The Sun

California Science Standards 5a:Students know the Sun, an average star, is the central and largest body in the solar system and is composed primarily of hydrogen and helium.

The Sun

Stars

• There are billions upon billions of stars in the universe.

​

​

​

​

What is a star?

• A star is a huge sphere or ball of very hot, bright gases that gives off great amounts of energy.

Stars Classified

Scientist classify stars by their:

​

• Size
• Color (blue stars are hottest and red stars are the coolest)
• Temperature
• Brightness (apparent brightness is the brightness as seen from Earth. A star might appear bright just because it is close. Real brightness is the luminosity – the amount of light a star produces)

The Sun Compared to other Stars

• The sun is average in size as compared to other stars, with medium surface temperature.

​

• Stars called giants have diameters that are 8-100 times larger than the sun’s diameter.

​

• Super giant stars can be more than 500 times larger than the sun.

​

• Other smaller stars are only about the size of Earth.

The Sun

• Our sun is Earth’s local star (it takes the Sun’s light 8.5 minutes, traveling at the speed of light, to reach Earth).

​

• The sun has no permanent features as it is made of gases (i,.e.: no mountains or oceans, etc.)

The Sun’s Gravity

• The sun is found at the center of our solar system.

​

• The Sun’s gravitational pull is strong enough to keep Earth and other objects in the solar system in orbit around it. In other words, the sun rules when it come to our solar system!

​

​

Size of the Sun

• The sun is larger than everything else in our solar system.
• The sun has 99.8% of the total mass of the solar system. The sun rules because of its massive size.

​

How big is the sun?

• In diameter – 1.4 million km (860,000 miles) which is 109 times Earth’s diameter.
• In volume – It could hold one million Earth’s inside of it!

​

Mnemonic Device: “www.hel.com”

​

The Sun provides Earth with:

• Heat
• Energy - powers photosynthesis
• Light

​

​

And affects or powers our:

• Wind – the sun’s uneven heating on the surface of the Earth creates wind.
• Weather
• Water Cycle – the sun powers the water cycle by causing water on Earth’s surface to evaporate.

The sun is the main source of most energy on Earth

​

​

The Sun is the main source of energy on Earth (cont.)

• Solar radiation provides the heat that keeps Earth warm and livable.

​

• Without the sun life could not exist.

​

The Sun’s energy works its way to nearly all living things:

​

• The sun powers photosynthesis – this is the process by which green plants and algae use sunlight to produce food.
• Plants will use some of this energy and then store the rest.
• When a consumer, such as a deer, eats plants, some of the stored energy is transferred to the deer.
• When another animal eats the deer, some of the stored energy is transferred again.
• In this way, the sun is the energy source for nearly all living things.

​

Where does the Sun’s energy come from?

• The temperature at the center of the sun is about 15 million ^◦C (27 million ^◦F)

​

• At that extreme temperature, and under enormous pressure, hydrogen atoms smash into each other and produce helium. Every time this happens, the sun releases vast amounts of energy as heat and light. This process is called fusion (or nuclear fusion).

​

• The fusion of an amount of hydrogen the size of a pinhead releases more energy than the burning of about 1000 tons of coal.

​

• The sun fuses 600 million tons of hydrogen every second.

​

Layers of the Sun

The sun has several layers:

​

• Core -the layer at the center of the sun

​

• Radiation Zone

​

• Convection Zone

​

• Photosphere -the surface of the sun – the part we see

​

• Corona -The sun’s atmosphere – only seen during a solar eclipse

4 Visible Features of the Sun

mnemonic device: “Follow GPS”

• Flares - brief bursts of energy and matter from the sun’s photosphere (similar to what happens during a volcano explosion on Earth) – much of it in ultraviolet, radio waves, and x-rays - releasing a fast-moving stream of particles into space

​

• Granules - hot, bright areas all over the sun, giving the sun a grainy look

​

• Prominences - bright loop or sheet of glowing gas in the corona (may appear or disappear in a few days or months)

​

• Sunspots - dark and cooler areas on the photosphere.

 Sunspots - Sunspots may be the size of Earth or larger. The number of sunspots increases and decreases over a period of about 11 years called, “the sunspot cycle”. Solar flares are generally produced here.

The Sun

Solar �Prominence

Granules or Graininess on the Sun

• Granules - hot, bright areas all over the sun, giving the sun a grainy look (when seen in contrast to surrounding cooler, darker areas).

​

Solar Flares on the Sun

• Solar Flares – Solar Flares are brief bursts of energy and matter from the sun’s photosphere (similar to what happens during a volcano explosion on Earth).

• Solar flares can release a fast-moving stream of particles into space (called solar winds) which, when headed towards Earth, may cause serious problems for communication and electrical systems on Earth. (Thankfully, Earth’s magnetic field does shield us from most of it)

​

Extra Information on Solar Flares & its Affects on Earth

• Although the Sun looks steady and constant, it can get violent every now and then. The surface of the Sun can sometimes explode, releasing a tremendous amount of energy - astronomers call these events solar flares.

​

• The number and strength of solar flares varies with the 11-year solar cycle. When the Sun is active and dotted with sunspots, there can be frequent solar flares.

​

• Solar flares pose one of the greatest risks to human space flight. When a powerful flare is aimed at the Earth, a tremendous amount of radiation passes through our region. Since the particles have been accelerated to nearly the speed of light, a dangerous radiation storm will come just minutes after a flare occurs on the surface of the Sun. During a powerful solar storm, astronauts will have less than 15 minutes to seek protection, or receive a potentially lethal dose of radiation.

​

• The radiation from a solar flare also contains radio waves, which act as noise or static, potentially disrupting not only air traffic and military activity, but also power grids and cell phones. �

Sunlight as Waves

• Energy from the sun travels in waves. There are several kinds of waves. Each carries a different amount of energy. Some of the waves can be seen as light, while others can be felt as heat.

The Sun’s energy travels in waves

​

​

For other activities on the Sun, go to: www.rrojas.com/5/science/earthscience

​