the sun, our favorite star!

The Sun, our favorite star!

WE CAN SEE IT REALLY WELL.

The Sun is the basis for all of our knowledge of stars. Why?

temperature kelvin degree Celsius degree Fahrenheit

symbol K °C °F

boiling point of water 373.15 100. 212.

melting point of ice 273.15 0. 32.

absolute zero 0. -273.15 -459.67

Humans 310 37 98.6

Sun 5800 5527 9980

Kelvin Temperature Scale

Today we will take a journey from the center of the Sun, starting just outside the core…

…and ending up deep in the corona.

Overview of Solar Structure(aka, our Sun as a jawbreaker)

Main Parts:

Corona

Chromosphere Photosphere

Convection Zone

Radiative Zone

Core

The Sun is made of mostly HYDROGEN and HELIUM

Rotation

25 Days at the Equator35 Days at the Poles

This twisting leads to the loopy structures we see!

The CoreFusion takes place here.

Fusion Animation http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html

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+ Energy4H 1He

The interior of the Sun…

• Energy is generated in the core, but how does it get out and end up as sunshine?

The next two layers of the Sun are all about getting the energy being made in the core out

into space!

How does energy get from one place to another?

1. Convection

3. Radiative Diffusion

2. Conduction

Convection and Radiative Diffusion are most important for the Sun!

Radiative Diffusion

The photons “diffuse”

outwards, heating the gas

as they go.• Photons can “scatter” off of

unbound electrons• When they scatter, the photons

share their energy with the electrons

• The electrons get hotter

Ionized gas

The Radiative Zone

Ionized gas

Here, photons bounce around in a

“random walk”

Eventually they make it out of the

radiative zone, but it takes a long, long

time!

Convection

Hot stuff rises…

Cool stuff sinks!

Hot water goes up to the surface while cool water sinks down -- cool water then gets heated and rises

a.k.a: BOILING

The Convective Zone

The Convective Zone is the layer just under the photosphere

Convective “cells”:As seen from the top, these are the granules we

see in the photosphere

Photosphere

Conduction

Metal of the pan heats by conduction…

…heat travels through the atoms

of the pan Not very important for stars!

PHOTOSPHERE

Characteristics• the part of the sun we see•one of the coolest parts at 6000K•densest part of solar atmosphere •contains sun spots, granules (ation)

Photosphere temperature is about 5800 K…

• Remember how the temperature and color of stars are related? The temperature of our Sun gives it its yellowish color!

Our Sun is really yellowish green, but our atmosphere absorbs and scatters some of the blue light.

The photosphere has some interesting features too…

Sunspots:Regions where magnetic field pokes

through the photosphere.Sunspots are cooler than surrounding

stuff, so they look dark!

Granules:Where the roiling, boiling convection zone

underneath bubbles up.

Sunspots• dark cooler (4000K vs. 5800K) regions on the sun• last several days to several weeks• caused by the sun’s magnetic field upwelling to the photosphere• occur in cycles• contribute to solar storms such as flares and coronal mass ejections

Sunspot pairsDescribe what you seein this image to someonein class

Explain what you see in this picture tosomeone else in class.

Granulation•Cover the sun’s surface•approx. 1000km across (Texas sized)• tops of convection cells•white centers are hotter than dark edges•flow can be up to 15000 mph• individual cells last 20 min

http://www.youtube.com/watch?v=zxzhfijFML8&feature=related

CHROMOSPHERE

Characteristics• red color due to hydrogen emission lines• temperature 4500K to 10000K•prominences form here •2500 km thick• spicules (jets of plasma) form here

Spicules• small jet like eruptions that last a few minutes• send material out into corona at 20-30 km/s

TRANSITION REGION• Region of rapid temperature change between chromosphere and corona

THE CORONA• temperature 1-3 million K•very irregularly shaped• strong x-ray emitter•uncertain as to why it is so hot•coronal holes are the origin of the solar wind•produces an absorption and continuous spectrumhttp://www.nasa.gov/mission_pages/sunearth/news/colorful-science_prt.htm

Coronal Mass Ejections

• Huge bubbles of gas ejected from the sun• Can cause problems with communications• Often occur with flares

SOLAR WIND

• low density gases (ionized hydrogen)• travels 300 to 1000km/s• sun loses 10,000,000 tons of mass

per year

Current Solar WindData can be found atwww.spaceweather.com

A short Video

Earth to scale.Yes, really.