Astronomy — Definition of a Sidereal Day The interval from the moment a given star passes directly overhead (on the local meridian) to the next time it passes overhead is called:

Introduction / Context:
Timekeeping in astronomy distinguishes between a solar day and a sidereal day. Understanding the difference explains why stars rise about four minutes earlier each night and why star charts shift as Earth orbits the Sun.

Given Data / Assumptions:

• The observation is tied to a fixed star on the celestial sphere.
• We measure the interval between successive meridian transits of that star.
• We are not measuring the interval relative to the Sun’s apparent motion.

Concept / Approach:
A sidereal day is the time it takes Earth to complete one rotation relative to the distant stars, about 23 hours 56 minutes. A solar day is the time between successive solar noons, about 24 hours, reflecting both Earth’s rotation and its orbital motion around the Sun. Because Earth advances in its orbit each day, it must rotate a little more for the Sun to reach the same meridian, making the solar day slightly longer than the sidereal day.

Step-by-Step Solution:

Verification / Alternative check:
Any introductory astronomy text lists sidereal day as star-to-star transit time; the 4-minute difference accumulates to about 2 hours per month of star-rise time shift.

Why Other Options Are Wrong:

• Solar day: Measured relative to the Sun, not a star.
• Both are similar: They differ by ~4 minutes; not interchangeable.
• None of the above: Incorrect since the correct term exists.

Common Pitfalls:
Assuming “day” is always solar; astronomy uses multiple reference frames (solar vs sidereal).

Final Answer:
one sidereal day