Comments on: Oh, be a fine girl, kiss me. https://habitablezone.com/2012/09/12/oh-be-a-fine-girl-kiss-me/ Sat, 25 Apr 2026 16:17:27 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: podrock https://habitablezone.com/2012/09/12/oh-be-a-fine-girl-kiss-me/#comment-18244 podrock Thu, 13 Sep 2012 06:04:08 +0000 http://habitablezone.com/?p=21789#comment-18244 Thanks, ER, I enjoy these essays. Thanks, ER, I enjoy these essays.

]]> By: ER https://habitablezone.com/2012/09/12/oh-be-a-fine-girl-kiss-me/#comment-18211 ER Wed, 12 Sep 2012 12:47:02 +0000 http://habitablezone.com/?p=21789#comment-18211 We can easily measure the color of a star, using photography and different colored filters that favor one end of the spectrum over another. But how do we measure the true brightness of a star, since that depends on two things: how bright the star actually is, AND how far away it is, neither of which we know ahead of time. We unravel the two by studying clusters of stars. By their very nature and appearance, we can assume all the stars in a cluster are roughly the same distance away from us. So the distance of the cluster is irrelevant in determining the relative brightness of its individual members. H-R diagrams were first made of cluster stars, because we knew the distance effect would drop out. An added bonus is that it is relatively safe to assume that all the cluster members have a common origin, and therefore, a shared history. They probably all formed at the same time from the same nebular material, even if they are different in brightness and color. <img src="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/images/openclust.jpg" alt="." /> We can easily measure the color of a star, using photography and different colored filters that favor one end of the spectrum over another. But how do we measure the true brightness of a star, since that depends on two things: how bright the star actually is, AND how far away it is, neither of which we know ahead of time.

We unravel the two by studying clusters of stars. By their very nature and appearance, we can assume all the stars in a cluster are roughly the same distance away from us. So the distance of the cluster is irrelevant in determining the relative brightness of its individual members. H-R diagrams were first made of cluster stars, because we knew the distance effect would drop out.

An added bonus is that it is relatively safe to assume that all the cluster members have a common origin, and therefore, a shared history. They probably all formed at the same time from the same nebular material, even if they are different in brightness and color.

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