Transcript STARS
Structure of the Sun Starting at the center and working outward The Core The Radiative Zone The Convective Zone The Photosphere The Chromosphere TheCorona Core •Innermost region of the Sun •Contains about 10% of the Sun’s mass •Nuclear Fusion occurs here •Nuclear Fusion- A nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy. Radiative Zone •Energy is transported away from the core by photons. A photon is what carries light over space •Photons are absorbed and scattered in random directions •It takes them 100,000 years to make its way through the zone Convective Zone In the region surrounding the radiative zone, heat is transferred by convection: A blob of gas near the bottom of the region is heated by photons emerging from the radiative zone The blob expands, becomes buoyant, and rises Near the Sun’s surface, the blob is surrounded by cooler gas, so it releases it’s heat to its surroundings Cooled, the blob becomes more compact, then sinks back down where the cycle will begin again Photosphere The visible surface of the Sun lies at the top of the convection region The presence of the convective blobs reaching the surface and cooling makes the photosphere appear splotchy or grainy. This effect is called granualtion. Photosphere Features of the Photosphere The presence of strong magnetic fields at the Sun’s surface can divert away hot blobs of gas convecting towards the surface This causes cool spots to form, 4,00 Kelvin as opposed to the normal temp of 6,000 Kelvin These cool regions appear as sunspots and are often wider than the Earth Chromosphere It is a thin layer, about 10,000 km, above the photosphere Temperature is 10,000 K. It is hotter than the photosphere and we believe it is caused by the Sun’s magnetic field but we are not exactly sure Most light emanated from the chromosphere is reddish due to H-alpha emission. H-alpha emission can be seen when Hydrogen’s one electron moves from the first energy level to the second Corona The corona is a large, low density envelope surrounding the Sun. It is heated by the Sun’s magnetic field and its temperature is roughly 1,000,000 K. The corona is the origin of solar X-ray emissions Magnetic Activity in the Corona Plasma in the corona often becomes trapped in magnetic field loops. These arcs of hot glowing ionized gas are called prominences and can be very large Some loop-like prominences are short-lived, lasting only a few minutes. Others can be more stable, lasting hours or days Plasma consists of a collection of free moving electrons and ions. Solar Flares Magnetic field lines in the corona can become kinked and break. Eventually they reconnect with A LOT of energy that needs to be released. The release of energy appears as a solar flare which is an extremely bright region on the sun Strong flares can affect satellite communications disrupting TV’s and phones Solar Flares The earth itself is strongly protected by its magnetic field. When there is a great deal of solar activity we experience this as a beautiful display of Aurora Borealis reaching out from the North and Aurora Australis reaching out from the south Coronal Mass Ejections Coronal mass ejections occur when massive solar explosions blast through the Sun's outer atmosphere and plow toward Earth at speeds of thousands of miles per second They occur during a solar flare. Large amounts of plasma are ejected from the Sun Coronal Mass Ejections If directed towards the Earth, CME’s could interfere with communications, satellites, cause power outages, damage electronics, and even endanger the lives of astronauts. Extremely large CME’s could severely damage power grids world wide. It is possible that we could be without power for months or even years. It is not an impossibility that we could see this happen Coronal Mass Ejections Normal Conditions: Earth’s magnetic field typically deflects the charged particles streaming out from the sun, carving out a teardrop-shaped volume known as the magnetosphere. On the sun-facing side, the boundary, or magnetopause, is about 60,000 kilometers from our planet. The field also traps particles in a doughnut-shaped region known as the Van Allen belts. Coronal Mass Ejections First Stages of Impact: When the sun fires off a coronal mass ejection (CME), this bubble of ionized gas greatly compresses the magnetosphere. In extreme cases such as superstorms, it can push the magnetopause into the Van Allen belts and wipe them out. Coronal Mass Ejections Magnetic Reconnection: The solar gas has its own magnetic field, and as it streams past our planet, it stirs up turbulence in Earth’s magnetic field. If this field points in the opposite direction as Earth’s, the two can link up, or reconnect— releasing magnetic energy that accelerates particles and thereby creates bright auroras and powerful electric currents. Solar Cycle Solar magnetic phenomena like sunspots, prominences, flares, and CME’s do not happen at random intervals. The magnetic field at the surface of the Sun varies in strength over time, reaching peak strengths roughly every 11 years. This cycle is due to the Sun’s differential rotation-The Sun rotates more quickly at the equator than at the poles Solar Cycle As the Surface of the Sun rotates differentially, it carries magnetic field lines with it, warping them with time. After several years, the warped field lines begin to kink. It is at these kinks that sunspots, prominences, and flares occur Solar Cycle The Maunder Minimum From 1645 to 1715, almost no sunspots were observed. This period of time correlates to the time known as the “Little Ice Age” during which temperatures in Europe and North America reached record lows- records that have still not been broken. Whether there is a casual connection between the solar cycle and climate on Earth is still uncertain and debated. The Maunder Minimum Roughly ever 11 years, the magnetic activity reaches a peak- the so called “solar maximum.” At this point the magnetic field of the Sun has become so twisted and messed up that the entire polarity of the Sun flips- the north pole becomes the south pole and vice versa. Most of the kinked field lines snap and reform in a simpler configuration The Maunder Minimum The Maunder Minimum is a long period wherein sunspot occurrence was noticeably very low. Data gathered by astronomers reveal a 30-year duration within the Maunder Minimum wherein only 50 sunspots were accounted for. Compare that to the usual 40,000 to 50,000 recorded in more recent years