Helium is lighter than air and just as the heaviest things will tend to fall to the bottom, the lightest things will rise to the top.

Helium weighs 0.1785 grams per liter. Nitrogen, which makes up 80% of the air we breathe, weighs 1.2506 grams per liter.

Basically, if you were to fill a soda bottle with helium and another with air, the one filled with helium would weigh a gram less than the bottle with air. It doesn't sound like a lot, but that's usually why blimps and balloons are usually really big, the one-gram difference really adds up in large volumes. Helium balloons follow the same principle as you do when you float in the water; the law of buoyancy. If the water you displace weighs more than you do, you will float.

Helium isn't the lightest element, hydrogen, weighing a mere 0.08988 grams per liter, is.

Wondering why we don't use that instead of helium?

Well, hydrogen balloons used to be really popular, but it is extremely flammable. The slightest spark will set off a huge explosion. The Hindenburg catastrophe was a direct result of that.

Stars twinkle for the same reason that the air shimmies above a radiator or a fire or hot pavement; because of warm air rising in the atmosphere.

Heat can move in one of three ways. The first is conductance (kun-DIK-tenss). In conductance, the heat passes trough something solid, such as wood or metal. This process is pretty slow.

Another way heat moves is radiation. In radiation, the heat passes directly through space in the form of photons, tiny packets of energy travelling at the speed of light. Radiation is the way that the sun's warmth reaches Earth.

Finally there's convection. In convection, heat warms the air. The warm air becomes less dense (and thus lighter) than the cool air around it, so it rises. Convection is the reason stars twinkle.

When air heated by convection rises, it tumbles and swirls. When light passes from the cool, dense air through the warm swirling, not-so-dense air and back again, it gets bent this way and that. That's why the air shimmies over a fire or a radiator.

As air warmed by the earth rises through the atmosphere, it breaks into bubbles of warm air. As light from the stars passes through the bubbles, it's bent back and forth. This is what makes the stars seem to twinkle.

The sky appears blue to us on a clear day, because the atoms of nitrogen and oxygen in the atmosphere separate the suns white light into its many colors, and scatter them throughout the atmosphere.

The wavelength of the blue light scatters better than the rest, predominates over the other colors in the light spectrum, and makes the sky appear blue to us. The scientific name for this phenomenon is the Tyndall effect, more commonly known as Rayleigh scattering.

This phenomenon describes the way in which light physically scatters when it passes through particles in the earths atmosphere that are 1/10th in diameter of the color of the light. The light spectrum ranges in wavelength from red to violet, and, since the wavelength of the blue light passes through the particles with greater ease than the wavelengths of the other colors of light, the sky appear blue to the naked eye.

The human eye has three types of light receptors, known as cones, located in the retina. The cones are either considered to be red, or blue, or green, based upon their strong response to light at these wavelengths. As light stimulates these receptors, our vision translates the signals into the colors we see.

When gazing at the sky, the red cones respond to the small amounts of red light scattered, and even less strongly to the orange and yellow wavelengths. Although green cones respond to yellow, their response to scattered green and green-blue wavelengths is stronger. Finally, colors near the strongly scattered blue wavelengths stimulate the blue receptors.

In short, the skylight stimulates the red and green cones almost equally, while stimulating the blue cones more strongly. For these reasons, our vision naturally adjusts as clearly as possible to separate colors.

Yes!

At least three different plants turn the tables on insects and eat them instead of the reverse. Each passively, but cleverly, lures its prey, captures its kill with ease, digests its meal by using its plant juices, and then prepares for its next unsuspecting victim.

The pitcher plant of Borneo and of tropical Asia, which has a back-up lure in place should the first fail, is the most notorious of the trio. This plant exudes the scent of sweet nectar that most insects find appealing, and when one approaches to investigate, it finds an equally attractive pitcher-shaped plant with a red-hued rim and cover. Once the insect steps over the rim to drink from the plant, it loses its footing on the smooth interior, slides to the bottom of the abyss, and lands in a pool of liquid, which digests the victim once it has drowned.

