The star discovered by P. Murdin had a period of ________ days.

• A. 5.6
• B. 2.4
• C. 7.8
• D. 9.1

Answer: (A)

The key idea is how we determine a variable star’s period from its brightness changes over time. You look at how the star’s light rises and falls and measure the time between successive peaks (or troughs) in that pattern. For the star discovered by P. Murdin, the brightness variation repeats on a cycle of about five and a half days. That repeating interval is the period.

Why this fits best: the observed light curve shows a consistent, return-visit cycle with that length, so it matches the data and the star’s classification (a short-period pulsator such as a Cepheid-type variable). The other options would imply cycles that are either too fast or too slow to align with the actual repeated pattern seen in the observations, so they wouldn’t reproduce the same sequence of brightness peaks across the data.