The Sun

By Moira Whitehouse PhD

A solar system is a collection of bodies revolving around a star.

Our particular Solar System consists of the Sun (our star), planets, moons (which orbit planets), comets, meteors and asteroids.

These bodies include things like planets, moons and many other objects.

Today we will examine our Solar System starting with the Sun, what it is and how it got there.

This singularity is described as an infinitesimally small, infinitely hot, infinitely dense, something - a singularity. Where did it come from? We don't know. Why did it appear? We don't know.

To answer that we must start at the “beginning”. According to scientists and the “Big Bang” theory, our universe sprang into existence as a "singularity” around 13.7 billion years ago.

The first question to be dealt with, how did the Sun get there?

From the Big Bang, the universe expanded for over 9 billion years when the beginnings of our Sun occurred.

Scientists believe that our Solar System was formed about 4.6 billion years ago from the collapse of a massive, rotating cloud of gas, dust and ice called the Solar Nebula.

The gas in this nebula was primarily hydrogen and helium, the dust was made up of the materials that are found in rock, and the ice was water, methane, and ammonia.

As this Solar Nebula cloud collapsed, it formed a flat disk with most of its matter in the center.

After about 10 million years, the hydrogen in the center got hot enough to fuse and the Sun started to “shine.”

The particles within the flattened disk collided fusing to form asteroid-shaped objects.

Some of these object hit one another and grew in size.

As more particles coalesced and grew larger, planets, moons (which orbit planets), comets, meteors and asteroidswere formed.

...and our Solar System came into being.

Although the Sun is mostly just a ball of hydrogen and helium, it can be broken down into distinct layers caused by temperature and pressure increases.

1. Core

The core of the Sun is the source of all its energy.

In the core, the temperature is (15,000,000° C or 27,000,000° F) and the pressure is 340 billion times Earth's air pressure at sea level.

This energy is a result of the extreme temperatures and pressure found at the center of the Sun.

The heat and pressure are so intense nuclear fusion reactions take place—hydrogen nuclei change into helium nuclei .

As a result of these collisions, two hydrogen nuclei fuse (join) to forming a helium nucleus.

Tremendous amounts nergy is released in this reaction.

The high temperature causes the hydrogen nuclei to zing around wildly slamming into one another at high speeds.

Fusion

Hydrogen nucleus with 2 neutrons

Hydrogen nucleus with 1 neutron

Helium nucleus—2 protons and 2 neutrons

neutron

proton neutron

Right now, about half of the amount of hydrogen in the core of the Sun has been fused into helium.

This took the sun about 4.5 billion years.

1. Core 2. Radiative zone

Moving from the inside out from the core, the second layer of the Sun is called the radiative zone.

Energy makes its way very slowly through this layer of the Sun.

It takes over 170 thousand years for the energy released in the core of the Sun to get out of the radiative zone!

Energy from the core of the Sun continually moves outward to the surface. This region is slightly cooler than the core and the energy can move by radiation—from one atom to the next.

1. Core 2. Radiative zone

3. Convective zone

Once out of the radiation zone the helium and hydrogen are cooler so the energy, originally produced in the core, requires a different way to move to the surface.

The cooler material near the top of the radiation zone sinks down pushing the hotter material up. As the hot material reaches the top of the convection zone it begins to cool and sinks, and as it sinks it heats up again and will rise again—a convection current.

The most efficient means of energy transfer is now convection i.e. the convection zone.

The energy is transferred much faster by convection than by radiation.

It takes only a little more than a week for the hot material to carry its energy to the top of the convection zone.

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere

The next layer in the Sun is the photosphere, the only layer visible to us on Earth.

The photosphere is the disk you see when observing the Sun in the sky.

http://www.swpc.noaa.gov

It is the apparent surface because the Sun is completely made of gases so there is no hard surface like there is on earth.

We call the region where this happens the apparent surface, or the photosphere.

When we look at the Sun there is a depth beyond which the gas is so dense that we can not see through it

Remember, it takes light from the Sun just over eight minutes to reach the earth.

Energy is transported through the photosphere once again by radiation.

Most of the light that we receive from the Sun on earth is energy that was released in the photosphere.

