How long does it take for Earth to rotate on its axis?

How long does it take for Earth to rotate on its axis?

• A. 1 day (24 hours)
• B. 1 year
• C. 27 days
• D. 12 hours

Answer: (A)

Earth spins on its axis and the time for that spin defines a day. The commonly used day length is about 24 hours—the solar day—because it’s the time from one local noon to the next, as the Sun returns to the same position in the sky. Because Earth is also moving along its orbit around the Sun, the Sun appears to drift slightly, so it takes a little extra rotation each day to realign with the Sun, about 4 minutes more than a simple 360-degree spin. If you measure the rotation against distant stars instead of the Sun, the rotation is a bit shorter: about 23 hours 56 minutes, known as a sidereal day. The other options describe orbital or half-day times, not the full rotation on its axis.

Earth spins on its axis and the time for that spin defines a day. The commonly used day length is about 24 hours—the solar day—because it’s the time from one local noon to the next, as the Sun returns to the same position in the sky. Because Earth is also moving along its orbit around the Sun, the Sun appears to drift slightly, so it takes a little extra rotation each day to realign with the Sun, about 4 minutes more than a simple 360-degree spin. If you measure the rotation against distant stars instead of the Sun, the rotation is a bit shorter: about 23 hours 56 minutes, known as a sidereal day. The other options describe orbital or half-day times, not the full rotation on its axis.