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" I REMEMBER THE FIRST TIME my child ever saw his breath on a cold winter day. We&amp;#039;d just gone out the back door onto our deck, heading for the car. It&amp;#039;d been one of those mornings--he didn&amp;#039;t want to put on his boots, we were running late (again), I still had to drop him off at daycare before I could get to an early meeting--and the last thing I needed was for him to stop in his tracks on our porch. But there he was, transfixed by something he&amp;#039;d never seen before: the condensation that forms when hot vapor meets cooler air. &amp;quot;What&amp;#039;s that?&amp;quot; he asked as he pointed in wonder at the steam coming from his mouth. &amp;quot;Why is it doing that?&amp;quot; A child marveling at the daily miracles of the natural world is hardly unusual. As any parent knows, all kids ask, Why? The problem is, most of us, when attempting to answer that question, have no idea where to begin. Here&amp;#039;s a start.  \u00BBUNIMAGINABLY HOT. Insanely hot. Hotter than Alabama pavement, hotter than a thousand McDonald&amp;#039;s deep fryers. The temperature of the photosphere--the sun&amp;#039;s surface--reaches 9932 degrees Fahrenheit. Nothing solid can survive there; titanium, for instance, one of the strongest metals, melts at 3035 degrees. And yet the sun&amp;#039;s surface is downright arctic compared with its core, where nuclear fusion takes place (meaning hydrogen molecules collide with one another to produce helium). There the thermometer reaches a toasty 27 million degrees.  Where Does the Rain Go After It Falls? \u00BBTHE EARTH&amp;#039;S WATER, like Madonna or herpes, never goes away; it just takes different forms. Rain is one of those forms. When rain falls on the ground, some of it flows directly to lakes, rivers, and oceans. But some sinks into the earth, seeping into the pores between rock and mineral grains below the surface. These pores link to form underground layers called aquifers, which conduct the water under the earth. Sometimes it takes months, sometimes years, but the aquifers eventually dump the water back into the ocean. The ocean water warmed by the atmosphere evaporates, forms clouds, and falls once again in Ecclesiastical fashion to the earth&amp;#039;s surface.  What Makes Lightning Think of the shock you feel when you walk across a rug and then touch a metal doorknob. Lightning is the same phenomenon writ large. As a puffy, dark thundercloud develops, part of it takes on an excess negative charge while another part becomes overly positive. To equalize things, a path of electrons shoots across a narrow channel in the air. Voil\u00E0--lightning. Though most lightning flows within and between clouds, sometimes a cloud with a negatively charged bottom will pass over a positively charged bit of earth. That&amp;#039;s when lightning zaps to the ground. We usually see the stuff as a single dramatic flash, but it&amp;#039;s really several quick segmented strokes. (Turns out lightning does strike twice.)  As for thunder, lightning&amp;#039;s sidekick, it&amp;#039;s caused by the bolt&amp;#039;s searing, 50,000-degree heat. The air around the lightning expands, and that in turn sends out rumbling sound waves. Sound, of course, travels more slowly than light, so we&amp;#039;ll always hear thunder later. And in case your parents never taught you the formula: A five-second delay means the lightning is about one mile away.  How Far Down Does Dirt Go Depending on where you are, dirt goes down as little as a few inches or as much as ten feet. What kids call dirt--and what scientists and H&amp;amp;amp;G subscribers call topsoil--is composed of disintegrated rocks mixed with a smattering of organic litter (dead leaves, dead animals, that apple you tossed in 1997). The more rain that falls in an area, the faster the rock erodes, the deeper the soil. Go to the Amazon forest, for instance, and your kids could dig happily for hours; go to an Arizona desert and they&amp;#039;d barely get started before they hit the subsoil, a much harder level made up mostly of clays and salts. If your children have heavy drilling machinery, they might be able to burrow through the subsoil, after which they will encounter bedrock. If they get through that, the earth&amp;#039;s molten core will make their dig to China really disagreeable.  What Happened to the Dinosaurs If your children have seen the Fantasia segment set to Stravinsky&amp;#039;s Rite of Spring, they probably think heat exhaustion caused dinosaur extinction. And in fact, some scientists have suggested that scorching temperatures killed off the great beasts. One postulated that since male gonads function in a narrow range of temperatures, the heat of the late-Mesozoic world prevented dinosaurs from reproducing--a theory Stephen Jay Gould has termed the &amp;quot;testicular frying hypothesis.