The Sundew plant, aptly named for the sticky fluid on the upper part of each leaf that appears to the insect to be dewdrops, packages its victim before digesting it. Small, hair-like projections, which cover the surface of each leaf, are responsible for the sticky fluid on each leaf that lures the insect to the plant. Once the insect touches one of these "hairs," it is stuck, and the other hairs on the upper side of the leaf bend inward towards the center of the leaf, to wrap it in a neat, tight package, thus ensuring that it will stay for dinner. The "dew," which for the insect turned out to be a don't, digests it over the course of two days, after which the crafty hairs reopen for business.

The Venus's-flytrap, hailing from parts of North and of South Carolina, is the most gripping of these predatory plants, and practices true Southern hospitality by inviting any fly to stop by at any time. The plant waits for visitors with its leaves spread open and, when a fly happens by and touches one of the hairs that rim the plant's leaves, the Venus's-flytrap snaps its jaws shut, and has lived up to its name. After the plant's juices digest the fly, its leaves reopen, and the unassuming plant awaits its next caller.

A rainbow is merely a large band of parallel stripes, blended at the rims, which displays the full spectrum of colors that make up the sun's white light. This brilliant display appears to the naked eye when the sun's light breaks up as it passes through, the prism-like raindrops during a rain-shower.

This immense, curved spectrum of light appears only when both the elements of sunshine and rainfall present. As the sunlight enters the falling raindrops, it breaks up into its true colors of red, orange, yellow, blue, and violet. These colors are always arranged according to their wavelengths, with red being at one end of the spectrum, and violet at the other. Once inside the droplet, the particles of colored light bounce from side to side, reflect off of the far side of the droplet, exit the droplet, and reassemble, according to their wavelengths, to form a rainbow.

Leaves change color in the fall, because the chemical changes in the leaves, as their nutrients drain into the tree’s branches, trunk, and roots for winter storage, cause the leaves to stop producing the green pigment chlorophyll.

Chlorophyll’s role in the leaves, to absorb sunlight and to use the sun’s energy, is no longer necessary, and the remaining chlorophyll in the leaves disintegrates.

When the pigment chlorophyll departs, secondary pigments, substances that also absorb light, emerge to take its place, and change the leaves’ colors to theirs. For example, yellow and orange leaves contain the pigment carotene, the same pigment that gives carrots their bright orange color.

Red, wine-red, and purple leaves contain the pigments anthrocyanins, which also lend their color to radishes, cabbage, roses, and geraniums. The main difference between carotene and anthrocyanins is that the anthrocyanins only form in the leaves in the fall when the weather becomes cooler, especially when the temperature falls to between 32 degrees to 45 degrees Fahrenheit.

One characteristic of the leaves’ color is that, for the most part, it is inherited. The variations in the color, however, are determined by weather conditions. The richest and most brilliant foliage appears after weeks of cool, sunny weather in places in the United States such as New England.

The color of the leaves fade as fall turns to winter, and the stems that secure them to the branches begin to loosen with the change in weather. The cells at the ends of the stems fall apart, leaving the leaves attached to the branches by the thin veins that, in warmer weather, transported water and nutrients to the leaves. At this point, virtually any movement can break the veins and the leaves tumble to the ground.

Although the yellow and red pigments last for a few days once on the ground, they soon disintegrate just as the green chlorophyll pigment did. All that remains are brown leaves colored by tannins, which also give tea its brown color. Without a water supply, the brown leaves carpeting the ground become dry and brittle, and the trees bare.

The moon, a satellite, or small body, rotates on its axis around the earth, and "shines" when the sun's light beams onto its surface, and is reflected back to earth. Unfortunately, only one side of the moon is visible to us on the earth, as it takes the moon the same length of time to orbit on its axis, as it takes for it to orbit the earth.

The lunar month is divided into halves. During the first half, lasting approximately 14 days, the sun's light unrelentingly strikes the moon, which has no atmosphere or air to protect it from these rays, and brings the temperature of the moon to above that of the boiling point. The second half of the lunar month plunges the moon into cold, dark nights.

