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.