Nick James

Abstract

Modern CMOS sensors are ideal for imaging total eclipses. They have high-resolution, are very sensitive and can support high frame rates. We are all familiar with the way that modern sensors form a colour image. In most cases the pixels are grouped into a square array of four with each pixel covered by a primary colour filter. This Bayer array of red, green and blue sensitive pixels is then processed in software to produce a colour image. Sony have recently introduced a family of sensors which use a similar technique but the four pixels are sensitive to different linear polarizations corresponding to 0°, 45°, 90° and 135°. This allows software to derive the linear polarization of each point in the image.

These sensors were designed for machine vision applications, in particular to suppress reflections when looking through windows, but they have an interesting application to imaging the solar corona during a total eclipse. The bright inner part of the corona that we see during totality consists of a very hot plasma. Light from the photosphere which scatters off the free electrons in the K-corona is strongly linearly polarized and this polarization depends on the viewing geometry and the 3D structure of the corona. Professionals have exploited this property in the past but reasonably priced cameras are now available within the range of amateurs.

This talk with discuss developments in the technology of polarization sensors with application to total eclipse corona imaging and will review some of the recent results from professional teams obtained at the 2023 and 2024 TSEs. I will also discuss my plans for the use of a relatively low-cost camera at the 2026 eclipse in Spain and some of the software tools that are available for analysis and visualisation.

BIO

Nick James (B.Sc., MIEE, C.Eng.) is a member of the British Astronomical Association, Director of its Comet Section and Assistant Editor of The Astronomer magazine. Professionally I am an engineer working in the space industry leading a team developing deep-space communication and tracking systems with a particular interest in precision position and time measurement techniques. My interest in astronomy started as a ten-year old when I received a small telescope for Christmas, and it has developed over the years to the point where I now have a fully equipped back-garden observatory. I am a Science, Technology, Engineering and Maths (STEM) ambassador and I regularly gives talks on astronomical subjects to a wide range of audiences.

I have been lucky enough to have been in the umbra 18 times, starting in Hawaii in 1991 and, most recently, in Mexico in 2024 and in the ant-umbra five times. Each eclipse is different and I try to use some new imaging technology at each one. All eclipse travel is memorable but my stand-out trip so far has to be the eclipse of December 2020 when Astro-Trails managed to arrange to get us into Argentina at the height of the Covid epidemic.