The period-luminosity relationship can be used to determine the distance to a Cepheid.
- Apparent magnitudes can be taken through photometric observation and plotted to create light curves such as the one below. (Source)
- Using this data, the average apparent magnitude m and the period in days can be determined. Here the data has an average apparent magnitude of 15.56 and a period of 4.76 days.
- The absolute magnitude M can be determined by inserting it into the period-luminosity plot. M = -3.6 (Source)
- Plug into d = 10 (m - M + 5)/5
d = 10 (15.57 - (-3.6) + 5)/5
d = 10 24.17/5
d = 10 4.834
d = 68,230 parsecs
- This particular Cepheid is 68.2 kpc away.