The Sun, our favorite star! The Sun is the basis for all of our knowledge of stars. Why? WE CAN SEE IT REALLY WELL.

Kelvin Temperature Scale 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 -273.15 -459.67 Humans 310 37 98.6 Sun 5800 5527 9980

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) The Sun is made of mostly HYDROGEN and HELIUM Main Parts: Corona Chromosphere Photosphere Convection Zone Radiative Zone Core

Rotation 25 Days at the Equator 35 Days at the Poles

This twisting leads to the loopy structures we see!

The Core + Energy Fusion takes place here. p n 4H 1He Fusion Animation http://astro.unl.edu/classaction/animations/sunsolarenergy/fusion01.html

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 2. Conduction 3. Radiative Diffusion Convection and Radiative Diffusion are most important for the Sun!

Radiative Diffusion The photons “diffuse” outwards, heating the gas as they go. Ionized gas Photons can “scatter” off of unbound electrons When they scatter, the photons share their energy with the electrons The electrons get hotter

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! Ionized gas

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

As seen from the top, these are the granules we see in the photosphere The Convective Zone Photosphere 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

Not very important for stars! 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

in this image to someone in class Sunspot pairs Describe what you see in this image to someone in class

Explain what you see in this picture to someone 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 spectrum http://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 Wind Data can be found at www.spaceweather.com

A short Video Earth to scale. Yes, really.