&amp;quot; Paleontologists haven&amp;#039;t found fossilized dinosaur testicles, so the theory must remain fanciful speculation, not science. Which is a good thing, if you don&amp;#039;t want to explain sperm counts to your kids yet. Tell them this instead: Most scientists believe the culprit was a meteorite that left a hundred-mile-wide crater under Mexico&amp;#039;s Yucat\u00E1n Peninsula. Immediately upon impact, an explosion flattened forests as far as a thousand miles away, caused magnitude-10 earthquakes, and threw up so much dust that it was too dark to see for six months. Temperatures dove, photosynthesis stopped, food chains were disrupted, fires raged. Wait, there&amp;#039;s more: Land creatures who survived the immediate catastrophe keeled over from carbon-monoxide suffocation, and acid rain killed water critters. In short, the whole thing was less pleasant than Times Square on New Year&amp;#039;s Eve.  Why IsThere a Face in the Moon? \u00BBON OCCASION, I&amp;#039;VE THOUGHT THE MAN IN THE MOON--with his drawn features and gloomy aspect--looked as though he were painted by Edvard Munch. But the real artist behind this lunar portrait was a shower of ancient meteors.   The face is an illusion caused by two types of rock. The lighter rock is feldspar, the same mineral that makes up most of the earth&amp;#039;s crust. The darker rock is basalt, the same black substance that makes up the lava in Hawaiian volcanoes. Millions of years ago, meteors crashed onto the lunar surface, exposing vast, dark basalt tracts, which Galileo called mare because he thought they looked like seas.   The man in the moon won&amp;#039;t be going away soon, for unlike the earth--a dynamic planet replete with volcanoes, earthquakes, and waters that redistribute surface sediments and change the configuration of coastlines--the moon is a huge, unchanging rock. So your great-great-great-grandkids will be staring at the same face through the windows of their hovercrafts.  Why Do Leaves Turn Bright Colors in the Fall? BLAME IT ON THE above-mentioned sun. Or, more precisely, the lack of it. The leaves of deciduous trees--oak, maple, beech, hickory, and poplar, for example--get their green color from the presence of chlorophyll, which is key to photosynthesis. Chlorophyll is the stuff that takes sunlight (along with water and carbon dioxide) and converts it into glucose--the tree&amp;#039;s food. But as the days get shorter and the sunlight more scarce, chlorophyll production slows down and stops. When that happens, another pigment present in leaf cells, carotene--responsible for the yellow and orange of corn, carrots, bananas, and egg yolks--is revealed. The reds, deep oranges, and purples we sometimes see in autumn leaves come from a third pigment, anthocyanin, which is a product of the glucose trapped in the leaves at the end of the season. Without their raison d&amp;#039;\u00EAtre--food production--the leaves become a liability, a waste of energy. The tree sheds them. Fortunately, other parts of deciduous trees can survive extreme cold. They awake in spring, and the cycle begins again.  Why Do We Have Hair? \u00BBUNLIKE MOST OTHER MAMMALS and the Baldwin brothers, humans do not have a thick layer of fur covering the body. We don&amp;#039;t need it. As our ancestors evolved and moved indoors, nature&amp;#039;s protective overcoat became unnecessary. But we did keep some dense patches of follicles around our most vulnerable areas. A clever idea. The hair on our heads, for instance, protects us from the sun and insulates us from the cold. (Most of the body&amp;#039;s heat escapes through the head, just like Mom and Dad said.) Head hair also acts like a cat&amp;#039;s whiskers, detecting dangers, such as low-hanging branches, before they slam into the skull. As for the body&amp;#039;s other clumps of hair--those under the arms and around the crotch--they serve a different purpose. They&amp;#039;re the storehouses for our bodies&amp;#039; pheromones, the chemicals secreted by humans to attract mates. Of course, not all of hair&amp;#039;s mysteries have been solved. For instance, scientists still don&amp;#039;t know what&amp;#039;s happening on top of Ted Koppel&amp;#039;s head.   JILL S. SCHNEIDERMAN IS THE EDITOR OF THE EARTH AROUND US: MAINTAINING A LIVABLE PLANET (W. H. FREEMAN, 2000), A BOOK OF ESSAYS ABOUT SCIENCE AND THE ENVIRONMENT. Artwork by students of Lewisboro Elementary School, South Salem, New York "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.esquire.com/lifestyle/a1588/hot-sun-kids-daddy-0301/>