The Sun’s Stable Diameter

The Sun’s Stable Diameter

The Sun has the reputation of being the most stable burning star that astronomers observe. Its extreme stability allows humans to exist on Earth. Variations in its burning, periods of significantly greater intensity followed by periods of lesser intensity would render advanced life impossible. Yet, astronomers designing detailed models of the physics of stellar interiors recognize that all stars, including the Sun, must exhibit at least some short-term fluctuations. What keeps the Sun’s Fluxuations within that “safe” range?

In principle, the Sun’s fluctuation should be easy to measure. Gravity operates to shrink the Sun while radiation works to expand it. Therefore, measuring the diameter at closely spaced intervals should reveal short-term fluctuations. In practice, however, the task of measuring the Sun’s diameter to the required degree of accuracy has been difficult.

The Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) satellite now overcomes the difficulty and makes these measurements possible. This amazing instrument supersedes the precision of ground-based telescopes by several hundred times. It can measure the solar diameter to an accuracy of better than one milliarcsecond (one part in 1,800,000)!

Results from the MDI-SOHO establish that the solar diameter varies by no more than 20 milliarcseconds. The findings also reveal a slight correlation between the solar diameter and the eleven-year sunspot cycle.1 Astronomers anticipated this relationship between solar diameter and sunspot activity since the sunspot cycle is driven by the Sun’s magnetic field. They expected the Sun to shrink slightly when the magnetic field is strong and to expand slightly when the magnetic field is weak.

However, the MDI-SOHO instrument recorded the opposite correlation: the solar diameter was largest when the magnetic field on the surface was strongest. The solution to this mystery comes from recognition that photons produced near the Sun’s core take nearly a million years to reach the surface. A deep-seated source for variations in the Sun’s diameter and surface magnetic field strength is consistent with the apparent out-of-sync correlation seen on the Sun’s surface. Since magnetic field disturbances travel faster through the interior than the photons arising from nuclear fusion, the magnetic field and radiation fluxuations arising from deep-seated disturbances will arrive at different times on the sun’s surface. These new findings, which verify predictions that arise from astronomers’ most detailed solar models, suggest some remarkable fine-tuning in the Sun’s make up.2

They confirm that Sun has indeed been specially designed to support life’s existence at this time. It has just the right structure, composition, interstellar environment, size, and age to produce the radiation flow necessary for the long-term maintenance of primitive life and the short-term sustenance of human life. These new results point to the God of the Bible as the maker of the Sun and Earth.

  1. M. Emilio, J. R. Kuhn, R. I. Bush, and P. Scherrer, “On the Constancy of the Solar Diameter,” Astrophysical Journal 543 (2000), 1007-10; W. A. Dziembowski, P. R. Goode, A. J. Kosovichev, and J. Schou, “Signatures of the Rise of Cycle 23,” Astrophysical Journal 537 (2000), 1026-38; W. A. Dziembowski, P. R. Goode, and J. Schou, “Does the Sun Shrink with Increasing Magnetic Activity?” Astrophysical Journal 553(2001), 897-904.
  2. Emilio, Kuhn, Bush, and Scherrer, 1009.