SP-402 A New Sun: The Solar Results From Skylab

TEMPERATURE AND DENSITY vary with height in the Sun's atmosphere according to these curves. Height in kilometers is shown increasing upward on the scale at left, measured from the top of the photosphere where sunspots are seen. Yellow and orange peaks are chromospheric spicules that jut up into the corona; the transition region between chromosphere and corona is shown as a dark yellow band, only a few hundred kilometers thick, which follows the spicule outlines.

TEMPERATURE AND DENSITY vary with height in the Sun's atmosphere according to these curves. Height in kilometers is shown increasing upward on the scale at left, measured from the top of the photosphere where sunspots are seen. Yellow and orange peaks are chromospheric spicules that jut up into the corona; the transition region between chromosphere and corona is shown as a dark yellow band, only a few hundred kilometers thick, which follows the spicule outlines.

At the top of the photosphere (zero height) the solar temperature is about 6000 K; below this, in unseen layers of the solar interior, the temperature increases as the center of the Sun is approached. Temperature continues to fall above the photosphere until a sharp minimum occurs in the low chromosphere. The temperature of the solar atmosphere then begins to rise, slowly in the upper chromosphere, and then rapidly, in steps, through the thin transition region. At a height of about 5000 km above the photosphere, in the corona, a temperature of 106 K and more is reached. Numbered temperature lines at lower left show familiar labora" tory temperatures such as (1) temperature at which gold melts, 1337 K; (2) melting point of iron, 1808 K; (3) boiling point of silver, 2485 K; (4) temperature of acetylene welding flame; and (5) iron welding arc. Higher temperatures to right of (5), which characterize most of the solar atmosphere, are seldom achieved in our terrestrial experience. Density of the gaseous solar atmosphere falls rapidly with height above the photosphere. (See the scale at top, expressed in grams per cubic centimeter.) Between the photosphere and the top of the transition region, in a range of less than 3000 km in height, density falls through 10 orders of magnitude. Even in the relatively dense photosphere, the solar gas is so thin that it would be considered a vacuum on Earth. Lettered lines at top give terrestrial densities such as (A) density of our atmosphere at an altitude of 50 km, (B) Earth atmosphere at 90 km; (C, D, E) ranges of vacuum densities achieved by laboratory vacuum pumps: (C) mechanical vacuum pump, (D) diffusion pump, and (E) ion pump.

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