Julian Blanco Torres 9-A

Biology Power PointThe sun and its radiation

effects

The sun:

• is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields. It has a diameter of about 1,392,684 km (865,374 mi), around 109 times that of Earth, and its mass (1.989×1030 kilograms, approximately 330,000 times the mass of Earth) accounts for about 99.86% of the total mass of the Solar System.

¿Why this name?:

• The English proper noun Sun developed from Old English sunne (in around 725, attested in Beowulf), and may be related tosouth. Cognates to English sun appear in other Germanic languages, including Old Frisian sunne, sonne, Old Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Norse sunna, and Gothic sunnō.

Characteristics:

• The Sun is a G-type main-sequence star comprising about 99.86% of the total mass of the Solar System. It is a near-perfect sphere, with an oblateness estimated at about 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometres (6.2 mi).

Core:

• The core of the Sun is considered to extend from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm3 (about 150 times the density of water) and a temperature of close to 15.7 million kelvin (K).

Radiative zone:

• Below about 0.7 solar radii, solar material is hot and dense enough that thermal radiation is the primary means of energy transfer from the core. This zone is not regulated by thermal convection; however the temperature drops from approximately 7 to 2 million kelvin with increasing distance from the core.

Convective zone:

• In the Sun's outer layer, from its surface to approximately 200,000 km below (70% of the solar radius away from the center), the temperature is lower than in the radiative zone and heavier atoms are not fully ionized. As a result, radiative heat transport is less effective. The density of the gases are low enough to allow convective currents to develop.

Photosphere:

• he visible surface of the Sun, the photosphere, is the layer below which the Sun becomes opaque to visible light. Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H− ions, which absorb visible light easily.

Atmosphere:

• The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere. They can be viewed with telescopes operating across the electromagnetic spectrum, from radio through visible light to gamma rays, and comprise five principal zones: the temperature minimum, the chromosphere, the transition region, the corona, and the heliosphere.

Effects:

• Sunburn (first degree or redness, blistering second degree) • Tan (immediate or delayed pigmentation) • Immune system disorders • sunstroke • LATE negative effects (chronic exposure).

• Cutaneous photoaging (premature aging of the skin that involves vascular dilation, wrinkles and blemishes)

• Photocarcinogenesis (appearance of skin tumors) • Eye disorders (cataract) • Immediate negative effects