After being in print for twenty years, the Chronological Encyclopedia of Discoveries in Space, covering everything that was learned on every single space mission in the 20th century, has finally gone out of print.
Behind The Black, c/o Robert Zimmerman
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"Useful to space buffs and generalists, comprehensive but readable, Bob Zimmerman's Encyclopedia belongs front and center on everyone's bookshelf." -- Mike Collins, Apollo 11 astronaut
"The Chronological Encylopedia of Discoveries in Space is no passionless compendium of information. Robert Zimmerman's fact-filled reports, which cover virtually every spacecraft or probe to have ventured into the heavens, relate the scientific and technical adventure of space exploration enthusiastically and with authority." -- American Scientist
Astronomers have for the first time measured the orbital motion of two supermassive black holes that orbit each other.
Based on the initial data, the two black holes appear to orbit each other every 30,000 years. Eventually, they will spiral into each other, merge, and in the process produce ripples in the surrounding gravitational field that will be detectable by future gravitational wave detectors.