Uranus 20" DK.
Posted 02 October 2012 - 10:29 AM
Attached is an observation made of Uranus made with Dr. Hugh Sasse using the University of Leicester's 20" DK planewave telescope, last night. Conditions were only average at best with seeing around AIII-IV and some drifting cloud. A bright waning Moon also hampered observations a little. The planet was examined both in IL and with a red W#25A filter, the results were as follows:
(i) Drawing 1 (IL) [2214UT- 2226UT]
The planet was examined at x356 and x540 and there appeared to be a brighter EZ. Just 'below' this was what appeared to be a darker greyish band. A brighter spot was suspected on the limb (indicated). Interestingly there appeared to be a slight change in colour compared to when we last observed the planet with a stronger cyan component being present.
(ii) Drawing 2 (W#25A)
Examined the planet in a deep red W#25A filter. Due to the presence of high cloud we had to reduce power to x288, but the disk size was just large enough to be able to make some observations. In particular, the brighter EZ seemed to still be present, along with the darker band which MAY have been easier to see in this filter (impossible to be certain). The brighter spot also seemed to be present. We made plans to observe the planet with a blue W#80A filter but alas clouds came up and we were forced to stop observations on this rather inconclusive note.
Posted 02 October 2012 - 06:43 PM
Beautiful. Are you serious, you can see such clouds on Uranus ?
Posted 02 October 2012 - 09:18 PM
Nice work Paul, as always one of my favorite observer/artists.
Posted 02 October 2012 - 10:30 PM
Posted 03 October 2012 - 05:41 AM
Posted 03 October 2012 - 06:24 PM
So let me tell you, you are lucky. I never seen any band on Uranus with my C14 because the few times I observed it, I never got a decent seeing for this planet to increase to a such power.
Last night I observed Jupiter easily at 434X for a real clear view and the moon at 782X !!! I should have had a look at Uranus but I don't.
Posted 03 October 2012 - 11:14 PM
Posted 04 October 2012 - 04:26 AM
a history of observation, theory, and discovery, you will find similar observations in the historical records.
Posted 05 October 2012 - 12:35 AM
About the the brightening you noted both in AL and red color I will try to check this at the same longitude you reported. If this is a bright spot it will have a certain duration and not drifting a lot.
Hope the weather will be with us, rainy now since a week and next week forecasted.
Posted 13 October 2012 - 11:41 AM
I engaged a new 250mm scope for getting a compromise with the seeing and the resolution ability.
It has a proven strehl ratio of 0.966 global on the tube, the central obstruction needs to be deducted for getting a true equivalent perfect diameter of 168-170mm approaching the cassegrain 305mm performance. Therefore the contrast levels are almost similar.
Last evening was average and in spite of this, during calm times (7/10 images) I could drawn the attached report for your perusal. It should interresting to compare with some other documents issued on the site (the oval brigthening near the limb in the south temperate belt).
The weather being stormy here it is difficults to perform better.
Posted 13 October 2012 - 01:14 PM
Posted 13 October 2012 - 10:53 PM
Posted 14 October 2012 - 03:36 AM
Also the Central meridians are 100 degrees apart between the two sketches, so actually the bright spot is on one limb in Paul's and the opposite limb in Stanislas' (just to confuse you more Pete!).
It's quite interesting that (if the mirror inversion between the two drawings is indeed due to telescope design or something like that) the two sketches agree very well indeed.
Posted 14 October 2012 - 06:14 AM
Pole or not is a result of a method and local conditions. This overall aspect is never until now duly assessed except by experience, of what.
This is not an argument.
The presentation of the sketch are clear if you follow, not on CN but on the japanese alpo the results given.
Uranus south given and rotation. Here the morning limb.
The brightening is not named as a spot but a brigthening.
Have you saw the limb darkening, because this may interfere with the brightening for getting a spot looking appearance.
You see, visual observers are prudent, imagers hardly thinking, and without assessments, also comparative assessments.
Now the brigthening is interresting to note and needs more data for a firm evaluation for saying this is the same.
In first, assessment with time to see if this is rotating with the planet, i got no enough time for.
In second, assessment day to day for collecting the same features.
In third, to assess what was changed around, the dark collar bordering the pole has gone.
When you see an imager getting a similar approach, ring me.
For the moment they stay on banding structure collected on a favorable period, because constrast had raised. And the banding idea stays on pure circles shape, nothing else can exist, and they don't know exactly behind desks.
Posted 14 October 2012 - 09:55 AM
Thats not fair to imagers or the technology behind the cams and processing software used these days. This isnt the days of tri-x or ektachrome anymore and the CCD is in another realm. I dont think your assesments of visual versus ccd is accurate.
