lux eterna

John Herschel, what a coincidence. Interesting. Addictive yes, not understanding is like a never ending itch. Also the brain needs a little exercise now and then. Thanks. 

The inverse function was unknown to me, that is where I got lost but now I can see how to proceed. The coming days will be occupied with Excel exersices - a perfect corona timekiller.

Thanks a lot for explaining !

No, I am not sure how to interpret this. I was just thinking like 10 to the power -1 equals 1 / 10. But not sure if that is applicable here.

@AKB Thanks, I think the answer may be there. I just have to spend a little time with it.

@vlaiv To look up RA/DEC conversion to Alt AZ and use altitude component is not an option. I need to do the math from scratch (the reason for this is an Arduino based project).

From your post :

1) sin(alpha) = sin(delta)*sin(phi) +cos(delta)*cos(phi)*cos(HRA)
2) sin(alpha) - sin(delta)*sin(phi) = cos(delta)*cos(phi)*cos(HRA)
3) cos(HRA) = ( sin(alpha) - sin(delta)*sin(phi) ) / ( cos(delta)*cos(phi) )
4) HRA = arccos( ( sin(alpha) - sin(delta)*sin(phi) ) / ( cos(delta)*cos(phi) ) )

I think I can follow you except for #1. The original formula (see the included picture above) was : alpha = 1 / sin( sin(delta)*sin(phi) +cos(delta)*cos(phi)*cos(HRA) ). How do you go from there to #1 ?

Edit : missed one "sin" ...

Hi all,

My trigonometry and mathematics skills are not quite up to this task, so I would appreciate if someone can show me how to proceed.

I am trying to design a formula that can tell at what time the sun reaches a user selectable elevation (aka altitude, not to be mixed up with declination). For the specific case of alt = 0 (sunrise/sunset) I have found a formula that looks good except that I need solar altitude as an input variable. An example: At what time will the sun reach -18 degrees (under my horizon) for a specific date, at a specific location ?

I have found two very informative pages with detailed descriptions. I think I understand most of  this one but here is where I fail to follow.

What is stopping me is that I cannot see how to transform the below formula to something like :
HRA = (some mix of sin, cos etc for declination, latitude and also elevation)

If I could calculate HRA for different scenarios, it would be easy to find out what time of day that corresponds to on my location.
 
The formulas use greek letters, I suggest using abbreviations like these instead :
za    zenith angle
lat    latitude
da    declination angle (+/- 23.5 degrees) = 23.5 * cos(360 * (DoY+10)/365)
ea    elevation angle (aka "altitude angle")
hra    hour angle = 15*(lst-12)
lt    local time (hours)
lst    local solar time (hours)
tc    time correction factor
doy    Day of Year (1 = January 1)
eot    equation of time

Thank you

Ragnar

If you are interested in general photography as well, I would recommend Photoshop. If (when) you are ready for the next steps, there are some handy plugins for PS, some are free while some are commersial (noise reduction, green tint removal, star fixing, vignetting removal etc etc).

After many years with PS, I took the step to PI, but I still need PS. I only use PI for the first steps, and it still makes me wonder how you can design such a non-intuitive user interface. On a learning curve scale from 0 - 10, I would put PS at 3 and PI at 15.

Ragnar

@tooth_dr This is an example, in "mask mode" I did Image-Adjustment-Brightness/contrast and inverted the mask (ctrl-I). This particular adjustment is "curves" but you can use the techniqe with whatever adjusment type you need.

Ragnar

14 hours ago, tooth_dr said:

I have been using Layer Masks routinely now, but it never occurred to use the overstretched image as the layer mask itself!  Great idea.  Do you have any links on where to learn more about this?

I found this guide https://www.donastro.org.uk/basic-layer-masking/

This "image-as-mask" method can be used in different scenarios, one is selective stretching, another selective colour manipulation. I use it the most for selective noise reduction (targeted for the darkest areas = inverted mask ( = "ctrl-I" )). Remember that you can adjust contrast & brightness etc of the mask while you are in "mask mode" (ctrl-click on the mask thumbnail). Even a gaussian blur of the mask can be done here. You can also use a brush here to add / remove parts of the mask (but that is often better done when you are out of "mask mode").

Ragnar

I like the natural look, relaxing for my eyes.

Ragnar

This is good, but there is so much potential with layered processing using masks. I often use a workflow like @BrendanC described, I just want to add a tip: The overstretched image above is just perfect to use as a mask. If you invert this mask (galaxies are black), editing will not do much difference to the galaxies.

