Download The sun, yellow dwarf star at the heart of the solar system

The sun, yellow dwarf star at the heart
of the solar system
By NASA.gov, adapted by Newsela staff on 10.28.16
Word Count 1,035
TOP: This image shows an enormous eruption of solar material, called a coronal mass ejection, spreading out into space,
captured by NASA's Solar Dynamics Observatory on January 8, 2002. BOTTOM: A solar eclipse captured by NASA's
Solar Dynamics Observatory on October 7, 2010. Courtesy of NASA.gov.
The sun is a type of star known as a yellow dwarf. A hot ball of glowing gases, it is at the
heart of our solar system. The sun's gravity holds the solar system together, by keeping
everything from the biggest planets to the smallest particles of debris in its orbit. Electric
currents in the sun generate a magnetic field that is carried out through the solar system
by the solar wind — a stream of electrically charged gas blowing outward from the sun in
all directions. The sun is responsible for the Earth's seasons, ocean currents, weather and
climate. Though it is special to us, there are billions of stars like it scattered across the
Milky Way.
93 Million Miles Away
With a radius of 432,168.6 miles, our sun is not an especially large star — many are
several times bigger — but it is still far more massive than our home planet: 332,946 Earths
match the mass of the sun. The sun's volume would need 1.3 million Earths to fill it.
The sun is located about 93 million miles from Earth.
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Sun Orbits The Galaxy's Center
The sun, and everything that orbits it, is in the Milky Way galaxy, a vast system containing
at least 200 billion stars. More specifically, our sun is in a spiral arm of the galaxy called
the Orion Spur. From there, the sun orbits the center of the Milky Way, bringing the planets,
asteroids, comets and other objects along with it. Our solar system is moving with an
average velocity of 450,000 miles per hour. Even at this speed, it takes us about 230
million years to make one complete orbit around the Milky Way.
The sun rotates as it orbits the center of the Milky Way. Since the sun is not a solid body,
different parts rotate at different rates. At its center, the sun spins around once about every
25 days, but at its poles it rotates once every 36 days.
Sun Formed 4.5 Billion Years Ago
The sun and the rest of the solar system formed from a giant, rotating cloud of gas and
dust called a solar nebula about 4.5 billion years ago. As the nebula collapsed because of
its overwhelming gravity, it spun faster and flattened into a disk. Most of the material was
pulled toward the center to form our sun. The sun now accounts for 99.8 percent of the
mass of the entire solar system.
Like all stars, the sun will someday run out of energy. When the sun starts to die, it will
swell so enormously that it will engulf Mercury and Venus and maybe even Earth.
Scientists believe the sun is a little less than halfway through its lifetime. They predict it will
last another 6.5 billion years before it shrinks down and becomes a white dwarf.
Hydrogen, Helium, Intense Heat
The sun, like others stars, is a ball of gas. By mass, it is around 70.6 percent hydrogen and
27.4 percent helium.
The sun's enormous mass is held together by gravitational attraction, producing immense
pressure and temperature at its core. The sun has six regions. Its interior is made up of the
core, the radiative zone and the convective zone, while the exterior consists of the visible
surface, or photosphere, the chromosphere, and the outermost region, or corona.
At the core, the temperature is about 27 million degrees Fahrenheit, while in the connective
zone, the temperature drops below 3.5 million degrees. The surface of the sun — the part
we can see — is about 10,000 degrees Fahrenheit. That is much cooler than the blazing
core, but it is still hot enough to make diamonds not just melt, but boil.
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Photosphere To Earth: 8 Minutes
The surface of the sun, the photosphere, is a 300-mile-thick region, from which most of the
sun's radiation escapes outward. It is not a solid surface like the surface of a planet, but
simply the outer layer of the gassy star.
We see radiation from the photosphere as sunlight when it reaches Earth about eight
minutes after it leaves the sun.
Sunspots And Solar Flares
Above the photosphere lie the wispy chromosphere and the corona, or crown, which make
up the thin solar atmosphere. This is where we see features such as sunspots and solar
flares.
Visible light from these top regions is usually too weak to be seen against the brighter
photosphere. However, during total solar eclipses, when the moon covers the
photosphere, these regions do become visible. The chromosphere looks like a red rim
around the sun, while the corona forms a beautiful white crown with streamers, forming
shapes that look like flower petals.
Magnetosphere
The electric currents in the sun generate a magnetic field that extends out into space to
form the interplanetary magnetic field. The volume of space controlled by the sun's
magnetic field is called the heliosphere.
The sun's magnetic field is carried out through the solar system by a stream of electrically
charged gas. Known as the solar wind, this stream blows outward from the sun in all
directions. Since the sun rotates, the magnetic field spins out into a large rotating spiral,
known as the Parker spiral.
Approximately every 11 years, the sun's geographic poles change their magnetic polarity.
When this happens, the sun's exterior becomes violently active and sunspots and solar
flares occur. These events can release huge amounts of energy and particles, some of
which reach us here on Earth. They can damage satellites and pipelines and affect power
grids, and our TVs and cell phones can stop working for awhile. A high-speed train may
run loose and if an astronaut happens to be on the moon at the time when the sun erupts,
he or she would be in great danger.
Myths And Comic Books
The sun has inspired mythological stories in cultures around the world, including those of
the ancient Egyptians, the Aztecs of Mexico, Native American tribes of North and South
America, the Chinese, and many others.
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If you're Superman (or a fellow Kryptonian), your powers are heightened by the yellow
glow of our sun, and you can even dispose of dangerous materials like Superboy once
did, by hurling them into the sun.
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