The Photosphere
of the Sun

Solar Photosphere as a Function of Depth

Depth
(km)
% Light from
this Depth
Temperature
(K)
Pressure
(bars)

0 99.5 4465 6.8 x 10-3
100 97 4780 1.7 x 10-2
200 89 5180 3.9 x 10-2
250 80 5455 5.8 x 10-2
300 64 5840 8.3 x 10-2
350 37 6420 1.2 x 10-1
375 18 6910 1.4 x 10-1
400 4 7610 1.6 x 10-1

Source: Fraknoi, Morrison, and Wolf, Voyages through the Universe
The Sun is a ball of gas, so it does not have a well-defined surface. When we speak of the surface of the Sun, we normally mean the photosphere.

Definition of the Photosphere

As we look down into the atmosphere at the surface of the Sun the view becomes more and more opaque. The point where it appears to become completely opaque is called the photosphere. Thus, the photosphere may be thought of as the imaginary surface from which the solar light that we see appears to be emitted. The diameter quoted for the Sun usually refers to the diameter of the photosphere.

Properties of the Photosphere

The adjacent table shows some properties of the photosphere. This table indicates that the solar atmosphere changes from being almost completely transparent to being almost opaque over a distance of about 400 km. Notice also that in this region the temperature drops rapidly as we near the surface, and that the pressure (measured in bars, where one bar is the average atmospheric pressure at the surface of the Earth) is very low - generally 1% or less of Earth surface atmospheric pressure.

Some Images of the Solar Surface

The following links provide current images of the solar surface. and here are two movies showing the variation of the solar surface over a period of days: For current solar images at various wavelengths, see the section on the solar spectrum.


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