A precise test of the theory of stellar evolution can be performed by measuring the average difference in energy between the neutrino line produced by { { } ^ { 7 } Be } electron capture in the solar interior and the corresponding neutrino line produced in a terrestrial laboratory .
This energy shift is calculated to be 1.29 keV ( to an accuracy of a few percent ) for the dominant ground-state to ground-state transition .
The energy shift is approximately equal to the average temperature of the solar core , computed by integrating the temperature over the solar interior with a weighting factor equal to the locally-produced ^ { 7 } Be neutrino emission .
Therefore , a measurement of the energy shift is a measurement of the central temperature distribution of the sun .

The energy profile of the { { } ^ { 7 } Be } line is derived analytically and is evaluated numerically .
The line shape is asymmetric : on the low-energy side , the line shape is Gaussian with a half-width at half-maximum of 0.6 keV and on the high-energy side , the line shape is exponential with a half-width at half-maximum of 1.1 keV .
The effective temperature of the high-energy exponential tail is 15 \times 10 ^ { 6 } K. The energy profile of the ^ { 7 } Be neutrino line should be taken into account in calculations of vacuum neutrino oscillations and of the absorption cross section for ^ { 7 } Be solar neutrinos incident on ^ { 7 } Li nuclei .

The characteristic modulation of the { { } ^ { 7 } Be } line shape that would be caused by either vacuum neutrino oscillations or by matter-enhanced ( MSW ) neutrino oscillations is shown to be small .
Other frequently-discussed weak interaction solutions to the solar neutrino problem are also not expected to change significantly the line profile .