Popular Misconceptions:

Popular Misconceptions in Astronomy

Instructions: MISCONCEPTIONS are in capital letters followed by a colon.
Scientific explanations or discussions follow.

ASTROLOGY | MOON | EARTH | METEORS | TELESCOPES

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-- ASTRONOMY AND ASTROLOGY --

ASTRONOMY AND ASTROLOGY ARE THE SAME:
ASTRONOMY is the science which investigates all matter-energy in the universe. It is based upon the scientific method, which states that theories must be grounded in observational fact and endure repeated testing as new observational data is acquired.
ASTROLOGY is the pseudoscience which entertains how the relationships of the sun, moon, planets, and stars influence the attitudes and lives of humans. The predictions purported by astrologers have no scientific basis in themselves and are the synthesis of Claudius Ptolemy, a Greek astronomer. About 140 AD Ptolemy wrote a series of four books called the Tetrabiblios which summarized all of the principles of astrology which are still practiced today. Astrology began about 3000 years ago in Babylon with what we today call mundane astrology. Predictions were applied to world or national events. To meet these needs, Babylonian astronomers were required to keep a continuous record of planetary movements. They did not seek answers to knowledge about the physical universe, but attempted to understand the motions of celestial objects in more of a mechanistic manner. By the sixth century BC astrology had spread as far east as India where it still flourishes today. Meanwhile, the Egyptians modified Babylonian concepts by developing a more personal version of astrology which was later synthesized into natal astrology by the Greeks after the conquests of Alexander the Great. The Greeks believed that our lives were preordained by the precise configuration of the sun, moon, and planets in the sky at the moment of our birth. This astrology is still practiced today by Europeans and Americans along with horory astrology which provide the daily horoscopes found in newspapers and tabloids alike.

-- THE MOON --

THE PHASES OF THE MOON ARE CAUSED BY THE MOON GOING INTO THE EARTH’S SHADOW:
The phases of the moon result from the revolution of the moon around the earth, and our observations of the hemisphere facing us, cycling through a day and night sequence. Only during a lunar eclipse will the moon intersect the earth’s shadow. The transition from the uneclipsed moon to the eclipsed moon takes about one hour. The phase cycle of the moon occurs in approximately 29 1/2 days. To demonstrate this, a light bulb and a small ball are all that are necessary. In a darkened room, allow the light source to represent the sun, the ball to stand for the moon, and your head will become the earth. Hold the moon in your left hand so that it is positioned between your eyes and the sun. You will notice the hemisphere facing you is in complete darkness. This is called the new moon. By revolving the moon in a counterclockwise direction around your head and observing the moon as it moves, you will see the moon progress through the waxing crescent phase (less than half lit), first quarter phase (half on, half off), the waxing gibbous phase (more than half lit--both limb and terminator appear convex), and finally the full moon phase (the hemisphere facing earth is totally illuminated). These phases will repeat themselves in reverse order (now called the waning gibbous, third or last quarter, and waning crescent moons) as the moon continues in its orbit around the earth, eventually moving completely into its own shadow to renew the new moon phase.

THE MOON HAS A HEMISPHERE IN PERPETUAL DARKNESS:
Nothing could be further from the truth. The moon has a portion of its surface (41%) that is never visible to earthbound observers, but all places on the moon experience a day and night cycle. When the moon is new and the hemisphere facing us it is not illuminated, the other hemisphere is in full illumination. A better term for the hemisphere not visible from earth would be the moon’s far side.

THE MOON REQUIRES 28 DAYS TO COMPLETE ONE PHASE PERIOD, AS WELL AS ONE PERIOD OF REVOLUTION AROUND THE EARTH:
The moon’s orbital period or sidereal period is 27-1/3 days, while the time the moon takes to complete a cycle of phases, its synodic period, is 29-1/2 days. The discrepancy arises because as the moon revolves around the earth, the earth is also revolving around the sun. In one orbital period (27-1/3 days), the earth has moved about 27 degrees in its orbit around the sun. While the moon has completed one orbit of earth, it is no longer in the same phase orientation. It will take the moon an extra 2-1/6 days of orbital motion until it has aligned itself in the same manner to be able to repeat the same phase. Therefore, a lunar phase period equals 27-1/3 days, plus 2-1/6 days, or about 29-1/2 days on the average. Rather than compromising between these two periods as most educators continue to do, it is better to emphasize the lunar phase period of 29-1/2 days. It is what we observe in the sky as we watch the moon cycling through its phases. The word month (moonth) is derived directly from the phase period. The phase cycle of the moon represented the first calendric systems used by early humans. It is also the most important time interval regulating eclipses. Solar eclipses can only occur when the moon is new, while lunar eclipses can only happen at the time of a full moon.

