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  • Writer's pictureMatt Russell

The Sun

Chaos is but unperceived order; it is a word indicating the limitations of the human mind and the paucity of observational facts. The words ‘chaos,’ ‘accidental,’ ‘chance,’ ‘unpredictable,’ are conveniences behind which we hide our ignorance.

Harlow Shapley (November 2, 1885 – October 20, 1972)

Harlow Shapley

born on a farm in Nashville, Missouri,

  • Shapley went to study journalism at the University of Missouri. When he learned that the opening of the School of Journalism had been postponed for a year

  • He decided to study the first subject he came across in the course directory.Rejecting Archaeology, which Shapley later claimed he couldn't pronounce, he chose the next subject, Astronomy

  • Shapley's 1914 PhD thesis on the orbits of 90 eclipsing binaries virtually created in one stroke a new branch of double-star astronomy.

  • He was part of the great debate; Curtis took the side that the spiral nebulae are 'island universes' far outside our own Milky Way

  • In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone

  • Shapley married Martha Betz, one of his five children, Lloyd, won a Nobel Prize in Economics in 2012

  • The Shapley-Ames Catalog of Bright Galaxies is a catalog of galaxies published in 1932 that includes observations of 1249 objects brighter than 13.2 magnitude

  • The Shapley Supercluster or Shapley Concentration (SCl 124) is the largest concentration of galaxies in our nearby universe that forms a gravitationally interacting unit, thereby pulling itself together instead of expanding with the universe

The Sun.

How was she born?

About 4.7 Billion years ago a giant cloud of Gas was starting to swirl., Mostly Hydrogen but also some helium and tiny amounts of “metals”, like oxygen 1% , carbon (0.3%), neon (0.2%), and iron (0.2%). Incredibly the Hydrogen and most of the helium would have been made about 9 Billion years earlier in the first 20 seconds of the Universe. The rest of the star stuff came from Stellar nucleosynthesis in an old generation of stars, long extinct. Blown into the universe as the stars shed their skin or exploded as supernovae.

The cloud had started to spin gently from a disturbance, maybe a shock-wave from another dying star or another cataclysm. now that massive cloud had a teeny tiny spin, the system started it’s collapse under gravity, and it started spinning faster and faster (like an ice skater with arms out, pulling her arms in to spin faster and faster)

Over the next 50 million years the gravity pulled and pulled tighter and tighter on this cloud of gas and under this intense pressure it got hotter and hotter and causing the Gas to ionize into a soup of atomic cores, protons and neutrons stripped of their electrons. But as this got hotter still and denser still, some of these cores would smash into one another and cause nuclear Fusion!!

Eventually the energy from this continual nuclear fusion in the dense hydrogen would create sufficient outward pressure to stop gravity pushing ever tighter, we now have a perfect ball of plasma, this is the Sun,

99.86% of the gas cloud was now a huge 696,000 km radius, near perfect, ball of hot Plasma with a nuclear reactor at it’s core. The spinning gas mostly fell into this ball of plasma, but some of the gas formed a disk like the arms of our spinning ice skater little eddies in this disc of dust and gas eventually accreting into the planets. The giant planets taking up 99% of the rest of the material, with EVERYTHING else taking a measly 0.002% of what’s left. (four terrestrial planets, the dwarf planets, moons, asteroids, and comets)

Jupiter is by far the most massive planet in the Solar System. It is approximately 2.5 times more massive than all of the other planets in the Solar System combined but would need to be about 75 times more massive to fuse hydrogen and become a star. But it is big enough that its barycenter with the Sun lies beyond the Sun's surface at 1.068 solar radii from the Sun's center

  • Fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result.

  • This energy, which can take between 10,000 and 170,000 years to escape from its core, is the source of the Sun's light and heat.


  • In about 5 billion years, when hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydro-static equilibrium,

  • the luminosity of the Sun will have nearly doubled, and Earth will receive as much sunlight as Venus receives today

  • Sun will expand into a sub-giant phase and slowly double in size over about half a billion years.

