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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…
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…