THE MOON DOES NOT ROTATE:
The moon completes exactly one rotation about its axis in the same period of time it takes to make one revolution around the earth. This period is equal to 27 1/3 days. That is why we always observe the same hemisphere of the moon facing us. To illustrate this concept, orbit around a person with your face looking in the direction of the person and one hand extended toward the person at all times. As you revolve around your partner, you will notice your arm also making a complete sweep around the room during the same interval of time that it takes to make one revolution. By remaining in the same location and completing one rotation, the room will appear to sweep around you in the same manner as before. The moon does rotate. If it didn’t, then your hand would always point in the same direction as you revolved around your partner. At first, your face might be visible, but in half a revolution your back would now be observed. If the moon did not rotate, all positions on its surface would face the earth during the time period of one revolution.

THE MOON HAS NO GRAVITY:
Any object which possesses mass (matter) has the force of gravity as a condition of its being. That goes for all matter: cars, baseballs, battleships, the moon, sun, planets, and all other objects found everywhere, regardless of whether they are large or small. The force of attraction felt by one object for another is directly proportional to the product of their masses and inversely proportional to the square of the distance to which they are separated. Isaac Newton put it this way: the force of attraction between two objects, F, is equal to G m1 m2/r^2, where G represents the universal constant of gravity; m1 and m2, the respective masses of the two attracting bodies; and r2, the square of the distance between the center of the two objects. When comparing the acceleration of an object at the surface of the more massive body, m1, the equation simplifies itself to a = m1/r2. When compared to the earth, the mass of the moon is 0.0123 of earth’s mass, while the radius of the moon is 0.2717 of earth’s radius. The acceleration of an object at the surface of the moon is 0.0123/(0.2717)^2 = 0.1667, or 1/6th that of earth. The moon attracts objects at its surface with a force of 1/6 that of earth. Therefore the moon definitely has a gravitational field which is noticeable when an astronaut is on its surface.

THE MOON APPEARS LARGER ON THE HORIZON THAN WHEN IT IS HIGH IN THE SKY:
This is called the moon illusion, and it is just your brain playing a psychological trick on your perception. You can prove this by holding a dime at arm’s length to cover the moon when it is in a rising position. A dime is about the same angular diameter as the full moon. Repeat the experiment several hours later when the moon has moved to a much higher position above the horizon to prove that the moon has really maintained its same apparent size in the sky. When rising, the eye sees the moon against far-off landscapes which may contain houses, trees, or mountains among many other things. Your brain knows that these distant objects would indeed look large if they were close to you. This psychological effect is transferred to the moon which is now made to appear bigger than reality by the brain. Another explanation is to say that when the moon is low in the sky, it will seem to be more remote than when it is high. If the images seen by the eye are of equal size, the disk, which is interpreted to be farther away, will look larger.

THE BLUE MOON IS REALLY BLUE:
The blue moon is not blue at all, since the light which we see reflected from its surface is only sunlight. A Blue Moon is really the second full moon which can occur during a month’s time. Since the phase cycle of the moon is 29 1/2 days, and a month has normally 30 or 31 days, Blue Moons occur very infrequently, about once every two to three years--in other words, once in a blue moon!

THE SURFACE OF THE MOON IS VERY REFLECTIVE:
Look at the full moon in the night sky. It appears bright, in fact brilliant enough to read the headlines of a newspaper by its light. The true tonal gradations of the lunar surface are actually dark gray to nearly black, an average reflectivity of only 7%, with extremes ranging from 3% to 30%. The lunar surface appears similar to a macadamized roadway. With about 93% of the sunlight absorbed by the lunar surface, the brightness of the moon is really a contrast difference between its dark surface and an even darker sky. That’s why the moon appears so bright at night.

