The bald eagle’s head is covered with white feathers. So why is it called the bald eagle?

Because one meaning of the word “bald” that is not commonly used anymore refers to white markings. “Bald” used to refer to people with white hair. Due to excessive hunting, environmental pollution, and loss of habitat, the bald eagle population became dangerously low at one point, prompting the U.S. Congress to pass a law protecting it. Bald eagles were once listed by the U.S. Fish and Wildlife Service as an endangered species, meaning they were close to being extinct. Thanks to the laws protecting it, these birds have rebounded a bit. They are now listed as threatened, which means they are not as close to being extinct as they once were, but their numbers are still few (only about 50,000 in the United States), and it is illegal to hunt them.

What is a “perfect” number?

Approximately 2,500 years ago the Pythagoreans defined a “perfect” number as one for whom the sum of its divisors, excluding itself, equals the number itself. For example, 6 can be divided by 1, 2, 3, and 6. If you add these numbers together, excluding 6 itself, the total is 6. Therefore 6 is a perfect number. Over the centuries, many mathematicians from all over the world have contributed to finding and defining perfect numbers.

Which planets experience the greenhouse effect?

The greenhouse effect describes a warming phenomenon. (In a greenhouse, closed glass windows cause heat to become trapped inside.) The greenhouse effect occurs when a planet’s atmosphere allows heat from the Sun to enter, but refuses to let it leave. A good example of the greenhouse effect can be found on Venus.

There, solar radiation penetrates the atmosphere, reaches the surface, and is reflected back into the atmosphere. The re-radiated heat is trapped by carbon dioxide, which is abundant in Venus’s atmosphere. The result is that Venus has a scorching surface temperature of 900 degrees Fahrenheit (482 degrees Celsius). The greenhouse effect can also be found on Earth and in the upper atmospheres of the giant planets: Jupiter, Saturn, Uranus, and Neptune.

Why do we say that someone with a hidden agenda has “an axe to grind”?

As a boy, Benjamin Franklin was sharpening tools in his father’s yard when a stranger carrying an axe came by and praised the boy on how good he was with the grindstone. He then asked Franklin if he would show him how it would work on his own axe. Once his axe was sharpened, the stranger simply laughed and walked away, giving young Franklin a valuable lesson about people with “an axe to grind.”

Why do we call wealthy members of society “the upper crust”?

In the days of feudalism, when noblemen gathered for a meal in the castle, those of higher rank sat at the head of a T-shaped table, and the rest sat in order of diminishing importance away from them.

For such occasions a yard-long loaf of bread was baked, and the honour of making the first cut belonged to the highest-ranking person at the head table, who would then pass the bread down in order of rank, but always keeping for himself the “upper crust.”

Why is taking the “hair of the dog” a hangover cure?

In the Middle Ages, people treated a dog bite with the ashes of the canine culprit’s hair. The medical logic came from the Romans, who believed that the cure of any ailment, including a hangover, could be found in its cause.

It’s a principle applied in modern medicine with the use of vaccines for immunization. “The hair of the dog” treatment for hangovers advises that to feel better, you should take another drink of the same thing that made you feel so bad.