Earth & Space Science

What is wrong with this sentence?

“At sunset we sat motionless, pondering the mysteries of the dark side of the Moon, when a shooting star  passed by the evening star.

Although this statement is easily understood, one could argue that it is filled with error.  One can never be motionless because we are on the surface of the Earth, which is spinning rapidly on its axis as it orbits the Sun, which is itself in motion.  The Sun never sets, but simply disappears from view as the Earth rotates.  There is no “dark-side” to the Moon.  We never see the far side of the Moon because the Moon rotates on its axis at the same rate it orbits the Earth so that the same side always faces us.  The “dark-side” is exposed to sunlight whenever the side facing us is dark.  Shooting stars (meteors) are glowing pieces of rock and dust and bear no resemblance to stars other than that they emit light.  The evening star is actually the planet Venus, and not a star at all.  Finally, the meteor was millions of miles in front of the evening star, and did not pass “by” it.

Many of our misconceptions are rooted in experience.  From our frame of reference, it makes sense to talk about sunrise and sunset, for we have no sensation of the Earth’s rotation.   It certainly seems like we are standing still because we don’t experience any wind or feeling of acceleration or movement.  Figure 7.4 is a photograph taken by the author while backpacking in California’s Sierra Nevada Mountains.  The shutter was left open for a few hours, allowing starlight to expose Mount Lyell.  The stars appear to be moving in an arc from right to left, and in the absence of other knowledge of astronomy, it is fair to conclude that the stars, like the Sun, rotate around the Earth.  In reality, the Earth is spinning on its axis, creating the apparent motion of the stars.  The line traveling at right angles to the stars was created by a satellite, and it is the only object in the photograph that is orbiting the Earth. 

Research studies have shown that many people share the same misconceptions about the universe.  For example, a large percentage of people believe that we experience summer at the point in our orbit where we are closest to the Sun (perihelion), and Winter when we are farthest from the Sun (aphelion).  This makes sense based upon our experience with other luminous objects.  We feel warmer when we approach a campfire, and colder when we move away from it.  However, our concept is challenged when we look at additional data.  For example, the Southern Hemisphere experiences winter when the Northern Hemisphere experiences summer.  How can two parts of the world experience different seasons if seasonality is based solely upon proximity to the Sun?

Diagrams can help clarify misconceptions, but may also be the source of misconceptions. Figure 7.5 is designed to show the reasons for the seasons.  The earth is tilted 23.5° on its axis, so on December 21, relatively little light hits the Northern Hemisphere, while much hits the Southern Hemisphere.  December 21st is the shortest day of the year in the Northern Hemisphere, and the longest in the Southern Hemisphere.  These factors explain why it is colder in the Northern Hemisphere on this day than it is in the Southern Hemisphere.  Although the diagram helps explain seasons, it can also lead to some confusion.  For example, the scale of the diagram is very misleading and does not represent the relative size of the Earth and Sun, nor the distance of the Earth from the Sun.  If drawn to scale, the Earth would appear as a tiny spec on the ellipse.

The following are a few common misconceptions in earth & space science.  For each, we have introduced contradictory data which one can use to disprove the misconception.

misconception: Space is a zero-gravity environment.

contradictory data:  The Moon is in space, and yet gravity is sufficient to cause it to orbit the Earth.

correct explanation: Astronauts experience weightlessness, not because they are in space, but because they are in orbit around the Earth.  They are in a continual state of free-fall towards the center of the Earth, but because they also have a tangential velocity, they orbit the Earth rather than plunge towards it.

misconception: Gravity is a strong force.

contradictory data: A small magnet can raise a paperclip against the force of gravity, even though the Earth is far more massive than the magnet.

correct explanation:  The gravitational attraction between protons is a factor of 1/1036 the strength of electromagnetic repulsion.  The gravitational attraction or repulsion of protons and electrons is negligible compared to electrostatic attraction or repulsion. Despite gravity being such a weak force, it is the main force between celestial bodies, because planets and stars do not carry any net charge and are therefore electrically neutral.  Gravity dominates the universe, even though it is an extremely weak force. If the strong nuclear force is assigned a strength of 1, the strength of the electromagnetic force is 1 ´10 -2, and the strength of the weak nuclear force is 1 ´ 10 -13 , then the strength of gravity is 1 ´ 10 -38.

