A day on Uranus is 17 hours and 14 minutes long
The core idea stands, but key numbers or details have changed.
TaughtUranus rotates once every 17 hours and 14 minutes. Voyager 2 measured it during its 1986 flyby by timing the planet's radio emissions and magnetic field, and that has been the figure ever since.
NowIn April 2025, using a decade of Hubble observations of Uranus's auroras, astronomers pinned the rotation period at 17 hours, 14 minutes and 52 seconds: about 28 seconds longer than Voyager's value, and a thousand times more precise.
What actually happened
Voyager's 1986 estimate carried an uncertainty that quietly grew over the decades: a tiny error in the rotation rate compounds every orbit, and by now the old figure was off by enough that planners could no longer say which way Uranus was facing. The coordinate system built on it had, in effect, drifted loose.
The fix came from watching the planet's auroras dance over eleven years of Hubble images and tracking the magnetic poles they mark. Twenty-eight seconds sounds like a rounding error, and for trivia it is. But it re-anchors the entire longitude system of Uranus, which matters a great deal if you ever want to send a spacecraft back and know where its features will be. The specific number in the textbook was simply the best 1980s measurement, and it has now been replaced by a far sharper one.
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Who was taught this
Still standard through 2025, so anyone who finished school between 1950 and 2025 learned the earlier version.