An ancient Greek hand-powered geared device from the 2nd century BC that modelled the Sun, Moon and calendars and predicted eclipses. It is often called the oldest known analogue computer.
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A black hole is matter packed so tightly that not even light escapes. We know they exist from their effects on nearby stars and gas, from X-rays, gravitational waves and one direct image.
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Earth's orbit takes about 365.24 days, not a whole number. An extra day roughly every four years keeps the calendar in step with the seasons.
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Ole Roemer made the first measurement in the 1670s from timing eclipses of Jupiter's moon Io. Armand Fizeau made the first Earth-based measurement in 1849 using a toothed wheel.
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Seasons are caused by the tilt of Earth's rotational axis, about 23.5 degrees, not by changes in Earth's distance from the Sun.
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In 1838 Friedrich Bessel published the first reliable stellar parallax, for 61 Cygni, using Earth's orbit as a baseline. Henderson and Struve made rival claims.
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Today the Moon's distance is measured by timing laser pulses bounced off reflectors left on its surface, accurate to about a millimeter. Ancient astronomers got a rough figure from eclipses.
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