astronomy SG - Our solar system consists of the Sun and all...

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Our solar system consists of the Sun and all the objects that orbit it. A typical galaxy is a collection of a few hundred million to a trillion or more stars, bound together by gravity. The universe is the sum total of all matter and energy. The Big Bang is the event that marked the beginnging of the expansion of the universe. When we say that the universe is expanding we mean that the average distance between galaxies are increasing with time. Based on observations of the universal expansion, the age of the universe is about 14 billion years. A light year is not time but is a unit of distance. The term observable universe refers to that portion of the universe that we can see in principle, given the current age of the universe. On a scale in which the distance from Earth to the Sun is about 15 meters, the distance from Earth to the Moon is small enough to fit within your hand. The number of stars in the Milky Way Galaxy is approximately a few hundred billion. An astronomical unit is the average distance between Earth and the Sun. The ecliptic plane is the plane of the Earth’s orbit around the Sun. It takes the Earth one year to orbit the Sun. Our cosmic address is you, earth, solar system, Milky Way Galaxy, Local group, local supercluster, universe. Galaxies are important to our existence because they recycle material from one generation of stars to the next, and without this recycling we could exist. When we look at an object that is 1000 light years away we see it as it was 1000 years ago. The total number of stars in the observable universe is about the same as the number of grains of sand on all the beaches on Earth. If we imagine the history of the universe compressed into one year, dinosaurs became extinct yesterday morning.
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Our solar system is one-third the age of the universe. Earth’s rotation carries most people around the axis faster than a commercial jet travels, and Earth’s orbit carries us around the Sun faster than the Space Shuttle orbits Earth. Our stars in the sky look the same from year to year because the stars in the constellations
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astronomy SG - Our solar system consists of the Sun and all...

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