How do black holes work?

As you assemble more and more mass together in a small volume, the gravity there becomes stronger and stronger. At first, it becomes more and more difficult to throw a ball upward hard enough to make it sail away from the mass into space. Eventually, you need a cannon to get the ball to leave. And by the time you get enough mass together, the gravity becomes so strong that light itself begins to have trouble escaping. Light falls in gravity, just like anything else. But it travels so fast that you barely notice it falling. However when the gravity becomes strong enough, light falls enough to cause some weird effects. A black hole forms when the gravity is so strong the even light is unable to escape from the mass.

Why do only certain orbitals exist in an atom?

Because the electrons in an atom move about as waves, they can follow only certain allowed orbits that we call orbitals. This limitation is equivalent to the case of a violin string—it can only vibrate at certain frequencies. If you try to make a violin string vibrate at the wrong frequency, it won't do it. That's because the string vibrates in a wave-like manner and only certain waves fit properly along the strong. Similarly, the electron in an atom "vibrates" in a wave-like manner and only certain waves fit properly around the nucleus.

Why is the Ming dynasty so famous?

The Mongols, who ruled China for 89 years, were overthrown by Hung-Wu in AD 1368. That marked the start of the Ming dynasty, which lasted until 1644. The Ming dynasty is remembered for making the administration strong, widespread and fair. Judges had to take a test to get a job. Chinese literature, art and philosophy reached new heights during Ming rule. Some of the best Chinese porcelain was manufactured at Jingdezhen. The yellow imperial bowls, red vases and highly decorated painted ceramics became popular. For the first time, both cotton and silk production did very well.

How hot is the Sun?

The Sun is extremely hot. The surface of the Sun (or its outer visible layer, called the photosphere) is about 10,000 degrees Fahrenheit (5,537 degrees Celsius)— about 50 times the temperature required to boil water. The core of the Sun, where solar energy is created, reaches 27 million degrees Fahrenheit (15 million degrees Celsius). It is so intense that nuclear reactions take place there.

Is there a simple rhyme to help recall how many days are in each month?

Yes. Many children learn this simple poem to help them remember how many days are in each month. Although the origin of the lyrics to "Thirty Days Hath September" is unclear, the use of old English dates this poem to at least the sixteenth century: Thirty days hath September, April, June and November All the rest have thirty-one, excepting only February Which hath but twenty eight-days clear And twenty-nine in each leap year.

Will the dinosaurs ever come back?

When the dinosaurs became extinct, the world’s environment was already changing. It was stressed by natural events, such as falling sea levels and volcanic eruptions, leading to the decline and disappearance of many plants and animals. Our modern world has continued to create many environmental changes and stresses— most man-made, including pollution and global warming—and our fragile ecosystem could not support the return of dinosaurs. (Imagine a large dinosaur roaming New York City!) However, some scientists argue that not all dinosaurs became extinct. The striking similarities between modern birds and some kinds of dinosaurs have led some people to believe that birds are living descendants of dinosaurs. Although not all dinosaurs were similar to modern birds, some did have features such as bony tails, claws on the fingers, beaks, and feathers.

How do I speak?

Human beings have vocal chords inside the larynx which produce sound. When air passes through a gap between the chords, these chords vibrate and produce a sound. All animals that can produce a sound have vocal chords, except birds which produce sound through a bony ring, called a syrinx.