MacRobert contrasts the effect of refraction upon our view of a planet:
The disk of a planet can be regarded as many points packed close together [yes, like a thousand points of light]. When one point twinkles bright for a moment another may be faint. The differences average out and their combined light appears steady.
Kanipe phrases it a little differently:
A planet’s light comes from every part of its disk, not just a single point. Thus, when the light passes through the atmosphere, the shift in position is smaller than the size of the planet’s disk in the sky and the twinkling isn’t as pronounced.
Still don’t get it? Let’s use a more down-to-earth analogy, supplied by Kanipe:
From the vantage point of a diving board, a dime on the floor of the swimming pool appears to shift violently about because the water acts like a wavy lens that continuously distorts the rays of light coming from the coin. But a submerged patio table, say, looks fairly steady because the water can’t distort the light rays coming from its greater surface area to the point that the table appears to shift out of position.
Submitted by Henry J. Stark of Montgomery, New York.
Thanks also to Frank H. Anderson of Prince George, Virginia,
and J. Leonard Hiebert of Nelson, British Columbia.
* * *
IF WATER IS HEAVIER THAN AIR,
WHY DO CLOUDS STAY UP IN THE SKY?
* * *
What makes you think that clouds aren’t dropping? They are. Constantly.
Luckily, cloud drops do not fall at the same velocity as a water balloon. In fact, cloud drops are downright sluggards: They drop at a measly 0.3 centimeters per second. And cloud drops are so tiny, about 0.01 centimeters in diameter, that their descent is not even noticeable to the human eye.
Submitted by Ronald C. Semone of Washington, D.C.
* * *
WHAT DOES 0º IN THE
FAHRENHEIT SCALE SIGNIFY?
* * *
During our school days, we were forced to memorize various points in the Fahrenheit scale. We all know that the freezing point is 32º and that the boiling point is 212º. The normal human body temperature is the inelegantly unround number of 98.6º.
Countries that have adopted the metric system have invariably chosen the Celsius system to measure heat. In the Celsius scale, 0º equals the freezing point.
The Fahrenheit temperature scale was created by a German physicist named Daniel Gabriel Fahrenheit, who invented both the alcohol thermometer and the mercury thermometer. The divisions of his scale aren’t quite as arbitrary as they might seem. Zero degrees was chosen to represent the temperature of an equal ice-salt mixture, and 100º was originally supposed to signify the normal body temperature. But Fahrenheit screwed up. Eventually, scientists found that the scale didn’t quite work, and the normal body temperature was “down-scaled” to 98.6º.
Submitted by James S. Boczarski, of Amherst, New York.
* * *
WHAT DOES EACH ONE-DEGREE INCREMENT
IN THE FAHRENHEIT SCALE SIGNIFY?
* * *
Although his scale was not based on the freezing and boiling points, Fahrenheit recognized their significance. The interval between the boiling point (212º) and freezing point (32º) numbers exactly 180 degrees on the Fahrenheit scale, a figure with which scientists and mathematicians were used to working.
The increments in a temperature scale have no cosmic significance in themselves. The Celsius system, for example, is less precise than the Fahrenheit in distinguishing slight variations in moderate temperatures. Thus while 180 increments on the Fahrenheit scale are necessary to get from the freezing to the boiling point, the freezing point (0º) on the Celsius scale and the boiling point (100º C) are closer, only 100 increments apart.
In most cases, the meaning of the one-degree increments in temperature scales has more to do with what is intended to be measured by the scale than with any particular mathematical requirements. The Fahrenheit scale, intended for use in human thermometers, was designed originally to have 100ºF represent the normal body temperature. Temperature scales now used by scientists, such as the Kelvin and Rankine scales, use absolute zero (the equivalent of -273.15º C or -459.67º F) as the base point. Rankine uses the same degree increments as Fahrenheit; Kelvin uses the Celsius degree.
Submitted by James L. Foley, of Calabasas, California.
* * *
WHY DOES JUST ABOUT EVERYTHING LOOK
DARKER WHEN IT GETS WET?
* * *
Come to think of it, reader Russell has a point. Drop some water on your new cream-colored blouse and you get a dark spot. Have a clod standing near you spill his Perrier on your navy blue blazer and the light liquid somehow manages to make the coat’s dark color even darker. Why is this so?
Elementary physics, it turns out. You lose the true color of the garment in three ways:
1. Even a thin coating of water will force light coming toward the garment to refract within the water film. The available light is thus disbursed.
2. The reflection on the surface of the water itself causes incoherent light scattering.
3. A combination of the two points above ensures that there will be less light available on the surface of the jacket to reflect back to your eyes. Thus the spot will appear darker than the rest of the jacket that doesn’t have to compete with water in order to reflect light.
Submitted by Kathleen Russell of Grand Rapids, Michigan.
Thanks also to Kent Parks of Raleigh, North Carolina.
* * *
IF ALL TIME ZONES CONVERGE AT
THE NORTH AND SOUTH POLES,
HOW DO THEY TELL TIME THERE?
