Popular Misconceptions in Astronomy
Instructions: MISCONCEPTIONS are in capital letters followed by a colon.
Scientific explanations or discussions follow.
-- PLANETS --
MISCONCEPTION—JUPITER WILL BECOME A STAR ONE DAY:
TRUTH: Based upon current theories of stellar formation, Jupiter would need about 70 times its mass to evolve into a star. Put in another way, about 70 Jupiter-like planets would have to be dumped into Jupiter in order for there to be sufficient material to create the internal temperatures and compression necessary to allow thermonuclear fusion to take place. Jupiter is destined to continue slowly cooling like it has been for the past five billion years since its formation. Incidentally, the least massive of stars, about 70 times the mass of Jupiter, would have a diameter slightly smaller than Jupiter. The Arthur C. Clark film, 2010, didn’t quite get it right. In that movie, Jupiter went stellar.
MISCONCEPTION—JUPITER, SATURN, URANUS, AND NEPTUNE ARE GAS GIANTS:
TRUTH: The Jovian, or Jupiter-like planets, which also include Saturn, Uranus, and Neptune, have extensive gaseous atmospheres which eventually become compressed into liquid oceans of primarily hydrogen and helium. As pressures increase, hydrogen is even forced into a metallic state which is the basis for creating the strong magnetic fields which surround all four Jovian worlds. It would be more appropriate to describe these planets as liquid worlds with extensive gaseous atmospheres.
-- THE SUN --
MISCONCEPTION—IT IS DANGEROUS TO LOOK AT THE SUN OR THE MOON DURING ANY ECLIPSE:
TRUTH: The word “eclipse” means to hide. During a solar eclipse, part or all of the sun is hidden by the moon. In a lunar eclipse the moon hides in the shadow of the Earth. A solar eclipse is dangerous to view when any portion of the sun’s light-emitting surface, called the photosphere, is visible to the eye. However, during the totality segment of any total solar eclipse, the moon’s greater apparent size hides the sun’s photosphere completely. This allows for visual inspection of the eclipsed sun with the unprotected eye or through telescopes or binoculars with the filters removed. The totality portion of an eclipse ends so rapidly that observers need to exercise extreme caution when even the smallest amount of sunlight again becomes visible. The dangers of viewing the sun when no eclipse is occurring are even greater than when viewing a partially eclipsed sun because the entire disk of the sun is visible. However, more people are apt to want to view the sun during the partial phases of a solar eclipse because interest in observing the eclipsed sun is very high. On the other hand, viewing the moon with telescopes or binoculars during any portion of a lunar eclipse poses no danger whatsoever. Observing the full moon is safe, since its brightness is about 0.0000023 that of the sun’s brightness. We do it all the time. Therefore, viewing the full moon as it enters the Earth’s shadow and become substantially dimmer is equally safe.
MISCONCEPTION—THE SUN WILL EXPLODE AT THE END OF ITS LIFETIME:
TRUTH: sun may be considered to be a typical star, five billion years of age, about midway through its life. At present it is converting hydrogen into helium in its core and will continue to do so for the next five billion years. As fusion continues, the accumulation of helium ash in the sun’s interior will cause the core to contract slowly and increase in temperature, thus boosting the amount of hydrogen burning occurring in the core. This will cause the sun to become slightly larger, cooler, and more luminous. Near the end of its existence as a hydrogen burning star, nucleosynthesis will cease in the core and shift to a thin shell surrounding the core, where hydrogen fusion will continue to supply the core with ever more helium ash. This additional material will continue to shrink the core making it even hotter, and rapidly expand the sun’s diameter as shell hydrogen burning accelerates. The sun will become a red giant star. About this time the sun will probably become variable, due to instabilities generated in its thin hydrogen burning shell. These instabilities will increase in intensity, eventually causing the sun to shed its outer layers to reveal its inert, hot interior composed primarily of degenerate helium gas. At this point the sun will be called a white dwarf star. Its diameter will be reduced to approximately 10,000 miles. Stars that go supernova are considerably more massive than the sun. The threshold is about nine solar masses, meaning that the star which goes supernova must possess about nine times the amount of hydrogen which the sun currently contains.
