skybadger

On 07/04/2022 at 23:10, Stu said:

Some info here

https://en.m.wikipedia.org/wiki/Solar_cycle_25

https://www.washingtonpost.com/weather/2020/12/19/solar-cycle-prediction-mcintosh/?outputType=amp

Was it the National Center for Atmospheric Research you were thinking about? Predicted a strong cycle, 233 sunspots.

That looks like it. I'd like to know why there is such a difference in basis for the prediction. But it is a big difference. 

Thanks for that Mark. I threw together a similar  thing using car  wheel bearings a while ago to hold a larger mount while I worked on it. The plan was/is to provide direct belt drive to the outer bearing surface using the belt around the we circumference which would provide the locking feature too. 

I like your approach better for a permanent capability. 

Lovely build. Have you a summary of the cost of the parts and the overall weight ?

Have you considered lightweighting the bracket  or making it in aluminium ? Maybe these aren't important for you,  just thinking forward to my next project....

Do you have any info on what the axial  loading limit is  on the bearings , ie what the telescope weight can be. 

Also, is that simple pin locking the removable Dec arm ? Very nice. Is it very solid ?

There was a contradictory prediction that expected a very strong max this cycle. It would be good to compare the current activity curve with that prediction. If only I could find it again. 

I notice more stars in the background of the triplet but better detail in the arms of the act image. Is this processing or a  contrast effect. I expect better higher contrast stars on the triplet and lower contrast on the sct so to have more detail in the arms is interesting. Both v nice images though.

My sky temperature readings never got lower than -10 due to the mistiness last week. Maybe that can be a proxy for transparency ? -25 or even -30 is typical for a good clear dark sky. 

When the prevailing wind is from the south or east in winter and the sky is clear (ie cloudless) it can still be quite hazy and the sky temp is again elevated. 

here's my offering for yesterday 

Its  a bit soft,  i need to work out how to get the tracking working on my alt-az. 

On 20/03/2022 at 07:35, Hughsie said:

First the Quark will provide you with the opportunity to capture some great images. I have one and should use it more but here are the reasons why I prefer the Lunt;

1) The Quark has a built in 4.2x telecentric Barlow. Depending on what refractor/camera you pair it with, full solar disc imaging may not be possible and so you need to produce mosaics and combine to achieve a full disc. My Lunt and ASI174mm produce full discs straight off the bat.

2) Flexibility. I start my imaging session taking a full disc image. I then add a 2.5x Powermate to capture closer but ‘wider fov’ images of areas of activity, stepping up to a 4x Powermate for closer views. The Quark just has its internal Barlow. I guess you could add another but I have rarely seen this done.

3) Tuning. With a pressure tuned Lunt it’s a simple case of turning the knob to achieve the darkest measure on the histogram for a given exposure/gain. When double stacked, I then adjust the histogram to achieve the lightest setting after adding the extra filter. Sounds complicated but it can be done in under a minute. With a Quark you have 6 or so settings and the filter needs to get up to temperature. This can take 10-15 minutes. When trying to image on a partly cloudy day this can be a pain when the sky is clear as the Quark warms up then you find it’s cloudy when it hits temperature.

4) Ambient temperature. In the Summer the Quark can shift off band as the filter further heats up. You then have to re-adjust tuning and wait.

5) Filter lottery. The filter inside the Quark are not necessarily the best. I have read stories on this forum and others of not all Quarks being created equal. I have not personally experienced this.

6) Energy Rejection Filter (ERF). I have used my Quark on both a William Optics Z61 and Z103 APO refractors. I would not want to use a Quark for any long period observation on the Z103 without adding an ERF on the front of the scope. A good quality ERF will cost c£500 to fit a 100mm aperture, admittedly cheaper for smaller ERF’s. It’s not a mandatory purchase but something worth considering if you are pairing the Quark with a quality APO refractor.

7) Double stacking. The cost is horrific to add another filter to the Lunt but once you bite that bullet, wow the level of extra detail puts a smile on my face every time. 

In summary, the extra cost of the Lunt provides more flexibility and convenience but it doesn’t fit everyone’s budget. Richard, if the Quark fits your budget stick with it as now the Sun is firmly back into its active cycle it will give you great views of our star.

Looking forward to seeing your images soon and welcome to the ‘light’ side!

I think this is a fair appraisal but... you can of course set the temperature on the quark to warm up at any time so its ready to go, typically at the last setting you used it, it hardly changes but moving blue/red is slow.

I find my quark goes off band through self heating  - it really needs that UV/IR pre-filter but I also found that made the image more blurry.

How are you getting those pictures via mobile ? Using just a phone holder ?

That may be true, but clean it first and then make that evaluation..have you any up close pics of the post cleaning surfaces ?

Why do you think there is damage?

