Polaris has been a guiding light of navigation for centuries. But Polaris also happens to be the closest cepheid variable to our sun. These, together with the type II-A supernovae constitute standard units of luminosity, used to estimate distances for far-away galaxies

Recently, it was discovered that our distance measurement of Polaris was off by 30%.

I'm not familiar though which measurements rely more on cepheids over IIa supernovae, so i'm curious what cosmological measurements will be affected by this adjustment

It is undoubtedly romantic that a star that has been a lighthouse for some many generations of sea explorers, it also represents a beacon for interstellar distances, and might still tell us things that we didn't know

  • $\begingroup$ Good question. It may not be a big change simply because the ladder of distance is calibrated by more methods then are listed here. In particular you've missed at least on important standard candle over medium distances. $\endgroup$ Dec 10 '12 at 5:43
  • 2
    $\begingroup$ Also, a link to some resource discussing the re-measurement would be nice. $\endgroup$ Dec 10 '12 at 5:48
  • $\begingroup$ This is not addressed to Polaris specifically, but I've heard this Terence Tao lecture on the cosmic distance ladder is excellent (though haven't taken the time to watch it myself yet): youtube.com/watch?v=7ne0GArfeMs $\endgroup$
    – Michael
    Jan 9 '13 at 9:42

There is nothing wrong with the Hipparcos parallax for Polaris. It is a very sound determination with very good statistical properties. The chance that it would be off by as much as claimed by Turner is zero (about 25 sigma offset in the parallax). Turner has based his assumptions in the past on a so-called Polaris cluster, which he presented by means of an HR diagram of the area around polaris. This diagram can not be reproduced, even remotely. It is a complete mystery how it was obtained, and it was certainly not obtained in the way this was described. He then refers to a F3V companion and tries to determine the distance modulus based on that star, but then completely forgets about the differences between precision and accuracy: the uncertainty in the distance determination of a star when only based on the spectral classification are much larger than the difference that Turner tried to establish. The claim from Turner originates largely from the assumption that Polaris would be pulsating in fundamental mode. However, when, as everyone else does, it is assumed to be pulsating in overtone, there is no discrepancy in the distance and luminosity at all. Details can be found here : http://adsabs.harvard.edu/abs/2013arXiv1301.0890V


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.