The stars don’t show up because their light is so dim that they don’t produce enough light on film in the short exposures used to take conventional pictures. But you have seen many photos of stars, haven’t you? These were undoubtedly time-lapse photographs, taken with fast film and with the camera shutter left open for at least ten to fifteen seconds. Without special film and a long exposure time, the camera lens can’t focus enough light on the film for the image to appear. Jim McDade, director of space technology for the University of Alabama at Birmingham, elaborates:
Even if you attempt to take pictures of stars on the “dark side” of the Earth during an EVA [an extra-vehicular activity involving astronauts leaving the primary space module, such as a spacewalk] in low-earth orbit, a time exposure from a stable platform of about twenty seconds is necessary in order to capture enough stellar photons to obtain an image showing stars, even when using fast films designed for low-light photography.
The same problems occur with digital cameras, film, and video cameras, as McDade explains:
A digital camera, a film camera, and the human eye all suffer similar adaptability problems when it comes to capturing dimmer background objects such as stars hanging behind a spacewalking astronaut in the foreground. The human eye is still much more sensitive than the finest digital or film camera.
Photographic film is incapable of capturing the “very bright” and the “very dim” in the same exposure. The lunar surface is brilliant in daylight. The photos taken by the Apollo astronauts used exposure times of a tiny fraction of one second. The stars in the sky are so dim that in order to capture them on film, it requires an exposure time hundreds of times longer than those made by the Apollo astronauts.
Those of us who live in the city have had the experience of going out to a rural area on a clear night, and being amazed at the number of stars we can see when there aren’t lights all around us on the ground. You can create the same effect inside your house. On a clear night, kill the lights in a room and look out the window. Depending upon the atmospheric conditions, a star-filled sky may be visible to you. Flip on the lights inside the room, look outside, and the stars have disappeared.
Why? Light from a bright object near us can easily dwarf light emanating from distant objects, such as stars. In the case of astronauts, the lights attached to the space vehicle or space station or even the lights on an astronaut’s helmet can wash out the relatively dim light from the stars in the background.
Even with sensitive film, the suits that astronauts and cosmonauts wear reflect a lot of light. The glare from the astronauts themselves will provide contrast from the dark sky background and faint stars. Any light emanating from the stars is unlikely to be exhibited when cameras are geared toward capturing clear shots of a space walker.
Perhaps the space conspiracists would stifle themselves if the Apollo astronauts had taken time-exposure photographs that could display the stars in all their glory, but they never did. As McBain puts it: “After all, they went to the Moon to explore the moon, not to stargaze.”
Submitted by Scott Cooley of Frisco, Texas. (For much more
information on the issues of photography in outer space,
see Jim McDade’s “Moonshot” Web site at http://www.
business.uab.edu/cache/Defaultb.htm.)
* * *
WHY DO SONIC BOOMS OFTEN
COME TWO AT A TIME?
* * *
Sonic booms are caused by the displacement of air around an aircraft flying faster than the speed of sound. Even slow-moving aircraft can produce pressure waves ahead of and behind the aircraft that travel at the speed of sound. But once supersonic speeds are attained, pressure disturbances called “shock waves” form behind the aircraft and reach the ground in the form of a thunderlike sound.
Many parts of the airplane are capable of creating shock waves, even the wings. But as the distance between the airplane and a person on the ground increases, only two shock waves are felt—the bow shock wave and the tail shock wave. Bill Spaniel, public information coordinator of Lockheed Aeronautical Systems Company, sent a clipping from Above and Beyond: The Encyclopedia of Aviation and Space Sciences, Vol. II, that explains the phenomenon:
As the distance between the airplane and the observer is increased, the distance between the bow and tail shock waves is also increased. A person on the ground may even hear two booms, with a time interval between the bow shock wave and the tail shock wave of one-tenth to four-tenths of a second.
These shock waves pattern themselves in a cone shape, and can be felt on the ground for miles on either side of the flight path.
If you haven’t noticed an increase in sonic booms since the introduction of the Concorde, the explanation is that supersonic aircraft travel at heights often twice that of subsonic widebodies. Although just as many shock waves are created at 65,000 feet altitude as at 30,000 feet, the intensity of the sonic boom is diminished by the extra mileage down to the ground.
Submitted by Dr. J. S. Hubar of Pittsburgh, Pennsylvania.
* * *
WHY DO WINTERGREEN LIFE SAVERS
SPARKLE IN THE DARK WHEN
YOU BITE INTO THEM?
* * *
Be the life of your next party. Buy a few rolls of wintergreen Life Savers Roll Candy, cut all the lights, gather your friends in front of you, and bite down hard and fast. You’ll sparkle in the dark. Your mouth will glow bluish-green.
The explanation for this delightful phenomenon comes directly from the research and development department of Life Savers Inc., which is now a division of Nabisco Brands:
Our manager of Candy Technology tells us that two ingredients are necessary for this reaction. The sparkling comes about because of a combination of mint flavoring and crystalline sugar. When you crack the crystal, the energy then stimulates a component in the flavoring to emit a light. The component in wintergreen is methyl salicylate.
