Sunshine!
isn't simple. Then again, what is? The astronomical sages have shown
us that even the daintiest thing loitering about the cosmos formed after
a series of highly complex stages. Even if you snip a leaf or a
siphon off a drop of remote pond, you will encounter far more than meets
the eye.
So, in this vein, the astronomer languishes on his vine-entwined gazebo
and gazes into the recession of cloud forms molding and dissolving
against boundless blue. The world awakens to a belated spring and with
it a landscape awash in sunshine: the most pervasive of all
astronomical phenomena. So close and intimate does the Sun seem that it
is difficult to remember it is more than ninety three million miles
away. And, so beloved and adored is Sol amongst all people that many
refuse to accept that it is an astronomical entity.
Today, we shed some light on sunshine. (And, yes, we're the very first people to come up with that witty word play.)
The sunshine that smarts the shoulder and dazzles the irises was once
amongst the greatest mysteries. Its origins, and, by extension, its
longevity, were unknown until the 20th century. Humanity was reliant
upon a fiery sphere of indeterminate composition and duration. We
know now that it took form about five billion years ago and will
continue to issue prodigious amounts of energy for billions of years to
come. We're so confident about the Sun's life span because astronomers
determined that it uses its own material as a fuel source: converting
hydrogen into helium deep within its core. We also know that the Sun
contains enough matter -and therefore sufficient fuel stores- to
continue energy production for aeons to come.
The sunshine that you see left Sol's photosphere about 8.3 minutes ago.
Light travels at about 186,290 miles a second and requires just over
eight minutes to move from the Sun to Earth. Though a 93 million mile
excursion through the unsounded deep might seem exhausting, it's the
easiest part of the trip, at least for the photons comprising sunlight.
The actual odyssey began in the solar core: the nuclear reactor
mentioned in the previous paragraph.
Comprising 1.5% of the Sun's volume, the core is a furious energy
machine: every second, 647 million tons of hydrogen is converted into
millions of tons of helium. A minute percentage is transmuted into
energy.* The Sun's interior is so hot (27 million degrees F; 15
million degrees C) that the protons-positively charged subatomic
particles- move quickly. As they have the same charge, the protons
would repel each other in cooler environs. In the sun's core, they
have so much energy they can fuse together despite the electrostatic
repulsion that would otherwise keep them separated. The hydrogen
turns into helium and energy!
This energy doesn't then just snap out of the Sun and onto Hawaiian
beaches. As soon as the energy emerges, it is almost immediately
absorbed by intervening material. Then, it is eventually re-emitted,
only to be re-absorbed; then re-emitted; re-absorbed, and so on and so
forth and back again. Meanwhile, it is struggling to liberate itself
from the roiling solar inferno. We use an example in the Star Dome
Astronomy class. Imagine that you have to walk to Los Angeles. You
have to walk 16 hours a day and we provide accommodations and
nourishment along the way. How long would the trip be? Perhaps 4 - 6
months? Now, imagine, that you walk back to Portland from Los
Angeles, but this time you stop at every third house and sit in the
living room floor until the owner kicks you out. The problem is that
you have to move in whatever direction the furious owner tosses you.
Though your destination is to the northeast, if you are kicked toward
the southwest, you have to walk toward the SW until you reach the third
house. Your direction will change with every explusion. With this new
complication added, how long would the journey require? Well, forever.
You'll never be in Portland again.
The core energy photons face the same exasperatingly protracted journey
involving innumerable absorptions and re-emissions until they finally go
through the radiative zone and then the outer convective zone before
reaching the uppermost layers and then freedom! This process requires
more than 100,000 years! The sunshine that strikes you everyday is
truly ancient starlight.
Also, the solar photons that hit Earth comprise less than a billionth of
those the Sun produces. The planets receive precious little of the
Sun's energy. Most of those photons scatter through interstellar
space. Few reach extragalactic distances and if an alien astronomer in
Andromeda captures an image of the Milky Way Galaxy, perhaps a
negligible part of the glow will consist of the Sun's contribution.
Sunshine is possible because a few of the Sun's photons strike Earth
soon after their 100,000 year ordeal of emissions and absorptions. One
can look outside on a clear day and almost hear the impacting photons
murmuring, "Oh, not again."
Deep in the Sun's core right now, our star is generating the energy that
will shine down on Earth 100,000 years or so from now. An optimist's
dream: an assurance that we have myriad sunny days not yet experienced.
*Here, we offer a bit more detail for those who crave
scientific satiation. When the astronomer tells you that the Sun
generates energy by converting hydrogen into helium, what does that
actually mean? What is happening: Well, in the Sun, we see a series of reactions called the
"proton-proton chain," which, itself, has three variants. We'll limit
ourselves to the most common sequence, as a means to elucidate the
concept without driving the reader to hopeless despair.
We start with two hydrogen atoms that combine to produce deuterium, a
hydrogen isotope with an extra neutron. This deuterium connects with
another hydrogen atom to make helium-3 (it has two protons, hence the
element changes to helium. Deuterium contains only one proton.
Remember that the proton number determines the element.) Two helium-3
nuclei fuse into a helium-nucleus (two protons; two neutrons) and in so
doing eject two hydrogen nuclei. Energy is released during this
sequence: the energy that eventually becomes sunshine. The gamma photon
is released in the second stage: the collision of deuterium and the
hydrogen nuclei.
Other proton-proton chains have been identified, but hopefully
discussing this one serves to explain that the fusion reactions are not
just one-hit wonders: they happen in stages.
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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
If we could capture all the energy the Sun produces in
one second, we could supply power for the entire world
for 500,000 years!
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Our apologies....yesterday's contribution from the Catacombs
of Infinite Knowledge fell through a space-time conduit and landed
here:
FROM THE CATACOMBS OF INFINITE KNOWLEDGE:
The Whirlpool Galaxy is drawing copious amounts of gaseous material from
its companion galaxy. Consequently, the Whirlpool Galaxy is experiencing
an epoch of prodigious star birth!
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