Ragnar

Can I have two please ? 😁 (what an idea... I love it !)

The outer halo is very clear so this is promising.

Ragnar

Nice catch with the diffuse surrounding areas clearly visible. On my screen I see a little magenta bias so I gave it a try in PS to get a bit more colour separation (colour contrast). Used curves, selective colour, HLVG and hue/saturation (hope you dont mind).

Ragnar

Good find ! 👍

It does not make sense with 4 + 3 pin connectors to each motor for just 4 channels used. What could be the reason to that ?

Ragnar

Hi all,

About a year ago, I got the idea of making a portable mount without need for any counterweights.

The main design is (almost) an English Mount with two tripods supporting a rotating bar pointing towards NCP. This is very stable, but one of the 6 legs must just barely touch the ground - otherwise it is not. A slider on a M6 threaded bar is pulling a braided fishing line that is connected to a "windshield wiper" type arm, which is anti-backlashed with a adjustable torsion spring.
The lower tripod can easily be replaced with some kind of base kit that fits on a sturdy table or even a balcony fence.

Some components :
omron encoder E6B2-CWZ6C 2000P/R 0.5M
stepper
mcu
RoboRemo app

I can control the whole thing with the small IR remote and / or via Bluetooth LE and the RoboRemo app. The Arduino sketch does PID speed regulation and dslr intervalometer & dew heater controller are also included. Polar alignment is pretty easy with the laser pointer.
After careful speed tuning I have approx 75 % success rate (no wind present) with my dslr and TS ImagingsStar71 APO (350mm / F5). I also tried it out with an extra dslr (135mm lens) so approx 5 kg total payload without any noticeable negative impact.

This is 350 mm FL @60 seconds with APS-C Nikon D7000.

And this is 87 x 60 seconds stacked and processed:

And what about the snail label in the pictures ? This project started with the idea of having a snail powered mount, as they seem to go slow enough and need no batteries 😉 ! But I settled with an artificial snail - it can run a whole night on 4 x 18650 batteries without draining them.

Ragnar 

7 minutes ago, malc-c said:

The only problem there is that unless a component glows or smokes there is no means of telling if the current draw is excessive or not as SW don't release technical data at this level. - but good suggestion otherwise.

 

Of course this is just a hit or miss troubleshooting procedure, but I once repaired a pcb that way just by using my hands to feel the slight heat from one faulty component. Which reminds me of another case when no heat was emitted, I increased the current to whatever was the maximum but no heat. I was going to ditch that pcb but decided to push it further so I connected it to my car battery (yes!) with long cables so nothing was jeopardized, and there was a nice flame from the faulty (tantalum) capacitor.

Ragnar

You could connect a amp meter in series with the supply and see if the board sinks more current than expected. If that is the case, try to locate any heat source among the different components.

Ragnar

I use a cheap laser tool combined with a plywood adapter, to get a east-west alignment line on the ground. Maybe you can adapt this idea to your own requirements.

Ragnar

That is a good start, and from now on everything will be easier as you develop the setup and your routines. Perfect timing as you will be well prepared when autumn comes (I think I would have started with the cabling 😉 ).

Ragnar

I like it very much, not overdone but still very fine details. If it was mine, I would keep adding data to it in coming seasons and the perimeter area could be more visible. Also the red jets (?) in this galaxy would be nice to see. But this is still an extraordinary image - congratulations !

Ragnar

You have the details in the spiral arms pretty good, and the processing is not overdone, I like that. Maybe you could tease out some detail closer to the core if you process another stack, aiming just at the core, and then blend the two versions together. I also find the colour a little towards magenta, maybe there are still some hidden colour data that could contribute. But averall a nice image of a not-so-easy target.

Ragnar

Thank you @MarkAR and @geordie85, I´m glad you liked it !

Ragnar

Hi all,

My last imaging for this season resulted in 11 x 10 minutes on M51, but I already had 23 x 15 minutes from previous seasons so here is some 7 1/2 hours of data.
The 23x15 minutes subs were taken under a pretty dark sky (SQM-L = 21.65), while the rest were approx 21.5. Used a modded Nikon D7000 in a 8" Meade LX200-ACF on HEQ5 Pro, guided with NexGuide. I am still amazed that stars were pinpoint in all 23 of the 15 minutes subs. I guess it helped that the OTA was pointing near zenith so flexure and mirror lock issues should have been minimal. Nowadays I stick to max 10 minutes subs.

Ragnar

The story makes the image interesting.

Ragnar

Thank you @oymd, I´m glad you liked it !

Ragnar