The 5.6-day period mentioned refers to which kind of astronomical measurement?

• A. Orbital period
• B. Rotation period
• C. Pulsation period
• D. Proper motion

Answer: (A)

The period describes how long it takes for the system to complete one full cycle of its repeating behavior around a partner. A 5.6-day cycle is characteristic of an object going once around another body, so that interval is the time it takes to complete one orbit. You’d observe this in a binary star or star–planet system as regularly repeating events—like eclipses or Doppler shifts—that line up with each orbit.

Rotation would be how long the object spins on its axis, which changes the interpretation if the variation comes from spots or surface features rotating into view. Pulsation would be the star expanding and contracting internally, producing brightness changes on a different timescale. Proper motion is an apparent drift across the sky with no fixed short cycle. So the 5.6-day interval most directly indicates the orbital period.