Posted by jlwile on February 20, 2011
A commenter asked a question before I left on vacation. I gave him a brief answer as a reply, but now I want to go into the details of my answer. As the commenter mentioned, he was doing research for a sermon and came upon some information that indicated the sun is shrinking at a rate of about 5 feet per hour. While that’s not a lot for something as big as the sun, it indicates that the sun is rather young. After all, if we extrapolate the sun’s size backward over time using that rate, we would find that the sun would have been touching the earth a “mere” 11 million years ago.
If this were true, it would be a clear indicator that the earth and sun are not billions of years old. After all, the earth would not be a haven for life if it were anywhere near the surface of the sun! So if the sun is (and always has been) shrinking at anywhere near a rate of 5 feet per hour, the earth and sun could not be very old.
The problem is that this argument is based on faulty ideas about where the sun gets its energy and, more importantly, it is based on faulty data.
Since this blog is all about what the data say, let’s start with that. In 1979, two astronomers (J. A. Eddy and A. A. Boornazian) gave a talk at the annual meeting of the American Astronomical Society. In their talk, they looked at data from the Royal Greenwich Observatory that were gathered from 1836 to 1953. Based on those data, they concluded that for the time period in question, the sun was shrinking at a rate equivalent to about 5 feet per hour.1 Those are the data that formed the basis of the “shrinking sun” argument.
However, you have to realize that the data were presented at a scientific meeting, and they were never fully published. This indicates that the data were quite tentative. Annual meetings are held by many scientific societies, and their purpose is for scientists to share what they are currently working on. Part of the reason scientists get together to share their results is so that others working in the same field can help them interpret their data, show them how their data could be improved, or point out flaws in their data. Since these startling data were never published in a peer-reviewed journal, you can bet that someone (either in the meeting or later on) pointed out their flaws.
Obviously, the data did cause quite a bit of stir. Indeed, in less than a year, Sofia and colleagues published a report in Science that examined both the Royal Greenwich Observatory data and other data related to the size of the sun. They concluded that, at most, the sun was shrinking at a rate of just over 1 foot per year.2 About a year after Eddy and Boornazian had given their talk, Irwin Shapiro published a report in Science that measured the size of the sun by looking at how long it took Mercury to transit across it. The data spanned from 1736 to 1973, and within the error of the measurements, there was no shrinkage throughout that entire period.3 The following graph makes this point very clearly. The circles and triangles with error bars are the data, while the dashed line is the shrinking that was supposedly measured by Eddy and Boornazian.
Clearly, then, the data from Eddy and Boornazian are simply not correct. The sun is definitely not shrinking.
From a theoretical point of view, the concept of a shrinking sun is pleasing to those who think that the sun is powered, at least in part, by gravitational collapse. While it has been known for some time that nuclear fusion provides most of the sun’s power, details regarding certain particles that come from the sun (solar neutrinos) indicated that nuclear fusion might not explain all the energy coming from the sun. As a result, gravitational collapse, which would cause the sun to shrink, could have been considered as a secondary means by which the sun produced energy. However, recent experiments have explained this apparent problem, so according to the most recent data, all of the sun’s power can be explained by nuclear fusion.4 As a result, there is just no reason to expect that the sun is shrinking.
Given the fact that the data clearly speak against a shrinking sun, and given the fact that there is no reason to think the sun is shrinking in order to produce the energy that comes from it, the idea that the sun is shrinking is not reasonable.
Despite the fact that the shrinking sun is not a reasonable argument for the idea that the sun is young, there is at least one other data set that indicates the sun is not billions of years old.
1. J. A. Eddy and A. A. Boornazian, “Secular Decrease in the Solar Diameter, 1836-1953,” Bulletin of the American Astronomical Society 11:437, 1979.
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2. S. Sofia, J. O’Keefe, J. B. Lesh, and A. S. Endal, “Solar Constant: Constraints on Possible Variations Derived from Solar Diameter Measurements,” Science 204:1306-1308, 1979.
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3. Irwin Shapiro, “Is the Sun Shrinking?”, Science 208:51-53, 1980.
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4. Arthur B. McDonald, Joshua B. Klein and David L. Wark, “Solving the Solar Neutrino Problem”, Scientific American, 288:40–49, April 2003.
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