To increase the chances that the astronomers get good weather at all sites, the participating telescopes allotted the EHT five nights to use over the course of 10 days. And with the weather, they were just lucky. Sure, there were technical glitches, but, as far we know, nothing catastrophic-no mechanical problems knocking a telescope out of commission for an entire night, no faulty cables or disk drives failing to capture data. IвЂ™ve been following the EHT for five years, and it has been rare to see an observing campaign go smoothly. The collaboration has been observing annually with smaller assemblages of telescopes since 2006, but this is the first year they have enough participating stations-and, thus, a powerful enough telescope array-to see actual images. Alright, things should be recording.вЂќДЄnd so the Event Horizon TelescopeвЂ™s long-planned bid to directly image a black hole began. вЂњTwenty seconds until we hit,вЂќ said Jason SooHoo, an MIT Haystack Observatory technician who was remotely monitoring the data recorders at some of the sites.Дoeleman turned to SooHoo. вЂњIt just goes down from there,вЂќ as night approaches. The higher a mediumвЂ™s tau, the more opaque it is to starlight. вЂњTauвЂќ measures the optical depth of a medium-in this case, the EarthвЂ™s atmosphere.

вЂњThe tau is 0.07 at Mauna Kea, and itвЂ™s the middle of the afternoon,вЂќ said Shep Doeleman. It was almost as if the universe had decided the time was right to reveal this particular secret.

At some sites, the weather could hardly have been better. The skies were clear in all the right places. That night-the first of five opportunities in a ten-night window-the decision was straightforward. They had until 4 pm local time to make the go/no-go decision.

Astronomers in the field checked in via phone, Slack, and Webex. A prime target is Sagittarius A*, the 4 million-solar-mass giant at the center of the Milky Way.Д®arlier in the day, Shep Doeleman, the director of the EHT, gathered with a handful of colleagues to oversee the global effort here at the projectвЂ™s command center, a modified faculty office at Harvard UniversityвЂ™s Black Hole Initiative. Using a technique called Very Long Baseline Interferometry, the astronomers would unite these geographically distant stations into a virtual Earth-size telescope capable of imaging the вЂњshadowвЂќ that certain supermassive black holes cast against the glow of surrounding, superheated matter. A crew wintering over in Antarctica, whom EHT astronomers trained months earlier, would operate the South Pole Telescope. Was the weather good in all those places simultaneously? If so, they had a shot at imaging a black hole.ДЇor this experiment, some 50 astronomers from around the world had traveled to high-frequency radio telescopes on four continents: ALMA and the Atacama Pathfinder Experiment inВ Chile the Large Millimeter Telescope in Mexico the Submillimeter Telescope in Arizona the Submillimeter Array and the James Clerk Maxwell TelescopeВ in Hawaii the IRAM 30-meter telescope on Pico Veleta in Spain. What mattered were the conditions in Hawaii, Arizona, Spain, central Mexico, northern Chile, and at the South Pole. Last Tuesday, the weather at the Event Horizon Telescope (EHT) command center in Cambridge, Massachusetts couldnвЂ™t have been much worse: it was rainy and barely 40 degrees F.

Clear the skies world quest