Karen Hill

The scale of relative hardness, developed by Stanley F. Rockwell around 1920, runs from C20 to C80. Each point on the Rockwell scale represents 80 millionths of an inch of depth when the steel is tested with a sharp point and a standardized weight. The higher the number, however, the harder the steel. In general, … Read more

A rearview mirror with a night position is actually two reflective surfaces. One is a shiny mirror that is about 90 percent reflective. Over it is a wedge of glass that is only about 4 percent reflective. The wedge is very thin and angled only a few degrees. In the daytime, the mirror is angled … Read more

Using a battery-operated device continuously for four hours would run down a battery faster than using it for an hour on, then an hour off, for four cycles. The reason is that batteries have a tendency to recover a little bit if not used for a time. A battery’s current comes from electrons that are … Read more

Newer magnets are made of materials that are far less likely to lose their magnetism over time than the old horseshoe magnets. Magnets are composed of many little magnetic regions called domains. The magnetic field of the whole magnet runs opposite to the direction of the domains that cause the field. That tends to make … Read more

The necklaces and other temporary chemical lights work by imitating the chemical reaction called bioluminescence that allows fireflies to light up. The reaction in the plastic tube is oxidation, as in burning, but the chemicals involved, called luciferins, produce more light than heat. When the proper chemical is mixed with diluted hydrogen peroxide from a … Read more

The simplest way, and one that is still in use with the aid of satellites, is just an elaboration of how scouts are taught to measure the height of trees, by constructing a triangle with some known values and then filling in the blanks. In the surveying method called triangulation, a baseline of a known … Read more

Sea level, actually mean sea level, is calculated as the average height of the sea surface taking into account all stages of ocean tides. It is measured at various locations by a network of tide gauges over a nineteen-year period. Scientists have long recognized the inaccuracy of these tide measurements, and satellites are offering more … Read more

A hollow tube called a pitot tube is mounted on the surface of the nose of an aircraft. As they board, passengers may be able to see this tube on the nose toward the bottom of the plane. The tube is parallel to the air that comes over the plane, and measures what is called … Read more

For many years, the international standard for defining all units of length was the meter as defined by the distance between two scratches on a platinum-iridium bar. The bar is stored in a vault at the International Bureau of Weights and Measures at Sevres, near Paris. In 1960, the basis of the standard was changed … Read more

Not a great deal is known about Roman mathematics because they were not terribly interested in it. Doing arithmetic probably played a much smaller role in the everyday lives of Romans than it does in ours. The Romans had signs for 1, 10 and 100, etc., but they did not have a place value system, … Read more

Objects weigh less the further they go below the earth’s surface. If you assume that the earth is a perfect sphere with a uniform mass throughout, and you went below the surface of the sphere, only the mass within your radius would contribute to your effective weight. The radius of the earth is 6,371 kilometers. … Read more

Theoretically, it would go all the way through and then back, oscillating back and forth forever. The brick would be exactly like a mass on a spring pulling it toward the center of the earth. Momentum keeps it going through the center, but after that the spring is slowing it down. The object goes all … Read more

Daniel Gabriel Fahrenheit, who devised the scale, wanted natural reference points, but he did not choose wisely. Fahrenheit, an instrument maker born in Danzig in 1686, developed three different temperature scales as his knowledge of natural phenomena increased. He chose points like the freezing temperature of water and the underarm temperature of a healthy adult … Read more

Standing near and touching the radio probably represent two different phenomena. In addition to traveling from one point to another, radio waves are being reflected and absorbed by objects in a room, and the pattern of reflection can cause interference as the spurious signal interferes with the original signal. Standing in the path of the … Read more

Daytime visibility is defined as the greatest distance at which it is possible to see and identify, with the naked eye, a prominent dark object against the sky at the horizon. Daytime visibility reports are estimates based on local landmarks and conditions. Nighttime visibility is the greatest distance at which it is possible to see … Read more

Yes, you can take your garden sundial to the same latitude in the southern hemisphere, but the numerals would have to be reversed in a mirror-image way. That is, for example, the displaced sundial would show 1 P.M. when it was 11 A.M. While the sun’s apparent path across the sky moves from east to … Read more