* * *
Imagine that you are a zoologist stationed at the South Pole. You are studying the nighttime migration patterns of Emperor penguins, which involves long periods observing the creatures. But you realize that while you watch them waddle, you are in danger of missing a very special episode of The Bachelor on television unless you set that VCR for the right time. What’s a scientist to do?
Well, maybe that scenario doesn’t play out too often, but those vertical line markings on globes do reflect the reality. All the time zones do meet at the two poles, and many Imponderables readers wonder how the denizens of the South Pole (and the much fewer and usually shorter-term residents of the North Pole) handle the problem.
We assumed that the scientists arbitrarily settled on Greenwich Mean Time (the same time zone where London, England, is situated), as GMT is used as the worldwide standard for setting time. But we found out that the GMT is no more! It is now called UTC (or Coordinated Universal Time—and, yes, we know that the acronym’s letter order is mixed up). The UTC is often used at the North Pole as the time standard, and sometimes at the South Pole.
We veered toward the humanities in school partly because the sciences are cut and dried. If there is always a correct answer, then teachers could always determine that we came up with the wrong answer. Science students were subjected to a rigor that we were not.
But when it comes to time zones, the scientists at the poles are downright loosey-goosey: They use whatever time zone they want! We spoke to Charles Early, an engineering information specialist at the Goddard Space Flight Center in Greenbelt, Maryland, who told us that most scientists pick the time zone that is most convenient for their collaborators. For example, most of the flights to Antarctica depart from New Zealand, so the most popular time at the South Pole is New Zealand time. The United States’ Palmer Station, located on the Antarctic Peninsula, sets its time according to its most common debarkation site, Punta Arenas, Chile, which happens to share a time zone with Eastern Standard Time in the United States. The Russian station, Volstok, is coordinated with Moscow time, presumably to ease time-conversion hassles for the comrades back in Mother Russia.
Early researched this subject to answer a question from a child who wondered what time Santa Claus left the North Pole in order to drop off all
his presents around the world. Based on our lack of goodies lately, we think Santa has been oversleeping big-time, and now we know that time-zone confusion is no excuse.
Submitted by Thomas J. Cronen of Naugatuck, Connecticut.
Thanks also to Christina Lasley of parts unknown;
Jack Fisch of Deven, Pennsylvania;
Dave Bennett of Fredericton, Ontario;
Paul Keriotis, via the Internet;
Peter Darga of Sterling Heights, Illinois;
Marvin Eisner of Harvard, Illinois;
Jeff Pontious of Coral Springs, Florida;
and Dean Zona, via the Internet.
* * *
HOW DO YOU TELL DIRECTIONS AT THE
NORTH AND SOUTH POLES?
* * *
You think time zones are a problem, how about giving directions to a pal at the South Pole. By definition, every direction would start with “Head north.”
In practical terms, though, the distances aren’t great at the science stations, and it’s not like there are suburbs where you can get lost. But scientists do have a solution to this problem, as Nathan Tift, a meteorologist who worked at the Amundsen-Scott South Pole Station explains:
If someone does talk about things being north or south here, they are most likely referring to what we call “grid directions,” as in grid north and grid south. In the grid system, north is along the prime meridian, or 0 degrees longitude, pointing toward Greenwich, England, south would be 180 longitude, east is 90 degrees, and west is 270 degrees. It’s actually quite simple. Meteorologists like myself always describe wind directions using the grid system. It wouldn’t mean much to report that the wind at the South Pole always comes from the north!
Submitted by Michael Finger of Memphis, Tennessee.
* * *
WHAT ARE WE SMELLING WHEN IT
“SMELLS LIKE RAIN IS COMING”?
* * *
This isn’t the type of question that meteorologists study in graduate school or that receives learned exegeses in scholarly journals, but we got several experts to speculate for us. They came down into two camps.
1. It ain’t the rain, it’s the humidity. Biophysicist Joe Doyle blames the humidity, which rises before rainfall. Of course, humidity itself doesn’t smell, but it accentuates the smells of all the objects around it. Everything from garbage to grass smells stronger when it gets damp. Doyle believes that the heightened smell of the flora and fauna around us tips us off subliminally to the feeling that it is going to rain. Richard A. Anthes, president of the University Corporation for Atmospheric Research, points out that many gaseous pollutants also are picked up more by our smell receptors when it is humid.
2. The ozone did it. Dr. Keith Seitter, assistant to the executive director of the American Meteorology Association, reminds us that before a thunderstorm, lightning produces ozone, a gas with a distinctive smell. He reports that people who are near lightning recognize the ozone smell (as do those who work with electrical motors, which emit ozone).
Kelly Redmond, meteorologist at the Western Regional Climate Center, in Reno, Nevada, also subscribes to the ozone theory, with one proviso. Ozone emissions are common during thunderstorms in the summer, but not from the rains from stratiform clouds during the cold season. So if it’s “smelling like rain” during the winter in Alaska, chances are you are not smelling the ozone at all but the soil, plants, and vegetation you see around you, enhanced by the humidity.
Submitted by Dr. Thomas H. Rich of Melbourne, Victoria, Australia.
