Our Star, the Sun
The Sun: Our Star A glowing ball of gas held together by its own gravity and powered by nuclear fusion
Radius: 700,000 km (435,000 miles) Diameter: 1.392 million km (865,000 miles) Circumference: 4.4 million km (2.7 million miles) Mass: 2.0 10 30 kg (In lbs that would be 4.4 w/ 30 zeros!) Density: 1400 kg/m 3 (3,080 lbs/m³ or 1.4 g/cm³ or 1.4 times that of water) about ¼ the earth s density, similar to the Jovian planets Rotation: We use sunspots to determine. Differential (faster at the equator (25 days), slower at the poles (31 days at 6 degree latitude); period about a month Core Temp: 27 million F Surface Temp: 10,000 F (5,800 K - above melting point of any known material) Apparent surface of Sun is photosphere not a solid surface 2011 Pearson Education, Inc. Physical Properties of the Sun
The Sun is the Largest Object in the Solar System The Sun contains more than 99.85% of the total mass of the solar system If you put all the planets in the solar system, they would not fill up the volume of the Sun 110 Earths or 10 Jupiters fit across the diameter of the Sun How big is the Sun?
Let s reduce the size of the solar system by a factor of 10 billion; the Sun is now the size of a large grapefruit (14 cm diameter). How big is Earth on this scale? A. an atom B. the tip of a ballpoint pen C. a marble D. a golf ball Copyright 2012 Pearson Education, Inc.
The scale of the solar system On a 1-to-10 billion scale: Sun is the size of a large grapefruit (14 centimeters). Earth is the size of a tip of a ballpoint pen, 15 meters away. Relative Distance of the Nearest Star Copyright 2012 Pearson Education, Inc.
Scales and Sizes In Astronomy Mercury s distance from the Sun. Is about half the Sun-Earth distance. It is half an Astronomical Unit. The star Sirius is about twice as massive as the Sun We say it has a mass of two solar masses. Sirius is about 25 times more luminous than the Sun. We say it has a luminosity of twenty-five solar luminosities. Copyright 2012 Pearson Education, Inc.
SOHO: Eavesdropping on the Sun SOHO: Solar and Heliospheric Observatory Orbits at Earth s L1 point, outside the magnetosphere Multiple instruments measure magnetic field, corona, vibrations, and ultraviolet emissions 2011 Pearson Education, Inc.
Sunspots What are they? What do they do to us? Why should you even care?
What is a sunspot Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity that draws off the convection of heat to the surface, thus cooling the surface. Sunspots are usually in pairs because of the magnetic activity causing North and South poles at either of the spots. Pic on next slide
NASA Image of sunspots, September, 2011
What do sunspots do to us? Sunspots are a main hotbed of solar flares and prominences from the sun. These are in turn pushed by their energy into space as solar wind once they break free of the sun's gravity These solar winds are comprised of highly charged particles hurtling towards Earth
Sunspot projecting a flare into space
What does that mean to you? All of those charged particles will wreak havoc with electronics. A particularly large solar flare caused blackouts over a large portion of Canada. The particles can also cause the Aurora Borealis over the northern latitudes, known as the Northern Lights. On a darker note this can also cause massive disruptions to communications, GPS, and military satellites. So if a bad solar storm were to hit, it could potentially cut off your phone from Facebook, cause your car to get wrong directions, and make the Air Force shoot a missile at the wrong building.
What happens with a solar flare.
Watch Youtube Video: Whats a Solar Flare or CME and WHY are they dangerous?
2011 Pearson Education, Inc. Day 2 Notes
Physical Properties of the Sun This is a filtered image of the Sun showing sunspots, the sharp edge of the Sun due to the thin photosphere, and the corona 2011 Pearson Education, Inc.
The Active Sun 1. Sunspots appear dark because they are cooler areas they have a regular 11 year cycle 2. Prominences Huge cloudlike structures of chromatic gases trapped by magnetic fields 3. Solar flares sudden brightening above a sunset cluster Auroras-display of color near poles caused by solar flares
2011 Pearson Education, Inc. What is the Sun Made of?
Interior structure of the Sun: The core is where nuclear fusion takes place The photosphere is the visible surface of the Sun. Below it lie the convection zone, the radiation zone, and the core. Solar atmosphere consists of the chromosphere, the transition zone (temperature rises dramatically), and the corona. 2011 Pearson Education, Inc.
Convection zone and Radiation Convection zone -Below photosphere where the material is in constant convective motion Radiation Solar energy is transported due to radiation
Photosphere Grainy appearance to sun when look in a telescope caused by granules, areas of hotter gases rising last 10 minutes and new ones arise causing a convection 90% of sun s surface are hydrogen 10% helium
Chromosphere Above the photosphere is a thin layer of hot gases. It is viewed during an eclipse as a thin red rim
Corona Outermost portion of the atmosphere Visible only when photosphere is covered Solar wind ionized gases that escape the gravitational pull of the sun and bombard parts of solar system, it can effect our atmosphere.
The Solar Interior Nuclear Fusion -Converts four Hydrogen nuclei into one helium releasing energy energy is released because some matter is converted to energy Causes the core to grow in size Sun can exist in its present state another 10 billion years
What is nuclear fusion in the sun? Nuclear fusion in the sun is a process by which rapidly colliding nuclei, like those of hydrogen and helium, fuse together at very high temperatures, to form nuclei of higher atomic weight. Nuclear fusion in the sun is a merger of smaller nuclei into heavier ones, releasing a lot of energy in the process.
