Sidereal day — definition and comparison with the solar day Which statements correctly describe a sidereal day?

Introduction / Context:
Timekeeping in astronomy distinguishes between rotation with respect to the Sun (solar day) and with respect to distant stars (sidereal day). Surveyors and astronomers use sidereal time for accurately predicting star positions for observations and instrument alignment. Understanding how a sidereal day compares to the solar day is essential for precise scheduling and pointing.

Given Data / Assumptions:

• Earth rotates on its axis while also orbiting the Sun.
• “Ordinary” solar day means the mean solar day used in civil timekeeping.
• Time can be expressed in standard hours, minutes, seconds.

Concept / Approach:
A sidereal day measures Earth’s rotation relative to the “fixed” stars. Because Earth advances a small angle along its orbit each day, it must rotate a bit more to bring the Sun back to the same meridian, making the solar day slightly longer than the sidereal day. Numerically, a sidereal day is about 23 h 56 m 4 s, roughly 4 minutes shorter than the mean solar day of 24 hours.

Step-by-Step Solution:

Verification / Alternative check:
Star transit timings and astronomical almanacs confirm the ~4-minute difference, accumulating to ~1 additional sidereal day per year relative to solar days.

Why Other Options Are Wrong:
Each of (a)–(c) is correct, making “All of the above” the appropriate choice. “None of these” contradicts established astronomical practice.

Common Pitfalls:
Confusing apparent solar time with mean solar time; assuming both days are exactly equal; overlooking that this difference drives the drift of star-rise times night-to-night.

Final Answer:
All of the above