you have a full view of its 91km width and 3.8km depth central mount and extensive terracing, couple that with a system of ejecta rays similar to but not as far reaching as those of ‘Tycho’. A small crater chain is seen running northward between ‘Copernicus’ and ‘Eratosthenes’ to the northeast. The two (2) larger craters ‘Tycho’ and ‘Copernicus’ are seen clearly right through to Full Moon and on into its waning phases.
‘Mare Imbrium’ is seen to grow over the period from around Day 8 to Day 11. It’s a fascinating area with a veritable feast of features to view. The diameter of this ‘Mare’ is 1,123km and it is the largest ‘Mare’ to be formed by lava flooding a single, very large crater caused by a huge impacting object long ago. There is an area of surface damage on the other side of the Moon at a point directly opposite the ‘Imbrium Basin’ said to be caused by seismic waves transmitted through from the original impact. This area is called ‘Van De Graaf’, a crater most of us won’t ever see, I guess!
There’s a heap of large craters in the southern highlands, ‘Newton’ at 137km and ‘Casatus’ at 96km which overlays ‘Klaproth’ at 119km and nearly a matching pair ‘Blancanus’ and ‘Scheiner’ at 115km. ‘Clavius’ is a huge crater at 225km and has been peppered with smaller craters. It is believed to have formed around four (4) billion years ago and is visible to the naked (young) eye right on the Terminator around 1 or 2 days after first quarter. Situated south of ‘Tycho’ in the southern highlands it’s the third largest visible to us and has a deepest point depth of 3.5km.
There is a nice pair in the south-western sector of “Mare Nubium’. These are ‘Mercator’ at a width of 45km and ‘Campanus’ at 49km. These two (2) are absolutely surrounded by Rilles, Faults and Domes which make this area very interesting indeed and well worth some time at the eyepiece. It is worth knowing for those new to the hobby that a quick look is just that, ‘a quick look’! You only see what is large enough to poke you in the eye, so take some time (it’s not going anywhere) to let your eye wander over the view before maybe inserting another eyepiece or two. Lean back think about what you’ve seen and then look again. Move you’re point of focus up and down the Terminator a little and come back to your study area again, only in this way will you see all there is to offer. I like to start with low power eyepiece and build up slowly to a higher power (magnification) you may even return to the lower power again for an all over view before moving on. It must be said that most of us do our viewing with simple inexpensive eyepieces such as ‘Plossl’s’ with the more expensive makes being a dream we all harbour to one extent or another. Birthdays and such are a good time to rectify that and $200 - $400 is a realistic price to pay for that ‘Good’ eyepiece!
Ok, away we go to the north on the Terminator at Day 10½ to one of my favourites. Off the north-western edge of ‘Mare Imbrium’ we have ‘Sinus Iridum’ or a more romantic name for this feature is ‘The Bay of Rainbows’, named by one Giovanni Riccioli. This beautiful spot is virtually unmarked by craters but does have a few ‘Wrinkle Ridges’ on its basaltic lava floor. This lovely Bay is surrounded from the southeast to the northeast by one of the Moons prettiest mountain ranges. The ‘Monts-Jura’ Range has at its south-west end the ‘Promontorium Heraclides’ with the north-eastern end being the ‘Promontorium Laplace’.
‘Sinus Iridum’ is around 236km wide and when the sun hits the ‘Jura Mountains’ on around day 10½ (give or take a few hours) it lights up the eastern face of the mountains to make a spectacular bow-shaped ridge (for want of a better word) with the foreground in the shadow and the background the black of space it gives the impression that one could pass underneath. I like to call this feature ‘the underground car park’ but I’ve had mixed responses to that. ‘Philolaus’ a nice crater of some 70km with the sun on the eastern side of its western wall is a very nice way to finish day 10½.
So another day brings another line-up of craters to view. To start Day 11 off we’ll have a look at ‘Schiller’ a crater of note because of its unusual dimensions. This somewhat elongated crater looks to be an amalgamation of 2 or 3 separate impacts that have blended together over time and has a double ridge running along the centre on the north-west floor that divides that part of the crater in two. ‘Schiller’ has a diameter of 179km x 71km and is a must view as it takes its place on the Terminator on Day 11 but Days 12-13 are really good so be patient.
‘Mare Humorium’ is in view in its entirety on Day 12 and is a fascinating area to spend some time. Three craters form the southern end of the ‘Mare’ and they are ‘Vitello’ with its distinct central peak and a diameter of 45km. ‘Lee’ at a width of 41km is open-sided and looks to have been flooded after formation in the distant past. The third member of this trio is ‘Doppel Mayer’ which gives one the impression that it is half ghost crater and half ordinary with one wall all but missing and its western wall and central peak lit up by the sun.
