by A total solar eclipse occurs on April 8 across North America. These events occur when the Moon passes between the Sun and the Earth, completely blocking the face of the Sun. This drops viewers into a doorway like dawn or night.
During the upcoming eclipse, the path of totality, where observers see the darkest part of the Moon’s shadow (the umbra), crosses Mexico, heads northeast through Texas, the Midwest and into Canada to briefly before ending up in Maine.
Total solar eclipses occur approximately every 18 months at some location on Earth. The last total solar eclipse to cross the US was on August 21, 2017.
An international team of scientists, led by Aberystwyth University, will be conducting experiments from near Dallas, located in the path of totality. The team includes PhD students and researchers from Aberystwyth University, NASA Goddard Space Flight Center in Maryland, and Caltech (California Institute of Technology) in Pasadena.
There is valuable science to be done during an eclipse that is comparable or better than what we can achieve through space-based missions. Our experiments may also shed light on a long-standing puzzle about the outermost part of the Sun’s atmosphere – its corona.
The Moon blocks the intense light of the Sun during a total solar eclipse. This means that we can see the faint corona of the Sun with incredible clarity, from distances very close to the Sun, out to a few solar rays. One radius is the distance equal to half the diameter of the Sun, about 696,000km (432,000 miles).
It is extremely difficult to measure the corona without an eclipse. It requires a special telescope called a coronagraph designed to block direct light from the Sun. This allows for less light from the corona to resolve. The clarity of eclipse measurements surpasses even space-based coronagraphs.
We can also observe the corona on a relatively small budget, compared to spacecraft missions, for example. An ongoing puzzle about the corona is the idea that it is much hotter than the photosphere (the visible surface of the Sun). As we move away from a hot object, the surrounding temperature should decrease, not increase. One question we will be investigating is how the corona is heated to such a high temperature.
We have two main science instruments. The first of these is Cip (coronary imaging polymeter). Cip is also the Welsh word for “glance”, or “quick eye”. The instrument takes images of the sun’s corona with a polarizer.
The light we want to measure from the corona is highly polarized, which means it is made up of waves that vibrate in a single geometric plane. A polarizer is a filter that allows light of a particular polarization to pass through, while blocking light of other polarizations.
The Cip images will allow us to measure the basic properties of the corona, such as its density. It will also shed light on phenomena such as the solar wind. This is a stream of sub-atomic particles in the form of plasma – superheated matter – that continuously flows out from the Sun. Cip could help us identify sources in the Sun’s atmosphere for certain solar wind streams.
The magnetic field in the Sun’s atmosphere is difficult to measure directly. But the eclipse data should allow us to study its fine-scale structure and trace the direction of the field. We will be able to see how far magnetic structures known as large “closed” magnetic loops extend from the Sun. This in turn will give us information about large-scale magnetic conditions in the corona.
The second instrument is Chils (a coronal high-resolution line spectrometer). It collects high-resolution spectra, where light is separated into its component colors. Here, we’re looking for a distinct spectral signature of iron have been emitted from the corona.
It consists of three spectral lines, where light is emitted or absorbed in a narrow frequency range. Each of these is generated at a range of different temperatures (in the millions of degrees), so their relative brightness tells us about the coronal temperature in different regions.
Temperature mapping of the corona provides advanced, computer-based information on its behavior. These models must include mechanisms for heating the coronal plasma to such high temperatures. Such mechanisms might include the conversion of magnetic waves to plasma thermal energy, for example. If we show that some regions are warmer than others, this can be replicated in models.
This year’s eclipse also occurs during a period of increased solar activity, so we could see a coronal mass eruption (CME). These are giant clouds of magnetized plasma that are ejected from the Sun’s atmosphere into space. They can disrupt near-Earth infrastructure, causing problems for critical satellites.
Many aspects of CMEs, including their early evolution near the Sun, are poorly understood. Spectral information on CMEs will allow us to obtain information on their thermodynamics, and their velocity and expansion near the Sun.
Our eclipse instruments were recently recommended for a space mission called the solar occultation mission (Mesom). The plan is to orbit the Moon to get more frequent and longer eclipse observations. It is being planned as a UK Space Agency mission involving several countries, but led by University College London, University of Surrey and Aberystwyth University.
We will also have an advanced commercial 360-degree camera to collect video of the April 8 eclipse and the observation site. The video is valuable for public outreach events, where we highlight the work we do, and helps generate public interest in our local star, the Sun.
This article from The Conversation is republished under a Creative Commons license. Read the original article.
Huw Morgan does not work for, consult with, own shares in or receive funding from any company or organization that would benefit from this article this, and has disclosed no relevant affiliations beyond their academic appointment.