Thanks also to George Gudz of Prescott, Arizona; Anne Thrall of
Pocatello, Idaho; Dr. Allan Wilke of Toledo, Ohio; Matthew Whitfield
of Hurdle Mills, North Carolina; Philip Fultz of Twentynine Palms,
California; and William Lee of Melville, New York.
* * *
WHY DO UNOPENED JARS OF MAYONNAISE,
SALAD DRESSING, FRUIT, AND MANY OTHER
FOODS STAY FRESH INDEFINITELY ON THE
SHELF BUT REQUIRE REFRIGERATION
AFTER BEING OPENED?
* * *
The three main enemies of freshness in perishable foods are air, heat, and low acidity. Foods such as mayonnaise, salad dressing, and canned fruit all undergo processing to eliminate these hazards. Burton Kallman, director of science and technology for the National Nutritional Foods Association, explains:
Unopened jars of perishable foods can remain at room temperature because they are sealed with low oxygen levels (sometimes under vacuum), are often sterilized or at least pasteurized, and may contain preservatives which help maintain their freshness.
All three of these foods contain natural ingredients that act as preservatives. Roger E. Coleman, senior vice president of public communications for the National Food Processors Association, differentiates between foods that must be refrigerated immediately and those that can remain unopened on the shelf:
Products such as marinated vegetables, salad dressings, and fruits, which contain adequate amounts of added acid ingredients such as vinegar and/or lemon juice, will not support the growth of hazardous microorganisms and only need to be refrigerated after opening to prevent them from spoiling. Other products, such as canned meats and vegetables, do not contain acidic ingredients and, thus, can support the growth of hazardous microorganisms. These products must be refrigerated, not only to retard spoilage but to keep them safe to eat after opening.
This last point is particularly important, for many foods that state “Refrigerate after opening” are perfectly safe to store back on the shelf after they are opened. So why the warning? Barbara Preston, executive director of the Association for Dressings and Sauces, writes:
Most commercial dressings (with the exception of those bought from a refrigerated display case) are perfectly safe stored at room temperature. The words ‘Refrigerate After Opening’ on the label are intended only to help preserve their taste, aroma, and appearance. They do not relate to spoilage. If an already opened jar of salad dressing is accidentally left out for several hours, don’t throw it away. There is no danger of spoiling…it just may not taste as fresh.
Submitted by Nancy Schmidt of West New York, New Jersey.
* * *
HOW CAN HURRICANES DESTROY BIG
BUILDINGS BUT LEAVE TREES UNSCATHED?
* * *
Think of a hurricane as heavyweight boxer Sonny Liston, a powerful force of nature. A building in the face of Liston’s onslaught is like George Foreman, strong but anchored to the ground. Without any means of flexibility or escape, the building is a sitting target. A building’s massive size offers a greater surface area to the wind, allowing greater total force for the same wind pressure than a tree could offer.
But a tree in a hurricane is like Muhammad Ali doing the rope-a-dope. The tree is going to be hit by the hurricane, but it yields and turns and shuffles its way until the force of the hurricane no longer threatens it. In this case, the metaphor is literal: by bending with the wind, the tree and its leaves can sometimes escape totally unscathed.
Richard A. Anthes, president of the University Corporation for Atmospheric Research, offers another reason why we see so many buildings, and especially so many roofs, blown away during a hurricane.
“Buildings offer a surface which provides a large aerodynamic lift, much as an airplane wing. This lift is often what causes the roof to literally be lifted off the building.”
We don’t want to leave the impression that trees can laugh off a hurricane. Many get uprooted and are stripped of their leaves. Often we get the wrong impression because photojournalists love to capture ironic shots of buildings torn asunder while Mother Nature, in the form of a solitary, untouched, majestic tree, stands triumphant alongside the carnage.
Submitted by Daniel Marcus of Watertown, Massachusetts.
* * *
WHY DOES THE MOON APPEAR BIGGER AT
THE HORIZON THAN UP IN THE SKY?
* * *
This Imponderable has been floating a
round the cosmos for eons and has long been discussed by astronomers, who call it the Moon illusion. Not only the Moon but the Sun appears much larger at the horizon than up in the sky. And constellations, as they ascend in the sky, appear smaller and smaller. Obviously, none of these bodies actually changes size or shape, so why do they seem to grow and shrink?
Although there is not total unanimity on the subject, astronomers, for the most part, are satisfied that three explanations answer this Imponderable. In descending order of importance, they are:
1. As Alan MacRobert of Sky & Telescope magazine states it, “The sky itself appears more distant near the horizon than high overhead.” In his recent article in Astronomy magazine, “Learning the Sky by Degrees,” Jim Loudon explains, “Apparently, we perceive the sky not as half a sphere but as half an oblate [flattened at the poles] spheroid—in other words, the sky overhead seems closer to the observer than the horizon. A celestial object that is perceived as ‘projected’ onto this distorted sky bowl seems bigger at the horizon.” Why? Because the object appears to occupy just as much space at the seemingly faraway horizon as it does in the supposedly closer sky.
Science Page 5
