The Sun is the most prominent feature in our solar system. It is the largest object and contains
approximately 98% of the total solar system mass. One hundred and nine Earths would
be required to fit across the Sun's disk, and its interior could hold over 1.3 million Earths. The
Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F).
This layer has a mottled appearance due to the turbulent eruptions of energy at the
surface. Solar energy is created deep within the core of the Sun. It is here that the temperature
(15,000,000° C; 27,000,000° F) and pressure (340 billion times Earth's air pressure at sea level)
is so intense that nuclear reactions take place. This reaction causes four protons or
hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha
particle is about 0.7 percent less massive than the four protons. The difference in mass is
expelled as energy and is carried to the surface of the Sun, through a process known as convection,
where it is released as light and heat. Energy generated in the Sun's core takes a million years to
reach its surface. The chromosphere is above the photosphere, solar energy passes through this
region on its way out from the center of the Sun. Faculae and flares arise in the chromosphere.
Faculae are bright luminous hydrogen clouds which form above regions where sunspots are about to
form. Flares are bright filaments of hot gas emerging from sunspot regions. Sunspots are dark
depressions on the photosphere with a typical temperature of 4,000°C (7,000°F). Corona is the outer part of the Sun's atmosphere. It is
in this region that prominences appear. Prominences are immense clouds of glowing gas
that erupt from the upper chromosphere. The outer region of the corona stretches far into space and
consists of particles traveling slowly away from the Sun. The corona can only be seen
during total solar eclipses.
It is a thin layer that produces the radiation transmitted into space. At this distance from the
sun, photons are more likely to escape than be absorbed. The main feature of this
region is as follows (i) height about 100 kilometers (ii) radiation temperature is about
5780 Kelvin (peak output is the center of visible light) (iii) photospheric temperature ranges
from 6600 Kelvin at the bottom to 4300 Kelvin (temperature minimum) at the top (iv) density is
about one hundred millionth of water (v) pressure is one hundredth of an atmosphere. The
photosphere is the transition from the convection zone to a convectively stable atmosphere. For
photons to freely leave the sun, the atmosphere does not have as many absorbing atoms
per unit volume. Decreasing density contributes to the transparency.
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