Youtube: Secrets of a Dynamic Sun The Sun – Our Star Our sun is considered an “average” star and is one of the 100 BILLION stars that make up the Milky Way galaxy. But by no MEANS does that make our star insignificant! Everything - from the fossil fuels we burn to the foods we eat – is ultimately derived from solar energy.

General Properties Average star 109 times Earth’s diameter 333,000 times Earth’s mass Consists entirely of gas (av. density = 1.4 g/cm3) Central temperature = 15 million 0K (27 million 0F) Surface temperature = 6000 0K (10 thousand 0F) Ultra-violet image

Structure of the Sun Because the sun is made of gas, no sharp boundaries exist between its various layers. Keeping this in mind, we can divide the sun into four parts: the solar interior (core) the visible surface, or photosphere two atmospheric layers: the chromosphere the corona.

Solar Interior

The Layers of the Solar Atmosphere X-ray Visible Sun Spot Regions Photosphere Corona Chromosphere Coronal activity, seen in visible light

Solar Interior: Nuclear Fusion • Nuclear fusion is the way that the sun produces energy. This reaction converts 4 hydrogen nuclei into the nucleus of 1helium atom, releasing a tremendous amount of energy. • During nuclear fusion, energy is released because some matter is actually converted to energy.

Nuclear Fusion Makes no sense without caption in book Nuclear Fusion Creating New Elements Makes no sense without caption in book

The Photosphere Radiates energy back into space, the part we see of the sun! Depth ≈ 500 km Temperature ≈ 5800 oK (10,000 oF) 10 Day Solar Animation

Obtained 24.10.2012 at 7:26 am EST with HMI instrument on board SDO spacecraft

Energy Transport in the Photosphere Energy generated in the sun’s center must be transported outward. In the photosphere, this happens through Convection. This convection creates a grainy texture called granules that are the size of Texas! Bubbles last for ≈ 10 – 20 min. Bubbles of hot gas rising up Cool gas sinking down ≈ 1000 km

Granulation Granules … is the visible consequence of convection

Sun Spots X-ray Visible They’re magnetism is 1000x’s stronger than the magnetic field of the sun! They occur in the photosphere and they were originally discovered by Galileo in 1610. * It is a dark spot on the sun that is cool in contrast to the surrounding photosphere. *Sunspots are cooler because of the Sun’s magnetic field.

Cooler regions of the photosphere (T ≈ 4240 K). Sun Spots Cooler regions of the photosphere (T ≈ 4240 K). Only appear dark against the bright sun. Would still be brighter than the full moon when placed on the night sky!

Chromosphere • The chromosphere is the next layer of the solar atmosphere found directly above the photosphere. • This burning gas is a few thousand kilometers thick. • Its top contains numerous spicules, which are narrow jets of rising material. They are typically thousands of kilometers high with a 10,000 kilometer maximum height They last 5-15 min.

 Obtained 24.10.2012 at 7:39 am ESTwith AIA instrument on board SDO spacecraft

Spicules

photosphere chromosphere

Prominences • Prominences are huge cloudlike structures consisting of chromospheric gases. • Prominences are trapped by magnetic fields that extend from regions of intense solar activity.

prominence  Obtained 24.10.2012 at 7:39 am ESTwith AIA instrument on board SDO spacecraft

Solar Flares Solar flares are brief outbursts that normally last about an hour and appear as a sudden brightening of the region above a sunspot. Solar flares release enormous amounts of energy, much of it in the form of ultraviolet, radio, and X-ray radiation. Solar flares intensifies solar wind. YouTube: Solar Flares

Corona • The corona is the outer, weak layer of the solar atmosphere. The temperature at the top of the corona exceeds 1 million K (1.8 million °F) which makes it the hottest layer – other than the core.

 Obtained 24.10.2012 at 7:38 am EST with AIA instrument on board SDO spacecraft

Solar Wind The streams of protons and electrons that boil from the corona are known as solar wind.  Obtained 24.10.2012 at 5:38 am EST with AIA instrument on board SDO spacecraft

Coronal Mass Ejection

Aurora Borealis Solar flares can intensify the auroras. Auroras are bright displays of ever-changing light caused by solar radiation interacting with the upper atmosphere near Earth’s poles. Solar flares can intensify the auroras.

YouTube: From Space Station YouTube: Over Norway

The Sun’s Magnetic Dynamo Since the sun is a huge ball of gas, it rotates faster at the equator than near the poles. This differential rotation might be responsible for magnetic activity of the sun.

Life Cycle of the Sun • It is thought that a star the size of the sun can exist in its present stable state for 10 billion years. As the sun is already 4.5 billion years old, it is “middle-aged.”

Death of a Star