  • It will then expand more rapidly over about half a billion years until it is over two hundred times larger than today and a couple of thousand times more luminous.

  • Bye bye rocky planets.

  • This then starts the red-giant-branch phase where the Sun will spend around a billion years and lose around a third of its mass, the inert helium core surrounded by a shell of hydrogen fusing via the CNO cycle.

  • Then suddenly the degenerate Helium ignites in the helium flash is a very brief thermal runaway nuclear fusion of large quantities of helium into carbon

  • 40% of the Sun’s mass will be converted to carbon in MINUTES!!!

  • Sun shrinks back down to 10 times it’s current size, 50 times the brightness, but slightly cooler, this is the Red Clump phase

  • becomes moderately larger and more luminous over about 100 million years as it continues to burn helium in the core

  • Then a similar process happens as when the hydrogen ran out when the helium runs out, except much faster, larger and brighter.

  • This is the asymptotic-giant-branch phase, and the Sun is alternately burning hydrogen in a shell or helium in a deeper shell

  • After about 20 million years on the early asymptotic giant branch, the Sun becomes increasingly unstable, with rapid mass loss and thermal pulses that increase the size and luminosity for a few hundred years every 100,000 years or so. The thermal pulses become larger each time, with the later pulses pushing the luminosity to as much as 5,000 times the current level and the radius to over 1 AU

  • The post-asymptotic-giant-branch evolution is even faster.

  • The luminosity stays approximately constant as the temperature increases, with the ejected half of the Sun's mass becoming ionised into a planetary nebula as the exposed core reaches 30,000 K.

  • Four thermal pulses are predicted before it completely loses its outer envelope and starts to make a beautiful planetary nebula ….just

  • The final naked core, a white dwarf, will have a temperature of over 100,000 K, and still contains an estimated 54.05% of the Sun's present day mass.

  • The planetary nebula will disperse in about 10,000 years, but the white dwarf will survive for trillions of years before fading to a hypothetical black dwarf.

“What we’ve shown is that the core will be hot enough in five to 10 thousand years after the outer layers have been ejected, and that is quick enough,”Albert Zijlstra of the University of Manchester “The sun is right on the lower limit of being able to form a planetary nebula.”

A couple of Mysteries.

The faint young Sun paradox

The apparent contradiction between observations of liquid water early in Earth's history and the astrophysical expectation that the Sun's output would be only 70 percent as intense during that epoch as it is during the modern epoch.

The issue was raised by astronomers Carl Sagan and George Mullen in 1972.

Explanations of this paradox have taken into account greenhouse effects, astrophysical influences, or a combination of the two.

The unresolved question is how a climate suitable for life was maintained on Earth over the long timescale despite the variable solar output and wide range of terrestrial conditions

Coronal heating problem

The temperature of the photosphere is approximately 6,000 K, whereas the temperature of the corona reaches 1,000,000–2,000,000 K. The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere How the Sun manages this feat remains one of the greatest unanswered questions in astrophysics, astronomers first discovered evidence for this mystery during an eclipse in the 1800s

Hopefully we will have an answer to this problem via the Parker Solar Probe

Parker Solar Probe now holds the record for closest approach to the Sun by a human-made object. The spacecraft passed the current record of 26.55 million miles from the Sun's surface on Oct. 29, 2018, at about 1:04 p.m, the spacecraft will repeatedly break its own records, with a final close approach of 3.83 million miles from the Sun's surface expected in 2024

Parker Solar Probe is also expected to break the record for fastest spacecraft traveling relative to the Sun, 153,454 miles per hour, both previous records set by Helios 2 in April 1976

Parker Solar Probe will sample just-heated particles, removing the uncertainties of a 93-million-mile journey and sending back to Earth the most pristine measurements of the corona ever recorded.

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