The Solar System :
THE SUN
Martin Crow
Crayford Manor House Astronomical Society
The Solar System :
The Sun and Earth Moon system
Last time:
The history of our understanding of the Solar system.
Martin Crow
Crayford Manor House Astronomical Society
The Solar System :
The Sun and Earth Moon system
This week:
The formation of the Sun (and Solar system).
About the Sun
The Sun’s effect on the Earth.
The Earth Moon system.
Martin Crow
Crayford Manor House Astronomical Society
The Sun
The formation of the Sun (and Solar system)
The Sun along with the rest of the solar system formed 4.567 x10⁹ years ago.
The age has been determined from radiometric dating of meteoritic material.
Martin Crow
Crayford Manor House Astronomical Society
Ideas regarding the formation of the Solar system were first
formulated by Emanuel Swedenborg, Immanuel Kant, and
Pierre-Simon Laplace in the 18th century.
This was called the ‘Nebula formation’ of the Solar system.
This idea fell in and out of favour, largely due to issues
surrounding the Sun’s angular momentum, but it is now known that they were
broadly on the right track.
The Solar system formed from the gravitational collapse of a Giant Molecular
Cloud GMC.
GMCs are many tens of light years in size and have masses between
10⁴ - 10⁶ solar masses.
They have an average density of 100 – 1000 particles per cubic centimetre.
This is similar to the very best vacuums created in the laboratory. The average
density in the solar vicinity is one particle per cubic centimetre.
In the air around us there are 10¹⁹ particles per cubic centimetre.
Martin Crow
Crayford Manor House Astronomical Society
The gravitational collapse is thought to have been triggered by shock waves
from nearby supernovae events.
Studies of meteorites containing pristine solar nebular material indicate five
separate events. Dr Caroline Smith
The high mass stars that gave rise to these supernovae are likely to have formed in
the same GMC that formed the Sun around 5 x 10⁶ years earlier.
GMC was mostly Hydrogen with around 2% consisting of heavier elements.
Anything heavier than Hydrogen is described by astronomers as metals.
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
So what makes the Sun shine?
The Sun has been shining for a very long time and how it did this was a mystery
until the 20th century.
Solutions that had been put forward were:
In an influential lecture in 1854, Hermann von Helmholtz proposed that
the Sun’s enormous radiated energy was caused be gravitational contraction.
Chemical burning would only account for 3000 years of heat, whereas,
Gravitational contraction could account for 20 x 10⁶ years.
This was at odds with geological evidence for the Earth being
hundreds of millions of years old.
In 1905 a way forward appeared when Einstein derived his famous relation
between mass and energy, E = mc2.
F.W. Aston discovered in 1920 that four hydrogen nuclei were heavier than
a helium nucleus.
Martin Crow
Crayford Manor House Astronomical Society
So what makes the Sun shine?
So the Sun shines by converting Hydrogen into Helium, the so called
Proton – Proton reaction which accounts for nearly all of the energy release.
This reaction will only occur at temperatures of 10⁶ - 14⁶ K.
The core temperature of the Sun is 15.7 x 10⁶ K.
The reaction converts 0.7% of the mass into energy (26.73 MeV) in
the form of gamma rays and neutrinos.
It can take up to 10⁵ years for the light produced in the core to reach the surface
But the neutrinos escape immediately.
Another reaction called the CNO cycle will work above 13⁶ K and accounts for
1.7% of the ⁴He produced.
Martin Crow
Crayford Manor House Astronomical Society
About the Sun
The life cycle of the Sun
0–100,000 years - Pre-solar nebula forms and begins to collapse. Sun begins to form.
10⁵ – 50 x 10⁶ years - Sun is a T Tauri protostar.
50 x 10⁶ years - Sun becomes a main sequence star.
Sun remains a main sequence star, continually growing warmer and brighter by
~10% every 1 billion years.
The habitable zone?
Martin Crow
Crayford Manor House Astronomical Society
The life cycle of the Sun
10 x 10⁹ - 12 x 10⁹ years - Sun starts burning hydrogen in a shell surrounding its core,
ending its main sequence life. Sun begins to ascend the red giant branch of the
Hertzsprung–Russell diagram, growing dramatically more luminous
(by a factor of up to 2,700), larger (by a factor of up to 250 in radius), and cooler
(down to 2600 K): Sun is now a red giant. Mercury and possibly Venus and Earth are
swallowed. Saturn's moon Titan may become habitable.
Martin Crow
Crayford Manor House Astronomical Society
The life cycle of the Sun
~ 12 x 10⁹ years - Sun passes through helium-burning horizontal branch and asymptotic
giant branch phases, losing a total of ~30% of its mass in all post-main sequence phases.
Asymptotic giant branch phase ends with the ejection of a planetary nebula, leaving the
core of the Sun behind as a white dwarf.
The Helix Nebula Credit: NASA, ESA, and C.R. O'Dell
Martin Crow
Crayford Manor House Astronomical Society
The life cycle of the Sun
>12 x 10⁹ years - The white dwarf Sun, no longer producing energy, begins to cool and
dim continuously; this continues for trillions of years, eventually reaching a black dwarf
state.
~ 10 x 1015 years - Sun cools to 5 K. Gravity of passing stars detaches planets from orbits.
Solar System ceases to exist.
Martin Crow
Crayford Manor House Astronomical Society
About the Sun
Distance – 1.496 x 10⁸ km or 8.32 light minutes.
Visual brightness – mag -26.74
Diameter – 1.392 x 10⁶ km or 109 x Earth
Mass – 1.989 x 10³⁰ kg or 333,000 x Earth
Surface temperature – 5778 K (5505° C)
75% of the Sun is Hydrogen and nearly all of the
rest is Helium.
The Sun accounts for 99.86% of the mass of the
Solar system.
Martin Crow
Crayford Manor House Astronomical Society
About the Sun
The centre of mass of the solar system (barycentre) is not at the middle of the Sun.
Martin Crow
Crayford Manor House Astronomical Society
About the Sun
The Sun does not rotate as a solid object.
Martin Crow
Crayford Manor House Astronomical Society
The structure of the Sun.
Martin Crow
Crayford Manor House Astronomical Society
The structure of the Sun.
Martin Crow
Crayford Manor House Astronomical Society
Granulation
Martin Crow
Crayford Manor House Astronomical Society
Photosphere including sunspot
with plages
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Chromosphere and prominence
Martin Crow
Crayford Manor House Astronomical Society
Filament
Martin Crow
Crayford Manor House Astronomical Society
Chromosphere, spicules and sunspot
Martin Crow
Crayford Manor House Astronomical Society
The Solar cycle
Sunspot polarity reverses
with each cycle.
Martin Crow
Crayford Manor House Astronomical Society
Corona - the solar wind
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society
Martin Crow
Crayford Manor House Astronomical Society