MISCONCEPTION—SUNSPOTS ARE STORMS ON THE SUN:
TRUTH: In one way sunspots are storms, but not in the traditional sense of peoples’ conceptions of storms. They have nothing to do with any meteorological effects which may be occurring on the sun. Sunspots are very quiet regions on the sun’s “surface,” which is known as the photosphere. Here the convective mechanism for releasing the sun’s heat has been dampened by an intensification of the sun’s magnetic field in that region. The area called the sunspot has become cooler, thus making it appear darker against the brighter, hotter photosphere. The intense magnetic field causes the outward flow of plasma in the sunspot’s vicinity to slow, thus causing the cooling and darkening of the area. In a very real sense, the high magnetic fields associated with spots could be called magnetic storms. It is in the vicinity of sunspots that other magnetically induced phenomena occur, such as the arcuate filaments of plasma that form in the sun’s corona, known as prominences, or extremely energetic flares which can produce intense auroral displays on Earth and disrupt the transmission of electricity by inducing direct current flows in transmission lines.
-- THE STARS AND CONSTELLATIONS --
MISCONCEPTION—POLARIS, THE NORTH STAR, IS THE BRIGHTEST STAR OF THE NIGHTTIME SKY:
TRUTH: Not so and not even close... It actually ranks as the 48th brightest star in the heavens, if the sun is included. Polaris, however, is relatively easy to spot even from an urban location, but its real importance stems from the fact that its position is near the place where the Earth’s axis intersects the heavens. As a result of the Earth’s rotation, the heavens to appear to wheel around a point in the sky which during the present era is very near to this star, making it an excellent marker to determine the direction north. The brightest star of the nighttime sky is Sirius, the Dog Star. Follow the three stars of Orion’s belt downward to this gem of the winter sky, then compare it with Polaris which can be found by following the pointer stars of the Big Dipper to the first relatively bright star that is encountered.
DEMONSTRATION: Lean your head all the way back and focus on the part of the ceiling which is directly over your head. You are now the Earth and your axis is passing up between your eyes. Rotate slowly and notice how the marks on the ceiling seem to circle the point which is directly over your head. In a similar fashion the two locations in the sky where the axis of the Earth points will be the pivots around which the sky circles.
MISCONCEPTION—POLARIS HAS ALWAYS BEEN THE NORTH STAR:
TRUTH: The Earth’s axis wobbles like a top, completing one cycle during a period of 25,700 years. This causes a slow change in the direction where the axis points. At present, the axis intersects the sky at a position that is very near to the star Polaris. Five thousand years ago when the Great Pyramid at Giza, and Stonehenge I were being constructed, the Earth’s axis pointed close to the star Thuban, in Draco the Dragon. About 12,000 years into the future the Earth’s axis will be directed towards the star Vega in the constellation of Lyra the Harp. This was the star that Ellie Arroway (Jody Foster) discovered to be the source of the extraterrestrial message in the movie Contact.
MISCONCEPTION—THE BIG DIPPER IS A CONSTELLATION:
TRUTH: The star pattern known by the name of the “Big Dipper” is most familiar to Americans. It is called the Plow in England, the Wagon in Germany, and the Steel Pan in the Netherlands. During the Civil War, slaves escaping the South through the network of safe havens, known as the Underground Railroad, referred to the Dipper as the Drinking Gourd. Its location is always found in the northern part of the sky, so the Drinking Gourd made an easy marker to follow as slaves made their way north to freedom. The Dipper is really an asterism, a group of stars which form a picture, but which has not been officially recognized by professional astronomers as a constellation. Ursa Major, the Great Bear, is the official name of the star pattern which Americans refer to as the Big Dipper. The Great Bear is difficult to see from urban locations, so the Big Dipper has continued to remain more popular in this country than its official version. Other familiar asterisms are the Little Dipper, the Pleiades and the Hyades found in Taurus the Bull, Orion the Hunter’s three belt stars, the Great Square of Pegasus the Flying Horse, the Great Summer Triangle, composed of the brightest stars of the constellations of Lyra, Aquila, and Cygnus, the Northern Cross, which is part of Cygnus the Swan, and the Keystone which comprises the body of Hercules the Strongman.
