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Assigned Reading Read Chapters 8.1 and 8.2 Colonel Cady Coleman, Astronaut: Lessons from Space Lead Straight Back to Earth, Wednesday, February 27, 2019, 5 pm Commonwealth Honors College Events Hall
The Sun: Our Star The Sun is an ordinary star and shines the same way as other stars of its type.
Why is the Sun important for life? Provides energy. Photosynthesis is the source of all food. Provides heat. Without the sun the temperature would be close to absolute zero. Provides light.
What can we learn about the sun just by looking? The sun is round. Sunspots The sun rotates.
The Sun's Rotation Nonuniform rotation: the equator rotates faster than the poles. Means that the sun is not a solid.
The Sun s Quick Facts Average star Spectral type G2 Only appears so bright because it is so close. 109 times Earth s diameter 333,000 times Earth s mass Consists entirely of gas (av. density = 1.4 g/cm3) Central temperature = 15 million 0K Surface temperature = 5800 0K
The Photosphere The bright part normally seen is called the photosphere, which is about 500 km deep. Photosphere means: light sphere. It is an almost perfect blackbody with a temperature of 5800 K. Deviations from a blackbody owe to absorption lines by gas in the Sun s atmosphere.
The limb is slightly fainter
What would you expect to see if you looked at the Sun now? The photosphere: the region where the blackbody radiation that we see is made. Only ~500 km thick. Thin gas: 3,400 times thinner than air. Its upper layers produces the absorption spectrum. Limb darkening: proof that the Photosphere has a thickness and that energy comes from below. Sunspots.
Total solar eclipse prominence chromosphere
Chromosphere Reddish in color, which is the origin of its name (chromos meaning ``color''). 2000-3000 km thick. Faint relative to the photosphere. About 10,000 K: hotter than the photosphere and much less dense. Emission-line spectrum.
Total solar eclipse corona
Corona Only visible during eclipses - the outermost layer. - Temp about 1 million K. -made up of very diffuse (but extremely hot gas). - coronal emission is dominated by X-rays.
Structure of the Sun
The Solar Atmosphere Apparent surface of the sun Heat Flow Only visible during solar eclipses Solar interior Temp. incr. inward
Sunspots Sunspots come and go with time. Big sunspots can live for several weeks. Come in pairs. Dark inside, lighter outside. Umbra and Penumbra.
The Atmosphere of the Sun Why are the Chromosphere and Corona fainter than the Photosphere even though they are hotter? Photosphere: 5,800 K, Chromosphere: 10,000 K, Corona: 1-2 106 K, continuum + abs. emission emission
Hotter blackbodies emit more radiation. The Corona does not emit blackbody radiation.
Sunspots Sunspots are part of the photosphere so are blackbody emitters. Brightness ~ σ T4 Are about 1000 K cooler than the rest of the Sun's photosphere, so appear as dark spots.
Granulation of the Photosphere Each Granule is about the size of Texas and lasts for only 10-20 minutes before fading away!
Energy Transport in the Sun -raysrays Radiative energy transport
Energy Transport near the Photosphere Energy generated in the sun s center must be transported outward. Near the photosphere, this happens through Convection. Cool gas sinking down Bubbles of hot gas rising up 1000 km Bubbles last for 10 20 min.
Granules: convective cells The granules are just densely packed convective cells. Convective cells are very similar to thunderstorms.
What would you expect to see if you looked at the Sun now? The photosphere Limb darkening: proof that the Photosphere has a thickness and that energy comes from below. Sunspots.