There are two possible hang-ups in producing the sparkling effect. First, the background atmosphere might not be dark enough (closets and bathrooms are highly recommended). Second, moisture seems to absorb the energy needed to produce sparkling. Do not expect good results in a sauna.
* * *
HOW DID ROMANS DO THE
CALCULATIONS NECESSARY FOR
CONSTRUCTION AND OTHER PURPOSES
USING ROMAN NUMERALS?
* * *
Our idea of a good time does not include trying to do long division with Roman numerals. Can you imagine dividing CXVII by IX and carrying down numbers that look more like a cryptogram than an arithmetic problem?
The Romans were saved that torture. The Romans relied on the Chinese abacus, with pebbles as counters, to perform their calculations. In fact, Barry Fells, of the Epigraphic Society, informs us that these mathematical operations were performed in Roman times by persons called “calculatores.” They were so named because they used calcule (Latin for pebbles) to add, subtract, multiply, and divide.
Submitted by Greg Cox of San Rafael, California.
* * *
WHAT ACCOUNTS FOR THE GREAT
DIFFERENCE IN CLIMATE BETWEEN THE
ATLANTIC COAST AND PACIFIC
COAST OF THE U.S.?
* * *
If you are like us, you glaze over during weathercasts on the local news. The intricacies of the weather map, complete with air flows and troughs, strike us as no easier to comprehend than quantum physics. Why waste five valuable minutes on a weather report when all we want to know is whether we need an umbrella or an overcoat? After all, the four minutes saved could be devoted to more important news, like a graphic depiction of another grisly murder or a juicy political scandal.
“It Never Rains in Southern California,” warbled Albert Hammond in his 1972 gold record. Not quite accurate, Albert, but not a bad meteorological generalization from someone who spent most of his life in Gibraltar. The weather is more moderate on the left coast and certainly much warmer in winter. Why is this?
The one principle we have managed to glean from those weathercasts is that the prevailing winds in North America move from west to east. We inherit the weather from the west of us. The sea is much slower to change in climate and temperature than land masses. Although the Pacific Ocean has its share of storms, they are relatively infrequent and are usually associated with moderate weather. So the West Coast receives relatively infrequent storms and moderate weather.
Sol Hirsch, executive director of the National Weather Association, told Imponderables that the Rocky Mountains are most responsible for the colder and stormier weather of the East Coast (and the Midwest, for that matter):
The weather in the east is determined by storm systems developing from the Rockies eastward that are generally moving in easterly or northerly directions, due to the rotation of the earth. In addition, the area east of the Rockies is exposed to cold air coming from Canada whereas cold air west of the Rockies is infrequent.
The collision of multiple fronts east of the Rockies manufactures storms and makes the weather patterns volatile and difficult to predict.
Of course, the volatility of weather in the East makes the job of a weathercaster considerably dicier than his West Coast counterpart’s. If a weathercaster in southern California predicts “85° and partly cloudy” during the summer and “75° and partly cloudy” during the other three seasons, he won’t be too far wrong.
* * *
IF WATER IS COMPOSED OF TWO PARTS
HYDROGEN AND ONE PART OXYGEN,
BOTH COMMON ELEMENTS, WHY CAN’T
DROUGHTS BE ELIMINATED BY COMBINING
THE TWO TO PRODUCE WATER?
* * *
We could produce water by combining oxygen and hydrogen, but at quite a cost financially and, in some cases, environmentally.
Brian Bigley, senior chemist for Systech Environmental Corporation, says that most methods for creating water are impractical merely because “you would need massive amounts of hydrogen and oxygen to produce even a small quantity of water, and amassing each would be expensive.” Add to this the cost, of course, of the labor and equipment necessary to run a “water plant.”
Bigley suggests another possible alternative would be to obtain water as a by-product of burning methane in an oxygen atmosphere:
Again, it’s a terrible waste of energy. Methane is a wonderful fuel, and is better used as such, rather than using our supply to produce H2O. It would be like giving dollar bills to people for a penny to be used as facial tissue.
The most likely long-term solution to droughts is desalinization. We already have the technology to turn ocean water into drinking water, but it is too expensive now to be commercially feasible. Only when we see water as a valuable and limited natural resource, like oil or gold, are we likely to press on with large-scale desalinization plants. In northern Africa, water for crops, animals, and drinking is not taken for granted.
Submitted by Bill Irvin III of Fremont, California.
* * *
WHY DOES YOUR VOICE SOUND HIGHER
AND FUNNY WHEN YOU INGEST HELIUM?
* * *
The kiddie equivalent of the drunken partygoer putting a lampshade on his head is ingesting helium and speaking like a chipmunk with a caffeine problem.
