July 23rd, Lecture 7.docx

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Astronomy & Astrophysics
Marija Stankovic

July 23 , Lecture 7, AST201H1 Star is stable. Pressure from heat generation pushes outward, and gravity pulls inward. The Solar Thermostat Sometimes there are slight variations. Just as, slight variation, that could happen inside the core of the sun. It is a mechanism. Help keep these things in balance, allow for constant production during sun’s lifetime. Thermostat: regulation of temperature. (insert slide, important) A slight drop in core temperature, leads to a large decrease in the fusion rate, that lowers the core pressure, causing the core to contract and heat up, thereby restoring the fusion rate to normal. Decrease the fusion rate, less energy, we have that equilibrium (gravitational power going in, disturbing the balance, thus shrinks). Temperature goes up, velocity goes up, more reactions happening. Bringing things back into balance. Interplay. If the sun’s core got a little hotter, the fusion rate would increase until the core expanded (because there is too much heat), then it would slow down. Sun has magnetic field. Air around one spot. Follow the magnetic field. (insert slide) Photosphere. Beneath it is temperature moves by circulation. Convection beneath the Sun’s surface: hot gas rises while the cooler gas descends. Bright spot is where the hot gas is rising and darker when the cooler air goes down. Some areas where magnetic fields are strong and they don’t allow hot air rise. Trying to gain understanding. Temperature drops from center to outwards. Outer layer of the sun is the chromosphere, a lot hotter. Chromosphere only can be seen during eclipse, so as the corona. Solar Wind A lot of high energy particles are being produced. Mainly protons. Carry a lot of energy, travel towards and all directions. Earth is protected by magnetic field of its own. Hot iron core, which rotates and produce effect (insert slide). This magnetic field reflects high energy particles. These particles interact with upper, that’s why we see northern lights. These can occasionally affect satellites and telecommunication. Luminosity- the amount of energy something produces per second. Buying a light bulb: a 100 watt. Watt is an unit of energy per unit time. It is a luminosity. Sun produces energy equivalent to 400x10 100W light bulbs. We call this the number the Sun’s luminosity. It tells us how bright the Sun is intrinsically, just like the wattage of a light bulb. When we look at the stars, we can see the difference. Some are brighter and some are less. However, from images we see how bright they appear to be, not actually what they are. We can’t tell how intrinsically how bright they are, and only if they are at the same distance. If they are the same distance away from us, we can have calibration. We can’t tell for sure which one produces more light. Another term called apparent brightness- how bright something appears to you. If a bulb has a luminosity of 100 W when viewed from 1m away, what would its luminosity be when viewed from 2m away? 100W. Regardless of the distance. Luminosity does not matter with distance. Specific for the lightbulb. Doesn’t depend on distance. Properties of
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