The sidereal day is about 4 minutes shorter than a solar day.

The sidereal day is about 4 minutes shorter than a solar day.

• A. True
• B. False
• C. It is 15 minutes shorter
• D. It is 4 hours shorter

Answer: (A)

The key idea is the difference between a sidereal day and a solar day. A sidereal day is how long it takes Earth to rotate once relative to distant stars—about 23 hours 56 minutes 4 seconds. A solar day is how long it takes for the Sun to return to the same point in the sky—about 24 hours. Because Earth is simultaneously orbiting the Sun, it has moved a little along its orbit during that rotation. After one full rotation, the Sun appears a bit to the east, so Earth must rotate a little more to bring the Sun back to the same meridian. That extra bit is about 4 minutes. So the sidereal day is indeed about 4 minutes shorter than a solar day.

The key idea is the difference between a sidereal day and a solar day. A sidereal day is how long it takes Earth to rotate once relative to distant stars—about 23 hours 56 minutes 4 seconds. A solar day is how long it takes for the Sun to return to the same point in the sky—about 24 hours. Because Earth is simultaneously orbiting the Sun, it has moved a little along its orbit during that rotation. After one full rotation, the Sun appears a bit to the east, so Earth must rotate a little more to bring the Sun back to the same meridian. That extra bit is about 4 minutes. So the sidereal day is indeed about 4 minutes shorter than a solar day.