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere

5. Chromosphere

The layer above the photosphere is the chromosphere.

Violent “flames” of hot gases called flares erupt in the chromosphere.

Flares can be as large as the Earth and last up to several hours.

Flares are very hot—twenty million degree F have been recorded.

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere

5. Chromosphere

6. Corona

The corona is the outer part of the Sun's atmosphere.

The outer region of the corona stretches far into space and emits a stream of electrons and protons that travels slowly away from the Sun.

This stream of charged particles is called the solar wind.

The corona is invisible from Earth. It can only be seen during a total solar eclipse.

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere

5. Chromosphere

6. Corona

8. Granules

The continuous rising and falling of hot and cool bubbles from the convective region produces a pattern on the photosphere that is referred to as granulation.

Sunspots are dark spots on the photosphere, typically with the same diameter as the Earth.

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere

5. Chromosphere

6. Corona

8. Granules7. Sunspot

Sunspots have cooler temperatures than the rest of the photosphere.A sunspot's life can be as short as an hour or two or as long as several months.

The number of sunspots on the surface of the Sun increases and decreases in a regular pattern, known as the solar cycle, with a maximum number of sunspots occurring every 11 years.

Flares emerging from sunspot regions.

7. Sunspot

1. Core 2. Radiative zone

3. Convective zone

4. Photosphere5. Chromosphere6. Corona

8. Granules

9. Prominence

They are immense arcs of glowing gases from the upper chromosphere that erupt into the corona.

Prominences appear in the chromosphere.

Prominences are not as violent eruptions as flares.

Although the Sun is huge compared to the other planets in our Solar System, it is only a medium-sized star.

It is relatively small compared to many of the stars in the Universe.

Red Giant and Supergiant stars can be much larger than the

Sun.

Before we go into the individual planets in the Solar System, let’s consider how planets in the solar system were formed.

The same cloud that formed the Sun now helps us see how individual and very different planets came about.

We will start with the “cloud”. Near the center of the cloud, rocky material condensed and the four inner planets formed.

Planetary Interiors

The heavier denser materials such as iron and nickel sank to the middle of the planets and the lighter silicate materials floated to the top.

Solar winds swept lighter materials (hydrogen, helium, water , ammonia) outward from the Sun.

The larger icy planets attracted the hydrogen and helium gas in the disc and grew in size—the giant gas planets.

These icy substances formed the outer planets.

Now we will look at the results:

http://www.spacescan.org Creative Commons licence

Here are the “players” in our Solar System

NASA

And here is where they “hang out”.

Under the International Astronomical Union (IAU) definition of a planet, there are eight planets in our Solar System. (Pluto is no longer considered a major planet.)

In order from the Sun are the four terrestrial planets--Mercury, Venus, Earth and Mars and the four gas giants-- Jupiter, Saturn, Uranus and Neptune. It also contains five dwarf planets—Ceres, Pluto (originally classified as the Solar System’s ninth planet), Makemake, Haumea and Eris.)

As well as the major planets and their moons, our Solar System includes two large areas where numerous smaller bodies including the dwarf planets gather together—the asteroid belt and the Kuiper belt.

The Kuiper belt extends well beyond Uranus, the last major planet in the Solar System, and is home to three of the five dwarf planets.

Objects in the Kuiper belt are largely frozen methane, ammonia and water.

NASA

NASA

The asteroid belt (shown in white), located between the orbits of Mars and Jupiter, consists of numerous irregularlyshaped bodies made of rock and metals called asteroids and one dwarfplanet, Ceres.

NASA

NASA

The five dwarf planets—Ceres, Pluto (originally classified as the Solar System’s ninth planet), Makemake, Haumea and Eris are much less familiar than the major planets.

We will now take a brief look at each of them.

Ceres, the smallest of the dwarf planets, is made of rock and the only one found in the asteroid belt.

Ceres as seen by the Hubble Space Telescope

Moon top left, Ceres bottom left—relative sizes

Wikipedia Commons

Like other members of this belt, it is composed primarily of rock and ice.

Pluto, the second largest dwarf planet, is the largest member of the Kuiper belt.

