The Centre of the Solar System Earth Science 11 Visible light view of sun Ultraviolet image of the sun The Sun Radio wave view of sun The Centre of the Solar System Earth Science 11 Infrared image of the sun X-ray image of sun

Like our Earth, the sun is made up of different layers.

Sun’s Atmosphere Photosphere – a thin "sphere of light", the visible surface of the Sun (5 800 K) Below the photosphere the sun is too dense for light to escape. Above the photosphere the sun is not dense enough to emit detectable light. In actual fact, the photosphere is less dense than the air we breath! (3400 times less dense!)

Photosphere

Sun’s Atmosphere Chromosphere – “sphere of colour” visible during solar eclipse; it is the inner atmosphere of the sun (10 000K) It is 1000 times fainter than the photosphere. It is 108 times less dense than the air we breathe.

Chromosphere

Sun’s Atmosphere Corona – is the sun’s outermost atmosphere. The outflow of gas in this region is called the solar wind. The solar wind is made of protons and electrons that have escaped the sun’s gravity. It has a temperature of 1 000 000 K. It has a density as low as 1 to 10 atoms / cm3

Corona

1 = photosphere, 2 = chromosphere, 3 = corona Why the outer layers of the Sun’s atmosphere are hotter is a puzzle. Not in notes.

Basic Structure of the Sun Average Density = 1.4 g/cm3 94.3% Hydrogen 5.6% Helium 0.1% Metals Surface Temperature = 5762 K Core Temperature = 15,000,000 K

By radiation and convection Not in notes.

The Sun's Interior Thermonuclear core - the central region of Sun where fusion takes place due to high temperatures and pressures. Convection zone - a layer inside a star where energy is transported outward by means of heat flow through the gases of the star (convection).

From the surface of the sun moving inward, density increases and temperature increases.

Surface Features Granules – are convection (heat) features about 1000 km in diameter and are seen constantly in the solar photosphere. They last for only 10 to 20 minutes before fading away. Sunspots - are temporary cool regions in the solar photosphere created by magnetic fields. They occur over an 11 year cycle.

Granules on the Sun’s surface Not in notes. A prominence

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Note the darker inner umbra and the outer penumbra Not in notes.

Sunspots can be used to measure the rotation of the Sun Near the equator the Sun rotates once in 25 days. The poles rotate more slowly, about once every 27 - 36 days.

Sunspots are low temperature regions in the photosphere Sun spots are about 4000 K (2000 K cooler than solar surface) and have magnetic fields up 1000 the normal solar magnetic field. They can be as large as 50,000 km and last for many months. The large magnetic fields in sunspots decrease the flow of heat via convection causing the sunspot to become cool.

Sunspot cycle Not in notes.

The Magnetic Dynamo Not in notes.

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Solar Magnetic Fields Also Create Other Surface Phenomena. Prominences Flares Solar wind Coronal mass ejections

Prominences: Cooler Than Photosphere. Not in notes. http://antwrp.gsfc.nasa.gov/apod/image/

Solar flares - Hotter, up to 40,000,000 K More energetic Not in notes.

Coronal mass ejections - eruption of gas, can reach Earth and affect aurora, satellites Not in notes.

Coronal Mass Ejection Earth’s magnetic field shields us from most of the damaging solar winds. Not in notes.

Solar Prominences: Are large sheets of dense, cooler glowing gases which burst out of the chromosphere. Can last for days or weeks. Are as large as 400 000 km or more! Most of them eject material into the solar wind.

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A solar prominence compared to the Earth! Photo taken by NASA space probe SOHO Not in notes.

Large Eruptive Prominence 24 July 1999 Not in notes.

Solar Flares Bursts of energy that travel outward from the chromosphere. They last only a few minutes.

Solar Flares Happen when magnetic field in an active region suddenly changes its structure. Large numbers of rapidly-moving ions and electrons are released. Much more energetic eruption than a prominence. These energetic particles collide with coronal gas and raise its temperature up to 40 million K.

Solar Flares They contribute up to 1% to the Sun’s brightness. Most of this is X-ray and UV radiation that reaches Earth in about 8 minutes. Electrons and ions reach Earth in a few hours or days.

Effects of a Solar Flare on Earth Ionization of Earth’s upper atmosphere is increased. Enhancement of ionosphere disrupts long-range radio communications. Power surges may occur, causing damage to transformers and blackouts.

Effects of a Solar Flare on Earth Eventually, ejected coronal matter also reaches Earth. Unless they are shielded for protection, astronauts are at risk from increased radiation. The northern and southern lights are brighter than usual and are seen farther away from the poles.

Coronal Holes Coronal holes are low-density regions associated with the sun’s magnetic field. Solar winds escape from coronal holes. False colour uv image of coronal hole (dark).

Coronal Mass Ejections Increase in number as sunspot number increases Can eject billions of tons of matter at speeds of up to 1000 km / s!

Our Sun in Different Wavelengths X-Ray Ultraviolet Visible Infrared Radio Not in notes.

By observing the Sun in different parts of the spectrum, we can get information about the different layers in the Sun's atmosphere. Not in notes. X-ray images show us the structure of the hot corona, the outermost layer of the Sun. The brightest regions in the X-ray image are violent, high-temperature solar flares.

The ultraviolet image show additional regions of activity deeper in the Sun's atmosphere. Not in notes.

In visible light we see sunspots on the Sun's surface. Not in notes. In visible light we see sunspots on the Sun's surface.

The infrared photo shows large, dark regions of cooler, denser gas where the infrared light is absorbed. Not in notes.

The radio image show us the middle layer of the Sun's atmosphere. Not in notes.

What makes the Sun shine? Thermonuclear fusion at the Sun's core is the source of the Sun's energy. Fusion is the joining of lighter nuclei to form a heavier, different element. As a result, energy is released. This energy is radiated outward toward the convection zone. Only at the core is the temperature and density high enough for fusion to occur.

What Makes the Sun Shine?

What makes the Sun shine? 1 Helium Atom + Energy fusion 4 Hydrogen Atoms E = mc2