The sun and solar system

The sun is the star at the center of our solar system.
It's about 93 million miles (150 million kilometers) from Earth.
Its heat, light, gravity, and wind affect all of the planets, moons, asteroids, and other solar system bodies.

The sun's influence doesn't stop there.
It stretches in a giant sphere that goes far beyond the known planets.
This sphere is called the heliosphere.
It is filled with solar wind and the sun's magnetic field.
Beyond the heliosphere is interstellar space–the space between stars.

A star is a big ball of gas. The sun is a medium-sized star.
It has a diameter of 864,950 miles (1.4 million kilometers).
It has been burning for about 4.5 to 5 billion years.
It often looks yellow when viewed from Earth, but it is actually white.
The sunlight appears yellow as it passes through Earth's atmosphere.

Structure and Movement of the Sun

The sun is made of mostly hydrogen gas, with some helium and heavier elements.
It has four layers.

The Layers
The core lies at the sun's center.
The core is a place of crushing pressure and high temperatures.
The pressure reaches 500 billion pounds per square inch (3.4 billion megapascals).
The temperature climbs to 27 million degrees Fahrenheit (15 million degrees Celsius).
These conditions ignite a process called nuclear fusion.
Hydrogen atoms are squeezed together so tightly that they combine, or fuse, to form helium.
This reaction releases lots of energy that eventually leaves the star as radiation, including sunlight.

The layer around the core is called the radiative zone. It is very dense.
Beyond that is the convection zone.
The convection zone is less dense.
It holds pockets of superhot gas that bubble up to the surface of the sun.
The surface of the sun is called the photosphere.

Solar Wind

Solar wind is a force from the sun that spreads throughout the solar system. Solar wind is not a movement of air, like wind on Earth.
It is the movement of particles sent from the sun at high speeds. Solar wind is really an extension of the corona layer of the sun.
The wind gets weaker the farther it travels from the sun. But it still reaches out to the orbit of Neptune and beyond.

The sun's gravity is very strong. The only way solar wind escapes is by moving very fast.
It leaves the sun at about 150,000 miles (240,000 kilometers) per hour. It speeds up as it gets farther from the sun.
By the time it reaches Earth, the wind moves at about 500,000 miles (804,672 kilometers) per hour.

The sun loses some of its mass as solar wind. It sheds about 1 million tons (910,000 metric tons) per second.
That may seem like a big number. But it's not much for a star as big as the sun.
At that rate, the sun sheds about 1 percent of its mass as solar wind every billion years.

Surface Events

Most of the action takes place in the sun's core. But the sun's powerful magnetic field also gives it an active surface. The sun's natural 11-year cycle gives rise to sunspots, solar flares, and coronal mass ejections (CMEs).
These surface events can have big impacts on Earth.

Sunspots
Sunspots are giant spots on the sun's photosphere where the temperature is much lower than usual. They're colder by about 3,500 degrees Fahrenheit (1,925 degrees Celsius). The spots are often larger than Earth.

On average, sunspots are about 8,000 miles (12,875 kilometers) across. Most sunspots last for a few days.
Some exist for only an hour. The longest existing sunspot on record remained for 200 days.

Sunspots appear and disappear as part of an 11-year solar cycle. During the first four years of the cycle, sunspots appear.
They normally form in groups of as many as 100 spots at a time. During the next seven years, they disappear. At the 11-year mark, the sunspots are gone.
The sun's magnetic field reverses and the cycle starts again.

The first record of sunspots was made more than 2,800 years ago in China. Galileo recorded his first sunspots in 1610.
But it wasn't until the 1900s that scientists understood what they were. They used the science of spectroscopy to examine the light coming from the sun.
The light coming from sunspots was different than the light around them. And scientists saw that the magnetic field was different there too.
It was as much as 1,000 times stronger than normal

Loading...

Viewing the Sun

Loading...

The sun's light and heat make life possible on Earth. Earth sits at an ideal distance from the star.
Planets closer to the sun are too hot. They may be stripped of their atmospheres.
Planets farther from the sun are too cold. They don't receive enough sunlight for plants.

Loading...

Astronomers use high-tech telescopes to observe the sun. But telescopes aren't needed to make basic observations.
The sun is the dominant object in Earth's sky. Amateur astronomers can observe it and learn about it without ever peering through a telescope lens.

Loading...

Sunrise and Sunset
The sun rises in the east every morning. It sets in the west every evening.
This pattern marks day and night on Earth. It's a simple observation, but an important one, because it has shaped the way humans live their lives.
It is not the movement of the sun that causes sunrise and sunset but rather the rotation of Earth around its axis. Astronauts in the International Space Station experience multiple sunrises and sunsets in a single day because their movement around Earth is faster than Earth's natural spin.

Loading...

Links&cite

Loading...

"Sun." PebbleGo, Capstone, 4 May 2023, www.pebblego.com.

You've reached the end of the book