Which of the following statements are true? A) 365.25 solar days in a year. B) 366.25 sidereal days in a year. C) 364.25 sidereal days in a year. D) Both A and B.

• A. There are 365.25 solar days in a year.
• B. There are 364.25 sidereal days in a year.
• C. There are 366.25 sidereal days in a year.
• D. Both A and B.

Answer: (D)

The question tests the difference between solar days and sidereal days and how many of each occur in a year.

A solar day is the time it takes for the Sun to return to the same local solar position, so a year contains about 365.24 solar days. In practice we often round that to 365.25 to align with leap-year practice. A sidereal day is the time for Earth to rotate once relative to distant stars, and it is shorter than a solar day by about 3 minutes 56 seconds. Because the Earth must rotate a bit more each year to account for its orbit around the Sun, there are more sidereal days in a year than solar days, roughly 366.24 to 366.26. Therefore, the statements that there are about 365.25 solar days in a year and about 366.25 sidereal days in a year are true; the idea that there are about 364.25 sidereal days is not correct.