Astronomy 8.1

The Sun

-An ordinary star that shines in the same way as other stars of its type. -By looking at the sun: Round, has sunspots, rotates.

Quick Facts about the sun

-Average star -Spectral type is G2 -Only appears so bright because it is so close. -109 times the diameter of earth. -333,000 times the mass of earth -Consists entirely of gas. (av. density 1.4 g/ cm cubed) -Central temperature: 15 million K -Surface temperature 5800 million K

The atmosphere of the sun

-Corona and chromosome are fainter even though they are hotter

Granules

-Densely packed connective cells. -Convective cells are very similar to thunderstorms

Energy Transport in the sun

-Energy generated near the suns center must be transported outward near the photosphere. This happens through convection -Bubbles of cool gas sink down and bubbles of hot gas rise up. Bubbles last for 10 to 20 mins.

The Solar Atmosphere

-From photosphere, chromosophere, corona the heat flows out. -Photosphere is the apparent surface of the sun. -Chromosphere and corona are only visible during a solar eclipse.

Corona

-Only visible during eclipses. -Outermost layer -Temperature of about 1 million K -made up of very diffuse (but extremely hot gas) -Coronal emission is dominated by X rays -Does not emit black body radiation

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 about absolute 0. -Provides light.

Chromosphere

-Reddish in 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

The Photosphere

-The bright part of the sun that we see -Means light sphere -An almost perfect blackbody with a temperature of 5800 K -Deviations from black body owe to absorption lines by gas in sun's atmosphere -Each granule is about the size of Texas and lasts for about 10-20 minutes before fading away.

What would you see if you looked at the sun?

-The photosphere: Region where the blackbody radiation is made. Only about 500 km thick. -Thin gas: 3,400 times thinner than air -Upper layers produce absorption spectrum. -Limb darkening: Proof that the photosphere has a thickness and that energy comes from below. -Sunspots

Structure of the Sun

From inside to outside: -Radiative envelope -convective envelope -Photosphere -Chromosphere -solar flare/prominences -Corona

Rotation of the sun

Non-uniform rotation. Equator is rotating faster than the poles. Means that sun is not a solid.

Total Solar eclipse

Prominence. Chromosphere

Sunspots

Sunspots come and go with time. Big sunspots can live for several weeks. Come in pairs. Dark inside, lighter outside. Umbra and Penumbra. Part of the photosphere so they are blackbody emitters. About 1000 k cooler than the rest of the sun's photosphere, so appear as dark spots.

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

Total Solar Eclipse

You would see the corona