I cleaned mine recently. Optical alcohol didn't touch the mould but a solution of water, a few drops of lemon juice or vinegar and a drop of detergent shifted it right away. I followed up with a wash with alcohol and it's squeaky and dust free  clean .

On 02/03/2022 at 13:32, Stu said:

🤣🤣. Well, I always thought the problem was that the heat was more concentrated at that point so you risked the secondary overheating, coming unglued etc. clearly not a problem on your scope 👍

I re-read this, I didn't mean to sound 'off'. You have prompted me to go and measure it now, on the next sunny day!. 

There's no glue on this scope to melt so that potential problem hadn't crossed my mind.  

Trying to do some physics I think it goes like this : 

The primary is 150mm and the secondary is 72mm in diameter, but reflects 85%s so I make that about 2.75W from solar collected by the scope ( primary shaded by secondary ) and 2.75  from direct solar heating to the surface of the secondary facing the sun, the lack of difference being due to the shading effect of the primary vs the lower reflectance of the front of the secondary. 

The equilibrium temperature will be the temperature at which the object ( the secondary mirror unit) will radiate the same amount of energy it receives. 

ie using Stefan-Boltzmann, P = σAT^4 where sigma = Stefan-Boltzmann constant σ = 5.670374419...×10⁻⁸ W⋅m⁻²⋅K⁻⁴.^[5]

So T = ( P/sigma.A)^(-4) which is ... 330K   or 57 Celsius

Using W = 1350 W/m^2 as the solar irradiance, 150mm as the diameter of the primary, 72mm as the diameter of the secondary, 85% as the reflectivity of the aluminised surface and 50% as the reflectivity of the surface facing the sun. 

If I repeat this for an OG of 100m diameter I get

input power into the glass = 1350* PI* 50mm^2*0.045 = 0.5W

where the transmissivity of BK7 glass is 95.5% so the absorptivity is 4.5%

Which means the equilibrium temperature turns out to be .. 153K . or roughly -120C

Well, nice to see its a chilly sunny day for the refractor users!

Anyone see where I went wrong ? 

On 28/02/2022 at 18:47, Stu said:

How else am I supposed to observe properly? 😉

I didn't realise just how big that is. Very nice. 

14 hours ago, Stu said:

Thanks! The secondary obviously copes with the heat ok??

Yeah no probs, compared to say a transmissive lump of glass ?

It's a 6* cassegrain. Unknown make.

Makes the solar image nice and bright and big with no transmissive optics 

That looks like my setup, white light and ha at the same time.

 really like to map ha features to white. The Herschel prism is a Russian one. Can’t remember the name of but works very well. 

I'm not sure there is much of a problem introduced by 9mm of oag. Rotator and tilter are more my problem. Oags can suffer from lack of stars at long focal lengths while you can move the guider and they have bigger fields but they do suffer from flexure. 

I think that wise.

The ir temp should remain constant. The sensor is internally compensated for temperature so regardless of enclosure temp should read a consistent and steady reading.

Very odd. I have two of these sensors and they don't do that. Coldest is -30 or so. 

Also, I don't understand why the delta is useful. The sky temp is the sky temp regardless of local ambient. It can be clear at 5 degrees if the wind is from the south and cloudy at -5 if the wind is from the north. 

I don't think Ive ever seen a centred flat on all my collimated scopes. it probably indicates a small degree of camera droop and sensor misalignment in the camera. They are only positioned according to the PCB fasteners. 

The donuts are out of focus dust shadows showing umbra and penumbra if they are small and a penumbra only for further away ones. The size is determined by the focal ratio and the distance. 

I've said this before, but sinking drain pipes into the garden to the clay layer, filling with concrete and a mortar bolt gives you a removable and very steady base to put a tripod pier on. You can pull the drainpipe out later if you can pull harder than the water suction of the soil. 

I happen to have a pier on abs that I used like this for a long time. Rock steady!

If you are building the go-to yourself, Onstep will get you started fastest, from commercial parts. There's a large wiki for it on the interweb.

As another data point I use :

ankher usb3 10 port hub on the mount. 

power to the hub controlled by the pier 8way remote switch, no power means the hub and attached devices is off. 

usb 3 cable to observatory pc 

Ethernet over powerline from house to observatory plus a WiFi extender in the obbo for all my alpaca WiFi devices. 

In general this has been very reliable. Powerline sometimes drops  but not often. Hub itself, very reliable. 

HTh

So the outcome of this is that someone has written an article that in general astronomers who know wouldn't agree with and it's been syndicated across retail websites, using the tools and practices of retail websites ? 

That's not a scam or particularly offensive. 

I suggest the action to take is to write a friendly  email to the author to improve the content or to write a piece yourself and get it syndicated. There's clearly a demand..

Otherwise this is just on par with slightly misleading television advertising.