The Robber Wore a Mets Baseball Cap . . . No, Red Sox
Studies have shown that eyewitnesses are notoriously unreliable. This is, of course, a critical issue in the legal profession. It is also relevant to understanding how we come to develop and believe erroneous ideas about the natural world. For example, most people believe that all stars are the same color, typically white, based on their experience observing the night sky. While some stars do indeed appear white, most actually do not. Check out the pattern of stars called Orion.5 The upper left shoulder star, Betelgeuse, has a distinctly red hue, while the lower right foot star, Rigel, is blue-white. You can see the colors best by comparing stars that are close together in the sky. The more you do so, the more you will see a variety of stellar colors.
As a second astronomical example, most people believe that all the objects we see in the northern hemisphere with our naked eyes are stars. Indeed, to the casual observer, they do appear pretty much the same except for differences in brightness and, if you now look carefully, color. But looking carefully is the key, since there are some fuzzy blobs that are distinctly unstarlike. Consider Orion again. Virtually everyone who sees it would swear that each of the "stars" in it is, indeed, a star. Not true. Next time you see Orion, check out his "sword," which dangles down directly between his legs, below his belt. (I'll never understand why anyone would wear a sword between his legs, but never mind.) Even without binoculars, you can see that the middle "star" in the sword is actually a fuzzy blob. It is diffuse and indistinct, unlike the sharp points of light that other stars, such as Betelgeuse, Rigel, and those in the "belt," make. In fact, the middle "star" in the sword is a very bright region of glowing gas called the Orion Nebula, as seen in figure 3.4a.
There is another fuzzy blob we normally perceive as a star in the constellation Andromeda (figure 3.4b). This blob is actually the galaxy Andromeda, some 2 million light years6 away (compare to the tens or
5 It is likely that you thought of the word "constellation" where I wrote "pattern of stars." The word "constellation" is indeed the common term that everyone understands, but it is not the definition astronomers normally use. A constellation comprises an entire region of the sky, along with all the stars and other objects in it. The entire sky is divided into 88 unequal-area constellations. We use the pattern definition of "constellation" when there is no chance for confusion. Otherwise, the patterns are called "asterisms."
6 A light year is the distance light can travel in one year through empty space, about 5.9 trillion miles or 9.5 trillion kilometers.
hundreds of light years' distance of most of the stars we can see with our unaided eyes).
Several factors participate in limiting our observational skills. First are the circumstances under which the observations are made. If you are observing the sky on a warm summer's night, more of your energy is focused on what you see in the sky, and less on keeping warm, than if you are observing in the winter when it is io°F (-i5°C). Likewise, you will see more if you have more time and less distraction. For example, you are more likely to see details of lunar craters, ejecta blankets, the phase of the Moon, and its mountains while watching the Moon alone than if you are watching the Moon with someone with whom you are planning an imminent amorous encounter.
Expectations are another factor. Suppose you are told to go out and examine the Moon every day for a week, without any further instructions. Chances are that you will make all your observations at night; that you will notice the change in the Moon's phases; and that you will observe surface features such as the craters and the dark, relatively crater-free maria (the dark gray regions of the Moon). Unless told to look for them, you are less likely to note that the directions of the points on the crescent Moon change; that the same features on the Moon are visible throughout the entire cycle of phases (the same side of the Moon always faces the Earth); that the Moon's size in the sky varies just slightly throughout the month; that despite appearances to the contrary, the Moon is not larger when it is on the horizon than when it is high up in the sky a few hours later; or that the Moon is up during daylight hours as much as it is at night. We will return to observing the Moon shortly.
This issue of expectations applies to observations on Earth as well. Different people focus on different things. For example, when looking at cars, I am interested in the make and model, which I can typically recall for a long time, but I am absolutely terrible at remembering colors.
Another influence on what we notice and remember is that we often lack the categories and the organizational structures in our minds to relate new information to old. We see only one Moon in the sky, but a category containing one thing is hardly useful in understanding it. Compare this to the classification schemes you have developed for various down-to-Earth items. If you like cars, then you may know them by manufacturer, horsepower, styling, performance (o to 60 mph in 8.7 seconds), features, colors, and country of origin, among other things. If you like stocks, you may know on which market they trade, their sector, their price-to-earnings ratios, their ratings, their recent annual performances, and so on. In either case, when a new specimen appears, you have ways of classifying and comparing it to items with which you are familiar. In astronomy and many other sciences, you may not have such powerful and familiar frames of reference to use in analyzing what you see or read about.
