2. 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.
3. ¿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.
4. 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).
5. 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).
6.
7. 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.
8.
9. 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.
10. 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.
11. 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.
12. 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
