Talk:W Virginis variable

Change in sentence on relative brightness

Sentences like '...this star is 1.5 magnitude less luminous...' are slightly ambiguous, since a lower numerical value in magnitudes means a higher luminosity -- a brighter star. I hope the sentence 'The luminosity of W Virginis stars are less than Cepheids (about 1.5 mag)' is clearer than 'The luminosity is about 1.5 mag less than Cepheids'. At least on other pages on the internet there are some unclear sentences if you don't know what it's about. —The preceding unsigned comment was added by 131.211.39.71 (talk) 22:00, 9 May 2007 (UTC).

Population I/II Cepheids

Edwin Hubble measured the distance of M31 by applying the period-luminosity relation to Cepheids that he found in M31. The relation had been discovered by Henrietta Leavitt in 1912, while observing Magellanic Clouds. The relation, however, was not calibrated then, because the distances of Magellanic Clouds were not known. The relation was later calibrated using nearer Cepheid variables in the Milky Way. As Walter Baade showed later, the variables used for calibration, were Population II Cepheids, or W Virginis variables; and the Cepheids found by both Leavitt and Hubble were Population I Cepheids, and these are brighter. Using the relation calibrated for W Virginis variables to calculate distance of a classical Cepheid leads to too small distance. JTMnen 15:40, 5 September 2007 (UTC)