New theory reduces suns size by 300 kilometres

A new study suggests that the Sun may be 300 kilometers smaller than previously thought.

London, Nov 20 : A new study suggests that the Sun may be 300 kilometers smaller than previously thought.

If the latest study carried out by a team led by Margit Haberreiter of the World Radiation Centre in Davos, Switzerland, turns out to be correct, then other properties of the Sun such as its internal temperature and density may be slightly different than previously calculated.

Because the Sun has no solid surface, its atmosphere merely gets thinner and more transparent farther from its centre. So, the Sun's 'surface' is defined to be the depth in its atmosphere where it becomes opaque to light.

Scientists generally measure this by observing the Sun with telescopes and measuring the distance between the centre of the Sun's disc and its edge (the place where its brightness suddenly drops off). This gives a radius of 695,990 kilometres, or about 109 times the radius of Earth.

But a second, completely different way to measure the Sun's size by using surface gravity waves called f-modes that ripple across the surface of the Sun like water waves on the ocean, reduces the sun's size by 300 kilometers.

This theory implies that these waves should appear only at the Sun's opaque surface, and observations of them can be used to measure the Sun's radius, since their wavelength is tied to their distance from the Sun's centre in a predictable way.

The wave method gives a radius of around 695,700 kilometres, about 300 kilometres smaller than the result from the light drop-off measurement.

Although the difference amounts to just 0.04%, it is large enough to matter when scientists try to gain insights on the Sun's interior by interpreting observations of sound using a technique called helioseismology.

Scientists suggest that new calculations of how light propagates in the Sun's atmosphere may have resolved the discrepancy in the Sun's radius in favour of the smaller measurement.

Using software that simulates the propagation of light through the Sun's atmosphere, the research team recalculated the precise spot where the light drop-off should occur. .

Their results suggest that there should actually be a small difference between where the Sun's atmosphere becomes opaque and the point where observers see the light drop-off.

The light drop-off happens 333 kilometres higher up in the Sun's atmosphere than the location of the opaque surface where the f-modes occur, according to the new calculations.

"Theoretical models of the Sun that are based on the larger radius need to be corrected", said team member Alexander Kosovichev of Stanford University in California, US. "A more accurate radius could lead to a better understanding of the Sun's interior," he added.

"It allows us to calculate more accurately the structure of the Sun and compare with the results of helioseismology, learning more about the constitution of the Sun," Kosovichev told New Scientist magazine.

Recent observations also suggest that the Sun contains only half as much oxygen as previously believed, which appears to conflict with the results of sound wave studies.

ANI