THE SUN

The sun is by far the largest

object in the solar system. It contains more than 99.8% of the total mass of the Solar System .

The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun’s light and heat influence all of the objects in the solar system and allow life to exist on Earth.

Characteristics of the sunEquatorial Radius: 695,500 kmEquatorial Circumference: 4,379,000 kmVolume: 1,142,200,000,000,000,000 km3

Mass: 1,989,000,000,000,000,000,000,000,000,000 kg

Density: 1.409 g/cm3

Surface Area: 6,087,799,000,000 km2

The Sun is an average star—its size, age, and temperature fall in about the middle of the ranges of these properties for all stars. Astronomers believe that the Sun is about 4.6 billion years old and will keep shining for about another 7 billion years.

Element

Abundance(percentage of totalnumber of atoms)

Abundance(percentage of totalmass)

Hydrogen 91.2 71.0Helium 8.7 27.1Oxygen 0.078 0.97Carbon 0.043 0.40Nitrogen 0.0088 0.096Silicon 0.0045 0.099Magnesium 0.0038 0.076Neon 0.0035 0.058Iron 0.0030 0.14Sulfur 0.0015 0.040

Composition of the Sun

Solar Winds•expanding atmosphere with a constant flow of tiny, fast, electrically charged particles.

•carries remnants of the Sun’s magnetic field, which affect the magnetic fields of the planets and larger satellites. The solar wind pushes the planets’ magnetic fields away from the Sun, turning them into elongated, windsock shapes.

•The solar wind spreads out as it leaves the Sun

•causes auroras—displays of colored light—in the atmosphere of Earth’s polar regions.

Heliosphere

- region through which the solar wind blows

Within the heliosphere, the Sun provides most of the heat and light that are present, and the particles in the solar wind interact with the planets and satellites in the solar system.

Layers of the Sun

Core

- innermost layer of the sun - it is where the energy that keeps the sun shining produced-16 million ºC. in a gaseous state.

Solar Envelope

- puts pressure on the core and maintains the core's temperature.

- The hotter a gas is, the more transparent it is. The solar envelope is cooler and more opaque than the core. It becomes less efficient for energy to move by radiation, and heat energy starts to build up at the outside of the radiative zone.

-is the lowest, densest level of the solar atmosphere.

- This is the light we see. That’s why we see this as the surface.

The photosphere is opaque (not transparent), because it contains negative hydrogen ions (a hydrogen atom with two electrons, instead of the usual one). Hydrogen ions block, absorb, and emit light, all of which prevent light from passing directly through a cloud of hydrogen ions.

“Sphere of Color”

-Very low density

-But also very hot

- Energy from below excites the

atoms and produces emission from

this layer.

-Predominant element – Hydrogen.

-Brightest hydrogen line

A prominence is a feature of a layer of the Sun’s atmosphere called the chromosphere. Magnetic fields suspend loops of gas—prominences—above the main photosphere layer. These loops are actually coo ler than the rest of the photosphere, but they still appear bright against the dark sky.

 

Corona

-outermost layer of the sun 

-Only visible during eclipses, it is a low density cloud of plasma with higher transparency than the inner layers.

-Its average temperature is 1 million K 

This picture of the corona was taken during a total solar eclipse on July 11, 1991, in La Paz, Baja California, Mexico.

Sunspot -cool, dark, temporary patches that appear on the outer visible layer (photosphere) of the Sun. Sunspots occur where areas of the Sun’s magnetic field loop up from the Sun’s surface, disrupting the convection of hot gases from below. Sunspots are typically about half the temperature of the surrounding photosphere and so appear darker.

-The largest sunspots can bewider than earth.

Importance of the Sun

The Sun provides Earth with vast amounts of energy every day.

The oceans and seas store this energy and help keep the temperature of Earth at a level that allows a wide variety of life to exist.

Plants use the Sun’s energy to make food, and plants provide food for other organisms.

The Sun cannot shine forever, because it will eventually use up its present fuel. The nuclear fusion reactions that make the Sun glow depend on the element hydrogen, but the hydrogen in the Sun’s core will eventually run out. Nuclear reactions have converted about 37 percent of the hydrogen originally in the Sun’s core into helium. Astronomers estimate that the Sun’s core will run out of hydrogen in about 7 billion years.

In 3 billion years, the Sun will be hot enough to boil Earth’s oceans away. Four billion years thereafter, the Sun will have used up all its hydrogen and will balloon into a giant star that engulfs the planet Mercury. At this point in its life, the Sun will be a red giant star. The Sun will then be 2,000 times brighter than it is now, and hot enough to melt Earth’s rocks. At this time the outer solar system will get warmer and more habitable. The icy moons of the giant planets may warm enough to be covered by water instead of ice.