Man has learned a great deal about the moon since the days when ancient man worshipped it as a goddess who ruled the night. Space flights made by the United States, the USSR, now Russia, and our Apollo moon landings, unlocked some of the moon's secrets, by enabling astronauts to collect the moon's soil and rocks, and to photograph the side of the moon invisible to us for scientific analysis. The primary goal of scientific studies of the data collected is to determine if, someday, man can actually inhabit the moon.

Quicksand consists of a buoyant blend of round granules of light sand, blended with water, or of light soil and gritty mud, or of mud peppered with pebbles. Water injects itself into the grains of any one of these mixtures, which separates and lifts them, causing them to tumble over one another, and rendering them helpless to support weighty objects.

Quicksand typically surfaces near the deltas of mighty rivers, or near shores, where a layer of stiff clay below collects and retains the water. Quicksand does not suck unsuspecting victims to their untimely deaths, a theory espoused my most until recently. This nightmarish theory did, however, provide good fodder for a host of low-budget horror films!

The discovery of quicksand's buoyant properties, akin to those of the salty Dead Sea, quashed this prevalent theory. Since quicksand is saturated with liquid, and far outweighs water, it allows anything or anyone who steps into it, to float higher than possible in water alone. The key to swimming in this non-chlorinated swimming hole, is slow motion. By moving slowly, when initially landing in quicksand, one provides the quicksand with the lead-time necessary to flow around one's body, thereby making swimming or floating possible.

Contrary to popular belief, "falling stars" are not stars at all, but are meteors, solid bodies that travel through space.

Meteors, ranging in size from that of a pinhead, to many tons, are visible to the naked eye at night, when the friction between the surfaces of the meteors and of the air, produces heat as the meteors enter the earth's atmosphere. The intense heat incinerates the meteors, which leave a blazing trail of light in their wake.

Most meteors do burn up when they enter the earth's atmosphere, with the exception of the large meteors, which are dragged through the earth's atmosphere by the earth's gravitational pull. After successful landings upon the earth, these huge bodies are renamed meteorites. Some scientists theorize that thousands of meteors fall to the earth during the daytime and the nighttime, but this theory is impossible to prove or to disprove, as most would necessarily land in water, which covers most of the earth's surface.

Generally speaking, meteors and meteor particles travel together in swarms like bees, with the exception of the loners, and travel in any direction they choose. Nature's spectacular fireworks show, a "meteor shower," comes into view when the swarms encounter the upper layer of the earth's atmosphere during the earth's perpetual revolution around the sun. The friction produced when the meteors and the meteor particles rub against the atmospheric air incinerates the swarms, and they fall towards the earth in a brilliant display of light.

The source of meteors traveling through space has yet to be explained satisfactorily. For thousands of years, the common belief held, was that meteors, or "falling stars," were literally from out of this world. In 467 BC, Roman historians recorded the extraordinary fall of a meteor to the earth.

The typical, bright, yellowish-orange upper part of a flame is due to the heating of unburned carbon particles.

The temperature of the fire and the material being burned are the factors that determine the color of the flame. The various colors of flames in a wood fire are due to the different substances in the flames.

The strong orange color of most wood flames results when sodium contained in the wood is heated.

The temperature of wood flames is lower than that of candle flames, which colors the wood flames orange, not yellow. If, however, some of the carbon particles in the fire are very hot, the color will be yellow. The product of the burnt carbon, when it has cooled, is black soot.

Since fire needs oxygen to burn, and since the bottom of a candle flame does not get much oxygen, it is the hottest spot in the flame and is blue in color.

The flame cools and changes color as it moves away from the source of the flame, because it is exposed to more oxygen. The temperature change causes the color of the flame to change from blue, at the hottest, lower portion of the flame, to the typical, bright, yellowish-orange or bright orange color with which most people are familiar with. Which shade of orange is seen at the upper portion of the flame, where the flame is the coolest, depends upon the material being burned.