What we think of as weight is the gravitational pull of the earth itself on a person or object. Therefore, asking the earth’s weight is essentially meaningless, because it has weight only in relation to another object. However, the mass of the earth, the quantity of matter in it, can be estimated by calculating its … Read more

It is widely believed that planet earth is gaining mass. A large number of small meteorites strike the earth every year, while the amount of material thrown out into space is comparatively negligible. Most of what is launched returns to earth as man-made meteorites. Everything that is sent into orbit remains in the range of … Read more

There is no maximum temperature, because there is no limit to the amount of energy you can put into anything. Absolute zero, minus 273.15 degrees Centigrade, minus 459.67 on the Fahrenheit scale, is theoretically the temperature at which all molecular activity ceases. It represents an absence of energy. There is the concept of a lowest … Read more

The treeline or timberline, the line on mountains and in polar regions beyond which trees will not grow, is mostly determined by temperature. Trees need a long enough and warm enough summer to ripen seeds, produce new wood and form buds. However, temperature is not the only factor, and the altitude above sea level is … Read more

Not everyone does, but those who do, do so because of a phenomenon called binocular rivalry. If you look through a sight with the left eye, what you see is not identical with what you see with the right, and the two images compete, rather than blending, as they normally do when you look at … Read more

Degree days are used as an approximate measure of energy demand to let utilities and householders keep track of what energy use for heating or cooling ought to be from day to day or year to year. To calculate degree days for a given day, add the high and low temperatures, divide by two and … Read more

The term humiture was coined in 1937 by O. F. Hevener, a meteorologist, to refer to the discomfort felt in the upper temperature ranges when the humidity rises. The higher the humidity, the warmer it feels to the human body, because it cannot evaporate sweat as easily. Many indexes have been devised to quantify the … Read more

The curved surface of a clear measuring cup, either glass or plastic, acts as a simple convex lens, very much like the ones in eyeglasses. The light rays passing through the cup are bent in such a way as to magnify the image from inside the cup. The result is that looking down into the … Read more

The measurement of rainfall is fairly straightforward, but snowfall presents problems that make measurements somewhat arbitrary. For rain, the meteorology department at Pennsylvania State uses a simple cylindrical tube to catch it. The amount that falls in a given period is poured into a smaller cylindrical tube that is carefully gradated and measured with something … Read more

The transporter in Star Trek will probably never be invented, scientists suspect. In a sense, the human genome project would be the first step in such a project, because you would need the whole genetic blueprint of a person, present in each cell, to copy the cells. But even if you had all that information, … Read more

In effect, a person who died in the icy vacuum of space would be freeze-dried, space experts theorize. The water in the body would freeze and eventually dissipate into space. Ice can evaporate without going through the liquid phase. Because there is no oxygen, there would be no decomposition, and there is little evidence that … Read more

There are two federal agencies that offer very accurate time signals by telephone, and one of them offers shortwave radio broadcasts of the same information. Dialing the United States Naval Observatory Master Clock at (202) 762-1401 puts you in touch with a time signal in hours, minutes and seconds, on a twenty-four-hour clock in Eastern … Read more

The space suits worn by United States astronauts are made of several layers of super strong fibers and other materials that are tough enough not to rupture in the vacuum of space. The materials in the nine or ten protective layers include: 1. Orthofabric, which is Teflon with Kevlar ripstop protection. 2. A layer of … Read more

Since we can’t actually weigh astronauts in weightlessness, body mass measurements are used to determine any change in weight. Weight, in this case, is what the astronaut would weigh under the influence of earth gravity. Such measurements are made with a spring-like device and a highly accurate timer. By measuring the time, or periodicity, between … Read more

On space flights in the past, the components of breathable air, oxygen and nitrogen, were brought up in canisters. However, when the space station built, plans were announced to have it carry equipment to recover oxygen indirectly from the carbon dioxide crew members exhale. astronauts NASA’s Johnson Space Center tested means to recycle air and … Read more

There are more grains of sand on earth than stars in the universe. The recently published data from Hubble Space Telescope images help confirm scientists long-held suspicion that the universe has many galaxies invisible to ground-based telescopes, so an increase from ten billion galaxies to fifty billion was not unexpected. Some estimates have gone even … Read more

