An upcoming total solar eclipse is set to darken skies over North America on April 8. These phenomena happen when the Moon slips in front of the Sun from Earth’s view, totally obscuring the Sun’s visage. This casts surroundings into a twilight-like darkness.
For the imminent eclipse, the totality’s path, where the deepest shadow of the Moon (the umbra) falls, weaves through Mexico, heads northeast across Texas, the Midwest, nips into Canada, and concludes in Maine.
Such total solar eclipses appear roughly every 18 months somewhere on our planet. The previous one that traversed the US occurred on August 21, 2017.
An international team led by Aberystwyth University will perform experiments from a location in the totality’s path near Dallas. The group includes PhD students and experts from Aberystwyth University, NASA’s Goddard Space Flight Center in Maryland, and Caltech in Pasadena.
There’s crucial science during eclipses that rivals or outdoes space mission achievements. Our tests might also illuminate a mystery about the Sun’s outer atmosphere – the corona.
The Sun’s dazzling light gets blocked by the Moon during a total eclipse, allowing us to study the faint corona with exceptional clarity, from close to the Sun, out to multiple solar radii. A single radius equals half the Sun’s diameter, roughly 696,000km (432,000 miles).
Without an eclipse, sizing up the corona is super tough. It needs a specialized telescope called a coronagraph that’s made to filter out the Sun’s direct light, making the corona’s dimmer light visible. The precision of eclipse observations beats even space-based coronagraphs.
Also, coronal study during an eclipse is more budget-friendly compared to, say, space missions. A baffling aspect of the corona is why it’s hotter than the photosphere (the Sun’s visible surface).
Logically, as we move away from a hot object, the temperature should fall, not rise. Why the corona reaches such intense heat is another question we aim to explore.
Our primary tools are two scientific instruments. The first is the coronal imaging polarimeter, or Cip – which also means “peek” in Welsh. Cip snaps photos of the corona using a polariser.
The corona’s light that we’re after is highly polarised; it consists of waves vibrating in just one geometric plane. A polariser allows light of a specific polarisation to pass, blocking other types.
With Cip’s images, we can gauge the corona’s basic traits, like its density, and gain insights into the solar wind. This flow of plasma – intensely hot matter – endlessly streams from the Sun. Cip might pinpoint solar atmosphere sources for certain solar wind currents.
Directly measuring the Sun’s atmosphere’s magnetic field is tricky. But eclipse data should let us examine its intricate structure and map the field’s path. We can observe how far large “closed” magnetic loops stretch from the Sun, informing us about the corona’s overarching magnetic conditions.
Our second tool is the coronal high-resolution line spectrometer, or Chils. It separates light into a spectrum of colors to capture high-resolution spectra. We’re hunting for a specific spectral line of iron from the corona.
This line consists of three narrow frequency range emissions or absorptions, each born at varying temperature levels (in the millions of degrees). Their relative intensity indicates the temperature across different coronal areas.
Charting the corona’s temperature helps refine computer simulations of its behavior. These models must factor in how the coronal plasma gets so hot. Potential heating methods might involve transforming magnetic waves into thermal energy. If we find hotter areas, these can be integrated into simulations.
This eclipse coincides with a period of intense solar activity, so we might witness a coronal mass ejection (CME). These tremendous plasma clouds, magnetized and flung from the Sun’s atmosphere into space, can disrupt Earth’s nearby infrastructure, jeopardizing critical satellites.
Many facets of CMEs remain enigmatic, such as their initial development near the Sun. Spectral data on CMEs will help us understand their thermodynamics, and their speed and growth close to the Sun.
Our eclipse tools are also being considered for a space mission dubbed Mesom, intending to orbit the Moon for more consistent, prolonged eclipse studies. Planned as a UK Space Agency project, it involves several countries but spearheaded by University College London, the University of Surrey, and Aberystwyth University.
We’re also bringing an advanced commercial 360-degree camera to capture video of the April 8 eclipse and our observation site. The footage will support public outreach, showcasing our work and fostering public interest in our nearest star, the Sun.
