To watch an eclipse, you need a pair of paper glasses with a solar-safe filter. You put them on, and you watch.
(Photo by the Exploratorium)
To transmit an eclipse to the world takes considerably more.
The Exploratorium, which has been broadcasting eclipses since 1998, hauls two tons of equipment to far-distant sites: four or more telescopes, six video cameras, six monitors, a switching board, a six-foot satellite dish, microphones, laptop computers, power generators, a hundred yards of wires and cables, three French hens, two turtledoves . . . and a crew of a dozen to run it.
When the crew arrives at Woleai, the Micronesian island from which we'll film the eclipse, they have two days to set up all the equipment and test it. It’s an intense time, made more fraught by the unknowns they’ll face in this remote location. They hold two full rehearsals, 24 and 48 hours before the broadcast, testing all their data connections from the island so there are no surprises on eclipse day. They need to trust that they’re ready to magnify, capture, interpret, produce, and transmit the event.
Magnify the Sun
If you look at the sun through those solar-safe glasses, it looks pretty tiny: you can easily eclipse it with your thumb. So the first step in making a solar eclipse viewable is to magnify and sharpen the image via telescopes. Our telescopes will peer at the sun in two different magnifications—the 60mm telescope will show the full sun's disk, while the 90mm one zooms in to just a portion of it.
What you see without and with a telescope. (Photos by the Exploratorium)
Over the course of an eclipse, different aspects of the sun are highlighted, from the sunspots visible in full sunlight (while viewing the photosphere), to the colorful prominences and Bailey’s Beads of the chromosphere around the edge of the sun, to the corona that snaps into view during totality. These different phenomena give off light with different characteristics, so to capture them, our telescopes are outfitted with filters that selectively admit or screen different wavelengths of light. Two of our telescopes have white-light filters that are best for viewing the photosphere, and two have H-alpha filters. These allow in light at the narrow wavelength (656 nm) emitted by the sun’s chromosphere, the realm of coronal mass ejections and prominences that create some of an eclipse’s most colorful effects.
Before the eclipse, the telescopes need to be aimed correctly and set so they can track the sun as it moves across the sky. Our telescope wrangler will spend a night or two doing this, an exacting process called drift aligning. On Woleai, the task of lining up the telescopes is made more difficult because from there, the North Star—that stellar landmark in the sky—probably will not be visible.
Setting up telescopes in China to capture the 2008 eclipse. (Photo by the Exploratorium)
Capture the Action
If you’re lucky enough to witness an eclipse firsthand, be sure to do it where astronomy buffs have set up telescopes—they’ll be certain to invite you to take a look, and you’ll capture an unforgettable image in your mind. But on our expeditions, no one sees through the eyepieces of the telescopes. Instead, we capture the images on video: each scope is attached to a high-definition video camera so we can transmit the eclipse live to viewers across the world. The crew watches the eclipse via TV monitors—or by using their trusty paper eclipse glasses.
Interpret the Event
Not only do we film the eclipse, we produce an hour-long educational broadcast. Two additional video cameras are trained on our teaching team: two NASA scientists and two veteran Exploratorium educators, who monitor the progress of the moon sliding past the sun and provide expert commentary. This trip, to the Micronesian island of Woleai, they will be joined by a local chief who will tell viewers about his home, which was populated long ago by adventurers in canoes who navigated by the sun and stars.
Exploratorium scientists explain how an eclipse happens on our broadcast of the 2008 event. (Photo by the Exploratorium)
Produce the Show
The video from all six cameras, plus audio tracks, feeds into a switching board, a device that allows the show’s director to select between all possible shots, including a roll of pre-produced videos and stills, to create the program we transmit to the world. Think about a TV sports show that cuts from a shot of the game action on the left, to another shot on the right, to a wide-view from overhead, to commentary by the sportscasters and a highlight from last week’s game. Those second-by-second, shot-to-shot decisions are orchestrated by the show's director.
Our show director at the switching board. (Photo by the Exploratorium)
Transmit the Signal
From the switcher, a single feed emerges for transmission. Actually, we transmit two video feeds: the produced show, and a raw, image-only feed directly from one of the telescopes. We also send two audio feeds: the ambient sounds, and a musical piece composed from the electronic video signal of the eclipse, a “sonification” also created in the moment. Now it’s all ready for transmission, via our satellite dish, to an orbiting communications satellite. We’re also in phone communication with various players, using satellite telephones, to make sure the transmission goes smoothly.
From Woleai, the signal is beamed up to the satellite, then bounced back down to Earth in Napa, California—taking a matter of milliseconds. Different parts of the video then take different paths: Some feeds will be downloaded directly from the satellite by television news stations and NASA-TV for their own broadcasts. Some is sent via fiber-optic cable to Los Angeles, where it will be captioned for hearing-impaired viewers. At the Exploratorium’s public event at the museum, we’ll add Spanish-language commentary to the video. All these feeds are then processed for streaming on our eclipse website and via our mobile app, making the eclipse visible to individuals and our partner museums across the world. The eclipse program will even be available in the virtual world of Second Life.
Our last eclipse broadcast was seen by people in Oak Ridge, Tennessee, and Izmit, Turkey; in Kuala Lumpur, Singapore, London, Paris, and Urumqi, China. They gathered at museums, in classrooms, or around their computer screens. As the midday sun disappeared behind a black disk, at an inaccessible location thousands of miles away from most, millions of people watched as one, riveted.
An audience watches a live eclipse broadcast at the Exploratorium. (Photo by Amy Snyder, Exploratorium)
For more eclipse information and to watch the live broadcast, visit our eclipse website.