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Gravitational deflection of starlight during the eclipse

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#1 thesmiths

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Posted 04 February 2024 - 05:32 PM

Some of you may have heard of the Eddington experiment done in 1919 to test the General Theory of Relativity. This experiment has been redone a number of times since then, with an amateur astronomer, Don Bruns, getting an extremely accurate result during the 2017 eclipse. A group of us are going to another series of measurements, primarily in Texas and Mexico, during the April 2024 eclipse. You can read up on some of the background to the proposed measurement in the post I did here: 

https://solarchatfor...=415517#p415517

 

 

 

 

 


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#2 R Botero

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Posted 05 February 2024 - 07:58 AM

Thank you for the link Doug.  I'll be in Mazatlan imaging with an ASI2600MC through my Stowaway at EFL 490mm....but on an Alt-Az mount.  If I do get any good frames out that setup that show stars, I may send you my data.  I am taking bracketed SER videos using SharpCap but will have everything automated and will try to enjoy the visual experience (being almost twice the duration of 2017).   Even using an Alt-Az mount, since none of my exposures are longer than 1s (for earthshine), I should have some untrailed stars in them.  

 

Roberto



#3 Coconuts

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Posted 06 February 2024 - 09:46 PM

Doug:  Great project.  Is Zeta Piscium close enough to show a measurable deflection?  HD6804 is a lot closer.  I think that this is the same as HIP5382.  What is its magnitude?  Would differential sun to stellar tracking elongate the close star in an exposure long enough to see it?

 

All the best,

 

Kevin



#4 thesmiths

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Posted 23 February 2024 - 11:01 AM

I'll be in Mazatlan imaging with an ASI2600MC through my Stowaway at EFL 490mm....but on an Alt-Az mount.  If I do get any good frames out that setup that show stars, I may send you my data.  I am taking bracketed SER videos using SharpCap but will have everything automated and will try to enjoy the visual experience (being almost twice the duration of 2017).   Even using an Alt-Az mount, since none of my exposures are longer than 1s (for earthshine), I should have some untrailed stars in them.  

 

Roberto

 

ALT-AZ will be a problem because of the field rotation. It will be necessary to stack the exposures and the software we developed assumes translations but not rotation. In fact, we discovered during testing that good polar alignment is fairly important.

 

Something that is extremely important is calibration. They key calibration required is what's called a zenith calibration. This is taken the night before or night after. Something like a series of 3sec and 10sec exposures for 1 minute total taken as vertical as possible. This is used to remove the geometric distortion inherent in any telescope.

 

We have developed some specialised software for this experiment. Here is a recent description of how it works and some processed examples taken with a Televue NP101is (with 0.8x reducer/flattener) and a ZWO 1600MM camera:

https://groups.io/g/...24/message/1318

 

The rms error across the full sensor can (after correction) be as low as 0.05 arcsec. Since the Einstein gravitational deflection is 1.75 arcsec per solar radius, this level of accuracy should be sufficient to see deflected stars outside of the corona.


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