MISCONCEPTION—CONSTELLATIONS ARE GROUPINGS OF STARS IN THE SKY WHICH FORM PICTURES:
TRUTH: Constellations are very much like states with official borders. Within these boundaries certain stars may be found to form a picture, but all stars within the boundary are considered members of the constellation. There is no official strategy with regards to how the stars of a particular constellation are to be connected to form a picture. Eighty-eight constellation boundaries encompassing the entire sky were sanctioned in 1928 by the International Astronomical Union, a world-wide congress of professional astronomers which deal with such matters. Constellations are useful to modern astronomers because they allow for an approximate location of all objects in the sky.
MISCONCEPTION—ALPHA CENTAURI IS THE CLOSEST STAR TO THE SUN:
TRUTH: The Alpha Centauri system is the closest stellar system to our sun. What we perceive as Alpha, is really a double star with its two components, 1 and 2, separated by about 17 seconds of arc. About 2.2 degrees away from Alpha lies very faint Proxima Centauri, also thought to be part of the Alpha Centauri system and currently on the sunward side of its orbit. Therefore technically, Proxima is the closest star to our sun. Alpha Centauri 1 and 2 are about 4.39 light years or 25 trillion miles from the sun. Proxima is 0.2 light years closer to the sun (4.19 light years distant) giving it an orbital period around Alpha Centauri of over 1.4 million years.
MISCONCEPTION—STARS ARE BURNING HYDROGEN:
TRUTH: Although it is customary for astronomers to use the words “hydrogen burning” in connection with the energy production inside the cores of stars, nothing could be farther from the truth. Combustion is a chemical process which releases energy. The elements which partake in the reaction are not changed in any way because of the reaction, but they are rearranged into different compounds after the combustion process. The “burning” which takes place inside of stars results in the creation of new elements through a process called nucleosynthesis. In the sun, four hydrogen protons are eventually fused into one helium nucleus. The process is much more complicated, but the concept is a valid one. In the fusion process some mass is converted into energy as helium atoms are created. This is the mechanism which powers most of the stars that we see in the sky. The sun’s mass consumption is about five tons of matter per second to produce the energy we observe coming from its surface.
-- SPACEFLIGHT --
MISCONCEPTION—THE FIRST AMERICAN IN SPACE WAS JOHN GLENN:
TRUTH: Alan Shepard rode his Freedom 7 capsule into a suborbital flight to become the first American in space on May 5, 1961. Shepard later walked on the moon during the Apollo 14 mission in late January 1971. He died on July 21, 1998 from cancer. John H. Glenn, Jr. was the third American (fifth human) to venture into space, but the first American sent into Earth orbit. Glenn flew on Mercury-6 (February 20, 1962) and more recently on the Space Shuttle Discovery, STS-95 (October 29 to November 7, 1998). Glenn logged over 218 hours in space. Although Shepard was the first American in space and Glenn the first American to orbit the Earth, the US was upstaged by Russian, Yuri A. Gagarin, on both counts. Gagarin, the first human to be successfully returned from space, rode aboard Vostok I on April 12, 1961. He also was the first human to orbit the Earth during the same mission which lasted 1 hour, 48 minutes. Gagarin died in 1968. Glenn was still alive as of July 2008.
MISCONCEPTION—THE SPACE SHUTTLE CHALLENGER EXPLODED:
TRUTH: From the video footage it may have looked like an explosion in the traditional sense, but there was little in the way of combustion (fire). What occurred was a failure of an O-ring on one of the two (right side) solid fuel booster rockets. The O-rings were the rubber seals used at the solid rocket booster joints. Their function was to prevent the escape of hot gases being created during the burn of the solid fuel rockets. After the Challenger accident, it was discovered that the O-rings material did not expand properly if the temperature was near freezing. The temperature on the morning of the launch was 32o F. When launch occurred, escaping gases from a malfunctioning O-ring heated and eventually ruptured the huge liquid oxygen fuel tank on which the shuttle rides during its ascent. The O-ring leak was visible in launch photos as a small flicker. At 72 seconds after liftoff, the lower strut linking the right booster to the external tank broke apart. The booster pivoted around its upper attachment, causing aerodynamic forces to disintegrate the shuttle rapidly and compromise the liquid hydrogen and oxygen compartments of the external fuel tank, sending all seven crew members to their deaths. The astronauts were probably alive, but most likely unconscious when the intact crew cabin impacted into the Atlantic Ocean two minutes 45 seconds later.
