Using Spectroscopy for Solar Applications

On Monday, August 21st, 2017, the Avantes Eclipse Team was there at the NCAR/ NASA observation post built on Casper Mountain, in Casper, Wyoming to observe and examine the eclipse from the path of totality. Nova, the creators of the award winning PBS science program, was there to document the eclipse experiments1 of Researchers like Dr. Steve Tomczyk, Sr. Scientist and Section Head at the National Center for Atmospheric Research, Hight Altitude Observatory2.

The Casper Mountain site provided Researchers an outstanding observation point along the path of totality, partly due to the reduction of atmospheric pressure at elevated altitudes but also the arid conditions of the high plains also enabled the Scientists to get the observations3 of the solar phenomenon as clear as possible.

Casper Mountain Eclipse Conditions

Casper Mountain was lucky to enjoy the best weather conditions for observing the solar eclipse. The Casper Mountain camp was located directly on the path of totality with a mild 76 degrees, low humidity and near cloudless sky located at approximately 8,000 ft. or 2,438 meters above sea level4.

The moon made first contact with the sun5 starting at 10:22 am MST local time. During this first contact stage, the observable light started to dim noticeably and temperatures started to fall. Shadows of the eclipse could be seen on the ground through devices fixed to serve as pinhole cameras. Telescopes used to look at the sun with the help of neutral density filters allowed viewers to observe sun spots on the surface of the sun. It took about an hour and twenty minutes for the moon to fully obscure the face of the sun, reaching second contact.

Viewers were able to get a short glimpse of Bailey’s beads6 and the diamond ring even before the eclipse reached totality at 11:42 am and the mountain top was shrouded in darkness. At the Casper Mountain site, totality lasted for two minutes and twenty-six seconds. The temperature dropped rapidly in the high mountain field set up as the observation post, falling from 76 degrees before first contact to 49 degrees at the lowest point.

An AvaTrek-Irradiance field kit including the AvaSpec-ULS2048x16-USB2 spectrometer, AvaTripod, Cosine Corrector and FC-UV400 400 µm fiber cable, was set up by the Avantes team. Starting at first contact, the team gathered spectra measurements every minute for the first hour of the partial eclipse phase. The team gathered spectra every 100 ms at 20 minutes before second contact at the onset of totality, through totality and lasting 5 minutes past third contact (end of totality). For 30 to 40 minutes longer into third contact, the team returned to a scan per minute sample rate.

Although the collected data will be a poor shadow in comparison to the data collected through telescope by the NCAR/ HAO team, the Avantes team is excited to share this data as a Spectra of the Month feature in the near future.

Observing the Corona

Although mankind has been able to reliably predict eclipses since Edmond Halley predicted the London eclipse in 1715 using Newton’s theory of universal gravitation7, still there is much that science should learn from a solar eclipse.

Since the sun is usually too bright to see directly, either with the advanced light sensing equipment such as telescopes and cameras or the human eye, a full eclipse gives a unique opportunity to directly see the sun. The intensity of light from the sun obscures the much fainter plasma corona that becomes clearly visible during an eclipse.

The Sun’s Corona Presents a Mystery

The body of the sun is a dense mass of superheated gas that churns constantly. This motion produces magnetic fields that are constantly churning and in flux. The sun’s turbulent and dynamic magnetic fields trail plasma outward from the denser gas core and form the fainter outer atmosphere, known as the corona.

The corona produces a fainter light compared to the chromospheres as the gases are less dense than at the surface of the sun. Although it is very far from the core and less dense, the corona is paradoxically much hotter than the surface of the sun. There are various theories, but still there is no scientific consent and this coronal plasma effect continues to be a mystery8. Data collected on August 21st by the High Altitude Observatory (HAO) and NCAR Researchers could be instrumental in giving answers.

By Kelvinsong - Own work, CC BY-SA 3.0, Link.

By Kelvinsong - Own work, CC BY-SA 3.0, Link.

Solar flares as well as other phenomena of solar weather are also a significant area of study. The sun’s churning magnetic fields occasionally erupt and let a jet of high-energy radiation to get away in what is called a coronal mass ejection. These huge explosions from the surface of the sun have the potential to be hazardous on Earth where technology can be badly affected. In addition, knowing more about these coronal mass ejections with data about the corona gathered during the eclipse may help Researchers better understand and predict these phenomena.