Knowing what questions to answer is a big step forward in understanding and classifying new things. Your observations of the Moon would probably provide you with completely different information and insights if you were told beforehand to determine such things as when the Moon rises and sets each day, what hours each day it is visible during the daytime, the angular distance between the Moon and the Sun, and how that angular distance is related to the Moon's phase. In other words, you will see different things and categorize them differently depending on what you are looking for.
The human memory is notoriously fallible when it comes to remembering details as time goes by—ask anyone who has written a computer program but not documented it well. Furthermore, your recollection of observations you've made in the past will change. If you saw comet Hale-Bopp, would you remember which tail was on top, the blue one or the white one?
Common incorrect beliefs from incomplete, inaccurate, or earlier observations include the belief that we see the same constellations throughout the year; that all constellations (i.e., asterisms) are in the shapes of the things they were named for; that no planets are visible
with the naked eye; that we see all sides of the Moon; and that the Sun always sets due west, among many others.
Our senses also have limitations and change with time. The senses in healthy young people are superbly capable of providing information necessary for survival. As we get older, our senses become less reliable, and eventually they often fail. Yet even the keenest senses possessed by a person in the spring of life are not good enough to provide reliable information about things that are very small or very distant or that do not emit signals we can pick up. Our unaided eyes cannot see viruses or bacteria, some of which are very harmful to us and other forms of life. Likewise, our eyes cannot see details of distant objects that are close together, like orbiting pairs of stars in the night sky. And even if we could catalog every visible object in our galaxy, we would be observing less than 10 percent of all the matter that must exist in it.7 Our senses have evolved to help us survive from day to day, not necessarily to comprehend all the facets of nature. Besides the dark matter in our galaxy and throughout the universe, there are tremendous quantities of matter in interstellar gas clouds that don't emit enough visible light to be detected. Telescopes sensitive to radio waves have revealed this otherwise invisible material. For example, using the Very Large Array (VLA) radio telescope system in Socorro, New Mexico, I made images of a vast, bizarre system of intergalactic gas that fills what appears in visible light telescopes to be empty space. Indeed, this gas cloud spans the distances between many galaxies.
Besides building telescopes with which to see radiation we can't otherwise detect, we enhance our sight by developing optical telescopes that
7 We know the amount of invisible, presently undetected matter that exists because of its gravitational effect on visible matter, such as stars. We can calculate the total mass that acts to keep stars, including the Sun, in orbit about the center of our galaxy. This is done by observing the orbits of stars and then using simple equations to relate the orbits to the gravitational forces that must be acting on those bodies. By subtracting the gravitational effects of all the observable matter, we can deduce how much invisible matter there is to help keep things in their observed orbits. The invisible matter is often called dark or missing mass. "Missing" is a misleading name, since it isn't missing—we just haven't found it yet. The nature of the dark matter is still under debate.
can see more detail (i.e., can separate objects that our eyes see as one), that can magnify, and that can make objects appear brighter. For example, telescopes allow us to photograph the individual stars in many binary star systems. They can also reveal billions of other galaxies that are too dim to be seen with the naked eye. Indeed, technological enhancements now exist for all our senses. These devices enable us to better understand the natural world, as well as to enjoy it and work with it.
When we possess incomplete information, due to the limitations of our senses or other factors, we don't have all the data we need to make a valid analysis and draw valid conclusions about what we sense or are told. That, of course, has never stopped anyone from convincing themselves they understand things about which they actually have less than complete knowledge.
One of the more interesting aspects of human behavior is that we tend to fill in gaps in information with ideas based on our own experiences, beliefs, and thought processes. I remember hearing about a talk by a college administrator who underscored the points he made with an impressive array of facts and statistics. After the lecture was over, a friend of his commented on how well he had supported his case. The friend went on to ask where these numbers could be found for future reference. "They can't," the administrator replied casually. "I made them up as I went along."
We go about filling in the gaps in our knowledge and our memories through a number of memory activities such as wishful thinking and common sense. While the former is fairly self-evident, the latter is incredibly complex, and its effects are far reaching. Furthermore, more often than not, conclusions about the natural world reached via common sense are wrong.
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