Observing the craterlets in Plato

Canopus Lim · Post by **Canopus Lim** » Wed Oct 04, 2006 12:16 am

Tonight I managed to catch the moon again.

After many weeks of lousy weather, finally the moon could be seen. I was doing generally observing of the craters. I still do not know many of the craters and spent half of my time learning their names. The scope used is 12.5 inch Obsession at f/5. Collimation was about 90 percent accurate.

I did another look at Plato again. Tonight the seeing was much better and I was able to use my 7mm Nagler T6 barlowed to give a magnification of 440x. Above that magnification, the moon looked like a reflection of waves.. it was waving and moving around too much.

This time round I OBSERVED (it cannot just be seen as it requires about half an hour of time at the eyepiece) 4 more craters! Refering to the CN diagram which are labelled A,B,C,D...etc.

I observed:
1. ALL (5/5) THE "BIG FOUR" (actually there are 5 instead of four)
2. ALL (4/4) THE "LITTLE FOUR"
3. (2/9) "Tiny 9"

Total 11 craterlets.

I did not compare diagrams while viewing. I drew the positions of the craterlets on a piece of paper and wrote down how clear I saw. Craterlets that had well defined ring shapes are A, B, C, D, W, e and f.

The level of difficulty in seeing the craters.
Starting with the easiest to the hardest:

A, W, B, C and D, e, f, g, h, q (hard), n (requires averted vision)

All in all, it was a very nice night and a great view of the moon. It is a real bonus to see the 2/9 of the tiny 9 which are a real challenge.

ykchia · Post by **ykchia** » Wed Oct 04, 2006 12:52 am

Hi folks:

Sky was bad so i also turned to the only visible object - luna for the past few days with a vintage C8 pointing out of the window and a mintron.

www.nightevents.blogspot.com

rgds
yK

jiahao1986 · Post by **jiahao1986** » Wed Oct 04, 2006 9:59 pm

Congratulations for seeing so many craterlets Yang Beng.

I also had a try yesterday despite high and low clouds constantly disturbing. Seeing was not good at my site either, such a big difference from east to west Singapore...

This time still no more than three of the big four...

Besides, just discovered this website http://www.alanchuhk.com/
from here you can download the book 'Photographic Moon Book', which contains relatively high resolution(probably not as high as you Obsession Dob), detailed lunar maps. The alignment of the maps should be just right for Newtonians. Maybe it can be helpful for you la.

Canopus Lim · Post by **Canopus Lim** » Wed Oct 04, 2006 11:10 pm

Jiahao,

Thanks. Where do you observe? In NTU campus?

jiahao1986 · Post by **jiahao1986** » Wed Oct 04, 2006 11:19 pm

Yeah, NTU campus, close to industrial area...

Canopus Lim · Post by **Canopus Lim** » Sat Apr 19, 2008 1:43 am

It has been quite a while since i observed the moon. Tonight the seeing was very good and the moon was near full moon. I wanted to test out my new toy, the 2008 version Paracorr... more on that later.

Firstly, since I was supposed to observe the moon, I brought along my Lunar Atlas..but I forgot to bring my torchlight so I could not read the book in the dark! Duh. Therefore, I ended up just comparing the views between my eyepieces with and without paracorr.

I can only say that for a Newt user like me, from what I observed, the Paracorr is really a significant improvement. With it, my 12.5" f/5 Newt performs like an Apo! For my 11 Nagler T6 eyepiece, it is diffraction limited across the entire FOV.

Due to this, the moon just look tack sharp from edge to edge. I do notice very slight unsharpness (it is sharp just that slightly less sharp than the centre) at the very edge of field, but that is because I can tell sharpness well. This is the second time I am using this new toy and I can say that with the paracorr on, the moon looks really 3D. The texture on the moon itself is significantly enhanced and many small details like small craters just pop out! The reason for this is because the Newtonian's coma has been reduced to such a small extent on a f/5 Newt, such that it is diffraction limited with my 11 Nagler (giving about 0.4 degree TFOV). The previous observing of Saturn with the Paracorr also gave me the impression that Saturn was more 3D than without the Paracorr. It was tack sharp from edge to edge for my 11 Nagler, 7mm Nagler and 8mm TV Plossl; these are the eyepieces I use for DSO in Singapore.

Secondly...the moon... since I forgot to bring my torchlight I had to settle in just gazing at the moon. Since I know the Plato region well, I decided to take a look. The seeing was very good, and the moon could take magnifications to 520x easily and have little 'boiling effects'. Depending on the moon's phase, the number of craterlets seen on the moon varies.

This time round, I did a quick count on the number of craterlets. From low power I could already easily see the craterlets so I decided to use my 5mm Baader Ortho (320x) without paracorr (as it cannot focus with it). This eyepiece is very good for revealing the craterlets as it has very low scatter, high transmission and cool rendition. Doing a quick count, I easily counted 21! That is not counting many others that were of lower contrast and did not appear when I counted (due to seeing). There were too many to count actually. If I were to estimate by adding in those that I never count, it would probably come to about 25 craterlets!
Once I actually saw much more craterlets than tonight and it was too many to count. Tonight I have counted about 21 and would estimate about 25.

That means, the best time I saw which literally had Plato marked with craterlets all over would run into about 30 plus craterlets. It was about 3/4 the number of craterlets taken with by the lunar spacecraft.

Thus, I am rather happy that I have seen even more craterlets than those mentioned at the start of this thread and verified the approximate number. Therefore, I would think the best kind of planetary scope is a large newtonian with well figured optics, well collimated and have a small central obstruction.

Observing the craterlets on Plato is a difficult test on the telescope/eyepiece performance as the craterlets are very small (high resolution) and very low contrast.

ariefm71 · Post by **ariefm71** » Sat Apr 19, 2008 10:01 am

Can we use Paracorr to signifantly reduce off-axis coma on Dall Kirkham scopes?

Arief

Canopus Lim · Post by **Canopus Lim** » Sat Apr 19, 2008 4:46 pm

I am not too sure... would need to test on a real Dall Kirkham. The Paracorr probably applies 'anti coma' to reduce the coma and how much the application is probably ideal for Newtonians f/8 and faster. Above f/8 I would think that instead of helping the views it creates coma in the opposite direction (that means the 'fan' head is pointing towards the centre instead of away). For a f/8 Newtonian, I would think there is no need to even have a Paracorr as the coma is very small.

Therefore, it depends on how much is the coma on a Dall Kirkham scope. If it is less than a f/8 Newtonian, I would think a Paracorr would make the view worse. The Dall Kirkham, like a Newtonian, coma depends on the f ratio.