WHEN THE MOON IS FULL, LUNACY REIGNS:
There is no statistical proof from hospital or police records that people are crazier, or that more crimes are committed, or that more babies are born when the moon is full. However, every nurse or policeman will tell you that this simply cannot be so. The misconception probably arises from the condition that the moon to the casual observer appears to be full in the sky for a period of four or five days around the actual full moon. If something weird happens during this period when the moon appears full and is visible nearly all night, then the blame can be "rightfully" attributed to the full moon. If there really would be a psychological effect attributed to the full moon, then there should be similar occurrences happening during the new moon phase. In both cases the moon and sun are pulling in tandem causing the greatest tidal strain to occur on the earth. No such phenomena are reported for the new moon phase.

-- THE EARTH --

THE SEASONAL EFFECTS ARE THE RESULT OF THE EARTH’S AXIS FLIPPING BACK AND FORTH:
The earth’s axis does slowly wobble like a top, completing one cycle in approximately 26,000 years. This motion is called precession, and it is responsible for a gradual change in the location of the position in the sky where the earth’s axis points. During the present epoch the earth’s axis is directed toward Polaris, the North Star, in the constellation of Ursa Minor. It is around this star that the sky appears to wheel once each day as the earth rotates on its axis. Five thousand years ago, when the Great Pyramid at Giza was constructed, the earth’s axis pointed towards Thuban in the constellation of Draco, the Dragon. Ironically, if the earth’s axis did flip back and forth during the interval of six months, it could be demonstrated that every position on earth would experience the same seasonal effects throughout the entire year.

[SEASONS]

THE SEASONS ARE THE RESULT OF THE CHANGING DISTANCE OF THE EARTH FROM THE SUN:
Most people believe this to be true. The seasons are caused, in reality, by the 23-1/2 degree tilt of the earth’s axis. During the course of a year, this one phenomenon changes the duration of time in which the sun is visible in the sky, the rising and setting positions of the sun along the horizon, and the noontime altitude of the sun. The earth’s orbit is slightly elliptical (oval) in shape. During a year’s time the earth’s distance from the sun varies between 91.5 to 94.5 million miles. We are actually closest to the sun around January 4th of each year and farthest from the sun on Independence Day, exactly the opposite of what one might expect.

THE EARTH ROTATES (SPINS) IN A PERIOD OF ONE DAY:
The earth rotates on average in a period of 23 hours, 56 minutes, 4 seconds. This is referred to as the sidereal day, and it is about four minutes shorter than the solar day which is what we regulate our clocks by. During this interval, the earth’s revolution around the sun carries us about one degree to the west in our orbit. This causes the sun to be shifted by one degree to the east. In order to bring the sun into a due south position to complete the interval of a solar day, an extra four minutes of time must be added to the sidereal day.

THE EARTH REVOLVES (ORBITS) AROUND THE SUN IN A PERIOD OF ONE YEAR:
Actually, the earth requires a period of 365.24 days (approximately 365-1/4 days) to complete one revolution. Our calendars normally have 365 days in a year. We give the earth 365 days to complete a task which actually requires 365.24 days. The result of this action over a period of four years is to place the earth about one day behind schedule with respect to its orbital position around the sun. We must, therefore, add one extra day to the calendar every four years to bring our planet back into synchronization with its position around the sun. If this were not brought about, the calendar would slide forward with respect to the seasons. In other words, the first day of spring would occur one day later every four years. Over a duration of 1460 years the seasons would have cycled through all of the calendar dates of the year.

A LEAP YEAR OCCURS EVERY FOUR YEARS:
This is almost true. The exception occurs with century years which are not divisible by 400. The year 2000 will be a leap year, but the century years of 1700, 1800, and 1900 were not leap years, because they did not produce a whole number when divided by 400. This is the main difference between the older Julian calendar (45 BC) and our modern Gregorian calendar used for civil purposes. The reason for the change arose because the Julian calendar overcorrected for the leap year by approximately 11 minutes, 14 seconds per year. From the adoption of the Julian calendar on January 1, 45 BC to the onset of the Gregorian system in 1582, the first day of spring had slipped backwards by 14 days, from March 25 to March 11, causing the observance of Easter to fall on earlier and earlier dates. If this were not corrected, eventually Easter and Christmas would be celebrated at the same time of the year. The Gregorian calendar was adopted by the Catholic nations of Europe in 1582 during the papacy of Gregory. During that year 10 days were dropped from the calendar so that the vernal equinox would occur on March 21. The day following October 4, 1582 became October 15. The calendar was now corrected to about 1 day in 3300 years.

