## When and why were leap years introduced?

The use of a 365-day calendar year with occasional leap years was introduced in 46 B.C.E. with the Julian calendar. The Julian calendar was formed by Julius Caesar, who had commissioned the Alexandrian astronomer Sosigenes to revise the calendar system. Sosigenes used a tropical solar year, which calculates to 365.25 days per year. This was slightly off, because the actual tropical solar year is 365.242199 days. This discrepancy caused there to be 10 days missing by the year 1582. That year, Pope Gregory XIII issued a papal bull (decree) to fix the Julian calendar. The Jesuit astronomer Christoph Clavius undertook the Pope’s decree and designed what is now known as the Gregorian calendar. In order to correct for the loss of one day every 130 years, the Gregorian calendar drops 3 leap years every 400 years. According to this system, years are leap years only if divisible by 400—thus, 1600 and 2000 are leap years; 1700, 1800, and 1900 are not. Because the solar year is shortening, today a one-second adjustment—called a leap second—is made (usually on December 31 at midnight) when necessary to compensate.

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## Are the terms “gnat’s eye” and “hair’s breadth” true units of measure?

Yes, but both are slang units of distance and diameter. The eyes of typical gnats tend to have diameters similar in size to a hair’s breadth—roughly 100–150 micrometers. An item would have to be very short in order to be gnat’s eye in length! A hair’s breadth is an informal unit of distance: it is used to denote a measurement of approximately 70 to 100 micrometers in diameter, or 0.1 millimeter, which is similar in thickness to real human hair.

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## Why do we say someone diverted from a goal has been “sidetracked”?

Early railroads had only a single track between destinations. Problems arose when a train was met by another going in the opposite direction or was about to be overtaken by a faster one. This dilemma was solved with the creation of sidings, short lengths of track built parallel to the main line where one train could pull over while the other went by. The train had been “sidetracked,” meaning that, for a time at least, it wasn’t going anywhere.

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## Why do we say that something worthless is “for the birds”?

In the days before automobiles, the streets were filled with horse-drawn carriages, and these animals quite naturally left behind deposits from their digestive systems. These emissions contained half-digested oats that attracted swarms of birds, which took nourishment from the deposits. The people of the time coined the expression for the birds as meaning anything of the same value as these horse-droppings.

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## Is the District of Columbia a state?

No, it is not a state or a part of any state. The District of Columbia, or D.C. for short, is a district in the national capital, Washington, D.C. The district, named after explorer Christopher Columbus, sits on the Potomac River on land that once belonged to the state of Maryland. Because the city of Washington—which was named after the nation’s first president, George Washington—covers the entire area, the names “Washington, D.C.” and “District of Columbia” have the same meaning. The area is 69 square miles (178 square kilometers) and a federal district, meaning it is an area reserved as the seat of the U.S. government. So, Washington, D.C. is almost like two cities in one—a federal city with government monuments, buildings, and parks (including the White House, the Capitol, and the Supreme Court), and an everyday city more than half a million people call home.

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## Why when suggesting an exhaustive search do we say,“Leave no stone unturned”?

The advice to “leave no stone unturned” comes from Greek mythology, Wherein the Oracle of Delphi, through his communication with the gods, had acquired great wisdom.

Euripides wrote that When the oracle was consulted about how to find a defeated general’s hidden treasure, he advised that the only way was “to leave no stone unturned.” The expression and the advice have been with us ever since.

## What is the difference between a porpoise and a dolphin?

At first glance, it’s hard to tell a porpoise and a dolphin apart from one another. Both are fascinating undersea creatures, both are carnivores, and both belong to the same scientific group: Cetacea. However, there are slight physical differences between the two: Porpoises tend to be smaller than dolphins and do not have pronounced beaks. Dolphins have cone-shaped teeth, while porpoises have spadeshaped teeth. Dolphins usually have a hooked or curved dorsal fin, and porpoises usually have a triangle-shaped dorsal fin. (Some have no dorsal fin at all.) There are over 30 species of true dolphins, including familiar species like the bottlenose, spinner, and spotted dolphins.

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## How is the body able to bend?

The human skeleton moves at its more than 230 joints, which are the places where bones connect. Those joints give you a basic range of motion. For example, everyone’s shoulder joints can rotate 360 degrees, and elbows can open and close to just under a 180 degree arc. The pull of ligaments—ropelike connective tissues that anchor one bone to the next around a joint—lengthen a bit to allow a joint to move, but keep the range of motion limited so that you don’t hurt yourself. So, the next time you are tempted to do a backbend or stretch your leg up to your ear, think of your joints and ligaments!

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## What happens when a person breaks the law?

Laws are enforced by the courts and the judicial system. If an adult breaks a law in the community or a business or organization does something illegal, they go to the judicial branch of government for review of their actions. The judicial branch is made up of different courts. The court leader, or judge, interprets the meaning of laws, how they are applied, and whether they break the rules of the Constitution. If a person or group is found guilty of breaking a law, the judicial system decides how they should be punished. In the United States, several laws have been written to protect the rights of someone accused of committing a crime. He or she is considered innocent until proven guilty in a court of law. Someone suspected of a crime is usually arrested and taken into custody by a police officer. Sometimes, the case is presented before a grand jury (a group of citizens who examines the accusations made). The grand jury files an indictment, or a formal charge, if there appears to be enough evidence for a trial. In many criminal cases, however, there is no grand jury. While awaiting trial, the accused may be temporarily released on bail (which is the amount of money meant to guarantee that the person will return for trial instead of leaving the country) or kept in a local jail. Trials are usually held before a judge and a jury of 12 citizens. The government presents its case against an accused person, or defendant, through a district attorney, and another attorney defends the accused. If the defendant is judged innocent, he or she is released. If he or she is found guilty of committing a crime, the judge decides the punishment or sentence, using established guidelines. The lawbreaker may be forced to pay a fine, pay damages, or go to prison.

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## Which is the windiest planet?

Although there are other windy planets (like Uranus), Neptune’s winds are the fastest in the solar system, reaching 1,600 miles (2,575 kilometers) per hour. Nep- 8 tune’s large, sweeping wind storms could consume the entire planet Earth!

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