Solar North vs Earth North Graph

Stephen, How hard would it be to add the Earth North, Solar North, and Zenith to your eclipse simulator? Here is an example from SEO:

Hi Rick, I’m not 100% sure what is meant by Earth North in this context - do you know? Otherwise, I have all the other data points available and it would just be a question of working out how to add them to the visualization (which is actually trickier than it sounds because of the how the graphics are implemented).

I’ve never quite understood why you would want anything other than local zenith in the 12 o’clock position - do you know why it might be useful to put celestial north there (other than creating a common frame of reference that is location independent)?

Thanks, Stephen. Let me explain how I would use it. Since I am going to be photographing the eclipse at 600mm, I know that some clipping of the corona will occur. I want to minimize the amount that I lose by orienting the long side of my camera frame to the long side of the corona. The long side of the corona extends from the rotational (E-W) axis of the sun. So, to get the most corona possible, I want the Sun’s North Pole to be pointing to the top of my camera frame.

My plan to make sure I orient my camera where the Sun is north-up in my frame was to compare sun spots in my image to the sun spots shown daily at spaceweather.com. Their image of the sun on the left of their home page is always sun north-up. This technique will work and I will certainly compare my image with the one from space weather the day of the eclipse, but it would be nice to have more than just an eye-ball approach. It would be nice to know what angle my camera has to be to the horizon to have the sun’s E/W axis aligned with the long edge of my image.
A friend sent me the map from Eclipse Orchestrator and it can be used to get the exact angle between earth north (celestial north?) and the solar north (Ns). With that information, I can preset the rotation on my camera (with an inclinometer) and just use the sunspot comparison as a double check.
Make sense? If not, I can send some pics

Hi Rick - if you had the data numerically rather than graphically, would that still be helpful? I think I could include:

  • Instantaneous parallactic angle, Solar north relative to zenith, Moon north relative to zenith
  • C2 position angle, parallactic angle, position angle relative to zenith
  • C3 position angle, parallactic angle, position angle relative to zenith

As the parallactic angle changes continuously through the course of the eclipse, you’d need to adjust frequently, unless that’s something your mount account for already?

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I think this would do it for me. Numbers only would be fine:

  • Instantaneous parallactic angle, Solar north relative to zenith, Moon north relative to zenith

My EQ tracker will keep the sun’s north up in my frame if I get it set correctly. The mount keeps objects from rotating in the frame

Thanks!! Hope you don’t go to too much trouble. It is a “nice to have"

I think the important angle (for me) is from Solar North to Celestial North. That is the angle in the SEO plot from above that matches what I get when I match sun spots to orient the sun. I’ve been wrong before , though

Quick question. In your eclipse simulator, is the sun oriented with its North up (like space weather.com), or is it oriented the way an observer on earth would see it as referenced to their personal horizon? Is the angle between the two handy? The angle probably has a name, but I can’t find it anywhere.

It’s zenith up - i.e. as an observer would see it from the ground without twisting their neck, if that makes sense!

You guys might want to be mindful of an eclipse simulation that has been published, available on the Predictive Science website. they are using some sophisticated modeling to predict the shape and relative location of the corona streamers, prominences, etc. As Rick points out, the 2017 eclipse corona had a strong east-west orientation. It appear that will not be the case this time. Because we are at solar maximum, the magnetic activity is much more variable and randomly distributed, with the result that the corona is likely to be evenly distrusted around the circumference of the sun, like petals of a flower.

That would mean that there may not be a sweet spot for orienting the horizontal axis of the camera. We may be taking a chance on cutting off more of the corona on the short dimension of the frame no matter what we do. This has me rethinking the 560 mm focal length of my main camera.

I’m still digesting this info, but it seem like it may pertinent to this conversation so I thought I’d throw it out.

Dave

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@whitacre.rick - the angle you’re looking for is called the ‘parallactic angle’. Some nice illustrations here:

https://www.petermeadows.com/html/parallactic.html

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I saw that too, Dave! Thanks!
Yes, if it stays this way, it makes my orientation project moot.

Thanks, Stephen! I need to find a calculator for that parameter. I will take it from here! Appreciate all the help!
Rick

If I am reading that correctly, it looks like a camera mounted on an equatorial mount and oriented so that the horizontal axis of the camera is tangent to the circle of rotation, the solar north would always be at the top of the frame. So a tracking mount or even Rick’s “Poor Man” manual tracker, would ensure the solar north orientation.

Dave

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I’m hoping to have it shown in the eclipse simulator by the end of the weekend… It’s something I’m already calculating anyway.

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My struggle is how to set that angle (tangential to the ecliptic) in practice. I can line up the sunspots and that will work, but I’d love to have a precise way to do it. The best I have come up with so far is to have the camera lens pointing at the horizon on the Meridian (RA level to the ground, Dec level to the ground). The angle of my camera in this orientation matches what is required to get sunspots to line up and give me Solar North. The angle on my camera also matches the angle on that plot I posted at the top. But is that the answer or coincidence? Will it work in Mexico? My brain hurts.

Rick, I did some research on this. I may be duplicating what you already know, but for what its worth…

First, I don’t think what you are after is the parallactic angle. That seems to be related to the relationship between the apparent rotation of the disk of the sun as a result of using an alt/az tracking system rather than equatorial. It doesn’t relate to the angle of the poles of the sun as viewed from earth. That seems to be independent the viewing position on earth and is called the “position angle” (P). P is defined as “The position angle between the geocentric north pole and the solar rotational north pole measured eastward from geocentric north. The range in P is +/- 26.31 degrees.”

It changes with what I assume is the orbit of the earth around sun and relates to the angle relative to the tilted sun that we are viewing it at any time of year. Though it doesn’t seem to be the quite the same value every year, it is a predictable value depending on the date. Also this is relative to the rotational north pole and not the magnetic poles of the sun.

See this site: Solar Rotation.

The left side of the app on that page will calculate the P (as well as a number of other things) based on the date. I plugged in todays date and came up with a P of 334.4, which is the angle on the disk of the current south pole. The supplement of which is 25.6, which is mighty close to the 25.8 you got lining up sunspots. (When the angle is relative to 360, the polar axis is tilted to the right of straight up, when it is relative to 0 is is tilted to the left.)

If this is the value you are after, then the angle on April 8 will be 333.77 or 26.23 degrees to the right of straight up.

I hope this helpful. At the very least, I learned something!

Dave

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By Jove, I think you’ve got it!!! I need to sleep on it, but I think this is what I have been looking for. Thanks so much!! I’ll let you know if I find any issues with this, but this makes me feel better that I can dial this in exactly.

Thanks, Dave!

I decided to get it all down on paper before my head exploded. Constructive criticism is always welcome. Also, if anyone wants to test this with their own EQ mount, please let me know how it works. Thanks! Rick

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