Astronomers will be watching from the arid land that holds some of the world's largest telescopes as the Moon blocks the Sun's disk and reveals its corona on July 2, 2019.

Any view of totality is enthralling, but the July 2nd total solar eclipse in the South Pacific, Chile, and Argentina is particularly tantalizing for astronomers. Totality will pass right over the arid lands that hold several of the best telescopes in the world — including those at Cerro Tololo Inter-American Observatory (CTIO), Gemini South, La Silla Observatory, and the future sites of the Large Synoptic Survey Telescope and the Giant Magellan Telescope.

La Silla Total Solar Eclipse simulation
Simulation of a total solar eclipse over the La Silla Observatory. (Simulation includes clear skies, but those don't come guaranteed!)
M. Druckmüller / P. Aniol / K. Delcourte / P. Horálek / L. Calçada / ESO

When the Moon blocks the Sun’s disk, it reveals the white light of the outer solar atmosphere. This corona is the source of the magnetic storms that the Sun sends our way, so it’s a subject of intense study — largely from space, where spacecraft use occulting disks to block the Sun. But a total solar eclipse lets us study this region from the ground. And the eclipse on July 2nd will let professional astronomers study this region from a place that has some of the best seeing on the planet.

At the CTIO, five groups of astronomers will be viewing the eclipse:

  • Jay Pasachoff (Williams College), who has witnessed 70 total eclipses, will lead a team in imaging the Sun’s corona.
  • Shadia Habbal (University of Hawai‘i) and her “Solar Wind Sherpas” will take spectra of the corona during totality to gather information on its composition, temperature, density, and motions.
  • Paul Bryans (University Corporation for Atmospheric Research) and his team will analyze the polarization of near-infrared light coming from the corona to measure the Sun’s magnetic field. These measurements will complement another project, Airborne Infrared Spectrograph, that will measure coronal emission lines from above most of the atmosphere that would otherwise absorb near-infrared light.
  • Miquel Serra-Ricart (Institute of Astrophysics of the Canary Islands, Spain) will watch how Earth’s atmosphere — especially its ionosphere — responds to temperature changes as the Moon’s shadow sweeps by.
  • Yoichiro Hanaoka (National Astronomical Observatory of Japan) will lead a team in probing the corona very near the Sun’s visible surface. Space telescopes with occulting disks often need to block regions much larger than the Sun’s disk, so they can’t see this region well. By combining efforts with other observations over the path of totality will increase the time period over which astronomers can observe this region.
  • Read more about each of these experiments here.

Professional observatories are also taking this opportunity to reach out to the community. In collaboration with the CTIO, the Gemini South observatory has held school and public talks on eclipse viewing and photography. Likewise, La Silla Observatory is taking the opportunity to host a public event, inviting Chilean schoolchildren and other members of the public for a viewing party, as well as lectures and workshops.

Other observatories not on the eclipse path, such as the Atacama Large Millimeter/submillimeter Array (ALMA), are also engaging in outreach, as well as handing out eclipse glasses for the event. And they’re not the only ones: Astronomers Without Borders, a nonprofit organization dedicated to uniting people across the world through astronomy, is providing eclipse glasses, too — ones that were collected following the American eclipse of 2017.

As always, eclipse-viewing — and experimenting — is weather-dependent. (Unless you’re flying above the weather!) While people may maneuver to see the eclipse from another vantage point, the astronomers at these large observatories will likely stay put. So for all those astronomers pointing their telescopes skyward on July 2nd: Clear skies!

Editor's note (July 2, 2019): Edited to make clear that astronomers will be observing near the world-class observatories, but not through them as these world-class telescopes are not intended for solar viewing.


Image of Dan Tilque

Dan Tilque

June 29, 2019 at 12:11 pm

This isn't the first time a solar eclipse has covered large telescopes. Back in the 90s, an eclipse covered the Big Island and there were several scopes up on Mauna Kea in the middle of totality. I don't recall exactly which ones were built at that time, but I'm pretty sure the first Keck scope was there.

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July 1, 2019 at 11:11 am

I assume Jay Pasachoff seeing 70 total eclipses includes lunar eclipses too? There hasn't been 70 total solar eclipses during his lifetime, has there?

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July 1, 2019 at 4:20 pm

Partial and annual solar eclipses included I assume!

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July 4, 2019 at 2:11 am

THere are a minimum of 2 solar eclipses every year, and depending on the exact Sun-Moon-Earth geometry, there are sometimes two partial or penumbral eclipses a month apart instead of one total or annular one. The maximum theoretically possible number of solar eclipses in one calendar year is five; two partial/penumbral eclipses in January and February, one total or annular in June or July, and two more partial or penumbral eclipses in November and December.

Even so, 70 solar eclipses in a professional lifetime seems quite high. He wouldn't have time to do anything except planning their next eclipse trip!

Lunar eclipses; again, a minimum of two per year, with the same constraints as the solar ones. It SEEMS like lunar eclipses are more frequent, because they happen ON THE MOON, and its' visible from half the Earth's surface. Solar eclipses happen on the EARTH, and only on narrow swaths of the Earth.

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July 2, 2019 at 9:23 am

I wonder how they keep the un-eclipsed Sun out of the big scope, just before and just after the total eclipse. Else something may get melted down...

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July 2, 2019 at 9:28 am

And they could look for nearby stars for another relativity test. Though today you probably could use radio telescopes in an interferromity network, to get high resolution of some point source of radio right next to the Sun, without waiting for an eclipse.

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