Pluto has three moons--Charon, Hydra and Nix.

However, compared to the Earth’s moon Pluto is relatively small—only one-fifth of the mass of the moon.

http://www.crh.noaa.gov

These elements may exist as a gas when Pluto is closest to the Sun) and freeze as Pluto moves further away.

Pluto’s atmosphere is probably made up of of nitrogen and methane.

The surface of Pluto is composed of about 98% nitrogen with small amounts of methane and carbon monoxide.

It is about three-fourth the size of Pluto and its surface is covered with methane, ethane and possiblely nitrogen ice.

Wikipedia Commons

Makemake is the third largest dwarf planet in the Solar System and is found in the Kuiper belt.

Makemake as seen by the Hubble Space Telescope

Haumea, with one-third the mass of Pluto, is another dwarf planet in the Kuiper belt.

Image of Haumea and its two moons.

NASA

Eris, the largest known dwarf planet in the Solar System, orbits the Sun outside the Kuiper belt.

Eris and its moon Hubble Space Telescope

It is the ninth largest object to orbit the Sun.It has one known moon.On average, it is three times further from the Sun than Pluto.

Size comparison of Eris, Pluto, Makemake, and Haume (plus four other celestial objects) with Earth. Ceres is shown here because it is closer than Neptune.

Wikipedia Commons

This size comparison of the Sun’s planets helps us see where Earth fits in.

The Sun is by far the biggest and most massive object in our solar system.

It would take one hundred and nine Earths to fit across the Sun’s diameter.

The interior of the Sun could hold over 1.3 million Earths.

Another size comparison, this one making Earth look a bit puny.

It makes up approximately 98% of the total mass of the solar system.

The Sun’s mass 333,000 times the mass of the Earth.

Even though the Sun is made mainly hydrogen and helium, it is very massive..

The gravity at the surface of the Sun is 28 times the gravity at the surface of the Earth

So if you weighed 100 pounds on Earth, you would weigh 2800 pounds on the surface of the Sun. Your body would be so heavy you wouldn’t even be able to pick it up.

As a result of this tremendous amount of mass, the Sun has an enormous amount of gravity.

The planets orbit the Sun as a result of its gravity.

The Sun and Earth both have mass so they both have gravity. As a result of the force of gravity, the two bodies are being pulled together and would eventually crash except:The Earth has inertia, it’s trying to go in a straight line, but the Sun’s gravity keeps pulling on it, keeping Earth (and the other planets) in orbit.The two forces the Earth’s inertia and gravity balance one another; as a result the Earth remains in an orbit around the Sun.

Earth

Gravitational pull of the Sun

Resulting path of the Earth

Earth’s inertia

Sun

The Sun’s gravity pulls its mass (mainly hydrogen and helium) into an almost perfect sphere. At the the center of this sphere (the core) of the Sun, the heat and pressure are so strong that fusion reactions in which hydrogen nuclei changes into helium nuclei occur. When nuclear fusion takes place inside the Sun, tremendous amounts of energy are released.

This energy is made up of many kinds of radiation. These different forms of radiation make up what is called the electromagnetic spectrum.

The electromagnetic spectrum includes gamma rays, X-rays, ultraviolent rays, visible light rays, infrared rays, microwaves (radar) waves, FM radio waves, TV rays and AM radio waves.

http://www.dnr.sc.gov

Electromagnetic Spectrum of Light from the Sun

When the solar wind reaches the earth the magnetic field of the earth will sometimes trap these electrons and protons and pull them into the earth's atmosphere.

Atoms in the earth's atmosphere accept energy from these high energy particles and then release that energy in the form of colored light.

This display of light is known as the Aurora Borealis when it occurs in the northern hemisphere.

The Sun is one of the billions of stars that make up the spiral galaxy called the Milky Way.

http://www.valdosta.edu/~cbarnbau/astro_demos/frameset_moon.html

The distance from the Sun to various other objects is shown in this clip:

The Sun has been “shining” for about 4.6 billion years and has enough fuel to go on for another five billion years or so.

At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately expanding out in the Solar System large that it will swallow up all the planets including the Earth.

After a billion years as a red giant, it will collapse into a while dwarf.