Blue moon once in a blue moon definition and meaning

From “where there’s smoke, there’s fire” khổng lồ “hard as nails,” several sayings just don’t pass scientific scrutiny



Are xanh moons really that rare? Phokhổng lồ by Flickr user bilbord99

Concepts from science và nature pervade our language’s common phrases, idioms and colloquialisms. The incredulous expression”Well, I’ll be a monkey’s uncle” stems from sarcastic disbelief over Darwin’s writings on evolution. To be “in the limelight”—at the center of attention—harks baông chồng khổng lồ how theater stages used to be lit by heating lime (calcium oxide) until it glowed a brilliant Trắng, then focusing the light emitted inlớn a spotlight.

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Someone as “mad as a hatter” exhibits behavior similar to 18th và 19th century hat makers who stiffened felt cloth with mercury—an ingredient that after continued exposure causes dementia. “Tuning in” to lớn someone’s message has its origins in the slight turns of a dial needed to focus on a radio signal.

These colorful expressions bring spice to lớn our language. Yet certain well-used phrases from science are misrepresentations of what they’re trying to express. Others are just plain wrong!

Some are obvious, yet we use them anyhow. A person who sagaciously shakes her head & says “A watched pot never boils” while you are waiting second after agonizing second for thử nghiệm results khổng lồ arrive or job offers to come in knows that if she sat down và watched a vessel containing water on a stove sầu over high heat for long enough, the water will eventually boil. Or the person who utters the placating phrase that “the darkest hour is just before dawn,” meant lớn give sầu hope to lớn people during troubled times, probably knows that well before the Sun rises, the sky gets progressively lighter, just as how well after the Sun sets, light lingers until the Earth rotates beyond the reach of the Sun’s rays. Thus, the darkest hour of the night (in the absence of the Moon) is midway between sunphối and sunrise.

A few phrases, however, have less obvious scientific inaccuracies. Here are a few for you lớn consider:

1. Once in a xanh moon: This poetic phrase refers to something extremely rare in occurrence. A xanh moon is the term commonly used for a second full moon that occasionally appears in a single month of our solar-based calendars.  The problem with the phrase, however, is that xanh moons are not so rare—they happen every few years at least, & can even happen within months of each other when the 29.5-day lunar cycle puts the full moon at the beginning of any month but February.

The usage of “xanh moon” as the second full moon in a month dates bachồng khổng lồ a 1937 Marine Farmer’s Almanac. But prior lớn that, blue moons meant something slightly different. Typically, 12 full moons occur from winter solstice to lớn the next winter solstice (roughly three per season), but occasionally a fourth full moon in a season could be observed. In such a case, one of the four full moons in that season was labeled “xanh.”

Readers may regọi that baby Smurfs are delivered lớn the Smurf village during xanh moons. If this were to lớn occur every xanh moon, we’d soon be awash in xanh creatures three apples high!


Can there be smoke with no fire? Photo by Flickr user Maarten Takens

2. Where there’s smoke, there’s fire: The phrase means that if something looks wrong, it likely is wrong. But let’s step back—do you always have sầu to lớn have sầu fire if you see smoke?

Answering that first requires defining “fire.” Merriam-Webster’s first definition of fire is “the phenomenon of combustion manifested in light, flame, and heat.” Combustion is the chemical reaction that occurs when fuel is burned in the presence of oxygen. So for a fire to lớn ignite và be sustained, it needs heat, fuel và oxygendenying a fire any of these three things will extinguish the fire; attempting lớn start a fire without one of three things will be futile.

In complete combustionwhat occurs when you light a gas stovethe fire produces no smoke. However, when most materials are burned, they undergo incomplete combustion, which means that the fire isn’t able lớn completely burn all of the fuel. Smoke is an airborne collection of little particles of these unburned materials.

The reason why these materials didn’t burn is because of pyrolysisthe breakdown of of organic material at elevated temperatures in the absence, or under a shortage, of oxyren. Think of it this way: a wood fire’s quick consumption of oxygen depletes the gas’s presence around a burning log, và this localized laông chồng of oxygen while the log is at high temperatures causes log to lớn char, breaking the log down inlớn a substance much richer in carbon content. The resulting charcoal, if still under high heat, can then smoldera flameless khung of combustionuntil all the fuel is consumed.

Smoke, then, can be considered khổng lồ be a sản phẩm of pyrolysis rather than of fire itself. You’re probably thinkingso what? To get the smoke, a fire needed khổng lồ be present at some point, right?

Not always. Let’s consider pyrolysis to lớn the extreme. For example, tobacco leaves heated khổng lồ 800 degrees Celsius in a pure nitrogen atmosphere undergo pyrolysis và release smoke without actually being on fire.