Still, many Imponderables readers want to know the answer to this question, so we contacted several chemists and physicists. They replied with unanimity. Perhaps the most complete explanation came from George B. Kauffman:
Sound is the sensation produced by stimulation of the organs of hearing by vibrations transmitted through the air or other mediums. Low-frequency sound is heard as low pitch and higher frequencies as correspondingly higher pitch. The frequency (pitch) of sound depends on the density of the medium through which the vibrations are transmitted; the less dense the medium, the greater the rate (frequency) of vibration, and hence, the higher the pitch of the sound.
The densities of gases are directly proportional to their molecular weights. Because the density of helium (mol. wt. 4) is much less than that of air, a mixture of about 78 percent nitrogen (mol. wt. 28) and about 20 percent oxygen mol. wt. 32), the vocal cords vibrate much faster (at a higher frequency) in helium than in air, and therefore the voice is perceived as having a higher pitch.
The effect is more readily perceived with male voices, which have a lower pitch than female voices. The pitch of the voice [can] be lowered by inhaling a member of the noble (inert) gas family (to which helium belongs) that is heavier than air, such as xenon (mol. wt. 131.29)….
Brian Bigley, a senior chemist at Systech Environmental Corporation, told Imponderables that helium mixtures are used to treat asthma and other types of respiratory ailments. Patients with breathing problems can process a helium mixture more easily than normal air, and the muscles of the lungs don’t have to work as hard as they do to inhale the same volume of oxygen.
Submitted by Jim Albert of Cary, North Carolina. Thanks also to
James Wheaton of Plattsburg AFB, New York; Nancy Sampson of
West Milford, New Jersey; Karen Riddick of Dresden, Tennessee;
Loren A. Larson of Altamonte Springs, Florida; and
Teresa Bankhead of Culpepper, Virginia.
* * *
WHY DON’T TORNADOES EVER SEEM TO
HIT BIG BUILDINGS OR BIG CITIES
* * *
The operative word in this mystery is seem. For all of our meteorological experts agree with Harold Brooks, the head of the Mesoscale Applications Group of the National Severe Storms Laboratory in Norman, Oklahoma, who states:
There is a myth that tornadoes don’t hit downtowns, but that is just a myth that comes from the fact that downtowns are small areas. If you randomly picked any other similarly sized areas in the middle of the United States, they wouldn’t get hit often, either.
In other words, tornadoes are non discriminatory offenders, and are subject to the laws of probability. The land covered by major population centers is tiny compared to the total expanse of North America, but a big city is theoretically just as likely to get hit as all the local trailer parks if they covered as much of an expanse as the downtown area.
There are portions of the United States where tornadoes are much more likely to hit, however. Tornadoes have been tracked in all fifty U.S. states, but the so-called tornado alleys are the midwestern area from Texas all the way north to the Canadian border, in the southeastern United States, and in the Ohio Valley and southern Great Lakes region, extending as far east as western Pennsylvania. But within that general area, trailer parks, skyscrapers, the Mississippi River, or the Dallas Cowboy cheerleaders can’t stop tornadoes.
One other reason why the perception may have spread that tornadoes don’t hit big cities is that many of the densest population centers, such as the Washington, D.C.–to–Boston and the San Diego–to–San Francisco corridors, are outside of “tornado alley.” Even so, tornadoes do sock big cities. Chuck Doswell, senior research scientist at the Cooperative Institute for Mesoscale Meteorological Studies, wrote us:
Tornadoes have recently hit the downtown areas of such cities as Salt Lake City, Utah; Miami, Florida; Nashville, Tennessee; and Fort Worth, Texas. In the Texas event, there were at least two tall buildings hit. One suffered enough damage that it was decided to demolish it rather than to repair the damage.
In 1970, in Lubbock, Texas, a violent tornado hit a large building with sufficient force to twist the structure. The only reason tall buildings are hit infrequently is that they don’t occupy very much space in this nation of ours. The more area covered, the greater the likelihood of being hit by a tornado.
Dr. T. Theodore Fujita, a tornado scientist who developed the scale commonly used to rank the severity of tornadoes, considered the role of skyscrapers and population density in thwarting the development of small tornadoes. The University of Chicago professor, who died in 1998, noted that since 1921, “practically no tornadoes occurred or moved across the central portion of Chicago.” Fujita theor
ized that perhaps the city’s higher temperature than surrounding areas (a phenomenon we discussed in our Imponderables book Why Don’t Cats Like to Swim?) and its man-made structures might be “acting against any tornado activity over the city.” Other major population centers that have been studied for tornado patterns, London and Tokyo, also seem to enjoy a relative dearth of small-tornado activity. But no expert seems to seriously think that even the highest skyscraper in the largest metropolis would scuttle an intense tornado from unleashing its fury.
Submitted by John Beton of Chicago, Illinois.
Thanks also to Laura Gunn of Ames, Iowa.
* * *
WHY DOES RINSING WITH HOT WATER
“SET” A STAIN? WHY IS RINSING WITH
COLD WATER MORE EFFECTIVE IN
ELIMINATING THE STAIN?
* * *
First the good news. As you increase the temperature of the water applied to a stain, the solubility of the stain also increases. Obviously, dissolving the stain is a good first step in eliminating the stain.
Science Page 2
