Space Science & Space Physics News

Looking Straight at the Sun

Thanks to some crucial calibrations, the world’s biggest solar telescope will have a clearer view of the Sun.

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The world’s largest solar telescope—the Daniel K. Inouye Solar Telescope (DKIST), which sits perched atop Mount Haleakalā on Hawaii’s island of Maui—will begin peering at Earth’s closest star later this year.

“First light is this fall,” said Stacey Sueoka, an applied optical systems engineer at the National Solar Observatory (NSO) in Boulder, Colo.

It has been a fraught road to first light. In 2017, a Native Hawaiian group lay down in the road leading to DKIST’s construction site and, hand in hand, delayed the delivery of the telescope’s primary 4-meter mirror.

The primary mirror is one of myriad mirrors that DKIST houses, and recently, a team of researchers that included Sueoka calibrated these mirrors as well as other parts of DKIST so that the telescope can look at the Sun more clearly.

“When you put on eyeglasses and everything suddenly becomes clear, you’re correcting geometric aberrations in your eyeball,” said James Breckinridge, an instrumentalist with the International Society for Optics and Photonics.

Sueoka and her colleagues devised eyeglasses, in the form of lab measurement-based computer modeling of the mirrors and their protective coatings, for DKIST because there are a lot of things that can hamper the ability of a telescope like DKIST to look at the Sun clearly. One of those things is what happens to sunlight when it enters DKIST and bounces off the telescope’s mirrors. That light, according to Sueoka and David Harrington—an astronomer at NSO who led the new research, which published in June in the Journal of Astronomical Telescopes, Instruments, and Systems—can, as it reflects from mirror to mirror, lose its original solar signature.

That series of reflections and incoming sunlight can heat the mirrors and deform them, further fogging DKIST’s picture of the Sun. Part of the reason has to do with the unprecedented size of the telescope, Harrington said.

“As you push the envelope to bigger apertures, there’s all kinds of optical issues you have to confront in order to make a telescope of high quality,” Harrington said. DKIST is a big telescope, and because of that it receives a lot of light—about 300 watts of energy.

“You need to remove the characteristics of the instrument if you’re going to study the nature of the source,” said Breckinridge, who was not involved in the new research. And that, he added, is what Harrington and his team did: “They have devised a wonderful scheme for calibrating the entire instrument.”

With its new specs, DKIST will be able to examine the atmosphere of the Sun, and it will study the Sun’s magnetic field. This, according to Breckinridge, will help scientists to better grasp things like what triggers solar storms—magnetic maelstroms that can lead to electrical surges and blackouts here on Earth.

After first light this fall, DKIST will take some of the clearest-ever pictures of storm features like solar flares and coronal mass ejections—explosive events that Harrington said astronomers still do not fully understand.

—Lucas Joel, Freelance Journalist

Citation: Joel, L. (2019), Looking straight at the Sun, Eos, 100, https://doi.org/10.1029/2019EO128193. Published on 19 July 2019.
Text © 2019. The authors. CC BY-NC-ND 3.0
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