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CEM60 or CEM60-EC

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#476 OzAndrewJ

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Posted 16 September 2019 - 11:14 PM

Gday Kevin/Gotak

Your SDE is better than mine in your long GA run but it is there and it is larger than your DEC seeing it seems.

Agreed, in the unguided ( and guided ) runs, the SDE is very clear, but PEMPro reports it as about 0.4 arcsec pk-pk now so not as critical, but certainly measurable ( and visible in the good seeing ).

That said, no "major" spikes or oversized oscillations are present in the guided data, so thats good. In fact it looks a bit like data from the very early 60ECs ie when unguided, there is drift and SDE

Guiding corrects the drift well, but only partially deals with the SDE.

( Comparing RA and DEC in the attached plot gives an idea of the difference between RA and DEC )

Again, the fastest frame rate here is around 2.1secs so may affect the data as its very close to the Nyquist freq for the SDE.

The unguided data would be nicer if you could collect at say 500ms or less

 

What's weird is your worm native PE seems to be showing through.

I disagree here ( at present grin.gif  ). I suspect what you are seeing is merely etching tolerances in the encoder grating

as if you overlap the data based on worm period, the data doesnt look the same for each pass.

ie as per above, the unguided tracking data of early models had SDE on a slowly changing baseline for the tracking rate, and the long slow errors changed based on sky position, hence suggesting it is mechanical tolerances in the encoder grid.

Have attached the unguided data run here plotted purely as raw with no drift removed

Shows very well the diffence in amplitude between RA and DEC in places,

Andrew Johansen Melbourne Australia

Unguided.jpg



#477 ksouers

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Posted 16 September 2019 - 11:17 PM

Your SDE is better than mine in your long GA run but it is there and it is larger than your DEC seeing it seems. What's weird is your worm native PE seems to be showing through.

 

Given I think you are using an 80mm and your t6? You should not see the impact much. A word of warning, larger payload seems to exacerbates the SDE so when you move up in aperture you might find the SDE value increasing.

 

I think we are at a place where these mount just have been proven to not really work as we expect them to. I don't know what iOptron's position really is I am trying to find out but so far no responses. 

Yes, it's the ED80 but not the DSLR. ASI183mm Pro, EFW8 full of glass, OAG w/ASI290, flattener, Moonlite focuser, and NUC. It's a pretty heavy rig, I think around 18 pounds. Oh, and I still have the guide scope on it but not used, it does help get some mass forward of the DEC axis. Overall quite well balanced.

 

I'm still struggling to discern the impact of this SDE issue.
For me, my final arbiter of decent guiding is my image, not squiggles across the PHD graph. Are the stars round? Well, round enough, my eye fails to see the very small elongation, especially after stacking. SFS tells me there is eccentricity but it's within the reject algorithm limits. Is it there with pixel-peeping? Probably, but that's not how I view the final image. I see the whole thing spread across my display or TV. Are my edge details sharp? Yes. Are fine structures discernible and well defined? Again, yes. Are the smaller, fainter stars sharp little pin-points? Still yes.

 

Did I just get super lucky and snag a good specimen? Perhaps, I have nothing to compare it to except my CEM25P, and yes it's been a significant improvement.

Or maybe it's that I just don't know any better. I've been at this for a couple years so I'd like to think I've become a bit more critical of my craft and equipment.

 

So, as far as I can discern the mount is working just fine for me right now. Improvements can always be made, of course. Digging into the nitty-gritty of a seemingly obscure issue to improve the product is admirable, even necessary. My biggest issues personally are with my imaging train, software, the weather, local light pollution, lousy seeing and post-processing. The mount is rarely part of my worries. It just works.

 

Kevin



#478 OzAndrewJ

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Posted 16 September 2019 - 11:28 PM

Gday Kevin

 

So, as far as I can discern the mount is working just fine for me right now.

And for many people, it is/was the same.

On going to longer FL ( ie smaller arcsec per pixel ), it may start to show as elongation in times of good seeing.

ie the error, for may people is on the edge of seeing limited.

To my mind, what your data so far shows is you have SDE, it is not large and you are not getting crazy excursions or oscillations when guiding, which is what some other mounts got recently when playing with new firmwares and faster guide rates. ( And possibly load )

If your SDE is truly 0.5 arcsec pk-pk and can be guided out without causing the mount to lose the plot, then just enjoy using it, but understand whats going on so if it does play up later ( ie if you change guide settings etc ) you know what to look for.