How it works! In the process of the hydrogen and helium fusing together, some mass is lost and converted into energy. Nuclear fusion in the sun is only possible when the repulsion between protons is overcome. For that to happen, energy and temperature at the suns core has to be really high.
The Suns core The total radius of the sun is 6.955 x 10^5 km (about 109 times the radius of Earth) Its core extends from the center to about 1.8 km, with a temperature of 14.5 million Kelvin.
Consider that four hydrogen atoms have a combined atomic mass of 4.032 atomic mass units whereas the atomic mass of helium is 4.003 atomic mass units, or 0.029 less than the combined mass of hydrogen. The tiny missing mass is emitted as energy as according to Einstein's equation: E=mc^2 E equals energy, m equals mass, and c equals the speed of light. Because the speed of light if very great (300,000 km/s), the amount of energy released from even a small amount of mass is enormous.
The conversion of just one pinheads worth of hydrogen to helium generates more energy than burning thousand of tons of coal. The sun is consuming an estimated 600 million tons of hydrogen each second; about 4 million tons are converted to energy. Even at the enormous rate of consumption, the sun has enough fuel to last easily another 100 billion years. However, evidence from other stars indicates that the sun will grow dramatically and engulf Earth long before all of its hydrogen is gone. It is thought that a star the size of the sun can exist in its present state for 10 billion years.
2011 Pearson Education, Inc. Day 3 notes
Physical Properties of the Sun Luminosity total energy radiated by the Sun can be calculated from the fraction of that energy that reaches Earth. Solar constant amount of Sun's energy reaching Earth is 1400 W/m 2. (W = watts) Total luminosity is about 4 10 26 W the equivalent of 10 billion 1-megaton nuclear bombs per second. 2011 Pearson Education, Inc.
We can draw an imaginary sphere around the Sun so that the sphere s surface passes through Earth s center. The radius of this imaginary sphere equals 1 AU. The solar constant is the amount of power striking a 1-m 2 detector at Earth s distance. By multiplying the sphere s surface area by the solar constant, we can measure the Sun s luminosity the amount of energy it emits each second. 2011 Pearson Education, Inc. Solar Luminosity
Doppler shifts of solar spectral lines indicate a complex pattern of vibrations 2011 Pearson Education, Inc.
Solar Oscillations (a) (b) The Sun has been found to vibrate in a very complex way. By observing the motion of the solar surface, scientists can determine the wavelength and the frequencies of the individual waves and deduce information about the solar interior not obtainable by other means. The alternating patches represent gas moving down (red) and up (blue). (b) Depending on their initial directions, the waves contributing to the observed oscillations may travel deep inside the Sun, providing vital information about the solar interior. (National Solar Observatory) 2011 Pearson Education, Inc.
Solar density and temperature, according to the standard solar model 2011 Pearson Education, Inc.
Solar Magnetism Sunspots come and go, typically in a few days. Sunspots are linked by pairs of magnetic field lines. 2011 Pearson Education, Inc.
Solar Magnetism Sunspots originate when magnetic field lines are distorted by Sun s differential rotation 2011 Pearson Education, Inc.
Solar Magnetism The Sun has an 11-year sunspot cycle, during which sunspot numbers rise, fall, and then rise again 2011 Pearson Education, Inc.
Solar Magnetism This is really a 22-year cycle, because the spots switch polarities between the northern and southern hemispheres every 11 years Maunder minimum: few, if any, sunspots 2011 Pearson Education, Inc.
2011 Pearson Education, Inc. Solar Convection Physical transport of energy in the Sun s convection zone. We can visualize the upper interior as a boiling, seething sea of gas. Each convective loop is about 1000 km across. The convective cell sizes become progressively smaller closer to the surface.
Solar Granulation Typical solar granules are comparable in size to Earth s continents. The bright portions of the image are regions where hot material is upwelling from below. The dark regions correspond to cooler gas that is sinking back down into the interior. 2011 Pearson Education, Inc.
Solar Spectrum A detailed spectrum of our Sun shows thousands of Fraunhofer spectral lines which indicate the presence of some 67 different elements in various stages of excitation and ionization in the lower solar atmosphere. The numbers give wavelengths, in nanometers. (Palomar Observatory/Caltech) 2011 Pearson Education, Inc.
Observations of Solar Neutrinos What are Neutrinos? Neutrinos are subatomic particles produced by the decay of radioactive elements and are elementary particles that lack an electric charge Neutrinos are emitted directly from the core of the Sun and escape, interacting with virtually nothing. Being able to observe these neutrinos would give us a direct picture of what is happening in the core. Unfortunately, they are no more likely to interact with Earth-based detectors than they are with the Sun; 2011 Pearson Education, Inc.
16.7 Observations of Solar Neutrinos Typical solar neutrino detectors; resolution is very poor 2011 Pearson Education, Inc.
Summary of the sun Main interior regions of Sun: core, radiation zone, convection zone, photosphere, chromosphere, transition region, corona, solar wind Energy comes from nuclear fusion; produces neutrinos along with energy Study of solar oscillations leads to information about interior Absorption lines in spectrum tell composition and temperature Sunspots associated with intense magnetism Number of sunspots varies in an 11-year cycle Large solar ejection events: prominences, flares, and coronal ejections 2011 Pearson Education, Inc.