Solar scientists hope an armada of amateur astrophotographers can record the inner corona’s evolution throughout the 2017 total solar eclipse.
Rosebud, Missouri, will see day turn to night just after lunch on August 21, 2017. The spectacle of a total solar eclipse will interrupt daily activities for about 2½ minutes, as the Moon blocks the bright solar surface to reveal the faint, delicate, and filamentary solar corona. Such an extraordinary event hasn’t been seen in the continental United States since 1979. But on that Monday in 2017, millions of Americans will see this rare event and experience firsthand the strangeness of having the Sun disappear from the sky.
If all goes well, a small group of volunteers in Rosebud will collect images of the eclipse for a unique project called the Citizen Continental-America Telescopic Eclipse Experiment. The Citizen CATE Experiment intends to open a new window through which to study the dynamics of the inner solar corona.
Given all the ground- and space-based telescopes involved in solar research, you might think there’s no need for such an effort. After all, telescopes from the National Solar Observatory (NSO) regularly observe the corona near the photosphere up to a height of about 1.3 solar radii. The Daniel K. Inouye Solar Telescope, now under construction on Maui, will observe this range with faster imaging and better spatial resolution. Meanwhile, spaceborne telescopes study the corona over a range from about 2.2 out to 30 solar radii and beyond.
But this coverage leaves an unprobed gap in our star’s atmopshere from about 1.3 to 2.2 solar radii. Fortunately, whenever the Moon completely blocks the surface of the Sun, the sky brightness as seen from the ground drops by a factor of 10,000 or more, making it easy for us to see and study this region of the solar corona.
A Golden Opportunity
The shadow of the Moon will hurtle across the United States at supersonic speeds, crossing the 2,400 miles from Oregon to South Carolina in about 90 minutes. Most viewers along this path will see the solar corona for only about 2 minutes. During totality they’ll likely see two broad coronal streamers extending east and west above the solar equator, plus a collection of thin filaments called polar plumes above the north and south poles of the Sun (pictured on the next page). Changes in the density of these delicate structures occur on time scales of 5 to 15 minutes, so while the 2017 total eclipse allows us to view polar plumes with excellent clarity, any given observer will get a frustratingly short glimpse of them.
To extend their time in totality, some astronomers have flown under the Moon’s shadow using supersonic aircraft, while others have established networks of telescopes on the ground along an eclipse path. Often, however, an eclipse path spans remote regions of the world or crosses vast oceans, so establishing even just two or three sites within the lunar shadow is a logistical challenge.
In contrast, the path of totality in 2017 will be accessible from thousands of convenient locations. In a 2012 paper titled “The U.S. Eclipse Megamovie in 2017,” researchers Hugh Hudson, Scott McIntosh, and others explain how citizen scientists positioned at various locations along totality’s path could collect images of the eclipse and combine them into a continuous video of the event. The Citizen CATE Experiment builds on the ideas introduced in that creative paper.
Instead of scattering themselves randomly across the eclipse path, our observers will be positioned at regular intervals, such that as the shadow of the Moon leaves one observer, it will fall on the next one to the east. In this way, Citizen CATE establishes a “relay race” of coronal observations, with one group of observers passing the baton to the next group every 2 minutes or so. Alexandra Hart, an accomplished solar imager from England, compiled the initial list of observing sites and found that, after accounting for access, the effort will require roughly 60 locations to assure continuous coverage or totality. After the eclipse ends, we’ll align and interleave the observers’ images and then assemble them into a continuous movie to reveal the dynamics of polar plumes for a full 90 minutes.
Since the small community of professional solar astronomers in the U.S. can’t possibly staff 60 observing sites, we’ll rely heavily on the help of amateur astronomers (see the box on the facing page).
