THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
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43.6667° N    70.2667° W
Founded January 1970
2022-2023: XLIV
Sunrise: 6:43 a.m.
Sunset: 4:11 p.m.
Civil twilight ends: 4:42 p.m.
Sun's host constellation: Libra the Scales
Moon phase: Waning crescent (7% illuminated)
Moonrise: 3:48 a.m.
Moonset: 2:53 p.m.
Julian date: 2459905.21
"If someone smells a flower and says he does not understand, the reply to
him is: there is nothing to understand, it is only a scent. If he persists,
saying: that I know, but what does it all mean? Then one has either to
change the subject, or make it more abstruse by saying that the scent is
the shape which the universal joy takes in the flower."  *Rabindranath
Tagore*

THE DAILY ASTRONOMER
Monday, November 21, 2022
Quantum Sun

Quantum mechanics powers the stars. Seems an absurd statement when one
regards the immense size of stars and the sub-microscopic quantum realm.
However, the Sun and the other stars shine so brightly because of quantum
physical processes.

First, all active stars generate energy through thermonuclear fusion: the
“fusion” of lighter elements to produce heavier ones. For instance, in the
Sun -and in all stars that are proceeding through the first phase of such
reactions- the lightest element hydrogen fuses into helium.


Through a series of steps, hydrogen fuses into helium. The diagram above
shows the steps involved in Branch I of the proton-proton chain sequence,
which is responsible for 83.3% of all energy produced within the Sun’s
core. Image: Image credit: Wikimedia Commons user Borb, via
File:FusionintheSun.svg
- Wikimedia Commons
<https://commons.wikimedia.org/wiki/File:FusionintheSun.svg>.

Thermonuclear fusion generates energy because a minute amount of the
material is transmuted into energy in accordance to the famous physics
equation

Where E = energy; m = mass and c = speed of light.

Although these atoms are unfathomably small -trillions of them could
snuggle within the period at the end of a sentence- and the percentage of
material transmuted into energy is slight (0.7%), 4 × 10^26 W of energy are
produced every single second. To put that value into context, that energy
release is equal to that produced by the detonation of 1 trillion megaton
bombs. If we could somehow capture one second’s worth of energy, we could
fulfill the energy demands of the entire globe for 500,000 years. (The
tricky bit is in the capture.) To create this prodigious energy, 4 x 10^38
protons fuse every second! While one would think that the Sun couldn’t
possibly sustain such reactions over the long term, one should remember
that the Sun consists of 10^57 particles, about 10% of which are located in
the core.

Such fusions occur because the Sun’s core temperatures and pressures are
enormous. Core temperature: 15 million degrees C (27 million F); pressure =
265 billion bar (3.84 trillion pounds per square inch.) The unrelenting
gravitational contraction of the Sun creates these high
temperature-pressure conditions conducive to thermonuclear fusion reactions.

However, none of this should work at all.

When one calculates the number of protons that should fuse under such
conditions, one finds that NONE of them should. Not one…ever! The problem
is that the positively charged protons experience an electrostatic
repulsion because their charges are the same. In fact, as one reduces the
space between protons, this repulsion increases in accordance with the
inverse square law. (One notices the same relation between massive objects
due to their gravitational attraction.) The closer the protons approach
each other, the more they struggle to separate. Although the prevailing
conditions in the core are extreme, they shouldn’t be sufficient to ignite
and sustain thermonuclear fusion reactions. Yet, they are.

The fusion works because the protons exhibit both particle and wave-like
behavior. The proton doesn’t just occupy a specific, rigidly defined
volume. Instead, its location can be described as a probability function:
it could occupy a range of locations. Because of the probability functions
of protons can overlap in regions of high temperature and pressure, they
can fuse. One refers to this phenomenon as *quantum tunneling*.

The protons fuse, incidentally, because the strong nuclear force, the
strongest of all the fundamental physical forces (gravity,
electromagnetism, weak nuclear and strong nuclear) overwhelms the weaker
electrostatic repulsion that would otherwise keep them apart.

The Sun literally shines because of the workings of the eerie,
counterintuitive workings of the quantum realm. The next time you feel the
Sun’s warmth on your face -or, if, like some of us, you harbor pleasant
memories of the Sun’s warmth- remember that it is only possible because of
quantum physics.


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