misconception: The “greenhouse effect” is a bad thing.

contradictory data: Without greenhouse heating, the Earth's average temperature would be about -73°C (-100° F), cold enough to freeze even the oceans.

correct explanation: The greenhouse effect is the process in which the atmosphere warms a planet.  Infrared radiation emitted from the Earth is captured by greenhouse gases, warming the atmosphere and keeping temperatures reasonable for life. Although the greenhouse effect is essential for life, the release of excessive greenhouse gases by human activity, particularly carbon dioxide released from the combustion of fossil fuels, is believed to contribute to global warming, a potentially devastating trend.

misconception: The Coriolis effect causes water in drains to rotate clockwise in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere.

contradictory data: In the same house, water in a kitchen sink may run one way, while water in a bathroom sink runs the other.

correct explanation: Although the Earth rotates eastward (towards the Sun) with constant angular velocity, points on Earth have very different linear speeds.  The North and South Poles have a linear speed of zero, while points on the equator travel at nearly half a kilometer per second.   A point on the equator travels 40,075 km (24,900 miles) per day while points at the poles travel nowhere.  When an object moves north or south from the equatorial regions and is not firmly connected to the ground, it maintains some of its initial eastward velocity as it moves.  Objects moving away from the equator veer relative to the more slowly moving Earth beneath them. The reverse happens moving from northern or southern regions (low linear velocity) towards the Equator (high linear velocity).   This causes currents to move clockwise in the Northern Hemisphere, and counterclockwise in the Southern (figure 7.6), but is too small to effect water running down a drain. Surface features, drain geometry and initial conditions affect the direction of a vortex in a drain.

misconception:  A tsunami is a “tidal wave”.

contradictory data:   The tides are caused by the gravitational pull of the Moon upon the waters in the oceans.  Tsunamis, however, occur at random intervals and are not correlated with the position of the Moon.

correct explanation: A tsunami is a series of waves formed when a massive amount of water is displaced by an earthquake or volcano.  Tsunamis are frequently called “tidal waves” because  they resemble a violent rushing tide as they approach land, but since they are not related to the Moon or to tides, oceanographers say that the term “tidal wave” is very misleading and should not be used.

Activity 7.7.1 – Clarifying Misconceptions in Earth and Space Science

Note to teacher:  The following is a list of common misconceptions in earth and space science. Give one to each student and instruct them to research  the misconception, explain why it is wrong by reasoning from observed facts and experiences, and provide a correct explanation.  Explanations are found in the answer section in this chapter.

1.     (example) The Great Wall of China is the only manmade object that can be seen from the Moon. No manmade objects are visible from the Moon and astronauts note that the Great Wall of China disappears from view earlier than more massive manmade structures such as highways, cities, and large ships.  The Great Wall of China is much narrower than modern freeways and highways, and if such roads cannot be seen from space, then neither would the Great Wall of China.

2.     It is possible to balance eggs on end on the vernal equinox.

3.     There is a dark side of the Moon

4.     Stars twinkle because they are on fire. 

5.     The tail of a comet travels behind it as it moves. 

6.     Planets traveling closest to the Sun travel slowest because they have the smallest orbits.

7.     The Moon orbits the center of mass of the Earth. 

8.     Raindrops are shaped like teardrops.  

9.     Polaris (the North Star) has always been in the direction of true north. 

10.  A magnetic compass always points North. 

11.  The North end of a compass needle points to the Earth’s magnetic north pole. .

12.  Rivers flow south. 

13.  There is a “up” and “down” in space

14.  Black holes are empty holes in space.

15.  All of the planets have solid surfaces

16.  The Sun is directly overhead at 12 noon. 

17.  The Sun does not rotate.

18.  Shadows don’t exist on overcast days because the Sun is not bright enough. 

19.  Clouds, fog and steam are water vapor. 

20.  The phases of the Moon are due to the shadow of the Earth. 

21.  The stars of a constellation are near each other. 

22.  The Sun rises in the east and sets in the west.

23.  Small earthquakes prevent big ones from happening. 

24.  Underground streams flow just like streams above ground.