Download Structure of the Sun, our nearest star

The Sun: Guided Notes
Structure of the Sun, our nearest star

The Sun’s INTERIOR
o __________________________

Comprises about 25% of sun’s interior

site of nuclear fusion
o __________________________ Zone

Energy produced in the core is carried outward by photons over LONG periods of time
o _________________________ Zone


Energy is carried outward by convection
The Sun’s ATMOSPHERE:
o The Photosphere

Lower atmosphere or “surface” of the sun

The only part of the sun we can normally __________

Granulation

“Blotchy” appearance

Granules are ______________________ cells in the photosphere

Brighter areas are __________________
o The Chromosphere

Visible during a solar eclipse or with the use of ________________

Appears pink because the gas here only emits certain wavelengths of light, mostly
__________________

“spiky” surface due to jets of _____________ that surge upward
o The Corona


Extremely hot temperature and low _______________________

Only seen using special filters (or during an eclipse)
Heliosphere
o The immense electromagnetic bubble containing our solar system, solar wind, and the entire
solar ______________________ field.
o It extends well beyond the orbit of Pluto, but within the Oort cloud.
Solar Phenomena

Solar Wind
o High-speed charged particles (mostly electrons and protons) constantly blowing off the Sun.
o May be viewed as an extension of the outer atmosphere of the Sun (the corona) into
interplanetary space.

Sunspots
o Can be seen on the granular photosphere
o Sunspots are cooler than the surrounding photosphere
o Indicate magnetic disturbances on the sun
o Sunspots reach a maximum about every 11 years

Solar Prominence
o Large regions of very dense ionized gas ejected from the photosphere and held in place by the
sun’s magnetic fields
o Return back to the surface of the sun along magnetic field lines
o may stretch 150,000 Km or more along the sun’s surface (10x the size of the Earth)

Solar Flares
o short-term outbursts on the sun, caused by the sudden release of energy stored in twisted
magnetic fields in the solar atmosphere.
o Release the energy equivalent of ten million volcanic eruptions.
o They can last just a few minutes or up to several hours.

Effects of solar flares
o Tremendous amounts of energy flung into space, including high-energy particles and
electromagnetic radiation
o When the radiation and particles reach the Earth's magnetic field, they interact with it to
produce auroras
o Solar flares can also disrupt communications, satellites, navigation systems and power grids.

Coronal Mass Ejection (CME)
o Coronal mass ejections can carry up to 10 billion tons of plasma traveling at speeds as high as
2000 km/s.
o Near solar maximum we observe an average of 2 to 3 CMEs per day
o Thought to arise when the sun’s magnetic fields suddenly rearrange, releasing an enormous
bubble of matter
The Sun: Guided Notes
Nuclear Fusion: Converting _________________ to ____________________
Nuclear fusion

The luminosity of a star is powered by nuclear ____________ taking place in the center (core) of the
star
o The temperature and density are sufficient to allow nuclear fusion to occur.
o Stars are primarily composed of hydrogen, with small amounts of helium.
o They are so hot that the ____________________ are stripped from the atomic nuclei.
o This ionized gas is called a ____________________.

The proton-proton chain
o At temperatures above 4 million Kelvin hydrogen nuclei ______________ into helium

Running out of hydrogen
o The star is kept in a delicate balance between ______________ trying to collapse it and
_____________________ pushing it outwards.
o As the hydrogen runs out, the energy released from fusion decreases and the gravity causes
the star to collapse.
o If the star is ___________________ enough the core temperature increases until helium
fusion starts.

Helium burning
o At temperatures above 100 million Kelvin helium can be fused to produce
___________________. This reaction is called the “Triple-Alpha Process”

Heavier elements
o Helium is fused with carbon to make heavier elements:
 oxygen, neon, magnesium, silicon, sulphur, argon, calcium, titanium, chromium and
iron
o It’s impossible to make elements heavier than ___________ through nuclear fusion without
putting in more energy.

Running out of helium
o Eventually the helium is exhausted, and the star collapses again.
o If it is massive enough, then the temperature increases enough to allow carbon fusion.
o The cycle repeats, fusing heavier elements each time, until the core
_________________________ cannot rise any higher.
o At this point, the star dies.