On August 21, 2017, the town of Lincoln City, Oregon, like many locales in the path of that date’s total solar eclipse, will have its big day in the Sun, then in the Sun’s shadow, and then back in the Sun again.
Eclipse-chasing tourists are expected to flood in. But one team of Sun-watchers and their telescope might stand out: They will have traveled near seven thousand miles from China to do science here.
“The telescope is one of the most advanced facility in the world for spectro-polarimetry during solar eclipses,” says team leader Zhongquan Qu. The team focuses on the corona, the Sun’s outmost layer. Qu is a professor of solar physics at the University of Chinese Academy of Sciences Yunnan Observatory in Kunming, and a member of the IAU Working Group on Solar Eclipses.
The Sun’s corona is usually visible only during solar eclipses, so this summer’s event affords many heliophysicists a rare observational opportunity, one that Qu’s team refuses to miss. They decided against Oregon’s capital Salem — which is also on the totality path — because many tourists there might be taking photos with their flashes turned on nearby, creating scattered and stray light that can ruin scientific observations. Lincoln is off the beaten path, and should draw smaller crowds.
THE TOTAL ECLIPSE CHASER
What makes Qu’s telescope special lies in its name: Fiber Arrayed Solar Optical Telescope, or FASOT for short. Using the innovative design of an optical fiber array, FASOT can not only obtain spectrographs from individual fibers but it can also re-construct images of the corona using the spectral signal and location information in each fiber. In an initial evaluation for a funding application to the National Natural Science Foundation of China, FASOT was also described as “the first major instrument that introduces the use of optical fibers for high-precision field spectro-polarimetry.” Spectro-polarimetry measures the polarization property of light, which enables scientists to obtain additional information about the source of that light (i.e. the corona), such as its magnetic field and geometry.
The imaging and spectrograph data from FASOT, says Qu, will allow researchers to know more about the detailed structure of corona, its magnetic field, and the formation of coronal mass ejection (solar flares). Together this set of knowledge will ultimately contribute to the understanding of solar mysteries like why the corona is so much hotter than the Sun’s photosphere and other areas closer to the center of the Sun.
FASOT’s last eclipse-chasing adventure landed the team in Gabon, Africa in November 2013. Qu and his colleagues have analyzed the data collected there and are about to publish the results in the journal Solar Physics. Highlights of that trip include the first green coronal line Fe XIV 530.3nm that has ever been observed since the 1930s, according to Qu. That line is the strongest one in coronal spectral lines.
For the upcoming total solar eclipse in the U.S., Qu’s team will focus on more coronal lines, such as a red coronal line, which is 637.4nm in wavelength. They also plan to use FASOT to see the most observed line in the solar spectrum, hydrogen-alpha 656.3nm.
Nevertheless, at least one scientist has reservations about FASOT the solar telescope, especially its reliability.
Having supported FASOT in its funding proposal — a quote from his written evaluation notes that “[it] may open the door to a new class of telescope facilities in solar physics” — Jan Olof Stenflo, a retired professor at the ETH and the University of Zurich, now expresses disappointment over the slow development of this instrument.
MORE TESTING NEEDED
Stenflo is an expert in solar magnetic fields and high-precision spectro-polarimetry. During a lecturing tour in China in 2011, he met Qu and offered a positive written assessment of FASOT to support its funding application. “More than five years later, I still have not seen any concrete demonstrations that the prototype can achieve its goals and be able to map solar magnetic fields (the reported eclipse observations are unsuited to serve that purpose),” says Stenflo in an email.
Stenflo suggests that the team still needs to prove the reliability of observations made by FASOT. He has doubts over the reliability “because the corona during a solar eclipse is much more difficult to observe than the million times brighter spectrum from the solar disk outside an eclipse, and it has never been demonstrated by disk observations that FASOT has been able to eliminate the various spurious polarization effects that can arise.”
Among the established telescopes in the solar physics field, FASOT is still new in town. When the final model — a 60 cm $1-million-dollar telescope upgraded from the current 30 cm $5000 version — is built in western China in five years, FASOT’s job will be to watch the Sun’s photosphere and chromosphere all year long: no more globetrotting to chase solar eclipses for corona observations. But the total solar eclipse in 2017 is on the horizon. If you happen to be in Lincoln City, Oregon on August 21, you might get a glimpse of the solar corona, and maybe you’ll also run into a telescope team from China trying to make the most out of the 116-second total solar eclipse.