Units & Measurement Trivia: Light-Years, the Metric System, and Classic Misconceptions

Sixty-four questions on the units we measure the world with — and the famous mistakes people make about them. Six parts: cosmic distances (why a light-year is a distance and not a time, what a parsec and an astronomical unit really are), the origin of the metric system (revolutionary France, the meridian survey, the original metre and kilogram), SI base units and the 2019 redefinition (the seven base units, the caesium second, and why the kilogram is now the Planck constant), temperature scales (absolute zero, why there is no 'degree Kelvin', and Celsius's upside-down original), classic unit confusions (knots, calories, watts vs watt-hours, carats vs karats, and the $125-million Mars units disaster), and everyday conversions and famous numbers. Many answers are numeric so you practise the figure, not just recognition, and every explanation links to Wikipedia or another source so you can verify it and read further. Several questions deliberately correct a popular but false 'fact'.