Each calendar year is exactly 365 days, 5 hours, 48 minutes, and 46 seconds. This is the amount of time between two successive crossings of the celestial equator by the Sun at the vernal equinox (the first day of spring). The fact that the year is not a whole number of days has affected the development of calendars, which over time generate an error.
The current calendar we use, called the Gregorian calendar, attempts to fix this by adding an extra day to the month of February every four years. These years are called “leap years.”
Yes. Even though it may feel awkward or embarrassing, it helps to tell your parents, a teacher, or a counselor about a bullying experience. A trusted adult can make you feel better by explaining why bullies behave the way they do and by reassuring you that what a bully says about you has nothing to do with who you really are.
Adults can help keep you safe if you’re being threatened, and come up with solutions to deal with the bullying. Many states have bullying laws and policies, and many schools have programs in place that educate parents and kids about bullying.
Absolutely! Strong, healthy teeth help you speak clearly, chew harder vegetables and meats, and help you look your best. Brushing your teeth helps prevent plaque, a clear film that sticks to your teeth. The sticky film acts like a magnet for bacteria and sugar. Bacteria eats the sugar on your teeth, breaking it down into acids that deteriorate tooth enamel, causing holes called cavities. Plaque also causes the gum disease gingivitis, which make your gums red, swollen, and sore. At around age six, you lose your baby teeth and a larger set of teeth begin to surface. Eventually, 32 new teeth will line your growing jaws, the last coming in around the age of 18.
These permanent teeth will perform all of your eating tasks for the rest of your life, so they are worth taking care of! Your four front teeth (on top and bottom) are sharp incisors that cut and tear off food when you bite, along with your four pointed canine teeth. The flat-topped bicuspids (premolars) and molars near the back of your mouth crush and chew your food.
As a matter of fact, yes! Researchers believe that regular contact with pets can reduce levels of stress and reduce blood pressure (the force of blood pushing against the walls of the arteries as the heart pumps out blood).
Pets offer stability, comfort, security, affection, and intimacy. Owning a dog also provides a great opportunity to get exercise and fresh air, since it will need to go for a walk every day.
Living creatures need oxygen to survive, and fish are no exception. Human beings 68 use their lungs to take in oxygen, and fish breathe using their gills. A fish’s gills are full of blood vessels that absorb the tiny particles of oxygen from the water.
The fish sucks the water in through its mouth and squirts it out through its gills; during this process, the gills take the oxygen from the water into the blood vessels. A fish’s gills are not constructed to take oxygen from the air, so they cannot breathe on dry land.
Located in Arizona and stretching to Colorado, the Grand Canyon is 18 miles (29 kilometers) wide, 227 miles (365 kilometers) long, and 6,000 feet (1,828 meters) deep in its deepest section. It takes about two days by foot or mule to travel from the top to the bottom.
Although it is not the biggest canyon in the world—Barranca de Cabre in northern Mexico and Hell’s Canyon in Idaho are deeper—it is known for its amazing landscape. The canyon’s walls are made up of rocks, cliffs, hills, and valleys formed millions of years ago, and it is home to hundreds of species of mammals, reptiles, and birds. Although people lived in the canyon some 4,000 years ago, today it is a national park and national landmark.
Eyelashes protect our eyes. They help keep small particles and dust out of our eyes, especially when the wind is blowing. Eyelashes are also super-sensitive, and they alert the eyelids to shut when something touches them. If you rub your finger against your eyelashes, you will find that your eyelid automatically shuts.
But be careful not to rub too hard—if you lose a lash it will take about four to eight weeks to grow back! Fortunately, your upper eyelid has between 100 and 150 lashes.
The metric system is a decimalized system of measurement. Designed during the French Revolution of the 1790s, the metric system brought order out of the conflicting and confusing traditional systems of weights and measures that were being used in Europe at the time. Prior to the introduction of the metric system, it was common for units of length, land area, and weight to vary, not just from one country to another but from one region to another within the same country.
As the modern nations gradually developed from smaller kingdoms and principalities, confusion multiplied. Length, for example, could be measured in feet, inches, miles, spans, cubits, hands, furlongs, palms, rods, chains, and leagues. Merchants, scientists, and educated people throughout Europe realized that a uniform system was needed, and in 1790 the French National Assembly commissioned the Academy of Science to design a simple decimal-based system of units. The three most common base units in the metric system are the meter, gram, and liter. The meter is a unit of length equal to 3.28 feet; the gram is a unit of mass equal to approximately 0.0022 pounds (about the mass of a paper clip); and the liter is a unit of volume equal to 1.05 quarts. Temperature is expressed in degrees Celsius; 0 degrees Celsius equals 32 degrees Fahrenheit.
Once seeds are fully developed, they need a good place to grow. If they just fell to the ground beneath their parent plant, they would struggle, competing against each other for sunlight, water, and minerals. Most seeds need to travel—by wind, water, or with the help of insects and other animals—to better places to germinate, or start to grow into new plants. Some seeds, like those from conifer and maple trees, have wings attached. Others, like those of dandelions, have parachutes made of tiny hairs. Both features allow the seeds to be carried great distances by the wind, and they sometimes land in spots that are good for germination. Water carries other seeds to good growing places; the hard, watertight shell of a coconut, for instance, allows it to travel many miles at sea before finding a beach where conditions are suitable for growth.
Seeds sometimes have to wait a long time before they find good places to grow, places where the sun, moisture, and temperature are right. Most seeds are designed for the wait, protected by a hard outer pod (except those of conifers). Some seeds wait years to germinate, and some just never do. But inside each seed pod is a baby plant, or embryo, and endosperm, a supply of starchy food that will be used for early growth if germination takes place. Then a tiny root will reach down into the soil, and a tiny green shoot will reach up, toward the light.
Carved into the southeast face of a mountain in South Dakota are the faces of four presidents: George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln. Known as Mount Rushmore, these 68-feet (20.7 meters) high granite sculptures were the brainchild of South Dakota state historian Doane Robinson. In 1923, he conceived the project to attract more people to the Black Hills of South Dakota.
Congress passed legislation that authorized the carving in what is today known as Black Hills National Forest. In 1927, the sculptor Gutzon Borglum and 400 workers began the project, using dynamite to remove unwanted rock. Mount Rushmore was completed in 1941.