Encyclopedia of the Solar System 2nd ed

The Sun 73

10

-3

A

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-2

A

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-1

A

1 A 10 A 10

2 A

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∝m

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∝m

1 mm 1 cm 10 cm 1 m 10 m

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Hz

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3 GHz

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10 GHz1 GHz100 MHz

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SPECTRAL IRRADIANCE (erg cm

-2

s

-1

∝

m

-1

)

WAVELENGTH

FREQUENCY

GAMMA RAY X RAY

ULTRA

VIOLET

VISIBLE

INFRARED

RADIO

LARGE BURST

(3B FLARE, 8/4/72)

(NONTHERMAL)

NON-FLARE

CONDITIONS

1B FLARE

POSTFLARE

2B FLARE

QUIET SUN

QUIET SUN

(THERMAL)

LARGE STORM

(NONTHERMAL)

SLOWLY-VARYING

S-COMPONENT

ACTIVE REGIONS

(THERMAL)

GRADUAL

BURST

(NONTHERMAL)

LARGE BURST

3B FLARE, 8/1/72

(NONTHERMAL)

LARGEST BURST

REPORTED

(NONTHERMAL)

FIGURE 2 The solar irradiance spectrum from gamma rays to radio waves. The spectrum is
shifted by 12 orders of magnitude in the vertical axis atλ=1 mm to accommodate for the large
dynamic range in spectral irradiance. (Courtesy of H. Malitson and NASA/NSSDC.)

by ionized plasma in the coronal temperature range of
∼1–2 million K. Emissions in shorter wavelengths require
higher plasma temperatures and thus occur duringflares
only. Flares also accelerate particles to nonthermal ener-
gies, which cause emission in hard X-rays, gamma rays, and
radio wavelengths, but to a highly variable degree.

2. The Solar Interior

The physical structure of the solar interior is mostly based

on theoretical models that are constrained (1) by global

quantities (age, radius, luminosity, total energy output; see

Table 1); (2) by the measurement of global oscillations