Understanding Stars

1. Understanding Stars Our Sun

2. Our Sun • What is the structure of our sun? • What makes the sun shine? • How do we know? • What tools do we use to study our nearest star?

3. What tools do we use? • Refracting telescopes- light passes through a lens to the eye • Good clarity, good power, good magnification, • High quality lenses needed, chromatic aberration • Reflecting telescopes- uses a mirror to focus light • Good clarity, good power, good magnification, glass not as high quality • Secondary mirror blocks some light • Radio Telescopes-focus incoming radio waves on an antenna, can be arranged in arrays • X-Ray telescopes- detect incoming X-rays, space telescopes, focus on learning about black holes • Gamma Ray telescopes - space telescopes to study visible light and gamma rays. • And others. . .

4. How do we know? • Spectroscopy - the study of the properties of light • Detailed study of this in physics • Depends on the wavelength • Think a rainbow = continuous spectrum

5. How do we know? • Absorption spectrum - when light is passed through cool gas under low pressure the gas will absorb some light and leave dark bands on the spectrum.

6. How do we know? • Emission Spectrum - when light is passed through HOT gas under low pressure the gas will emit some light and these appear as bright bands on a dark spectrum. These act as finger prints to stars and tell us the chemical composition of stars.

7. Structure of the Sun • Photosphere = visible surface • Interior • Atmospheric layers (2) • Chromosphere • Corona

8. Photosphere • Visible surface of the sun • Appears to have a grainy texture. • Called granules • size of TX • last 10-20 min • Due to convection within the sun • Composed of 90% hydrogen, and <10% helium.

9. Sunspots • Dark areas on surface (photosphere) • Dark due to lower temperature • Show sun activity and rotation of sun • More spots = higher solar activity, 11 year cycle

10. Chromosphere • Layer of atmosphere, thin (few thousand km) • Visible during an eclipse • Magnetic field evidence of the sun present in this layer.

11. Prominences • Arches or loops of chromospheric gases • Extend into corona • Ionized gases that are trapped by magnetic fields. • Show areas of intense activity

12. Corona • Outermost portion of solar atmosphere • Origin of solar wind, aka space weather • Energy travels at speeds up to 800km/sec. • Solar flares

13. Solar Flares • Explosive solar events • Release enormous amounts of energy in form of UV, radio, and X-rays • Cause an increase in intensity of solar wind due to atomic particles that are ejected

14. NASA SDO example • SDO = Solar Dynamics Observatory • M5.6 class solar flare (Almost X class) • 7/2/2012

15. Why does the sun shine? • Nuclear fusion (opposite of fission) in the interior or core. • Stars use nuclear fusion to combine light/low mass elements into heavier/higher mass elements. • Matter is converted to energy • 4 hydrogen combine to form one helium. • One proton in each hydrogen atom, atomic mass = 4.032 atomic mass units • One helium atom, atomic mass = 4.003 atomic mass units

16. Why does the sun shine? • Stars use nuclear fusion to combine light/low mass elements into heavier/higher mass elements. • Results in a small loss of mass as the mass is converted into energy • Difference in atomic masses = 0.029 atomic mass units. • Energy! E = mc2