Universe

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Planets travel around the sun in paths called orbits. Each planet has its own orbit around the sun, and one orbit around the sun is called a year. All planets travel in the same direction around the sun.

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  • How many modern constellations are there?

    Q: How many modern constellations are there?

    A: As of 2014, there are 41 modern constellations, which are constellations added to the catalogue after 1600. Four of them, Carina, Puppis, Pyxis and Vela are derived from Argo, a constellation catalogued by Ptolemy.
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  • Why did people once believe that Earth was the center of the Universe?

    Q: Why did people once believe that Earth was the center of the Universe?

    A: The belief of early astronomers that the Earth was the center of the universe stemmed from limited astronomical tools and geocentric attitudes. The Ptolemaic Model, developed around 100 A.D., presented the Earth-centered solar system in which most early Roman astronomers believed.
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  • What is the temperature of a black hole?

    Q: What is the temperature of a black hole?

    A: According to NASA, the temperature of a black hole with the mass of the sun is only one ten-millionth of a degree over absolute zero. Scientists determine this by measuring the temperature of the radiation that comes from a black hole.
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  • Why do some stars appear brighter than others?

    Q: Why do some stars appear brighter than others?

    A: The apparent brightness of a star viewed from Earth varies based both on the type of star and its distance from the planet. The apparent magnitude differs from a star's absolute magnitude, which describes its brightness from a set distance, rather than the varying distances of stars seen from Earth. The lower the apparent magnitude, the brighter the star is as seen from Earth.
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  • What are some facts about the Aurora Borealis?

    Q: What are some facts about the Aurora Borealis?

    A: Aurora Borealis occurs when materials from the surface of the Sun collide with the atmosphere of the Earth. Experts make predictions about the occurrence of Aurora Borealis based on events taking place on the Sun and the speed of matter being thrown from the Sun's surface. Aurora Borealis is visible in portions of the Northern Hemisphere, including Canada, Scandinavia, North America, Siberia and Northern Europe.
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  • Who discovered the planet Saturn?

    Q: Who discovered the planet Saturn?

    A: It is impossible to determine who discovered Saturn, as it is one of five planets that are visible without the aid of instruments. Saturn has been widely observed by people for thousands of years, although its unique and complex system of rings are only visible using a telescope.
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  • What happens after a supernova?

    Q: What happens after a supernova?

    A: Depending on the size of the star before it explodes as a supernova, the core of the star either shrinks back into a tiny neutron star or becomes a black hole. If the star is only a few times bigger than the sun, the core becomes a tiny neutron star. If the star is much bigger than the sun, the chances of it becoming a black hole are much greater.
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  • Do the planets travel around the sun in a path called an orbit?

    Q: Do the planets travel around the sun in a path called an orbit?

    A: Planets travel around the sun in paths called orbits. Each planet has its own orbit around the sun, and one orbit around the sun is called a year. All planets travel in the same direction around the sun.
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  • How many solar systems are there in the universe?

    Q: How many solar systems are there in the universe?

    A: There are billions of stars, and no one knows how many solar systems there are. The Earth's galaxy, the Milky Way, is so large that it would take an object 100,000 years to cross it traveling at the speed of light.
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  • Q: Are there other universes out there?

    A: There is no definitive answer as to whether other universes exist, although many astronomers believe it is highly likely and have several theories on how or where they exist. Some people theorize that an infinite number of universes could have formed following the Big Bang, with each one having its own laws of physics.
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  • Q: What is Ptolemy's universe theory?

    A: Greek philosopher Claudius Ptolemy believed that the sun, planets and stars all revolved around the Earth. This belief gave way to the ancient Greek theory of a geocentric or Ptolemaic model of the universe. "Geocentric" refers to the belief that the Earth is the center of the universe.
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  • Q: Who disproved the Ptolemaic theory of the universe?

    A: Nicolaus Copernicus' 16th-century assertion that the Ptolemaic theory of the solar system was wrong was considered revolutionary. However, his published findings in 1514 weren't widely accepted because his studies were based on naked-eye observations. Galileo Galilei used a telescope to disprove the Earth-centered solar system.
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  • Q: How do you explain the Big Bang Theory to kids?

    A: Explain the Big Bang Theory to kids using simple terminology and metaphors they can understand to help them relate the new concepts to concepts they already know. For example, remind them that one year is the amount of time it takes to get from one birthday to the next to help them understand just how long ago it was 14 billion years ago, when scientists believed the big bang occurred.
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  • Q: How large is the universe?

    A: As of 2014, the size of the universe is unknown. Clues to its size can only be found within the limits of the observable universe, which is a sphere with a diameter of about 92 billion light-years.
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  • Q: Does the universe end?

    A: Scientists believe the Universe is infinitely large and does not end. However, only part of the Universe is visible from Earth. The Observable Universe is a sphere around the Earth, and anything beyond this sphere cannot be observed from Earth because of continuing expansion over a long period of time.
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  • What is our solar system called?

    Q: What is our solar system called?

    A: The planetary system, containing Earth, is officially named the "Solar System," which consists of the Sun and its orbiting objects. PlanetsOfTheSolarSystem.net explains that the Sun does not have a scientific name, but is alternately called "Sol," based on Roman mythology. The name "Solar System" derives from the ancient Roman alternative.
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  • Q: What are some world facts?

    A: Observed from space, the United States is the brightest country on the brightest planet in the Solar System because Earth's water makes it the brightest planet and the United States is abundant in artificial lighting, especially at night. Russia is the largest country in the world, Vatican City is the smallest country, and 39 million Vatican Cities could fit inside Russia. In 2011, the global population topped 7 billion people and is expected to reach 10.5 billion by 2050.
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  • Q: How was the universe created?

    A: Scientists generally believe that the universe was created from an event known as the Big Bang; however, the actual cause of the Big Bang remains unknown. The phrase "Big Bang" was coined by scientist Fred Hoyle.
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  • Q: How do black holes form?

    A: Universe Today explains that black holes are the result of objects collapsing under the force of gravity until the acceleration needed to escape from them exceeds the speed of light. Any object can, in principle, become a black hole if it collapses to sufficient density. They can also be formed from two neutron stars colliding together. According to Universe Today, there are supermassive black holes in every galaxy.
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  • Q: How did the Milky Way get its name?

    A: The Milky Way's name stems from the Greeks, who referred to the galaxy as galaxias kyklos, or milky circle. The Romans, who called it via lactea, or "the road of milk," altered the term from its original Greek origins.
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  • Q: What does the Milky Way Galaxy look like?

    A: The Earth's home galaxy, the Milky Way, is known as a spiral galaxy because of its shape when viewed face-on. If seen edge-on, the galaxy would appear to be a flat disk-like structure.
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