Lesson_ Earth’s Place in the Universe.pptx - Lesson...

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Lesson: Earth’s Place in the Universe Introductory Astronomy
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Objectives Relate Earth’s size and location to other objects in the solar system and within the universe Describe how the celestial sphere and constellations are used to locate objects in the sky Account for the apparent motion of the sun and stars and the changing appearance of the moon Explain how Earth’s tilt causes the seasons Explain the cause of retrograde motion of the planets and how distances in space are measured
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What’s our place in the Cosmos? What is our location in space? Astronomy research has shown that we live on a ordinary rocky planet called Earth, which is one of the eight planets orbiting around the sun which is a star. The sun is only one of the many stars in the galaxy, but the sun is the biggest. There is over 100 billion star and it all referred to as Milky Way Galaxy, but that’s only 1 of 40 large group of the stars in the galaxies. There are spread out all of the universe.
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How did we come to be? The Big Bang model is the prevailing cosmological theory of the early development of the Universe. According to this model, the Universe was once in an extremely hot and dense state that expanded rapidly in a tremendous explosions, or Big Band. This rapid expansion of space-time caused the young Universe to cool and resulted in its current continuously expanding state, except in localized regions where gravity has caused matter to collapse into stars and galaxies. The Big Bang essential created two elements: hydrogen and helium. All the other elements, the ones found in the periodic table, have been produced by stars and recycled within galaxies from one generation of stars to the next. This is why it is said that we are made from the same material as the stars.
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How can we know what the Universe was like in the past? Light takes time to travel from one place to another. In our everyday life, the light travel time is usually very short because the distance are small. Flip the light switch on the wall the light bulb appears to be instantly activated. Light is fast, but not infinitely fast. For example, light takes 8 minutes to travel from the Sun to Earth. Therefore, when we look at the Sun as it existed 8 minutes ago in the Sun’s reference frame. It takes light 4.3 years to travel from the nearest star system, Alpha Centauri, to Earth. So we see Alpha Centauri as it existed 4.3 years ago. It takes some light billions of years to travel from distant galaxies to Earth, and thus we see those galaxies as they existed billions of years ago. The general rule is the farther away we look in distance, the farther back we look in time.
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What are the limitation to what we can see in the Universe? We cannot see the entire Universe because its finite age limits how far light could have traveled. The Universe is about is about 14 billion years old, so we can only see to a distance of 14 billion light years. We refer to this as our observable Universe. Every year, our observable Universe
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