On spectroscopy and also globular cluster ages
First off, I want to spread the word far and wide about this great site with resources for teaching spectroscopy. I've been working for a long time to complete a lab for an on-line astronomy course, but did not want to use simulated spectra, but real spectra. I tried my hand at projecting some spectra and capturing images, but although they turned out ok, I didn't think they were good enough for a lab. Well, just the other day I used "spectrum incandescent bulb" as the magical search terms in Google images and found Brian's images. They are great and even better, as you can see at the bottom of his page he gives permission to use the images.
On to a completely different topic -- when I was first studying astronomy, the conventional wisdom was that there was controversy because the ages of globular clusters were determined to be ~15 Gyr, and the age of the universe derived from Hubble's constant was estimated to perhaps be as low as 10 Gyr. Although it is gone from his website, Bob Rood, who taught me stellar structure and evolution, used to have an image of his license plate, which read "15 Gyr".
Now that it is 2006, we all know that WMAP tells us that the age of the universe is very precisely known to be 13.7 Gyr. I have not been following the literature, but a burning question I've had is, "what happened to the ages of the globular clusters?" Everyone now says that they are 13 Gyr old, not 15 Gyr, so the controversy is gone. But even though we all know that WMAP revised the age of the universe, who reset the ages of the clusters without telling me? I asked our colloquium speaker the other day, since his entire talk was about precise calibrations of stellar parameters, why does everyone accept that the globs are now all 13 Gyr? My question wasn't phrased very eloquently, but I don't think that he had a good answer, either. I talked with Richard afterwards, and he tells me that the biggest change comes from improvements in the distance scale from Hipparcos. Still, it seems that the change in the ages of the globular clusters happened without as much fanfare as the change in the age of the universe, which makes me skeptical. I suppose I will have to devote some of my voluminous spare time to getting back into the literature to find out exactly what happened.
On to a completely different topic -- when I was first studying astronomy, the conventional wisdom was that there was controversy because the ages of globular clusters were determined to be ~15 Gyr, and the age of the universe derived from Hubble's constant was estimated to perhaps be as low as 10 Gyr. Although it is gone from his website, Bob Rood, who taught me stellar structure and evolution, used to have an image of his license plate, which read "15 Gyr".
Now that it is 2006, we all know that WMAP tells us that the age of the universe is very precisely known to be 13.7 Gyr. I have not been following the literature, but a burning question I've had is, "what happened to the ages of the globular clusters?" Everyone now says that they are 13 Gyr old, not 15 Gyr, so the controversy is gone. But even though we all know that WMAP revised the age of the universe, who reset the ages of the clusters without telling me? I asked our colloquium speaker the other day, since his entire talk was about precise calibrations of stellar parameters, why does everyone accept that the globs are now all 13 Gyr? My question wasn't phrased very eloquently, but I don't think that he had a good answer, either. I talked with Richard afterwards, and he tells me that the biggest change comes from improvements in the distance scale from Hipparcos. Still, it seems that the change in the ages of the globular clusters happened without as much fanfare as the change in the age of the universe, which makes me skeptical. I suppose I will have to devote some of my voluminous spare time to getting back into the literature to find out exactly what happened.
posted by Chris at 10:16 PM
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