Understanding Stars

Our Sun

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?

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. . .

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

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.

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.

Structure of the Sun

Photosphere = visible surface

Interior Atmospheric layers

(2)– Chromosphere– Corona

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.

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

Chromosphere

Layer of atmosphere, thin (few thousand km)

Visible during an eclipse

Magnetic field evidence of the sun present in this layer.

Prominences Arches or loops of

chromospheric gases

Extend into corona Ionized gases that

are trapped by magnetic fields.

Show areas of intense activity

Corona

Outermost portion of solar atmosphere

Origin of solar wind, aka space weather

Energy travels at speeds up to 800km/sec.

Solar flares

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

NASA SDO example

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

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

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