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How astronomers measure a star's distance by looking from both sides of the Earth's orbit: parallax Hold a thumb at arm's length and blink one eye, then the other: the thumb jumps against the background. Astronomers do the same with the whole orbit of the… Earth & Space4 min read How a 2,000-year-old bronze machine predicted eclipses with the number 223 In 1901, divers pulled a corroded bronze machine from a shipwreck off the Greek island of Antikythera. One dial ended in the number 223, written in Greek… History4 min read Why Mars sometimes walks backwards across the sky Every 26 months or so, Mars slows down, stops, and drifts backwards against the stars for a couple of months before carrying on. Ancient astronomers built… Earth & Space4 min read