Explaining The Early Universe PDF

# Explaining The Early Universe ## What Is The Big Bang Theory? - Astronomers study celestial bodies such as stars, the Moon, and planets. - The Big Bang Theory states that the universe and everything in it began in an event 13.7 billion years ago. - Before the Big Bang there was no energy, matte...

# Explaining The Early Universe ## What Is The Big Bang Theory? - Astronomers study celestial bodies such as stars, the Moon, and planets. - The Big Bang Theory states that the universe and everything in it began in an event 13.7 billion years ago. - Before the Big Bang there was no energy, matter, or celestial bodies. - The Big Bang gave rise to all the energy and matter in the universe. ## What Evidence Supports The Big Bang Theory? - The universe started out very small, hot and dense and has been expanding and cooling ever since. - Galaxies are collections of stars moving away from each other. - There is background radiation from every part of space which was first detected in the 1960s. - Space probes have mapped the background radiation. ## Why Do Scientists Think That The Universe Is Expanding? - Visible light is a spectrum of energy ranging from higher-energy, shorter-wavelength, violet-coloured light to lower-energy, longer-wavelength, red-coloured light. - A spectroscope can separate white light into its wavelengths of color. - If a star is moving toward you, its wavelengths become compressed and shifted toward the violet end of the spectrum. - A red shift occurs when a star's wavelengths get longer and are shifted toward the red end of the spectrum if the star is moving away from you. - Astronomers have observed a red shift in many individual stars and galaxies indicating that they are moving away from Earth and each other. - The distance between stars and galaxies is increasing. ## A Model For The Expanding Universe - The raisins in the uncooked bread dough all move away from each other as the bread bakes. - In a similar way, galaxies in the universe are moving away from each other as the universe expands. *** # Galaxies ## What Is A Galaxy? - A galaxy is a large group of stars, gas, and dust held together by gravity. - There might be as many as several billion galaxies in the universe and each galaxy might contain billions of stars. - Our Sun is part of the Milky Way galaxy. - A nebula is a dense cloud-like collection of gas and dust in space. - Some nebula are places where stars are born. ## What Kinds Of Galaxy Shapes Are There? - Spiral galaxies: Look like a pinwheel from above and a plate with a ball in the center from the side. - Elliptical galaxies: Have the shape of a flattened circle and range from a perfect sphere to a stretched-out sphere like a football. - Irregular galaxies: Do not have any regular type of shape like a sphere or a pinwheel. - Irregular galaxies have lots of gas and dust, which are the building blocks of stars. ## How Are Star Clusters Different From Galaxies? - Star clusters are groups of stars that are found within galaxies. - Globular clusters are collections of 100 000 to 1 000 000 stars held together by gravity. - Open clusters are collections of up to a few thousand stars. *** # Stars ## What Is A Star? - A star a massive, gaseous, spherical object in space that gives off light and other forms of energy due to nuclear reactions that take place at its core. - Nuclear reactions transform elements of one kind into elements of another kind. - For instance, hydrogen atoms fuse and become helium atoms during the life of a star. - Nuclear fusion releases tremendous amounts of energy. ## What Does The Color Of A Star Reveal? - The color of a star reveals clues about its surface temperature. - Red stars are fairly cool, about 3000°C. - Yellow stars, such as our Sun, are fairly hot, with a surface temperature of about 6000°C. - Whitish-blue stars are extremely hot, ranging from 20 000°C to 40 000°C. - The color of a star also reveals clues about what the star is made of and how it is moving. - The Doppler effect is the change in the wavelength of light from an object due to its motion. ## How Long Do Stars Last? - The "life" of a star depends on its mass. - Low mass stars (red dwarf stars) use up their hydrogen slowly and can last as long as 100 billion years. - As they use up their hydrogen, they lose mass and end their lives as small, dim white dwarf stars. - Intermediate mass stars like our Sun use up their hydrogen more quickly over about 10 billion years. - When the hydrogen is used up, the core of the star contracts, the temperature rises, and the outer layers of the star expand. - These cooler outer layers have a red color, so stars at this stage of their lives are called red giants. - As they continue to age, they get smaller, cooler, and dimmer becoming a white dwarf and, eventually, an even cooler, darker black dwarf star. - High mass stars use up their hydrogen relatively quickly, and may only last millions of years. - When nearing the end of its life, the core of a high mass star collapses in a dramatic, powerful explosion called a supernova For very high mass stars, the remaining core contracts further, resulting in a rapidly rotating, unimaginably dense neutron star. ## What Is A Black Hole? - Astronomers believe that extremely massive stars can contract greatly into a super-compact, super-dense object called a black hole. - The force of gravity in a black hole is so great that not even light can escape it. *** # The Sun And Its Planetary System ## What Is The Sun Like? - The Sun is a huge sphere of mostly hydrogen gas. - The nuclear reactions that take place at its core generate heat, light, and other forms of energy that radiates outward in all directions. - Over 110 Earths could fit across the Sun's diameter. ## How Did The Planets Of The Solar System Form? - A solar system is a group of planets circling a star. - A planet is a