Well, here we are again! So let’s begin with one or two vagaries. Like, what is a ‘Blue Moon’?
This phenomenon has been researched at great length and the jury is out, so to speak Astronomically, it is two Full Moons in the one month.
Craters on the Terminator Etc.
Well, here we are again! So let’s begin with one or two vagaries. Like, what is a ‘Blue Moon’? This phenomenon has been researched at great length and the jury is out, so to speak Astronomically, it is two Full Moons in the one month. If we figure that a synodic period is 29.53 days (one lunar month) and that a normal month is only slightly more at 30 days then from virtually anywhere we can have a ‘Bluey’ about every 2 ½ years.
I read in a book somewhere that we little folk think the moon is larger when it is rising than when it is at the zenith for instance. Sorry people, not so. The moon only seems to be larger at that time because we have something to compare it to, such as buildings, mountains, trees, etc.. It even looked bigger to me when I was at sea many years ago with nothing to compare except the horizon. Ah! Just an old romantic, I guess.
Looking at the moon when it is only a small sliver (hardly worth looking at from a features point of view) is the time when we can see a fair amount of ‘The Dark Side’. You can see if you look closely when it is new moon and conditions are good that nearly the whole globe is illuminated by earth-shine. This occurs when the moon is roughly between us and the sun. Due to the fact that the earth reflects 10 times as much light
as does the dark lunar landscape. The earth, from the moon is around 6 times bigger than the moon appears to be from us. So! When earth is full in it’s phase (as seen from beyond) it is 60 times the brightness of a full moon.
Let’s now move along to having a look at the moon through a telescope or a pair of binoculars. We already know of the moon’s phases, so let’s take it one step further to day by day. If we view our target every night from say, Day 2 onward we have a whole new line up of craters etc., to look at on what we call the ‘Terminator’. This will continue until we reach the full moon and then recede or reverse until ‘New Moon’ occurs again and so on. There is a difference on the ‘Waning’ phases. However, as the sunlight shines on the moons surface it highlights or hides as it goes, so we see lighted or shaded areas much the same as we do here on earth.
For instance, on Day 8 ½ or so, of viewing features like the ‘Straight Wall’ (Rupes Recta) are seen right on the terminator but it looks better on Day 9 ½ because of a different perspective (the setting sun shines from the west) the wall is one day seen in shadow and on the another day the sun shines directly onto the scarp to illuminate the whole 110 km in stark relief.
Alright folks, I would like, at this stage correct the ‘No Water on the Moon’ statement I made in the first article. At this point there is ‘NO’ water on the moon but there may be water as ice in some of the deep, southern Polar Craters – time will tell, I reckon, Eh!
So, maybe we will start at about ‘Day 3’ of the crescent and travel south to north along the Terminator toward ‘Mare Crisium’ and beyond. We can start with a nice crater ‘Richt’ on the edge called ‘Biela’, the sun shines nicely on its western face. Although there are many, many more craters worthy of comment we can only discuss some, so on down to ‘Rheita’ at 70km and the ‘Rheita Valley’ at about 450km is said to be the longest valley on this side of the moon and is made up of and overlapping chain of small impact craters. North we go to a crater of some 74km, ‘Stevinus’ has a central mountain peak and is accompanied by several ‘small fry’ queezed between itself and crater ‘Reichenbach’ with crater ‘Snellius’ at 81km diameter just to the northeast. The Snellius Valley lies to the west of that toward the Terminator.
There are four (4) really large craters in this section. They start with crater ‘Furnerius’ at some 130km diameter with several small craters on its floor. The second crater ‘Petanius’ which also has a large central mountain peak and a beautiful big ‘Rille’ that runs all the way from centre to the southwest edge of the crater. The craters sides have subsided to give a terraced effect. ‘Vendelinus’ one of the four is a crater of around the same dimensions as ‘Petavius’ and several over-laying craters give the correct impression of very old age. A mass of small craters peppered the surrounding area. We now move on down the central edge of ‘Mare Fecunditatis’ to the last of our four large craters in this area. ‘Langrenus’ is visible on several day (2, 3 & 15) and is some 132km wide, it also has a central mountain peak. The raw beauty of both ‘Petanius’ and ‘Langrenus’under some magnification is truly unreal! It, (Langrenus) has also become terreaced over time and is slightly elongated or appears that way. The peaks in these craters are caused by the rebound of material after the impact and I think they add character to an otherwise, flat whole in the ground that is most craters. The ‘Mare Fecunditatis’ region is home to many Wrinkle Ridges and ghost craters and the ‘Mare’ itself is an impressive 900km x 600km. My God! I think I need to take a few deep breaths.
Well people, we are half way and now move into the Northeast sector or quadrant of the moon. This area is probably not as busy but none the less interesting to the lunar viewers. ‘Bilharz’ is a little beauty at 43km. The surrounds here are ‘Pock’ marked with small craters eastward to the somewhat odd shaped crater ‘Firmicus’ at 59km. There’s a fine crater chain just west of these last two with ‘Tarunticus’ way out and just becoming visible with the sun on it’s tips.
‘Mare Crisium’ is one of my favourite regions and is home to two (2) of the finest little craters available in ‘Picard’ and ‘Pierce’ 24km and 19km respectively. So sharp one gets the impression they were put there with a stick. ‘Crisium’ itself is around 570km and is known as the Ringed Basin. The mountainous edges of the basin are breathtaking when seen in my 304mm Skywatcher Dobs. The wrinkle ridges and other small craters can be seen really well around day 15 or so. It is and incredibly old and beautiful landscape and can be viewed for hours.
There are several craters worthy of mention such as ‘Tisserand’ at 41km – ‘Macrobius’ at 64km and ‘Cleomedes’ another big one at 132km, with a collection of smaller craterlets (if there is such a word) on it’s floor together with a ‘Rille’ (lava tube) of some note. These all show up well in our 252mm and 304mm scopes. We mainly use the 25mm E/P supplied with the scopes, together with a 21mm and 17mm Hyperian (Baader) and sometimes even more power to get up close. These eye pieces yield 48x, 57x and 70x respectively and the view is incredible. I personally think close enough is great – too close seems to spoil it somehow. Like looking 40 million light years at a galaxy, I would rather see a good ‘fuzzy’ than a washed out swirl of stars.
Anyway, on we go to ‘Geminus’ at 87km and ‘Messala’ at 116km a large but (I feel) unimpressive crater, ‘Franklin’ however, is a nice sharp crater that shows up well. We have ‘Endymion’ at 124km. these bigger craters can be seen well though good binoculars of 10 x 50+, preferably larger but 10 x 50 are easier to manage.
Last but not least, ‘Strabo’ at 60km is a really good crater on which to end our first journey along the Terminator on or about Day 3. I once again have the honour of declaring my information sources and highly recommend them to anyone who wishes to view the Moon through it’s many phases.
The best can only be obtained with the best!