September 12, 2017: Our Sun

Let me just start out by saying that this ISN’T a post about the recent eclipse.  But it’s been inspired by the eclipse.  This is a post all about our glorious sun!

I’ve become a lecturer at the Public Nights at my astroclub, the Denver Astronomical Society, and gave my first lecture last week.  This is different from our monthly Open Houses.  At the Open Houses, a couple dozen members bring their scopes out to Chamberlin Observatory and line them up on the lawn in front.  We also throw open the doors to the Observatory, and hundreds of people line up to have a quick look through the big scope inside.  That happens once a month, around the first quarter moon.

By contrast, Public Nights are twice a week.  We take small groups of about 20 or 30 or so – who have signed up in advance at the DAS website – on up to the 1894 20″ Clark refractor in the dome and show them a few things in the sky, instead of just one, and at a more leisurely pace.

Before showing them the scope, we also give them a lecture.  The lecture is either about 25 minutes long, to give the telescope operators time to check the sky, select targets, open the dome, and set up and point the scope.  If it’s cloudy, the lecture is 55 minutes long; we then give them a tour of the Observatory and scope, and they get to come back on another night for free to get their look through the scope.  The days of the month that we do this, about 8-9 times a month or so, are divided into different teams, because we’re all volunteers, and that’s a lot of time each month.  I’m on Seal Team Six.  When we’re not out killing Somali pirates on the high seas, we’re showing the public the skies.  And trying to edumacate them, too.

The lectures are on various topics, whatever the individual lecturer has prepared – it’s a Powerpoint presentation.  We’re all amateurs, but we do the best we can.  The eclipse inspired me to learn more about, and lecture on, the sun.  I spent a solid month reading up on Old Sol.

I mean, how often do you really, REALLY think about the sun?  We only look at thousands of suns all the time when we look at open clusters, globular clusters, double stars.  We look at dead suns when we look at planetary nebula; we look at the birth of suns when we look at diffuse nebula. But do we ever really think about all those suns, what their deal is, how they work?  After all, the only sun we ever get to study up close and personal is our own, right here in our neighborhood.  Every other star we ever see is too far away – light years away – to do much science on them.

The only chance we ever get to study how any of those other stars work is by studying how our own star works.  

I start off the lecture by going through some basic facts about the sun:

  • It is 4.5 billion years old, 93 million miles away, and 865,000 miles wide
  • That’s 109 earths wide, and it can hold 1.3 million earths inside
  • The sun is the mass of 333,000 earths; 99.8% of the entire solar system’s mass
  • Its energy is the ultimate source of power for everything on earth
  • It is a gigantic ball of hydrogen (75%) and helium plasma (25%)
  • The temperature at the core is 15 million degrees Kelvin
  • The pressure at the core is 250 billion earth atmospheres
  • It also has trace amounts (<0.1%) of other elements:  C, O, N, Si, Mg, Ne, Fe
  • It is halfway through its life, and will “die” in another 5 billion years

I talk about how the sun makes energy through thermonuclear fusion, the same as hydrogen bombs.  Through a process called the proton-proton chain, under the incredible pressures and temperatures at the core of the sun, four hydrogen atoms are fused into one helium atom.  A hydrogen atom has an atomic mass unit of 1.0078.  Four of them weigh 4.0312.  But one atom of helium weighs 4.0026.  That means there’s 0.0286 atomic mass units that have gone missing with each fusion.

Or have they?  Fusion has actually converted that missing mass into energy, by Einstein’s famous formula, E = mc².  This means that the energy (e) from that tiny atomic mass (m) is multiplied by the speed of light (c) squared.  As you know, the speed of light is an absolutely ENORMOUS number – 186,282 miles per second, almost 6,000,000,000,000 (that’s six trillion) miles per year.  And that number is squared.  

The amount of energy from converting just 1kg of hydrogen into helium could power the US for two weeks.  The sun converts 700 million tons of hydrogen into 695 million tons of helium every second.  The “missing” 5 million tons of mass are converted into energy.  That’s ONE MILLION times the energy used by the entire planet in a full year.     