spherical object made mainly of rock or gases, which orbits a star and is large enough that its own gravity holds it in a spherical shape. - Planets spin on an imaginary line called an axis-a motion called rotation. - Planets also travel around the Sun-a motion called revolution. - A widely accepted hypothesis states that the planets began to form from the gases and other matter left over after the Sun formed. - The rocky bodies closest to the new Sun were blasted with its radiation and became the rocky, inner planets: Mercury, Venus, Earth, and Mars. - Farther out, away from the Sun's intense heat, the outer planets kept their gases and became the gas giants: Jupiter, Saturn, Uranus, and Neptune - All planets except for Mercury and Venus have at least one moon. ## What Other Objects Make Up The Solar System? - Throughout much of the early history of the solar system, stray rocky material and dust pounded the planets and their moons. - Craters provide evidence of these interactions. - Some of this rocky material remains in the form of asteroids- small objects that orbit the Sun, mainly found between Mars and Jupiter. - Rocky material left over from the formation of the solar system is also found at its outer limits in a region called the Oort cloud - From this region come comets- objects made of rock and ice that orbit the Sun. *** # Measuring Distances In Space ## How Big Is The Universe? - Distances between most objects in space are so great that it is hard to imagine them. - The unit that is commonly used to describe distances in space is the light-year. - Light moves faster than anything else in the universe at a speed of nearly 300 000 km/s. - Light from the Sun takes about 8 min to reach Earth. - Light from the Sun takes about 5 h to reach Neptune, the most distant planet in our solar system. - To reach the star that is nearest to us, called Proxima Centauri, light must travel about 4.2 years. - A light-year represents the distance that light travels in one year. - So the distance to Proxima Centauri is 4.2 light-years. - Most stars in the universe are hundreds, thousands, and even millions of light-years away from us. - The universe is huge. ## How Can Distances In Space Be Measured? - Long ago, people invented a technique for calculating distances on the ground indirectly: triangulation. - Triangulation involves creating an imaginary triangle between an observer and the object. - You need to know the length of one side of the triangle, called the baseline, and the size of the two angles created when imaginary lines are drawn from each end of the baseline to the same point on the distant object. - For thousands of years people measured the distances to stars using triangulation and an effect called parallax. - Parallax is the apparent change in position of a nearby object when it is viewed from two different points. - To measure distances from Earth to stars, the longest possible baseline is the diameter of Earth's orbit. - Sightings have to be taken six months apart. - If a star is close enough up to 1000 light-years, it will appear to move in relation to more distant stars. - Then its distance can be determined using triangulation. *** # Earth, Moon, And Sun Interactions ## What Causes The Seasons? - Earth's axis is tilted on an angle of 23.5°. - This axis tilt causes light from the Sun to strike Earth at different angles during its orbit around the Sun. - As Earth orbits the Sun, Earth's axis always points in the same direction. - However, the amount of sunlight that falls on Earth's surface at different points in its journey is different. - This difference is what causes the seasons. ## How Did The Moon Form? - Scientists think that long ago, as Earth and other inner planets were forming, a huge, planet-sized object slammed into Earth. - The intense impact ejected large and small pieces of the young planet. - These pieces went into orbit around Earth and, over time, built up into the object that we know today as the Moon. ## What Is An Eclipse? - An eclipse is the total or partial blocking of sunlight that occurs when one object in space passes in front of another. - There are two kinds: solar eclipses and lunar eclipses. - Both types involve the interaction of the Sun, Earth, and Moon. - In a solar eclipse, the Moon passes between the Sun and Earth, briefly blocking our view of the Sun. - People who observe where the full shadow of the Moon falls on Earth's surface see a total solar eclipse. - People who observe where only part of the Moon's shadow falls see a partial solar eclipse. - In a lunar eclipse, Earth passes between the Sun and the Moon, briefly plunging the Moon into darkness as Earth's shadow moves across it. - When the Moon lies fully in Earth's shadow, people see a total lunar eclipse. ## What Are Constellations? - As viewed from Earth, stars seem to make unchanging patterns in the night sky. - These patterns look like familiar objects, which people long ago grouped and named. - These groupings of stars into familiar patterns and shapes are called constellations. - Stars in the night sky all look as if they are close to one another and equal distances from Earth. - In reality, all stars are separated from one another and from us by hundreds, thousands, or millions of light-years. - Because stars and other sky objects look as if they move around Earth, Greek astronomer Ptolemy and many other people several thousand years ago thought that Earth was at the centre of the universe. - In the early 1500s, a Polish astronomer named Copernicus proposed a model of the heavens in which planets, including a rotating Earth, revolved around the Sun. - Italian astronomer Galileo confirmed Copernicus' model. - In the early 1600s, a German mathematician named Kepler predicted that the planets revolved around the Sun in elliptical orbits, not circles as was thought. - An ellipse is the shape of a flattened circle.