We’re now compiling a list of diverse volunteers, and we will begin training this team in early 2017. One of the first Citizen CATE volunteers, retired professor Fred Isberner, has already taken eclipse data with our prototype telescope and detector. With no previous experience with digital astronomy imaging, Isberner learned to use the prototype telescope with assistance from Bob Baer at Southern Illinois University, Carbondale. Then, with help from TravelQuest International and 62N, we shipped the telescope to the Faroe Islands — where Isberner was vacationing — for the March 2015 solar eclipse. Braving poor weather, he set up the instrument and captured 30 seconds of totality between clouds! His experiences have provided invaluable lessons about training, technical issues, and logistics.
Sixty Telescopes, One Design
Co-aligning thousands of images from 60 telescopes will involve a significant effort, but one way to minimize the required processing is to make the telescopes as similar as possible.
The fully portable eclipse instrument will likely use a 90-mm f/5.5 doublet refractor and an equatorial mount on a tripod with a battery-powered right ascension drive. At the prime focus will be a 4-megapixel, rapid-readout detector, powered by a laptop collecting images at roughly 10 frames per second. Each CATE observer will also take calibration data to determine image orientation, which requires a white-light solar filter. Finally, user-friendly software will be provided to facilitate instrument setup, focus, calibration, and data collection, as well as to make a first-look movie of the combined images on eclipse day.
Our last chance to practice taking solar eclipse data before the August 2017 event is coming up soon. On March 9, 2016, the Moon’s shadow will cross parts of Indonesia and the Pacific Ocean. With funding from NASA, and in collaboration with my colleagues from the University of Wyoming, Southern Illinois University in Carbondale, Western Kentucky University, and South Carolina State University, we will be making further tests and collecting coronal data during this eclipse.
Our plan is to train undergraduate students at each of these schools (which, not coincidentally, are all located along the path of the 2017 eclipse) to take images with CATE prototype instruments. But perhaps more importantly, the students will become experts with the equipment. They’ll return to their home states to train volunteers well in advance of the U.S. eclipse, and each will travel along the eclipse path to a second state to train more volunteers.
After the 2017 eclipse is over, I hope our volunteers can take ownership of the instruments and bring them home. After all, these modestly sized telescopes can address various other citizen-science projects, such as observing sunspots, variable stars, and the occasional comet. In order to transfer ownership to the volunteers, the Citizen CATE Experiment cannot rely on public funds to purchase the equipment.
Therefore, we’re seeking donations from private and corporate sources. Two companies have generously contributed to the Citizen CATE project: DayStar Filters will supply the telescope optical tube assemblies and neutral-density filters for capturing partial phases and MathWorks has agreed to provide software for image acquisition and processing, as well as funding to cover equipment and other costs for the project. The project has funds for about 35% of a 60-site experiment and is seeking more sponsors to make this unique citizen-science experiment a success.
Having the instruments remain in the hands of the CATE volunteers is the best way to ensure that they’ll continue to be used after the eclipse. Our hope is that the fleet of instruments and the team of volunteers from Citizen CATE will jump-start advanced citizen-science astronomy efforts across the U.S.
Join Our Team!
The Citizen CATE Experiment is seeking motivated volunteers to make observations across the U.S. on the day of the 2017 eclipse. Some experience with astronomical observing is preferred. Each volunteer will be expected to take part in several teleconferences and time-sensitive practice observing campaigns in the months leading up to the solar eclipse. You’ll also be expected to make your own travel arrangements and to get to your assigned observing site at your own expense.
In return, the CATE project will teach its volunteers how to collect scientific data with the instrument and detector. If our fundraising efforts are successful, ownership of the CATE instruments will be transferred to the volunteers after the eclipse. These observers will also be recognized on each scientific paper that results from the experiment and be offered a selection of follow-up citizen-science projects to work on after the 2017 eclipse.
More details about the eclipse and post-eclipse citizen-science projects are described at our website: sites.google.com/site/citizencateexperiment/. Or contact author Matt Penn via email at [email protected].
Matt Penn became an avid amateur astronomer at age 10 using a 3-inch reflector. He’s currently an associate astronomer with the NSO and telescope scientist for the McMath-Pierce Solar Facility on Kitt Peak in Arizona, and he specializes in infrared spectropolarimetric observations and instrumentation. NSO is operated by AURA under contract to the National Science Foundation.