Andrew Johansen Melbourne Australia



#479 ksouers

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Posted 17 September 2019 - 07:43 PM

Andrew, as always thank you very much for the analysis and advice. It is very much appreciated.

 

Unfortunately no testing tonight, someone ordered clouds for dinner.

Tomorrow is supposed to be "clear", for here that means hot and high humidity and likely milky sky.

 

 

Kevin



#480 ksouers

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Posted 18 September 2019 - 08:43 PM

Sky cleared up a bit tonight. As expected it's a bit milky but I did get a test in.

 

.5 second cadence, subframes, ~10 minutes, intersection of meridian and CE.

 

Attached File  PHD2_GuideLog_2019-09-18_192420.txt   92.01KB   5 downloads

 

 

Kevin



#481 OzAndrewJ

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Posted 18 September 2019 - 09:19 PM

Gday Kevin

It actually ran at 750ms, but that still gives good data

Very similar to your prev data, but this time less drift in RA

I have plotted your raw RA/DEC so you can see the difference in amplitudes

( I normally use the DEC data as an idea of seeing )

I also plotted the data in PEMPro and overlapped the RA based on worm period

The SDE ripple is clearly extracted, and with the faster framerate, you can see how well it repeats

As long as it can be guided using a slow cadence, without chucking a wobbly, being around 1.2 arcsec pk-pk, it will probably be within the seeing, but it is clearly there.

Andrew Johansen Melbourne Australia

Unguided Run2.jpg Unguided overlapped.jpg

 



#482 gotak

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Posted 18 September 2019 - 11:44 PM

Encoder for a constant +/- 1" move around zero point. Yeah, it's rubbish isn't it?



#483 RossW

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Posted 19 September 2019 - 03:03 AM

Gday Kevin

It actually ran at 750ms, but that still gives good data

Very similar to your prev data, but this time less drift in RA

I have plotted your raw RA/DEC so you can see the difference in amplitudes

( I normally use the DEC data as an idea of seeing )

I also plotted the data in PEMPro and overlapped the RA based on worm period

The SDE ripple is clearly extracted, and with the faster framerate, you can see how well it repeats

As long as it can be guided using a slow cadence, without chucking a wobbly, being around 1.2 arcsec pk-pk, it will probably be within the seeing, but it is clearly there.

Andrew Johansen Melbourne Australia

attachicon.gif Unguided Run2.jpgattachicon.gif Unguided overlapped.jpg

 

1.2" peak to peak? Looks like PemPro is a bit off lately. You can clearly see it is around 2 arc-sec p2p from the guide graph. PhD2 measures it as 1.9" p2p, so it seems to be more reliable. In any case, that is a horrible case of SDE.

 

Screenshot 2019-09-19 16.36.26.png

 

Periodic error for the CEM60EC is supposed to be <0.3" RMS (roughly 0.84 p2p or less) so your mount isn't even close to being in spec. And yes, SDE is a "periodic error", so it should be covered by the iOptron guarantee.

 

Good luck with any successful imaging with scopes over 1 metre in focal length, because if you check the smaller stars in single subs (not a stacked master) you'll easily see the elongation and measure high eccentricity.

 

iOptron have recently been successful in inhibiting the fast oscillations (3 to 5 Hz) that their encoder mounts sometimes have, but I have yet to see any evidence that they can solve this slow (0.2Hz) SDE oscillation with firmware. 

 

But in any case if you're happy with that mount then good for you Kevin.



#484 OzAndrewJ

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Posted 19 September 2019 - 03:40 AM

Gday Ross

PhD2 measures it as 1.9" p2p

Yep, but PHDs plotting software also lies at times ;-)

I learnt that the hard way last week.

 

 1.2" peak to peak? Looks like PemPro is a bit off lately.

Maybe, but it might be just averaging it out a bit. Some regions show it as 2arcsec and others 1

Not so sure on how much is seeing blending in, but as you noted, its way bigger than specs.

The math behind FFT and IFFT ( esp when it comes to magnitudes ) can be very dependent on good data rates, hence why multiple datasets should be used wherever possible.

 

Good luck with any successful imaging with scopes over 1 metre in focal length

Not so much the focal length than the arcsec per pixel.

Kevins data reminds me more of the early 60ECs, ie they had drift and SDE but could be guided.