The energy is carried out of the core by photons – little packets of light.  Or, to be more accurate, by electomagnetic radiation, spread across the entire spectrum – gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves.  The photons initially produced by the fusion are extremely energetic, and fall into the gamma ray part of the spectrum.  The photons travel at the speed of light, as they always do, regardless of wavelength.  Because of the density of matter in the sun, they travel only a few inches, if that, before smacking into an atomic particle and being absorbed.  However, the photon is almost instantly emitted, at a slightly lower energy level.  This goes on over and over again – re-absorption, and re-emission, lather, rinse, repeat.

The photons get bounced around a lot.  As a result, they take what is called “a random walk” around the interior of the sun in a section of the interior called the radiative zone, named that way because the photons are being absorbed and emitted throughout the zone.  They move here and there, but not in a straight line towards the surface.  It takes almost 200,000 years for the photons to make it about 200,000 miles outward from the core, through the radiative zone, to the convective zone.  It then takes only 10 days or so to get through the cooler (only 300,000 degrees!) and less dense convective zone, simply being carried upwards by the heated hydrogen plasma.  Take a look at this convection near a sunspot:  

The granulation on the surface of the sun, called the photosphere, is caused by convection.  This is just like how oatmeal bubbles rise up to the surface of a pot on your stove.  The heat makes it rise, and then it cools and sinks back down.  By the way, each of those “little” granulations in that video is about the size of Texas.

After bouncing around inside the sun for about 200,000 years and 10 days, it takes the photons only 8 ½ minutes to get from the surface of the sun to the earth, 93 million miles away.  That’s the speed of light, my friends.  

Most important in this long litany of facts about the sun is that it has a differential rotation.  Because the sun is a giant ball of gas, the sun’s takes about 25-26 days to make one complete rotation at the equator, and about 36 days at the poles.  The reason this is important is that the sun is actually not a giant ball of gas.  It’s really a giant ball of plasma.

When exposed to high temperatures and pressures, gas becomes plasma, the fourth state of matter after solid, liquid, and gas.  The electrons get stripped away from the atoms, leaving charged particles behind.  Because the particles are charged, they create a magnetic field.  Remember in high school science class, wrapping a wire around an iron rod, connecting the two ends of the wire to a battery, and making your own electromagnet?  Because the sun is nothing but charged particles, the sun is like that everywhere, all the time.

And because the sun is rotating at different rates in different places, the magnetic field lines in one location can’t keep up with those in a faster location.  The magnetic field lines get stretched.  And stretched some more.  And they keep on getting stretched.  Some of these stretched magnetic field lines poke out through the surface of the sun, and take some plasma with them.  These are called prominences.  These are fiery loops of plasma, following the magnetic field lines, arcing above the surface of the sun, and then coming back down to the surface.  If you have an H-alpha scope, you should be able to spot some prominences.  During the eclipse, I looked at the sun through a regular white light telescope and saw a few prominences leaping off the edge of the sun.

Here is some footage taken by the NASA’s Solar Dynamics Observatory of a prominence.   Although this looks like it was taken in H-alpha, it was actually taken in the extreme ultraviolet.  It’s referred to here as coronal rain.  Each second of the footage is actually six minutes; meaning one minute of the video is six hours.  Take four minutes and watch this video in fullscreen HD, and tell me it isn’t the most gorgeous thing you’ve ever seen:

When those magnetic field lines finally get stretched too far, they break.  When they break, the enormous amounts of potential energy stored in them is released in an instant, and the sun emits flares and coronal mass ejections.  A CME is a giant cloudlike mass of millions of tons of plasma that is expelled violently from the sun at well over a million miles an hour. This mass arrives at earth’s orbit in one to three days.  If earth is nearby, the CME interacts with earth’s magnetic field.  This causes increased auroral activity, allowing the aurora to be seen far further south than usual.  It is also extremely dangerous to satellites in orbit and power grids on the ground.  Watch this SDO footage of a CME:  

 


You may be asking yourself, “Yeah, yeah, that’s neat and all, but so what?  How does all this solar stuff affect me?”  

The sun creates what’s called space weather in the solar system, both in terms of the everyday solar wind and CMEs.  The solar wind starts out as the lovely corona we saw during the eclipse, and continues out into the solar system for billions of miles in all directions outward from the sun.  The solar wind – and a CME – is plasma:  streams of charged particles.  The earth’s magnetic field generally protects us from the effects of this, but sometimes the particles are so energetic that they can get through.

