A brief broadcast to the galaxy
On November 16, 1974, a group of scientists including Frank Drake and Carl Sagan gathered at the Arecibo Observatory in Puerto Rico to celebrate a major upgrade to its radio telescope. To demonstrate the new power of the instrument, they beamed a three-minute message towards Messier 13 (M13), a dense globular cluster of about 300,000 stars on the edge of the Milky Way galaxy. The broadcast was a technical demonstration than a serious attempt to contact aliens; M13 is roughly 25,000 light-years away, so a round-trip communication would take 50,000 years.
The message itself was a simple infographic, composed of 1,679 binary digits. This number was chosen because it is the product of two prime numbers, 23 and 73, suggesting the data could be arranged in a rectangular grid of 73 rows by 23 columns. The transmission, sent at a frequency of 2,380 MHz, had an effective power of about 20 gigawatts, making it detectable by a similarly sized telescope almost anywhere in the galaxy. The content, designed by Drake and his colleagues, included depictions of the numbers one to ten, the atomic numbers of important biological elements, the formulas for the components of DNA, a graphic of the double helix, a stick figure of a human, the 1974 Earth population (4.3 billion), a map of our solar system, and an image of the Arecibo telescope itself.
The silent giant
For 53 years, the Arecibo Telescope was the largest single-aperture telescope on Earth. Its main collecting dish was a massive 305-meter (1,000-foot) spherical reflector built into a natural sinkhole. The surface consisted of 38,778 perforated aluminum panels supported by a mesh of steel cables. A 900-ton instrument platform was suspended 150 meters (492 feet) above the dish.
The observatory led in radio astronomy, atmospheric science, and solar system radar astronomy. It discovered the first binary pulsar in 1974, providing early evidence for gravitational waves. It also mapped the surfaces of Venus and Mercury and discovered the first exoplanets in 1992.
The telescope's life ended abruptly. After damage from Hurricane Maria in 2017 and a series of critical cable failures starting in August 2020, the National Science Foundation announced the telescope would be decommissioned. Before a controlled demolition could occur, the remaining support cables failed. At 7:55 a.m. local time on December 1, 2020, the instrument platform crashed into the dish below, completely destroying the telescope. The National Science Foundation has announced it will not rebuild the main telescope but will establish a new science education center on the site.