Then recently, we saw firmwares that could suppress the SDE a fair bit, but couldnt be guided and went wildly out of control at times..

The biggest problem is the testing is being done with different firmwares as well, so its not apples to apples.

It really needs a precisely controlled set of tests on a bench, but very few users would be able to do that.

 

Irrespective of any of that, i agree kevins data would indicate it is nowhere near spec.

 

Andrew Johansen Melbourne Australia



#485 gotak

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Posted 19 September 2019 - 06:13 AM

The big problem is they are not responding to some of us in emails anymore.

3 emails, zero response. For me that's pretty much the final chapter. And it does not appear the 40 or 120 versions owners are getting much either.

Not sure exactly what's going on in the minds of ioptron but I know what's going on in my mind.

I am also very sorry to see I am not the only person seeing such large magnitude oscillations. And if that's the case then we are likely looking at something that impacts more cem60ec then not.

Edited by gotak, 19 September 2019 - 06:15 AM.


#486 John Miele

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Posted 19 September 2019 - 01:45 PM

I have been silent for a while but I check this thread every day. I got my "reworked" CEM60EC back from ioptron a couple weeks ago but I literally am so disheartened, I didn't even want to try it and see if it's any better. I'm afraid I'll see the same issues even though they said everything checked out fine mechanically and they installed new firmware. But what I'm reading here is worrying me that the SDE issue could be as bad or worse than the original wild excursion issue I had. I guess I'll just have to take a deep breath and try it out this weekend so I can add another data point to the herd...John



#487 mikefulb

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Posted 19 September 2019 - 02:05 PM

I'm still in disbelief there is no way to disable the encoders via the hand controller. It would make troubleshooting this behavior so much easier you would think and at least let people get use the mount as a cem60 until the firmware is ironed out.
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#488 gotak

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Posted 19 September 2019 - 02:51 PM

I'm still in disbelief there is no way to disable the encoders via the hand controller. It would make troubleshooting this behavior so much easier you would think and at least let people get use the mount as a cem60 until the firmware is ironed out.

There's a reason why they don't let you disable.

 

In the CEM120ECs there's a solder bridge that can be used to enable or disable the encoders. Some brave folks did just that and they found PE of epic scale.

 

So I suspect if we do that with the 60s you'll find that some copies have very large PE.

 

I wonder if the SDE issue is the alignment of the reader head....


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#489 mikefulb

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Posted 19 September 2019 - 03:40 PM

There's a reason why they don't let you disable.

 

In the CEM120ECs there's a solder bridge that can be used to enable or disable the encoders. Some brave folks did just that and they found PE of epic scale.

 

So I suspect if we do that with the 60s you'll find that some copies have very large PE.

 

I wonder if the SDE issue is the alignment of the reader head....

Do people with CEM60's (no encoders) find large PE commonly?  My understanding is as a whole the CEM60s were very good but maybe I'm wrong.

 

That sounds like a really poor engineering decision to make it a hardware only method to toggle encoder input.

 

I guess to give people that option easily and the users find they can guide better without encoders would be a bit of a bitter pill.


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#490 ksouers

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Posted 19 September 2019 - 04:35 PM

1.2" peak to peak? Looks like PemPro is a bit off lately. You can clearly see it is around 2 arc-sec p2p from the guide graph. PhD2 measures it as 1.9" p2p, so it seems to be more reliable. In any case, that is a horrible case of SDE.

 

attachicon.gif Screenshot 2019-09-19 16.36.26.png

 

Periodic error for the CEM60EC is supposed to be <0.3" RMS (roughly 0.84 p2p or less) so your mount isn't even close to being in spec. And yes, SDE is a "periodic error", so it should be covered by the iOptron guarantee.

 

Good luck with any successful imaging with scopes over 1 metre in focal length, because if you check the smaller stars in single subs (not a stacked master) you'll easily see the elongation and measure high eccentricity.

 

iOptron have recently been successful in inhibiting the fast oscillations (3 to 5 Hz) that their encoder mounts sometimes have, but I have yet to see any evidence that they can solve this slow (0.2Hz) SDE oscillation with firmware. 

 

But in any case if you're happy with that mount then good for you Kevin.

Hi Ross,

Here is a single sub from a couple nights ago.

 

2019-09-19.png

 

This should get you to the sub to download and see for yourself.