Latitude and longitude are also used on the moon by the astrogeology department of the United States Geological Survey in Flagstaff, Arizona, which maps extraterrestrial bodies. Like the earth, the moon has an axis of rotation and an equator, so latitude is indicated in degrees of latitude north or south of that equator, just as … Read more

According to NASA, astronauts do not use compasses in space, but near-earth orbit would not change the behavior of the magnetic needle significantly. If the compass were in the cockpit of an orbiter, it would probably behave much as it does on earth. The needle would follow the lines of the planet’s doughnut-shaped magnetic field … Read more

Many researchers think the phenomenon of the moon showing the same face, called gravitational phase locking, occurs because of the uneven distribution of matter in the bodies involved. Normally, when two bodies join in holy matrimony and decide to go around together forever, their spins would stay what they were beforehand. But because they may … Read more

Astronomical temperatures are usually estimated from spectroscopic measurements. The spectroscope was invented in 1859 by two German scientists, Robert Wilhelm Bunsen of Bunsen burner fame and Gustav Robert Kirchoff. It was first used to analyze the elements in a substance heated to incandescence, each element gave off characteristic wavelengths of visible light. Bunsen used the … Read more

What makes that question interesting is that it presumes there is some reason you couldn’t. The moon is just as much out in daytime as it is at night. In the daytime, the sun is so much brighter than everything else that the moon may not be noticeable even when it is visible. At night, … Read more

Yes, sometimes, but it is not a simple slowing because of friction with a stationary air mass. The effect of the atmosphere on the rotation came about because of the way the sun’s heat and the absence of it alternate to stir up the atmosphere. The resulting wind patterns sometimes speed up the earth and … Read more

Stars and to a lesser extent planets twinkle simply because we are seeing them through the many layers of the atmosphere of the earth. These layers of different densities move around, bending or scattering sortie of the light. The upshot is that all the rays of light that could reach your eyes from a star … Read more

Scientists believe the earth’s tilt results from the impact of another celestial body during the later stages of the formation of the solar system. The planets are believed to have formed when smaller bodies were drawn together by gravity, hitting each other at high speeds. One of the later, larger impacts may not have been … Read more

Planets and moons are not perfectly round, of course. They only seem spherical, or almost spherical. Earth, for example, is flattened at the poles, and Jupiter and Saturn, because their extremely dense atmospheres are all we can see, appear even flatter at the poles. The reason that stars, planets and so forth are even almost … Read more

It is a common belief that the direction of rotation of a bathtub or toilet vortex is determined by the hemisphere it occurs on. Theoretically, water draining from a bathtub is affected by the Coriolis force, the inertial force caused by the earth’s rotation. It would have a tendency to go straight down. North or … Read more

There are two main theories on the origins of the earth’s water. Some believe the water was here from the start, some think it came later, from comets. Years ago, people tended to assume that the water concentrated at the earth’s surface was locked up inside and slowly emerged over the 4.5 billion years of … Read more

Yes, but you won’t see our summer stars, but their summer stars. You see another set of constellations, including many we never see, summer or winter. As you travel south, the constellations near Polaris, our north star, get lower and lower in the sky. The Dig Dipper would disappear by the time you get to … Read more

The zodiacal signs originate in Babylonian astronomy during Neo-Babylonian times around 7th century BC. The real sky that the zodiac corresponds to is simply those constellations through which the sun appears to move during the course of the year as seen from the earth. People living anywhere on the surface of the earth would pretty … Read more

No, and in fact there are submarine volcanoes, called guyots or seamounts. Their molten rock spreads on the ocean floor and is eventually cooled by sea water, creating what is called pillow lava. At depths below 6,600 feet high pressure prevents the explosive formation of steam that results when water meets molten rock at higher … Read more

While scientists have calculated a mean sea level for the earth as a whole, it is only a mathematical average value taken from a series of observations around the world. In fact, there is no single “sea level,” and the large bodies of water in the world have different and constantly varying levels because of … Read more

We have all been taught that the tides are chiefly the result of the gravitational attraction of the moon on the waters of the earth’s oceans. But there are actually two rotational systems involved, and two bulges of water. First, the moon goes around the earth, or so it appears. Actually, both the earth and … Read more

Scientists have estimated how much the sea level would rise, but the exact amount of land lost would require a very complicated worldwide coastal survey. Perhaps only the military knows. Melting the East Antarctic Ice Sheet would raise sea levels about 60 meters worldwide, or about 200 feet, while melting the West Antarctic Ice Sheet … Read more