-- GRAVITY AND RELATIVITY --
MISCONCEPTION—ISAAC NEWTON INVENTED GRAVITY:
TRUTH: Isaac Newton (1642-1727), the great English physicist, never invented gravity. Gravity was one of the four fundamental forces created during the birth of the universe 13.7 billion years ago. It is a condition of any object which possesses mass. Newton was the first person to explain accurately how the force of gravity acted upon matter within our universe. Standing on the shoulders of such eminent scientists as Galileo and Kepler, Newton postulated that the force of attraction between two objects was directly proportional to their masses (the quantity of matter which they contained) and inversely proportional to the square of the distances between these bodies. Mythology recounts that Newton’s inspiration for his idea was triggered by observing an apple fall from a tree at his home in Woolsthorp, England. He pondered the question as to whether the same force of gravity that accelerated the apple towards the ground was responsible for holding the moon in its orbit around the Earth. His investigations led Newton to the conclusion that they were the same force, and the unification of the heavens and the Earth was the result.
MISCONCEPTION—SPACE, MASS, AND TIME ARE CONSTANTS:
TRUTH: Space (length, width, and height), mass, and time are actually variables. The only constant in the universe is the speed of light in a vacuum. Traveling at speeds near that of light (186,282.397 miles/second) would cause our perceptions of the universe to alter with respect to space and time. Specifically, a detected object traveling close to the speed of light would appear to be compressed in the direction of motion. Clocks in that object would appear to be keeping time at a slower pace than clocks in the frame of reference of the observer. The mass of the perceived object would also be increased.
MISCONCEPTION—IT IS POSSIBLE TO TRAVEL FASTER THAN THE SPEED OF LIGHT:
TRUTH: Only the limitlessness of the human mind can imagine an object traveling as fast, or faster than the speed of light. For matter bounded by the laws of physics in this universe, an increase in speed results in an increase in the kinetic energy of the body being accelerated. Since mass and energy are the same (E = mc2), some of the energy is converted into increasing the mass of the object. At the speed of light, the mass of an object becomes infinite. If all of the matter in this universe were converted into energy, there still would not be enough force available to accelerate the smallest amount of matter to the speed of light. The mass-energy equivalence of this universe is thought to be conserved or remains the same.
MISCONCEPTION—A LIGHT YEAR IS A MEASUREMENT OF TIME:
TRUTH: A light year is a standard astronomical yardstick for measuring the distances between objects outside of our solar system. One light year represents the distance that light travels during a period of one year. This distance is equivalent to approximately 5.8 trillion miles.
-- MISCELLANEOUS --
MISCONCEPTION—COPERNICUS WAS THE FIRST PERSON TO GIVE US THE CONCEPT OF A SUN-CENTERED UNIVERSE:
TRUTH: Actually, it was the Greek, Heracleides (388 BC-315 BC) and later, Aristarchus of Samos (310 BC-230 BC) who first entertained the heliocentric notion that a rotating Earth could be in revolution around the sun. The concept lost favor to the geocentric model of the universe which was the synthesis of hundreds of years of inductive reasoning practiced by Plato, Eudoxus, Aristotle, Hipparchus, Ptolemy, and others. The Greeks never intended their ideas to represent reality, but by the time of the Renaissance, Ptolemy’s geocentric model was thought to portray accurately the true order of the cosmos. Copernicus realized the inexactness of the cumbersome geocentric models to predict accurately planetary positions and borrowed ideas from earlier Greeks to simplify the system into a heliocentric model. Copernicus computed the mathematical details of this system to show how the revolutions of the planets around the sun could account for the observations of planetary motion witnessed in the sky. Ironically, after Copernicus completed publication of his theory in 1543, under the title of De Revolutionibus Orbium Coelestium, (On the Revolutions of the Heavenly Spheres), astronomers could not decide by observation which theory produced the better fit. It appears that the simplicity of the Copernicus’s theory began to win converts, particularly in the Protestant countries of Europe. The dilemma of which theory was superior was finally settled by Johannes Kepler in 1609 when he used the Copernican model to solve correctly for the changes which Tycho Brahe had observed in the positional shifts of the planet Mars. When Kepler used ellipses to explain planetary motions, Tycho’s data could be made to fit precisely with the orbital characteristics of Mars. In short order, the reinvented heliocentric theory as proposed by Copernicus became one of the cornerstones of Renaissance thought.
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