Energy from the Sun Energy Energy is a quantity that describes how much force an object has experienced over a distance or can potentially experience in a given situation. Energy can be transferred from one object to another, or transform from one form to another. It can neither be created nor destroyed. Kinetic Energy: energy that an object has because of its motion Potential Energy: energy that an object has because of its position What is the Sun? The Sun IS NOT an average, yellow star. Size and Distance of the Sun
The Sun is 109 times the diameter of Earth Over 1,000,000 Earths could fit inside the Sun. Earth The Sun is 150 million kilometers away from Earth. It takes light 8 minutes to travel to Earth from the Sun. This distance is defined as 1 Astronomical Unit (AU) Moon
Mass of the Sun Keplers 3rd Law of Planetary Motion P is the period of the orbit, d is the average distance of the planet from the Sun, G is the gravitational constant of the Universe M is the mass of the Sun m is the mass of the planet When the planet mass is totally insignificant compared to the mass of the Sun: For Earth, d = 1.496x1011 m, P = 1 sidereal year MSun = 2 x 1030 kg 333,000 times Earths mass
Rotation of the Sun Galileo saw sunspots that appear to move across the face of the Sun. Conclusion: the Sun rotates on its axis. Rotation rate: 27 days (equator) to 31 days (poles) Movie made from Galileos sunspot drawings from June 2 July 8, 1613 Luminosity of the Sun
Luminosity is the total energy output per unit time. It is related to brightness by the distance: So Weve measured the distance to be 1.496x1011 m Brightness is also a directly observable quantity. The Suns brightness at Earth is 1,361.5 W/m2 So L = 3.8 x 1026 watts 10 trillion times the power consumption of all Earths nations combined The Spectrum of the Sun Visible light is a tiny fraction of the Electromagnetic Spectrum
Gamma rays--billions of waves per inch Radio waves--up to miles-long wavelengths Low Energy Waves High Energy Waves Surface Temperature 5800 K Thermal Spectrum Composition of the Sun The spectrum of the Suns light reveals its composition.
The Sun is White The Sun produces all the colors of the rainbow in roughly equal amounts, which is white light. If the Sun were yellow, then white T-shirts would look yellow in the mid-day sunshine. When you observe the Sun safely, by projecting its image through a pinhole camera or a telescope, you see that it is white.
Dont stare directly at the Sun! The UV radiation can damage your eyes. Magnetic Field When an external magnetic field is present, single energy levels in an atom/ion/molecule split into additional levels. The amount of splitting and the new energy levels present depend on the strength and direction (north or south) of the external magnetic field. Examining the solar spectrum for the Zeeman Effect allows us to map the magnetic field on the surface of the Sun. The Suns Layers
Looking at the Sun in different wavelengths of light reveals different parts of the Sun. Radio light: Wavelength = 17.6 cm See radiation from Suns atmosphere, Corona The Suns Layers Looking at the Sun in different wavelengths of light reveals different parts of the Sun.
Visible light (white light): Wavelength = 400-700 nm See radiation from Suns surface, Photosphere The Suns Layers Looking at the Sun in different wavelengths of light reveals different parts of the Sun. Visible light (H-): ): Wavelength = 656.3 nm See radiation from layer
just above Suns surface, Chromosphere The Suns Layers Looking at the Sun in different wavelengths of light reveals different parts of the Sun. Extreme Ultraviolet light: Wavelength = 30.4 nm See radiation from Suns atmosphere, Corona
Image from STEREO mission The Suns Layers Looking at the Sun in different wavelengths of light reveals different parts of the Sun. Extreme Ultraviolet light: Wavelength = 17.1 nm See radiation from Suns atmosphere, Corona
Image from STEREO mission The Suns Layers The Different Parts of the Sun During a total eclipse of the Sun, the very bright Photosphere is blocked and the Suns outer atmosphere becomes visible (in white light). We call it the Corona Spacecraft, like SOHO and STEREO, place a disk in front of their cameras to create an eclipse. They are then able to take images
with a larger view of the Suns Corona It extends far out into the Solar System, in fact we live in it! Hydrostatic Equilibrium There is no evidence that the Sun has changed its size, temperature, or luminosity in billions of years. We therefore conclude that it is in a state of equilibrium. The forces acting on it are: Gravity from its mass Pressure from its temperature These forces must be in balance to create
equilibrium. Internal Structure Use the Doppler Effect to measure motions on the surface. Seismic (acoustic) waves can be mapped out by their appearance on the surface. Just like seismology on Earth. Helioseismology reveals changes in density and pressure at different depths inside the Sun. The Different Parts of the Sun Core T = 15,700,000 K
Density = 162 g/cm3 Radiative Zone Energy transported by light Convective T = 10,000,000 Zone K Energy transported by convection Photosphere Visible surface Far less dense than Earths atmosphere T = 5,800 K Chromosphere
Sunspots: T = 4,000 K Thin layer above photosphere Produces most of Suns UV Corona light Tenuous, extends out millions of T = 10,000 K kilometers Emits X-rays T = 1,000,000 K
Energy Source The Suns luminosity has been sustained for billions of years (geologic and fossil evidence suggest at least 3.8 billion years). What energy source could last that long? Chemical Burning?: If the Sun were made of coal, burning (oxidizing: chemical potential energy thermal energy) it could only sustain the luminosity for ~1,000 years. Energy Source
The Suns luminosity has been sustained for billions of years. What energy source could last that long? Gravitational contraction?: compression of gas from gravity heats the gas. gravitational potential energy thermal energy (randomized kinetic energy of the gas particles) original source of energy for the Sun. could only sustain the Suns luminosity for ~10 million years.
