THE SOUTHWORTH PLANETARIUM
207-780-4249       www.usm.maine.edu/planet
70 Falmouth Street  Portland, Maine 04103
43.6667° N,                    70.2667° W
Founded January 1970
             "The Winter Solstice occurs at 11:48 p.m.tonight.  E-mail
us if you want a wake up call so you can experience it for yourself."


THE DAILY ASTRONOMER
Monday, December 21, 2015
Lunar Golf and Stellar Gold

[Do you have astronomy questions?   Send them to [log in to unmask]
We will include them in future articles.  Just let us know if you
would like us to attribute the question to you, or if you would prefer
to remain anonymous.   As you can tell from today's article,
pseudonyms are also allowed.]

Someday, when we're feeling ambitious, we'll up-end Pandora's Jar and
contend with the shower of parchment pieces that flutter onto the star
dome carpet in one fell swoop.   For now, we'll extract the questions
one by one.  During our hiatus, the jar's content increased
dramatically. (The staff mathematician insists that we don't use the
adjective "exponentially," unless, of course, we're referring to an
exponential function.   We can do that...ah, we think..)

Today, Pandora takes us to the moon and to the heart of a massive star.
What better way to begin a winter!




"How far did Alan Shepherd's golf ball so when he hit it on the moon?
Could somebody theoretically hit a ball hard enough to make it leave
the moon altogether?"
                           -Anonymous,  somewhere on Earth

Hello, Earth!
Many people know that Apollo 14 astronaut Alan Shepherd hit a golf
ball on the moon.   In so doing, he became the first person to ever
play golf on another world.    Having hit the golf ball in the moon's
low gravity environment, the ball likely remained above the surface
for more than a minute.  During that time, the ball might have
traveled more than two miles.  Nobody actually calculated the precise
distance the ball traveled.   Physicists have estimated the ball's
traveling distance based on their knowledge of the environment and by
making assumptions about the force  Shepherd applied to the ball on
impact and the angle with which he struck it.     They estimate it
might have landed between two and two and a half miles from the impact
point.     Text book physics problems provide one with all the
information required to solve the problems.   In real life situations,
much of the information is unknown and therefore answers are
predicated on ms-informed presumptions   We cannot truly know
precisely how far Shepherd's ball traveled.   However, he undoubtedly
holds the record for the longest drive in history, far surpassing Mike
Austin's highly impressive world record 515 yard drive.*

One can make a golf ball travel for quite a distance on the moon for
two reasons.  First, the moon's gravity is only one sixth as strong as
Earth's.    So if you strike a golf ball up at an angle, it will
describe a parabolic arc ascending to a high point, at which its
vertical velocity is momentarily zero, and then descending back down
to the surface.    On Earth, a golf ball doesn't remain in the air for
long as the planet's gravity quickly pulls it back down.     On the
moon, a golf ball will travel much farther because the comparatively
weak surface gravity will accelerate it back to the surface more
slowly.     During that time, the ball travels with a constant
horizontal velocity, at least in theory.

On Earth, however, air resistance impedes the ball's travel.   As this
resistance is proportional to the velocity squared, the faster a ball
moves, the greater the impeding resistance becomes.      The second
reason a golf ball travels farther on the moon is its lack of
atmosphere.   There is no air resistance on the moon to slow the
ball's travel.    The faster one hits a golf ball, the farther it
moves as no fluid resists it.

As for making a ball leaving the moon altogether, well, a human truly
couldn't.    The moon's gravity is weaker than Earth's, but still
quite strong.    The moon's escape velocity is about 5,310 miles per
hour!    In order to escape its gravity field, an object would have to
at least move at this velocity.   Not even the strongest human could
launch a golf ball at such a speed.    One can make a golf ball travel
for a couple miles on the moon, but the ball would always end up
landing back on its surface.


"On television, somebody said that if you have a ring of gold, you
have something made in an exploding star.   Could you explain?   Also,
I hope you appreciate my pseudonym.  It seemed fitting."
                             -Gollum,


Well, Gollum,

Almost all of the elements are forged inside stars.   The early
material Universe consisted primarily of hydrogen and helium.  The
first generation of stars, like the stars we have today, generated
energy through thermonuclear fusion reactions.   During these fusion
processes, light elements are forged to create heavier elements.  In
the process, some of the initial matter is transmuted into energy
because, as Relativity tells us, matter is just energy in a different
form.      The most massive stars can proceed through a series of
fusion reactions. At first, hydrogen is converted into helium.   After
exhausting the core hydrogen stores, the star will then fuse helium to
create carbon.     Provided the star is sufficiently massive, the star
will then fuse carbon to make oxygen along with a series of other
reactions.   Once the star reaches the iron stage, the reactions stop.
   Fusing iron is an endothermic process, meaning that the star has to
invest more energy in fusing iron than the fusion reactions would
impart back into the star.      The balance between the compressing
gravity and expanding energy pressure, called 'hydrostatic
equilibrium- is violently disrupted.   The outer layers collapse onto
the core, precipitating an extremely powerful explosion called a
"supernova."     The supernova provides the ample energies necessary
to fuse all the elements heavier than iron, including the all too
precious gold.

So, the person on the television was correct:  gold can only be
manufactured in exploding stars.   Then again, we, ourselves, are here
because an ancient star exploded, thereby imparting the heavy elements
necessary for life to have developed on this planet.



*Mike Austin achieved this record in 1974, whereas Alan Shepherd hit
his golf ball in 1971.   So, to be accurate, since Shepherd hit his
ball first, one should say that Austin's attempt to break Shepherd's
record was unsuccessful.    Of course, Alan Shepherd enjoyed the
advantage of having played golf on a world with 1/6th Earth's surface
gravity.