 

https://1drv.ms/u/s!...cymh2c?e=m0G5Pi

 

 

Like I said, it is working for me. I'm not defending iOptron. They've definitely dropped the ball and they need to make this right.

 

 

Kevin



#491 ksouers

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Posted 19 September 2019 - 05:01 PM

Andrew, thanks again for the analysis.

Is there anything else you would like to try?

 

Well, there seems to be an arm-load of data to support that iOptron is not living up to their claims. They will likely continue to ignore pleas for an update or response. It is probably not in their best interests to answer and say something incriminating, but then it is also not in their best interest NOT to answer. That's just bad customer service and PR. Honestly, I can wait out iOptron. But that's just me.

 

John Miele, I think you got your mount about the same time I did, October-November 2018? I had the excursions also, but not anywhere near as bad as you did. I loaded the beta firmware over the weekend and as far as I can tell it seems to have eliminated them. Do you know if they loaded the beta or current production firmware? If you don't have the beta, give it a try.

 

 

 

Kevin



#492 OzAndrewJ

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Posted 19 September 2019 - 05:27 PM

Gday Kevin

Is there anything else you would like to try?

I doubt there is anything else you can do at present, other than try different firmwares when the moon is full

You have data from several nights that is pretty consistent and shows the SDE is clearly evident in your mount.

You can guide ( so far ) without any strange excursions

Based on your imaging scale, it would appear the SDE sits just within the seeing/resolution for your system, but may show up if you drop the arcsec per pixel.

Sooo, understand its there in case it does go south later

Andrew Johansen Melbourne Australia

 

And to put all this in a bit of perspective, i made a plot of my AZEQ5 vs your 60EC

Your unguided data is still as good as ( or better ) than my guided :-)

The ripple in my data was due to loose belts out of the box

 

Shootout.jpg

 

 

 



#493 ksouers

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Posted 19 September 2019 - 05:38 PM

Thanks Andrew. Yes, I understand the problem is still there. And when I put the RC on in a few weeks it will likely become more evident. I have no illusions about that.

 

I do have questions though. Please correct me if I'm wrong, but do not all, or most, encoders have SDE? The problem with iOptron is one of magnitude, not that it exists. Is this correct?

 

If that's the case has anyone compared the iOptron encoders to others? It would be nice to know how far out of whack they are compared to others.

 

 

Kevin



#494 cytan299

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Posted 19 September 2019 - 06:14 PM

Thanks Andrew. Yes, I understand the problem is still there. And when I put the RC on in a few weeks it will likely become more evident. I have no illusions about that.

 

I do have questions though. Please correct me if I'm wrong, but do not all, or most, encoders have SDE? The problem with iOptron is one of magnitude, not that it exists. Is this correct?

 

If that's the case has anyone compared the iOptron encoders to others? It would be nice to know how far out of whack they are compared to others.

 

 

Kevin

For all practical purposes, Astro-physics mounts with absolute encoders do not have an SDE problem because it is extremely small. I’m sure that’s true for other premium mounts as well.

 

See link https://groups.yahoo.../messages/60571

 

cytan


Edited by cytan299, 19 September 2019 - 06:20 PM.

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#495 OzAndrewJ

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Posted 19 September 2019 - 06:45 PM

Gday Kevin

Please correct me if I'm wrong, but do not all, or most, encoders have SDE?

All encoders are electro mechanical devices that have fabrication tolerances and as such errors.

There are lots of different designs for encoders, and SDE is simply a "characteristic" of encoders that use sinusoidal interpolation to gain extra resolution.

I posted a link to a good site that gives a simple description of the process.

https://www.linearmo...inear-encoders/

The quality of the electronics that creates the sinewaves is one of the major sources for error

 

The problem with iOptron is one of magnitude, not that it exists. Is this correct?

Correct, and also the variance between units, but that comes down to quality control and precision in the electronics as well as installation.

As with everything, you get what you pay for.

 

If that's the case has anyone compared the iOptron encoders to others?

As noted by Cytan, several users here and elsewhere have posted data from their AP mounts and they show no detectable SDE ( against the sky ). The posts on the AP site at present re the testing going on with the new MACH2 also indicate the SDE is virtually undetectable, both against the sky and also on the bench, but its not cross checked by production units in the wild. That said, i suspect its correct, based on the quality of encoders used.

