The Sun – Describe characteristics of the Sun (S6C3PO2 high school) Lesson Objectives: Describe the structure of the Sun Describe sunspots, prominences, and solar flares

The Sun’s Layers The Sun is an ordinary star but it’s important to us because it is the center of the solar system and the closest star to Earth. Almost all life on Earth depends on energy from the Sun Just like Earth, the Sun is made up of different layers. Like other stars, the Sun is an enormous ball of gas that produces energy through fusion of hydrogen (H) atoms producing Helium (He) in its core where temperatures can reach 15 million degrees C. The energy produced in the core travels outward through a thick layer called the radiation zone. After the radiation zone the energy moves by a process called convection. Thus this layer is called the convection zone. Energy then passes to the Sun’s atmosphere.

The layers of the Sun’s Atmosphere The photosphere is the lowest layer (inner layer) of the Sun’s atmosphere and the layer from which visible light is given off. The photosphere often is called the surface of the Sun, although the surface is not a smooth feature. Temperatures there are about 6,000 K. The chromosphere is above the photosphere (middle layer). This layer extends about 2,000 km above the photosphere. Way above the chromosphere is the corona (outermost layer). This is the largest layer of the Sun’s atmosphere and extends millions of km into space. Temperatures in the corona are as high as 2 million K. Charged particles continually escape from the corona and move through space as solar wind. This is the layer you observe during a solar eclipse.

Surface Features The Sun appears to have a smooth outer layer, but it has many features, including sunspots, prominences, and CMEs. Sunspots – Areas of the Sun’s surface that appear dark because they are cooler than surrounding areas. Ever since Galileo’s drawing of the sunspots, scientists have studied the movement of the spots and concluded that the Sun rotates as well. But not as a solid mass like the Earth. Instead, the Sun rotates faster near its equator (25 days) than at its poles (35 days).

Sunspots and Suns’s rotation

Surface Features Sunspots cont. Sunspots are not permanent . They appear and disappear over a period of several days, weeks, or month. The number of spots increases and decreases in a fairly regular pattern called the sunspot, or solar activity cycle. When many large sunspots occur the Sun is at its maximum which occurs every 10-11 years. Periods in between are called minimums.

Solar progression of maximum

Prominences and Solar Flares Sunspots and strong magnetic fields are found together on the Sun. The magnetic fields might cause prominences, which are huge arching columns of gas. The gases near a sunspot may suddenly brighten and rapidly shoot outward as a solar flare.

Prominence Solar flare

CME When large amounts of electrically-charged gas shoot out from the Sun’s corona, the event is called a Coronal Mass Ejection (CME) also known as solar wind. CMEs can damage satellites and cause radio interference. Near the poles they can produce a display of shifting colorful lights in the night sky known as Aurora Borealis or northern lights; Aurora Australis. These displays tend to occur at Earth’s poles. 8.24.14 CME STEREO NASA

Aurora Borealis/Northern lights

Aurora Borealis/Northern lights

The Sun – an average star The Sun is an average star. It is middle aged and its absolute magnitude is also average. The Sun shines with a yellow light. The Sun is Earth’s closest star and sunlight reaches Earth in 8 minutes. Light from other stars takes many years to reach us. The Sun is unusual in that it is not close to other stars. Most stars are found in groups of 2 or more stars that orbit each other and are held together by each other’s gravity. Stars found in groups are called clusters.

ISN Response Draw the Sun Label following the layers: core, photosphere, chromosphere, and corona. Draw a prominence and a solar flare. Explain the difference between the a prominence and solar flare. Answer: Why are the Aurora Borealis also know as the Northern Lights? What do you think the Aurora Australis are also called?