Below these on the western side of the ‘Mare’ are a couple of ‘Rilles’ with ‘Rupes Liebig’ in the centre. This fault extends for some 150km and is visible on both days 12-13. ‘Mersenius’ is a good clear crater of 84km diameter on the western side of ‘Mare Humorium’ and is around 3.8 billion years old. It shows a heavily worn rim in the northern section. ‘Mersenius N’ sits atop the south-eastern wall. The floor of this crater is basaltic lava and has a bulge in the centre that reaches some 450m. ‘Mersenius’ is surrounded by typical highland selenography including ‘Rimer Mersenius’ a long system (230km) of collapsed lava tubes (rilles) that run off to the north-east. The northern end of ‘Humorium’ is allocated to a really good specimen in ‘Gassendi’. This large crater of about 110km in diameter is well visible on Days 11-15 with its two (2) namesakes “Gassendi A’ sitting on top of its northern wall and ‘Gassendi B’ about 10 degree or so to its north. ‘Gassendi’ itself was flooded during the flooding of ‘Mare Humorium’, so all that is visible now is the tips of the outer walls and its central mount, although the inner or southern rim is all but gone it is still visible as a raised ridge with a parallel ridge on the crater floor. The hight of the outer rim varies from around 200m to as high as 2.5km and the floor displays a really outstanding system of ‘Rilles’ which have been named ‘Rimea Gassendi’. The abundance of mountains, rilles and clefts added to the rugged surrounds to the west make the ‘Gassendi’, ‘Humorium’ area a must for your moon viewing night.
‘Kepler’ is a ‘Copernicus’ in miniature with its very own ejecta rays. It has a width of 35km and is situated west of the much larger and well defined ‘Copernicus’. ‘Reiner’ at 30km and ‘Marius’ at 42km, make up a nice triangle to the west. ‘Kepler’ stands out clearly from Day 11 onward well into the waning phases of the Moon. It can be a challenge on Full Moon so use those filters and be guided by ‘Copernicus’ and look slightly west as stated above.
Moving on to the north our journey takes us through the eastern side of the enormous area known as ‘Oceanus Procellarum’. This huge ocean of lava is a whopping 2600km wide and extends from Day 10 through to Full Moon east to west and from roughly ‘Letronne’ crater in the south to well beyond ‘Aristarchus’ in the north. To me (except for one or two features) it is a rather bland area and I usually move north to ‘Aristarchus’ crater. This outstanding crater was also named by Giovanni Riccioli in honour of a Greek Astronomer and is situated on the ‘Aristarchus Plateau’ an elevated volcanic area in the eastern ‘Procellarum’ region. This plateau rises some 2km above the ‘Oceanus’ floor and ‘Aristarchus’ at 40km shares with another crater called ‘Herodotus’ at a width of 36km.
Running away to the north is a most impressive feature known as ‘Schroters Valley’. The valley cuts its way through the plateau for some 200km and stands out well in the eyepiece. Also to the north-east is a system of ‘Rilles’ and many small crater-lets. The ‘Rilles’ known as ‘Rimea Aristarchus’ show many small caved in areas and the whole region can hold your attention for quite a spell.
To the north-east we have the ‘Harbinger Mtns’. Now these are relatively small at 90km long by around 1.7km high but come up well under a ‘wee’ bit of magnification, (around 88x in my 12inch or 304mm Skywatcher Dobs). The ‘Gruithuisen Mtns’ lie further to the north and consist of a couple of ‘Domes’ each around 20km wide and 1km high, they sit nicely in the open and invite inspection.
Once again we travel a short distance (relatively speaking) to the north to a line of craters in the 39-40km bracket named ‘Mairan’, ‘Sharp’ and ‘Harpalus’. These although only of medium size are really well defined craters and coupled with ‘Bianchini’ on the rim of ‘Sinus Iridum’ they make an attractive foursome. ‘Mare Frigorus’ continues on toward Day 13.
A little to the north-east we have ‘J Herschel’, this is a fairly large crater at 165km and I would assume it was named after John Herschel the son of William Herschel and I would further assume that the crater ‘Herschel’ was named after William himself. Now the latter although preciously discussed on Days 8-8½ is of similar diameter but with a depth of 3.8km. It can be found of course next to ‘Ptolemaeus’.
Ok! Now we only have four (4) more worthy of note this time. They are another pair similar to ‘Atlas’ and ‘Hercules’ in appearance (roughly) and sit down on the northern ‘Cusp’. I think they only have the label of pair because they sit side by side not because they happened at the same time. Their names are ‘Anaximenes’ at 78km and ‘Philolaus’ at 70km and you will find them set in some really battered terrain just to the west of ‘Goldschmidt’ a crater with ejecta rays fanned out to the east away from the smaller ‘Anaxagoras’ with a width of 51km.
That brings us to the end of our trip down the Terminator on Days 9½ through 12. I hope you got something from that and I’ll be back to finish up on Days 13-15.
Usual thanks to:
Moon Maps from www.astrovisuals.com.au
‘Exploring the Moon’ – by Steve Massey www.myastroshop.com.au
These are truly invaluable tools.