Ice floats because water molecules occupy more space in the solid state than in the liquid state, so that a given volume of ice is lighter than the same volume of water. The way molecules fit together in ice crystals is not as compact as in water. They don’t change size, it is just the … Read more

The big East Coast storm of December 1992 was called a northeaster when it came up from the south because the surface winds and the high-level winds of such a storm often go contrary to one another. The high-altitude winds moved the storm from south to north, but the surface winds spiraled from the northeast. … Read more

Rocks that erode on the continents contain salt, which is brought by the rivers to the ocean. In fact, fresh water rivers carry a certain amount of dissolved minerals. Most of it is common table salt, NaCI, or sodium chloride. Once the salt gets to the sea, it tends to stay there and accumulate. Sodium … Read more

Although archeologists tend to uncover things, that is not necessarily because ruins have sunk beneath the surface of the earth. Instead they are usually covered over with newer buildings or natural deposits of sand and debris. There are exceptions, for example, in Mexico City, the Aztecs built temples on a lake bed, where they did … Read more

Meteorologists joke about building trailer parks to attract tornadoes, and there is more than a grain of truth in the jest, because trailer parks tend to occupy the kind of terrain that allows tornadoes to develop. About 80 to 90 percent of the time, tornadoes are the offspring of a thunderstorm that is rotating, spinning … Read more

Big waves can damage a coastal reef when they break, but 100 miles at sea, waves do not affect the sea floor. As a rough formula, if the wavelength, the distance between successive crests, is less than four times the depth of the ocean at that point, the waves do not affect the bottom. In … Read more

The strength of what meteorologists call the updraft in a thunderstorm is what determines the size. A storm forms at a place in the atmosphere where the air is moving up very rapidly. When the air cools in the cold upper atmosphere, its water vapor condenses into a storm cloud. Eventually precipitation forms in the … Read more

The arrow on a weather vane points into the wind. If the arrow is to the north, the wind is from the north. The tail of the weather vane is heavier than the nose, and in some but not all weather vanes, there is some type of flap that moves as the wind blows so … Read more

The most common rainbows form when sunlight enters raindrops. The drops act like prisms and disperse the sun’s light into the familiar spectrum of colors: red, orange, yellow, green, blue, indigo and violet. Rainbows are round by necessity because of the geometry involved in seeing them. You see a rainbow when you have the sun … Read more

It is never too late for hurricanes, but there is a difference in when they usually occur during the year. The official hurricane season in the Atlantic begins June 1 and ends November 30. To become a hurricane, a storm must first be a tropical storm, and tropical storms in the Atlantic have formed in … Read more

Ball lightning is a poorly understood and comparatively rare phenomenon. So if you ever see one, try to take a picture. Perhaps 1 percent of the population will see ball lightning in a lifetime. Though there have been thousands of reports of ball lightning, it is still very hard to study, because scientists do not … Read more

A ring around the moon means rain or snow is coming soon. The old folk rhyme is accurate, because high clouds typically streak out ahead of a fall or winter storm. This veil of wispy cirrus clouds, about 20,000 feet up, is mostly ice crystals that act like tiny prisms in the sky. They refract … Read more

There is sometimes lightning in a snowstorm, although it is somewhat rare. In fact, the biggest snowstorms are those marked by thunder and lightning, a phenomenon meteorologists call “thunder snow.” Most “regular” thunderstorms are summer events in which warm, moist air in the lower atmosphere has very cold air over it. In this unstable system, … Read more

It can certainly get so cold that precipitation is highly unlikely, because the colder the air is, the less water vapor it can hold. At temperatures around 40 degrees below zero Fahrenheit, it is very difficult to produce precipitation, and if it does snow, there is very little of it. At very low temperatures there … Read more

The South Pole is considerably colder than the North Pole. At about 56 degrees Fahrenheit below zero, the average temperature at the South Pole is about 35 degrees lower than the average at the North Pole. The coldest weather on record was minus 129 degrees, recorded at Vostok, Antarctica, on July 21, 1983. There are … Read more

The earth spins under a plane as it travels, at 15 degrees per hour. But that doesn’t mean much when everything else on the planet including the atmosphere spins with the earth. The air mass that supports the plane as it travels is rotating along with the earth, under its gravitational pull and at the … Read more

