Footage of the collapse of the Arecibo Observatory 305-meter telescope. Credit: Courtesy of the Arecibo Observatory, a U.S. National Science Foundation facility

Video 1. This video was taken from the vantage point of the Arecibo operations building (Building 1), where the Arecibo telescope operators conduct telescope operations. At the center of the video is the telescope platform, including the Gregorian dome. The catwalk, used to walk from the ground up to the top of the platform, is seen to extend from the left side of the frame to the top of the platform. Tower 4, the location of the August 10th auxiliary cable failure and the Nov 6th main cable failure, stands vertically to the left of center. Next a small puff of “smoke” can be seen emanating from the top of Tower 4, which is the beginning of the failure of Main Cable M4-2, followed by M4-1 and M4-3 and the remaining Tower 4 auxiliary cable. The auxiliary cables were added in the 90’s to support the added weight of the Gregorian dome. With support no longer provided by Tower 4 cables, one second later, the corner of the platform begins to drop. With the Tower 12 cables, off the frame to the left, and Tower 8 cables, off the frame to the right, still connected to the platform, the platform swings down toward a point mid-way between the two towers. Next the support cables from Tower 12, off the frame to the left, slice through the middle of the catwalk, which comes crashing down into the dish. After that, the 328 ft long bow-shaped azimuth arm and Gregorian dome begin to separate from the platform. Next the seven Tower 4 backstay cables that connect the top of Tower 4 to the ground begin to pull the top section of Tower 4 to the ground. The fate of the top section of Tower 12, off the frame to the left, is similar to that of Tower 4. The top section of Tower 12 is seen entering the top left corner of the frame and then, tumbling down the hill, to rest in front of the operations building. Trees in the left of the frame suffer considerable damage as they are sliced by the falling Tower 12 top section and cables.

Video 2 This video, which starts with a view of the top of Tower 4, was taken from the vantage point of an Arecibo Observatory drone, utilized for monitoring the condition of Tower 4 support cables. Four cables are seen in the center of this video. The top cable does not support the telescope platform, but instead supports the catwalk described in the narrative for the previous video. The three lower cables are, from left to right, M4-1, M4-2, and M4-3. Note that a number of individual wire strands of the M4-1 and M4-2 cables are noticeably broken at the beginning of this video. The M4-3 cable does not appear to have any broken wires at the beginning of this video. The first indication of the coming failure is the breaking of another M4-2 wire, accompanied by a puff of “smoke” and chips of paint flying away from the surface of the cable. Four seconds later the entire M4-2 cable appears to disintegrate. The failure of M4-2 is followed a fraction of a second later by the failure of M4-1, followed a fraction of a second later by the failure of M4-3. The drone operator then swings the drone around to view the reflector dish and fallen platform, azimuth arm, Gregorian dome, and the falling cables and catwalk. The top section of Tower 12, near the Visitor Center, can be seen tumbling down the hill to the left of the operations building. The Tower 12 backstay cables that connect the top of Tower 12 to the ground cause damage behind Tower 12, well away from the edge of the telescope dish.

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