Because they’re charged particles, they effect anything that uses electricity.  Just like running an electric charge through a wire will create a magnetic field, a magnetic field of charged particles will induce a charge in electric wiring and circuitry.  The plasma from the CME induces a charge in the wiring/circuitry which can exceed what it can handle.   This includes satellites – whose electronics can get overloaded and fried.  This also includes power grids – whose wires also experience these induced charges, causing them to get overloaded with charge, burning out transformers, and leading to blackouts.  

This happened in 1859.  Well, not blackouts, because Edison wouldn’t invent the electric light bulb for another twenty years.  But on the morning of September 1, 1859, British astronomer Richard Carrington saw a huge increase in sunspot activity on the sun, and then a sudden flare.

That night, auroras were seen as far south as Cuba, Hawaii, and sub-Saharan Africa.  The aurora over the Rockies were so bright that the glow woke gold miners, who began preparing breakfast because they thought dawn was breaking. People in the northeast could read a newspaper by the aurora’s light.

Telegraph systems all over Europe and North America failed because of the induced current that flowed through them and overloaded them.  In some cases, these overloads started fires; they also gave telegraph operators electric shocks.  There was so much induced current running through the wires that some telegraph operators could continue to send and receive messages despite having disconnected their power supplies.

Ah, that’s ancient history.  Something like that would never happen now.

Well, think again.  It happened in Quebec in 1989 and in Malmo, Sweden in 2003.   A particularly large CME hit the earth in the middle of the night in March, 1989.  As a result, aurora were seen as far south as Texas and Florida.  More importantly, the entire province of Quebec lost power for 9 hours as its electrical grid was overloaded from the induced charge, leaving almost 7 million people without power.  

If you’re thinking, “This only effects people who live way up north, not me,” well, not only did this impact Quebec, but because Quebec is a net exporter of hydropower, it impacted New England and the Northeast as well.  When the hydropower supply crashed, they had to find alternate sources of power during that period, straining their grid as well.  Something like this can easily have a ripple effect throughout the grid, just as an overload in Ohio caused a blackout that took out the entire northeast in 2003, effecting 55 million people.  Fortunately, the Quebec blackout occurred in the middle of the night when there was plenty of spare generating capacity to take up the slack.  

If you’re thinking, “Ah, 1989, that’s practically ancient history!  Surely we’ve upgraded the electrical grid since then!”  Well, you’d be wrong again.  The nationwide high-voltage grid, originally built in the thirties, forties, and fifties, HAS NOT been upgraded over time to protect it from CMEs.  It would cost tens of billions of dollars to do so.  In October, 2003, the city of Malmo, Sweden experienced a similar blackout after a CME hit, leaving them without power for over an hour. Satellites were also damaged.  

The video above showed the CME of 2012.  Solar astronomers estimate that the 2012 CME was of about the same magnitude as the 1859 solar storm.  As you saw, the 2012 CME was not aimed directly at the earth; fortunately, it flew off to the side.  Lloyd’s of London estimates that a similar event as the 1859 solar storm, occurring today, directed at earth, would inflict 1 to 2 TRILLION dollars in damage to electrical equipment and systems.  

All of modern life is based on such systems – and they would all be fried to a crisp by such a CME.  It would take years to recover.  Our modern economy, our entire modern way of life, would be lost.  Think about that the next time you’re standing outside on a bright sunny day!  

My lecture only scratches the surface on some of what I consider to be the more interesting aspects of our sun.  Notice what I’ve left out – the sun’s birth, evolution, and death.  There’s just too much information about the sun to pack into even a 55-minute lecture.  Topics like those will have to wait for another lecture.

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3 thoughts on “September 12, 2017: Our Sun

  1. Another great one Jon!

    On Tue, Sep 12, 2017 at 6:51 PM Light-Polluted Astronomy wrote:

    > Jon posted: “Let me just start out by saying that this ISN’T a post about > the recent eclipse. But it’s been inspired by the eclipse. This is a post > all about our glorious sun! I’ve become a lecturer at the Public Nights at > my astroclub, the Denver Astronomical Soci” >

    Liked by 1 person

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