Pyrolysis without fire can also occur in more familiar circumstances. Imagine blackening a piece of fish on a pan using an electric range, where electricity heats metal coils on the cooktop until they are incandescent, but not on fire. Leave the fish unattended for too long và it will start khổng lồ char & smoke. But why bother with putting fish in the pan? Those looking for fireless smoke need khổng lồ go no further than melting a slab of butter in a sauxẻ pan. All oils và fats used in cooking have sầu smoke pointsthe temperature at which they start khổng lồ degrade into lớn a charred goo of glycerol and fatty acidsas seen in this đoạn Clip.

Sure, leaving these smoking substances on the range for too long will cause them khổng lồ eventually combust (oils và fats, after all, do have flash points), but before that, you have a whole lot of smoke with no fire!


What toàn thân part really decomposes first in a dead fish? Phokhổng lồ by Flickr user clayton_maxwell

3. The fish rots from the head down: The phrase seems khổng lồ pop up more frequently when political scandals or accusations of malfeasance make headlines. The origin of the phrase is murky, likely stemming from folk proverbs of Europe & Asia Minor. But the meaning is simple–if a system is corrupt, its leaders instigated the corruption.

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The authoritative ring to lớn this phrase belies its accuracy. Fish, in fact, start khổng lồ rot from the gut. According khổng lồ David Groman, an expert on fish pathology at the University of Prince Edward Islvà, the proverb is a “poor metaphor. And, I must say, it’s biologically incorrect,” he told Anmãng cầu Muoio of the business magazine Fast Company.  “When a fish rots, the organs in the gut go first. If you can’t tell that a fish is rotting by the smell of it, you’ll sure know when you cut it open và everything pours out–when all the internal tissue loses its integrity and turns into liquid.”

The reporter then got hold of Richard Yokoyama, manager of Seattle’s Pike Place Fish Market, who said “Before I buy a fish from one of our dealers, I always look at the belly. On a fish, that’s the first thing to lớn go. That’s where all the action is–in the gut. If the belly is brown and the bones are breaking through the skin, I toss the fish out. It’s rotten.”

Unfortunately for scientific accuracy, saying “The fish rots from the belly outward” lacks gravitas và is unlikely to be picked up by the punditsphere.


Are steel nails really that hard? Photo lớn by Flickr user tinspoon

4. Hard as nails: The saying is often used to describe a person who is stern, unyeilding, unsympathetic, bordering on ruthless. An early appearance of the phrase can be found in Dickens’ Oliver Twist, when the Artful Dodger và the other street urchins describe their pickpocketing work ethic.

But let’s take a step back–are nails really that hard? The hardness of a material can be estimated relative to other substances according to where it falls on Mohs scale of mineral hardness. This scale, which ranges from one through 10, was developed by the German geologist in 1812 lớn help hyên ổn classify the minerals he encountered in his excursions. Talc, a soft mineral easily powdered, is a one on the scale. The malleable element copper sits at a three. Quartz—the clear crystal common in svà or the spiny lining on the inside of a geode—is a seven. Diamond, the hardest natural substance on the planet, is a 10.

Mohs’ scale is an ordinal scale, which means that it doesn’t estimate the degree to lớn which one substance is harder than another. Rather, it is based on the idea that materials that fall at higher values on this scale can scratch anything with lower numbers, & that materials with low hardness numbers cannot scratch anything with a higher hardness value. On this scale, a  steel nail used to fasten wood together would hit at about 5.5. Feldspars, such as the pink minerals of đá hoa cương, are harder than those nails, as are topaz, quartz, sapphires and of course diamonds. Even unglazed porcelain, which is about a seven on the scale, is harder than an average nail.

But not all nails are created equally. The nails used in wood are are made of  low-carbon or “mild” steel, meaning that the chemical composition of their alloys are only between 0.05 khổng lồ 0.6 percent carbon. Nails used lớn fasten concrete together, for example, have sầu higher percentages of carbon–approaching one percent–which can push the hardness up to as high as a nine on Mohs scale.

So the more correct version of this phrase would be, “Hard as high-carbon steel nails,” but somehow that just doesn’t have the same ring, does it?


Diamonds, unfortunately, will revert back to lớn graphite after several million years. Phokhổng lồ by Flickr user Kim Alaniz.

5. Diamonds are forever: Thanks to the DeBeers khẩu hiệu, adorning your honey’s neck, wrists & fingers with bits of pressurized carbon has somehow become a metaphor for true and timeless love. Of course, no object that you can hold in your hvà can last forever. But diamonds have sầu a special reason for being incapable of eternity–without the extreme pressures of the deep Earth where they formed, a kim cương will slowly revert baông chồng into graphite–which is why the older a đá quí is, the more inclusions it’s likely khổng lồ have.

Although it usually will take millions of years for the roông chồng on your finger khổng lồ become ready for use in pencils, some mineral forms of carbon seem to quickly flash between diamond and graphite depending on the pressures that they are exposed to in the lab. For those mutable sometimes-gems, diamonds are in fact transient.

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What comtháng phrases push your buttons when viewed under the microscope of science? Or perhaps you have the inside scoop on whether wet hens really get angry? Let us know!

Mohi Kumar is a science writer, editor and essayist based in Houston, Texas, and also a freelance editor for