Eclipse Experiments

Avantes was privileged to offer three spectrometers for use in NCAR High Altitude Observatory eclipse experiments9. The perfect conditions at the Casper Mountain observation post facilitated Dr. Tomczyk and his team to gather a large amount of data in the near infrared and visible wavelengths from the solar corona and chromospheres.

In one test, the HAO team employed the new AvaSpec-NIR512-2.5-HSC-EVO to capture the NIR spectra from the full corona out to 10 solar radii. In another test, dual channels will collect NIR (AvaSpec-NIR256-1.7-USB2) as well as Visible (AvaSpec-ULS2048CL-USB2) spectra from paired telescopes in order to collect spectra of the layers of the sun’s chromospere - the area between the corona and the photoshpere. The data is expected to offer a topographical map of the chromosphere layers by taking measurements in quick succession every 8 milliseconds, and evaluating this against the moon’s passage rate.

The data gathered at the Casper Mountain observation post will be examined10 and decoded for new understanding and approaches into the nature of immediate solar system for years to come. Eventually, HAO and NCAR will be releasing their data11 to other Scientists and Researchers around the world; however, HAO team’s preliminary reports are very optimistic.

What can Spectroscopy Tell Us About the Sun

It is a well-known principle that every element of the periodic table has a unique spectral signature, which means every element absorbs a unique pattern of wavelengths. Spectrometers employ gratings to divide light into component wavelengths that, when a detector array collects, enables measurement of energy at every wavelength of the dynamic range of the detector. The sample’s elemental composition can be determined by examining the light reflected by any number of samples and spotting the absorption lines (wavelengths that are absorbed and not reflected) created by the sample.

Spectra data gathered during the eclipse on August 7th, 1869 resulted in the discovery of a mysterious and never before seen element due to faint absorption line in the green range at 530.3 nm12. Since this “new” element was identified in the corona of the sun, it was originally known as Coronium. Researchers of the era tested different methods to find the source of this new element for years. The work of Grotian and Edlen in 1939 eventually cracked the mystery when they concluded that the chaotic interaction and intense heat of the sun’s gases generate a form of highly ionized iron plasma (Fe 13+) different from anything that can be generated in laboratories on Earth13.

With advancement in computing power and optical technology since earlier eclipse events, there is no end to the possible new insights that may come due to the work of Dr. Tomczyk and other Scientists examining the great North American eclipse of 2017.

References

  1. http://www.pbs.org/wgbh/nova/space/eclipse-over-america.html
  2. https://www2.hao.ucar.edu/term/people/steve-tomczyk
  3. http://curious.astro.cornell.edu/about-us/112-observational-astronomy/stargazing/technical-questions/692-why-are-telescopes-located-in-remote-places-intermediate
  4. https://en.wikipedia.org/wiki/Casper_Mountain
  5. http://aa.usno.navy.mil/solareclipse?eclipse=22017&place=Casper+Mountain%2C+Wyo.&lon_sign=-1&lon_deg=106&lon_min=18&lon_sec=52&lat_sign=1&lat_deg=42&lat_min=45&lat_sec=09&height=2480
  6. https://www.nasa.gov/image-feature/the-baileys-beads-effect-during-the-2017-total-solar-eclipse
  7. https://www.theguardian.com/science/the-h-word/2015/may/03/halleys-eclipse-newtonian-selling-science-history
  8. https://phys.org/news/2016-12-mystery-coronal.html
  9. https://www.sciencenews.org/article/wyoming-eclipse-physics-corona
  10. https://www2.ucar.edu/atmosnews/in-brief/128125/ncar-take-rare-infrared-measurements-during-solar-eclipse
  11. https://agu.confex.com/agu/fm17/preliminaryview.cgi/Paper277529.html
  12. https://sunearthday.nasa.gov/2006/locations/coronium.php
  13. http://laserstars.org/spectra/Coronium.html

This information has been sourced, reviewed and adapted from materials provided by Avantes BV.

For more information on this source, please visit Avantes BV.

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