Current energy source for Jupiter and Saturn. Nuclear Fusion proton-proton chain most common nuclear reaction for Sun-like stars. 4 protons a helium nucleus, positrons, neutrinos, and gamma rays mass of the 4 protons > the mass of the helium nucleus, the positrons, and the neutrinos combined. mass gamma ray photons:
the energy equivalent to the missing mass by the equation E = mc2 Random Walk Photons bounce off of electrons imparting energy to the plasma (pressure and temperature increase) Plasma is very dense in core and radiative zone Can take 10,000 -100,000 years for the energy generated in the core to escape to the surface. Extra Slides
Age of the Sun We think that the Sun and Solar System formed from a single interstellar cloud all at the same time. So the oldest rocks in the Solar System should gives us an approximate age for the Sun as well. Rocks are dated using their relative abundances of radioactive elements and their decay products. The oldest rocks on Earth are 4.6 billion years old as are the oldest meteorites ever examined. So the Sun is at least 4.6 billion years old. The oldest fossils of life on Earth are 3.8 billion years old. So the Sun must have reached equilibrium by at least that age.
It burns through fuel at the rate of its luminosity. We figure that about less than 1% of its mass is available to convert to energy through fusion. This gives a total lifetime of the Sun at about 10 billion years. Sun The Sun is Above Average Most stars in the Universe are small, cool, low-mass dwarfs. The Sun is larger, hotter, and more massive than these. There are stars that are much larger, very hot, and many times
more massive than the Sun. But these stars are quite rare compared to the Sun or the lowmass stars. The Sun is also not median, mid-range, or most frequent (mode) in the measures of size, temperature, brightness, or mass. Energy Comparisons Food Calories Joules Lifting a lemon 1 meter
2.388 X 10-4 1 Car moving at 60 mph 86 3.6 x 105 Burning a liter of oil 287
1.6 x 106 Human daily diet 2 X 103 8.4 x 106 Lightening bolt 106 1010 Heat a house (1 year)
107 1011 1-megaton H-bomb 1 x 1012 5 x 1015 Major geomagnetic storm 1012
1016 Earthquake (magnitude 8.0) 6 x 1012 2.5 x 1016 Annual U.S. energy usage 1016 1020 Impact of dinosaur extinction
asteriod 1019 1023 Annual sunlight on Earth 1021 1025 Large solar flare 1022
Annual solar energy output 1030 1034 Supernova (exploding star) 1040 1044 Nuclear Fusion neutrinos () have very little mass, and travel near the speed of light. They hardly react with
anything. They can escape directly from the core, unlike photons. Hence we can observe them to probe directly the conditions in the core of the Sun. To do this we build giant tanks filled with different liquid compounds and put them far underground. Since neutrinos hardly react to anything we expect to detect only 1 neutrino per day interacting with the liquid in the tank! After decades of experiments weve now actually detected the amount that we expect. But found that we were detecting all the types of neutrinos, not just those produced by the proton-proton chain. This means that neutrinos must have some mass in
order to be able to oscillate between the different types. Suns Orbit The Suns orbit is 3D. It takes the Sun about 250 million years to orbit the Galaxy. So the Sun has completed about 18 orbits since its birth (4.5 billion/ 250 million).
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