Posted 14 October 2012 - 11:56 AM
Posted 15 October 2012 - 08:42 PM
Posted 16 October 2012 - 01:09 AM
Unfortunately this is not a matter of aperture mainly.
The question of scope is mainly lead by the D-d factor combined by the PTV level (or RMS for others). This implies an equivalent perfect diameter that own more or less the properties of this perfect diameter in terms of FTM curve.
For the featuring size on this planet this enough representative.
This way is interresting for comparison between diameters or scope in use. Otherwise we are discussing of the sexe of the trade names long time and useless. In other this means a potential that is degraded by the seeing level.
For instance my C8 equals the mewlon 180 that i owned and solded, now the 250 cassegrain equals almost the Meade 12 which is not bad.
Now when equivalent perfect diameters are defined the comparison between sizes is surprisingly not so crucial because the contrast is lead by this formula well verified with the FTM curve evaluations: c=c' * w/(w+5/6*D)
D the perfect dia, w width of the feature (elongated), c' the contrast actual on the planet.
If you get 1 or 2% on the planet, at the exit of the scope you will have less. Normal because a scope is a low pass filter. Sothat between 10 and 15" the gain is not null, not 1.5x but say 15% more in term of contrast.
Presently for capturing we need contrast.
Also it is necessary to know the scope characteristics (d, PTV actual) for getting the efficiency. Diffraction limited
commercial means only PTV3.3 (just for seeing the airy disk and the 1st diffraction ring well blurred in fact). In that case the strehl ratio is substantially less than 80% sothat the 15" may be less performing than the 10".
Just the idea because the intrinsic scope data are not identified. The 250 in use here equals 168mm perfect.
Hope this may be clear for you and an help.
Posted 16 October 2012 - 04:15 AM
Many thanks for all the comments, I feel I should addressed some of the points raised here. First of all the telescope used to make the observations;
This was a a 20" Dall Kirkham. No star diagonal was used so North (as indicated by WINJUPOS) is at the bottom of the picture. To confuse matters, NASA have a different defintion of north than the IAU, the NASA definition puts north at the actua pole, the IAU definition (used here) puts north where the northern magnetic pole is located.
No star diagonals were used in this drawings, the image is drawn as it came out of the eyepiece. The markings on Uranus are always vague and ill-defined, even with a telescope as large as this, considerable care has to be taken since the disk is so small and one can easily be decieved. Nevertheless, I am reasonably sure the bright spot and brighter EZ were present.
Now the comparison with Stanislas-jean. Given the curvature of the EZ, some sort of star-diagonal must have been used. It looks as though this drawig was made some 12 days later, and is at a different CM longitude, so unless this is a long lived spot which has drifted in longitude (which I think unlikely), it must be a different feature.
Finally, the comparison between imaging and visual. This argument is probably one of the most pointless arguments in astronomy. Each method has its pros and cons, and in the end both processes require the input human brain (with all its subjectetivity). While it is true some imagers are content just to take pretty pictures, this is also true of some visual observers, I have seen a few drawings which are simply artistic interpretations, not scientific ones.
What we have to do is catagorise between observers, and artists. The observers should represent the scientific area of amateur astronomy. That is not to say the artistic way is any less valid, if that's what gives people pleasure out of astronomy then so be it.
I think most of what Stanislas said has been lost in translation, but I agree: your survey of imagers is wrong, I know quite a few British imagers and they are first class dilgent observers. Don't make sweeping statements which are blatently not true.
Posted 16 October 2012 - 04:20 AM
Taras, you also have to look for some time, you can't just take a quick look, I spend about 15 minutes examining the disk of Uranus at various powers to try and build up a picture of what's there. Of course it maybe that you are sensitive to different colours (this is why people who are sensitive to red have difficulty seeing the markings of Venus).
Posted 16 October 2012 - 04:52 AM
This is not the same feature. The sketch I performed here in past are performed with a diagonal mirror.
But what I note is brightenings are on this temperate belt.
Last evening I checked again the Uranus at CM 280°, 260° last report here, and the brightening is still here.
Now regarding magnifications for use on this planet the higher the better indeed but considering the seeing level on the moment. 30min arc represent the full moon size with the nake eye, it's a pretty size for collecting features with 500x on good nights, with 20min of arc (still enough) it can be catched still something, under this is problématic with regards to contrast levels. This means here 333x which is enough with a 200mm of good facture.
At final in spite of these conditions the features are not strong and illness indeed but here, as you reported also.
I donot spend more than few minuts for drawing what is reported, I spend time after in order to confirm or try to confirm what was at the first look. This verification stage take some long minuts.
Posted 17 October 2012 - 02:34 AM