The Sun?

The Sun is a star! There are an incredible amount of stars in the universe. Yay! What is a star…? Useful Links: A star is a huge sphere of very hot, glowing gas. Stars produce their own light and energy by a process called nuclear fusion. Fusion happens when lighter elements are forced to become heavier elements. When this happens, a tremendous amount of energy is created causing the star to heat up and shine. Stars come in a variety of sizes and colors. Our Sun is an average sized yellowish star. Stars which are smaller than our Sun are reddish and larger stars are blue.

The Sun – Our Star One of many stars in the Milky Way, but extremely important to us…why? – Provides energy, helps in understanding other stars b/c they’re too far away

Solar Data The diameter of the Sun is thus 109 times as great as the Earth's diameter. About 1.3 million Earths could fit inside the sun. The mass of the sun is 2 x kilograms, about 332,000 times the mass of the Earth. Volume of the Sun is about 1.5 million times that of Earth’s Mean density of Sun = 1408 (kg/m 3 ) Mean density of Earth = 5514 (kg/m 3 )

Solar Parts A ball of gas, which can be generally thought of as having four “layers”: – Solar interior (core, radiation zone, convection zone) – visible surface (photosphere) ‘visible’ ‘layer’ – two atmospheric components chromosphere corona

Photosphere Appears orange due to granules – size of Earth and only last 8-10 minutes – ‘boiling effect’ cause by circulation of energy in the convection zone

Solar Activity Composition surface = 74% Hydrogen, 25% Helium, 1% other Sunspots: dark regions on the Sun that are slightly cooler than surrounding surface, and are associated with very strong magnetic activity.

Sunspots Observed throughout antiquity (try looking at the sun at its lowest point in the sky, or through a cloud bank and you can occasionally see them unaided) Deduction of Solar Rotation rate and differential rotation nature from sunspot observation Dark spot? Not really. Many X brighter than Full Moon. Its relative. Plage = lighter areas around the sunspots

Chromosphere Layer above the photosphere Not visible to the naked eye Hot, low density gas produces an emission spectrum Appears red due to concentration of hydrogen gases

The Corona Only visible when the solar disc is covered (during a solar eclipse or with a coronagraph) Very hot, High energy, low density particles escape the gravitational pull of the Sun Released as streams of ions and radiation outward from the Sun = Solar Wind

Sunspots

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Prominences/Flares Flares are massive eruptions from the surface of the Sun resulting in huge amounts of charged particle energy ejected into space (CMEs – Coronal Mass Ejections) Threating to astronauts, damaging to communication systems Kill shot? Radio/X-Ray/UV radiation Prominences are large looping structures of solar material tapped by magnetic fields.

Aurora Borealis/Australis Colors

Solar Interior

A. The sun, like all stars, is powered by nuclear fusion in its core. B. The specific nuclear reaction that occurs in the sun involves converting hydrogen to helium. C. Core temperatures: 27 million degrees Fahrenheit in the Sun’s core. i. At such high temperatures, gas is completely ionized, containing free moving protons and electrons. ii. Protons are positively charged and repel each other electrically at close range; however, at T > 10 Million K, proton speeds can be ­­­­fast enough to overcome electrical repulsion, and undergo a nuclear fusion

II. Nuclear Fusion A. Mechanism: NUCLEAR FUSION : Four protons (hydrogen nuclei) slam together in several steps to yield a helium nucleus (2 protons, 2 neutrons) plus energy in the form of gamma rays. B. Reactions:

Missing Matter -> Energy Matter is converted to energy according to Einstein's famous formula: – E = mc 2 c = speed of light (3x10 8 m/s) M = mass (kg) E = energy (Joules [J]) – A Joule is a unit of energy equivalent to the energy needed to apply a force of 1 Newton through a distance of one meter.

How much energy in matter?

The equivalent of energy that would be produced by burning 1000 tons of coal!!

C. Energy Production i. Mass of resulting Helium (4.003 AMU) is slightly less that the mass of the original 4 Hydrogen atoms ( AMU). Difference of _0.0002_AMU. ii. Missing mass was converted directly to ENERGY and emitted, in amounts according to Einstein’s equation: iii. Because the speed of light is very great (3x10 8 m/sec), the amount of energy released from even a small amount of mass is a large amount_.

Solar Fusion iv. Each nuclear fusion reaction that takes place (on an atomic level) in the core produces a very small amount of energy, not even enough energy to raise a housefly a few inches. But, millions of these reactions in the core convert 5 million tons of mass to energy every second !!!!! force / pressure_. v. The energy produced in the form of gamma rays is created by surrounding gas, which heats up, expands and helps maintain the sun’s outward force / pressure_. If fusion in the core were to stop, the force of gravity would overcome the outward force of pressure and the sun would collapse inward on itself.

Solar Fusion How long can such fuel consumption keep up before the Sun run’s out? – The Sun can last for a long time, however it will not last for another 100 billion years – In about 4.5 billion years, the Sun will swell into a Red Giant star.