Astrophysicists Recalculate Sun Energy Escape to 170,000 Years From 3,000-30,000

Q: Is the sunlight warming your face today truly ancient, or is it brand new?

It is both ancient and brand new: the energy is ancient, but the photon that reaches your skin is newly emitted. Astrophysicists have shown that energy created by nuclear fusion in the Sun’s core can take roughly 170,000 years to work its way to the surface. It does not stream straight out. In the Sun’s dense interior, photons are constantly absorbed, re-emitted and scattered in a slow “random walk.” A 1992 recalculation by Romas Mitalas and Kenneth R. Sills found that earlier estimates were too short because they assumed photons could travel farther between interactions than they actually can in the Sun’s densest layers. That means the energy warming your face today likely began its journey long before recorded human history. But the specific photon you receive is not the same one created in the core. In the Sun’s interior, photons repeatedly lose their identity as they are absorbed and replaced by new photons at different energies. By the time energy reaches the photosphere, it is emitted outward as fresh visible, infrared and ultraviolet light. So in strict physical terms, the sunlight hitting you left the Sun’s surface only about 8 minutes and 20 seconds ago. In a deeper sense, the energy it carries is extremely old, having spent tens of thousands to hundreds of thousands of years migrating outward from the core. That is why both descriptions are accurate.

3 articles · Updated · ScienceAlert · Jul 21

170,000 years is the revised estimate for energy to move from the Sun’s core to its surface, far longer than earlier 3,000-30,000 year calculations.
Mitalas and Sills found those older estimates assumed a roughly constant photon step length of 0.5 to 1 centimeter, missing the Sun’s much denser inner layers.
Their recalculation showed the step length falls below 0.1 centimeter across more than 50% of the Sun’s radius, forcing photons into a much slower random walk through the plasma.
Once that energy reaches the surface, the picture changes completely: sunlight then crosses 150 million kilometers to Earth in just over 8 minutes.