THE AURORA IS CAUSED BY REFLECTED SUNLIGHT FROM THE ICE CAPS OF THE POLAR REGIONS:
The Aurora is really an electrical discharge which occurs high in the earth’s atmosphere. Trapped protons and electrons from the Van Allen radiation belts, situated thousands of miles above the earth’s surface, follow lines of magnetic force down into the earth’s atmosphere where they strike gas molecules causing them to glow. The earth’s magnetic field creates two oval-shaped areas where the charged particle intensity is highest and the auroras are most frequently observed. Auroral activity takes place at altitudes between 350 miles to 60 miles above the surface of the earth, and in the locations of greatest frequency can occur on about 250 nights during a year.

A COMPASS NEEDLE ALWAYS POINTS TOWARDS THE NORTH:
Since the north magnetic pole is located approximately 700 miles south of the earth’s true geographic north pole, a compass needle will tend to point in the general direction of north. At positions where true geographic north lies directly north of the north magnetic pole, a compass needle will point directly north. In any other location there will always be some deflection of the needle either to the east or west of the true north position.

THE EARTH WAS CONSIDERED TO BE FLAT DURING THE TIME WHEN COLUMBUS DISCOVERED THE NEW WORLD:
This misconception is generally true for the uneducated masses, but not so for anyone who had received a formal education and who could read. Columbus could read, and he was familiar with Greek texts which spoke of a spherical earth as well as the circumference of the earth. It was the earth’s circumference that was in disagreement among European scholars of Columbus’s time. Columbus thought that the earth was about 18,000 miles in circumference, and that the East Indies were only about 3000 miles away. Despite this misconception, Columbus was a keen observer who had sailed widely and who had witnessed the changes in the sky which were consistent with a spherical earth. Convincing a superstitious crew that the earth was round and not inhabited by monsters who lurked in uncharted oceans was more difficult.

-- METEORS, METEORITES, AND METEOROIDS --

METEORS FALL TO THE EARTH’S SURFACE:
A meteor is the flash of light left by a falling meteorite, which hits the ground to end its flight. Meteoroids are the same objects which can be found orbiting the sun in space. They most likely originate from the asteroid belt as rock or ice-rock fragments formed through the collisions of asteroids and comets. One of the worst misuses of the word "meteor" can be found in the name of Meteor Crater, the best preserved meteorite crater in the world. It can be found along I-40, just to the west of Winslow, Arizona. The correct name of this formation should be Meteorite Crater, since it was forged by such an object striking the earth’s surface about 25,000 years ago. By the way, Meteor Crater is a must visit if you are on vacation near the Grand Canyon. If it were not for the fact that Meteor Crater is owned privately, it would certainly be a national monument, and more people would have become familiar with its grandeur. Just remember, Meteor Crater was formed by a meteorite.

-- TELESCOPES --

THE TELESCOPE WAS INVENTED BY GALILEO:
The telescope was invented in the year 1608 by a German/Dutch optician named Hans Lippershey (1570?-1619?). It is not known whether it was Lippershey himself, his son, or a worker in Lippershey’s Dutch optical shop who first stumbled across the discovery. Lippershey tried to market these first telescopes as military devices to the Dutch Government. Galileo, hearing of the invention through his correspondences with other scientists in Europe, built his first telescope in one night, sometime during the fall of 1609. Galileo also recognized the military significance of the telescope, but he also comprehended the scientific importance of the telescope as a tool for expanding humankind’s understanding of the universe. In this sense, he accelerated the birth of astronomy as a modern science.

TELESCOPES ARE CONSTRUCTED TO PRODUCE MAGNIFICATION:
Telescopes are an extension of the human eye, and in this capacity, their most important qualification is to gather light. An object too faint to be seen by the unaided eye must first be made bright enough to be seen before it can be studied. This has always been the main function of any telescope--to gather light, not to magnify an image. Every time the magnification of a particular telescope is doubled, the field of view and image brightness decrease to 1/4 of their original values. It is possible to magnify an image into invisibility, or to produce empty magnification, where further magnification of an image produces no increase in the amount of detail which can be revealed in the object under scrutiny. The light-gathering "power" of a telescope must, therefore, reign supreme in any consideration of a telescope’s usefulness.

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