Two years ago, scientists towed telescopes and other equipment into fields and up mountains across the United States for a celestial spectacle: the 2017 Great American Eclipse.
Now, theyre at it again. On July 2, the next total solar eclipse will be visible shortly before sunset from the Pacific Ocean and parts of Chile and Argentina.
Eclipse watchers hope to study some of the same solar mysteries as last time, including the nature of our stars magnetic field and how heat moves through the suns wispy outer atmosphere, known as the corona (SN Online: 8/11/17). But every eclipse is different, and this years event offers its own unique opportunities and challenges.
“There are all sorts of outside things you have to be lucky about” in watching an eclipse, says astronomer Jay Pasachoff of Williams College in Williamstown, Mass., who will be viewing his 35th total solar eclipse from the Cerro Tololo Inter-American Observatory in northern Chile. Here are some of the challenges, and potential rewards, facing astronomers.
1. The sun is in a period of low solar activity.[hhmc]
One of the main reasons, scientifically speaking, to observe a total solar eclipse is to catch a glimpse of the corona, whose wisps and tendrils of plasma are visible only when the suns bright disk is blocked. This region could hold the key to predicting the suns volatile outbursts, including giant burps of plasma called coronal mass ejections that can wreak havoc with satellites and power grids if they hit Earth (SN Online: 4/9/12). But the corona is one of the least well-understood parts of our nearest star.
Still, “some of the science we can do is contingent on whats happening on the sun at that particular time,” says solar physicist Paul Bryans of the National Center for Atmospheric Research in Boulder, Colo.
In every eclipse, the corona looks different, thanks partly to the suns 11-year magnetic activity cycle. Magnetic fields in the corona guide the motions of its wisps and whorls, and determine when the sun gives off more powerful bursts like flares or the mass ejections. Scientists have never measured the coronas magnetic fields directly (SN Online: 8/16/17), but they keep trying.
In 2017, the sun was in a period of low magnetic activity (SN Online: 8/19/17), showing a pitiful number of sunspots, flares and coronal mass ejections. This year, its even quieter. “We are in the minimum of the sunspot cycle,” Pasachoff says. “If you look at an image of the sun today, its entirely blank.”
Thats both lucky and unlucky. Low solar activity means certain features in the corona, such as plasma plumes that stream away from the suns poles, will be more visible now than when the sun is more active. Catching a glimpse of those magnetically controlled plumes could give relatively rare insights into how the corona behaves.
But low activity also means that scientists are less likely to catch a fleeing coronal mass ejection, like those detected by Adalbert Ding of the Institute for Optics and Atomic Physics in Berlin and colleagues in 2015 and 2017 (SN Online: 5/29/18).
Although such an eruption is unlikely, its not impossible. The sun “does produce explosive events during this quiet phase,” Bryans says. “Part of the reason were doing these experiments is to predict when events like these happen.”
How to watch the eclipse[hhmc]
San Francisco's Exploratorium will broadcast live from Cerro Tololo Observatory in Chile starting at 4:00 p.m. EDT.
TimeAndDate.com will livestream the eclipse from 3:15 p.m. to 5:50 p.m. EDT.
Scientists are getting ever closer to measuring the coronas magnetic field. In 2017, solar physicist Jenna Samra of the Harvard-Smithsonian Center for Astrophysics and her colleagues spotted a particular wavelength of infrared light in the corona for the first time (SN Online: 5/29/18). This wavelength, emitted by iron molecules that have lost several electrons to the coronas extreme heat, is particularly sensitive to magnetic fields. Future observatories that focus on it could reveal more about coronal magnetism.
This year, Samras team will be looking again, in hopes of confirming that 2017 detection. She plans to fly an aircraft in the shadow of the sun with a special spectrometer aimed out the window. Over the last two years, she and her colleagues have improved the instruments sensitivity by a factor of 20, meaning the corona will look 20 times as bright as it did in 2017.
“We want to understand which of our emission lines are useful for future measurements of the magnetic field,” she says.
2. Less of the total eclipse will cross land.[hhmc]
Most of 2017s total eclipse was visible from land, covering about 4,600 kilometers from near Salem, Ore., to Charleston, S.C. That gave scientists a comparatively long time in the dark — about an hour and a half from coast to coast. Comparing the coronas appearance from west to east let researchers measure how the corona changed over that period.
This year, the path of totality covers a chunk of the southern Pacific Ocean and a narrower swath of land, roughly 2,000 kilometers from western Chile to eastern Argentina. A partial eclipse will visible across other parts of the two countries as well as Paraguay, Uruguay, Bolivia, Peru, Ecuador and parts of Brazil, Colombia, Panama, Costa Rica and Nicaragua.
Sea to shining sea[hhmc]
The 2019 total eclipse will cross part of the Pacific Ocean and South America. While it will spend less time over land than the 2017 eclipse, the duration of totality — when the sun is fully blocked by the moon — seen from land will be almost as long, about two and a half minutes. The spot with the longest duration of totality will see four minutes and 32 seconds of darkness.
The moon is also closer to Earth this time. So the spot with the longest duration of totality will see four minutes and 32 seconds of darkness, but unfortunately, that spot is in the middle of the southern Pacific Ocean. (In 2017, the same period was about two and a half minutes.)
Back in Chile, scientists can expect about two and a half minutes of totality. Because totality will happen a few hours before sunset, around 4:39 p.m. local time, many researchers are heading as far west in the country as possible to catch the maximum amount of obscured daylight.
Some groups still hope to get a longer stretch of corona watching time. Solar Read More – Source
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