We know the readheads for the IOPtrons have a listed 2arcsec spec,

ref https://www.celeramo...ercury_1200.pdf

( page 3 near the top under "rotary accuracy"

Based on what i have read, the renishaws used by AP have a published SDE of below 0.1 arcsec, but i havent heard the details on the model they are using. Either way, their specs are much tighter, and the cost goes up accordingly.

 

 

It would be nice to know how far out of whack they are

Not so sure they are out of whack, just at a cost/performance point where they come a cropper in some setups.

No different to comparing a commercial worm to a precision ground and lapped one.

You get what you pay for, and as per my data for my AZEQ5, the 60EC is already lightyears ahead of it.

If they can fix their firmware, it wil be an amazing product, but it needs to be consistent.

 

Andrew Johansen Melbourne Australia



#496 ksouers

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Posted 19 September 2019 - 09:53 PM

Wonderful explanation, Andrew. That really cleared up a lot of things for me.

 

So, as I understand it the error is phase-locked and repeatable, thus predictable. So one problem I see is that each unit will need to be calibrated independently due to manufacturing variance.

When I updated the software I had to run what they called a calibration routine. Now whether or not that was what you or I or anyone else would recognize as calibration is another story. It may have simply been determining end points of it's cycle, not actually mapping out an error table.

 

This shouldn't really be that hard, but then I've pulled my hair out for weeks over code issues "that shouldn't be that hard" while sorting through some 5,000 lines of code.

 

Thank you, Andrew, for your patience and tutelage.

 

 

Kevin



#497 RossW

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Posted 20 September 2019 - 04:48 AM

Hi Ross,

Here is a single sub from a couple nights ago.

 

attachicon.gif 2019-09-19.png

 

This should get you to the sub to download and see for yourself.

 

https://1drv.ms/u/s!...cymh2c?e=m0G5Pi

 

 

Like I said, it is working for me. I'm not defending iOptron. They've definitely dropped the ball and they need to make this right.

 

 

Kevin

Hello Kevin,

 

Yes 0.41 eccentricity is a great result, no doubt about it, but if you ever wish to use an f/10 SCT on that mount you'll certainty see the crippling effect of that hugh SDE in your images. In the end, you (and quite a few others it seems) paid an extra $1,500 for a mount with an encoder that most likely performs worse than the standard non-encoder CEM60. The CEM60 may have < 10 arc-sec p2p period error, but it is a very slow oscillation that can be easily guided out. The 60EC's SDE oscillation is relatively fast and can't be guided out. You'd need to be sending corrections much faster than 1 per second to guide that error out effectively IMHO, but as you know the encoder firmware cannot be guided at that rate due to instability. As a result, that SDE oscillation will most likely be a permanent feature of your mount if iOptron can't tame it via firmware.


Edited by RossW, 20 September 2019 - 05:01 AM.

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#498 ksouers

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Posted 20 September 2019 - 06:44 AM

Hi Ross,

Yes, we are in agreement. Always have been.

 

I offered my experience as an example of what might actually be the true limitations of the mount; 600mm FL, .83 pixel scale, long exposure. Far below the expectations of many, if not most, purchasers including myself.

Within that range the mount offers good performance. Outside that it's a disaster.

 

 

Kevin



#499 souls33k3r

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Posted 20 September 2019 - 07:21 AM

Simple question, is CEM60 still a better choice then if we are going to guide any way? If compared with EQ6-R of course. If you had the choice to do this all over again, which one of these two mounts you'd buy?

#500 ksouers

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Posted 20 September 2019 - 08:00 AM

Simple question, is CEM60 still a better choice then if we are going to guide any way? If compared with EQ6-R of course. If you had the choice to do this all over again, which one of these two mounts you'd buy?

The short answer is no, I would not buy the 60EC again in it's current state of development.

If they ever resolve the SDE issue, it's a resounding yes. In all other aspects it's a good mount. I would expect the plain vanilla CEM60 to be good as well.

 

I can't comment on the CEM60 directly as I've never used one, but reports on it are pretty good and have been for years. And, yes there have been some lemons. As there have been with Losmandy and AP and even Paramount. Oops happen, though less often with the small batch mounts.

 

When I bought the 60EC I was actually in the market for a 120EC, but it was reported having issues. At the time of purchase there were reports of good performance on the 60EC and possibility that the SDE issue had been solved. So I went with the 60EC, thinking of it as an interim step to a more robust mount in 2-3 years or perhaps to mitigate some loss in the event I lost interest in the hobby by then. 

 

 

Kevin




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