Natural pearls and cultured pearls feel slightly rough or gritty when brushed lightly on the front teeth. Imitation pearls are glassy-smooth, or plastic-smooth, to the bite. The tooth test does not work as well if the teeth are capped, however, as their sensation is somewhat deadened. Natural pearls and cultured pearls are both made by … Read more

If they are properly maintained, structural engineers believe skyscrapers will last forever. After proper design, the key is the integrity of the materials. Steel or concrete can be damaged by things like acid rain, but if damaged material is replaced, the building will survive. If a structure like the World Trade Center were abandoned and … Read more

If the coin fell straight down on edge and did not catch on the many overhangs and projections of a building of that era, it could build up its velocity to 150 miles an hour. If the penny fell flat, the drag of the air through which it fell would be much higher and the … Read more

Terrestrial dust is mostly tiny fragments abraded from larger things. Some of it may be even smaller things aggregating together to form motes of dust. The larger things that turn to dust can be almost anything in the world, from shoes (one study found fragments of shoe leather to be a significant part of the … Read more

One simple reason why ice is slippery is that pressure and friction from shoes or skates can melt a very thin layer at the top of snow or ice. It then forms a watery lubricant between ice and skate (good) or ice and shoe (bad). Skis also glide on a layer of water. The process … Read more

The deepest cave in the world found up to 1992 is in France, the Reseau Jean Bernard. Its total depth, not just the length of its shaft, is 5,256 feet, almost a mile straight down. The longest system of underground passageways in the world is the Mammoth Cave system in Kentucky. The numbers change with … Read more

The hole in the earth’s ozone layer and ozone pollution are two very different and basically unrelated problems. Down here, ozone is dangerous to health, but in the upper atmosphere it is protective of health. Ozone, or O3, is a gaseous molecular form of oxygen with a distinctive odor. It is a powerful oxidizer and … Read more

Yes, glacier ice purer than regular ice, and it is not surprising that some entrepreneurs have marketed it commercially for drinks. There are several scientific and aesthetic reasons for the superiority of glacier ice. First, the ice in glaciers is relatively pure water because after thousands of years of compression of the tiny snow grains … Read more

On average, the earth is certainly as smooth as a billiard ball. The earth is more than 12,000 kilometers in diameter. Mount Everest is less than 10 kilometers high, and the profoundest depths of the ocean are around 11 kilometers. Thus, the most extreme variations in the earth’s surface are roughly on a scale of … Read more

The famous soil found in Georgia, South Carolina and elsewhere in the southern Piedmont region is mainly a grayish-white clay called kaolin colored by a small amount of iron oxides. It doesn’t take a lot of red paint to paint a barn red, and it doesn’t take a lot of these iron oxides to color … Read more

New oil is being naturally cracked, or distilled, inside the basins of earth this very minute, petroleum geologists believe. It is believed that petroleum is created when deposits of incompletely oxidated plant and animal sediment are subjected to great heat and pressure from overlying sediments, causing partial distillation. Such deposits and sediments collect in ocean … Read more

Silver does not oxidize, or rust, on exposure to air. In fact, compared with most other elements, it is not particularly reactive. It does, however, react with sulfur or sulfur compounds, like hydrogen sulfide in the air, forming tarnish, a compound that is chiefly silver sulfide. Silver sulfide, A025, also called argentous sulfide, is 87.06 … Read more

On the contrary, it is a thin waterproof protective layer called a patina, that forms when copper is exposed to air. One of the challenges in the 1986 restoration of the Statue of Liberty was maintaining it. Copper and copper-rich alloys used for roofs or statues oxidize slowly to yield an insoluble mixture of hydroxo-carbonate … Read more

There are several ways to approximate an eruption date. Historical excavations can reveal when a known settlement was covered by lava. For prehistorical eruptions, some large ones near polar regions left a layer of ash trapped in the polar ice, and oxygen isotopes can be used to tell when the ice solidified around it. However, … Read more

The short answer is that light behaves like a wave of electromagnetic energy, and any material that can transmit the wave is transparent. So why do some materials transmit the wave, while others absorb or reflect the light energy? The answer is more complex. It involves the state of the electrons in the material and … Read more