Astronomy and the Universe PDF

# The Universe Have you ever gazed up at the stars and wondered what was out there? Astronomers have been studying the Universe for thousands of years, trying to make sense of it all. ## What is the Universe? The short answer is that it is a mystery. According to NASA, the majority of the Univers...

# The Universe Have you ever gazed up at the stars and wondered what was out there? Astronomers have been studying the Universe for thousands of years, trying to make sense of it all. ## What is the Universe? The short answer is that it is a mystery. According to NASA, the majority of the Universe is made up of a thing called Dark Energy. It is called Dark Energy, not because of any wicked or malevolent force behind it, but simply because it is mysterious and cannot be directly observed. Like the wind, it cannot be seen, but we can see its effects. And, like the wind driving a sailboat, Dark Energy seems to be the driving force that shapes and moves the observable elements of the Universe. The observable elements of the Universe include everything we can touch, see, hear, measure, or detect. It includes galaxies, black holes, stars, planets, rocks, dust, particles, and all living things. No one knows the size of the Universe but scientists estimate that the visual Universe is around 93 billion light-years across. A light year being the distance light travels in a year or about 9 trillion kilometers. That is to say, if you are thinking about crossing it, you had better tell your mom you won't be home for lunch! ## The Birth of Modern Astronomy The first astronomers noticed patterns, or constellations, among the stars and gave them names such as Orion the hunter and Pegasus the winged horse. Forty-eight of today's 88 recognized constellations can be mainly contributed to the Ancient Greeks and Babylonians although astronomy in China, Egypt, Central America, and India was also important in those far off days. By tracking the movement of constellations and planets across the night sky, astronomers were able to predict eclipses, meteor showers, and comets. Sailors were also able to use the constellations for navigational purposes on long voyages. The birth of modern astronomy began in the 16th century. It was Nicholaus Copernicus who first promoted the idea that the Sun and not the Earth that was the center of our solar system. Shortly after, Galileo Galilei, who is popularly known as "the father of modern observational astronomy", used a telescope to observe the Solar System. In doing so, he discovered the four brightest moons of Jupiter and proved that there are objects in the Solar System that do not revolve around the Sun. In 1668 Isaac Newton made the first reflecting telescope. The reflecting telescope used curved mirrors instead of the lenses of the conventional telescopes of the time. This solved the problem of light separating into colors when it is passed through a prism or a lens. Thanks to the continual improvement of telescopes, astronomers Pierre Laplace was able to propose the concept of Black Holes in 1798 and Charles Messier to identify nebulae, star clusters, and galaxies a few years later. ## The Universe's Mysteries New Astronomy or astrophysics, as it is now known, was born in the mid-nineteenth century. Photography had a huge impact on astronomy. The first photograph of the moon was taken in 1841 and in 1857, W. D. Bond took the first pictures of the stars. With the introduction of the photometer by Karl Friedrich Zollner in 1861 astronomers were able to accurately measure the brightness of different stars. The next major breakthrough occurred in the 1930s when Karl Jansky wondered what the noise was that was showing up in radio receivers that were operating at high frequencies. To find the source of the noise, he built a special receiver that he could move to pinpoint the source. To his astonishment, he discovered that the noise was coming from outer space! When Grote Reber learned of this, he concluded that the noise was thermal rather than audio and built the first parabolic reflector radio telescope which could detect radio waves at an incredible 3000 MHz. Astronomers can use the information picked up by radio telescopes to create images of galaxies billions of lightyears away, as well as to observe the composition of interstellar clouds and the properties of stars. However, due to the Earth's atmosphere, telescopes distort the light coming from stars and other objects in outer space. And so, in 1990 the Hubble Space Telescope was launched aboard the Space Shuttle Discovery on April 24, 1990. Thanks to this advanced technology, astronomers have made incredible discoveries about our universe and the mysteries it contains. ## Galaxies All the stars you can see on a clear night belong to our galaxy that is called the Milky Way. There are hundreds of billions of stars in our galaxy alone, and there are billions of galaxies in the universe. No one knows for sure how the galaxies formed. Some scientists think that small particles came together to form stars which came together to eventually form galaxies, while other scientists believe that the universe was once one huge cluster of cosmic matter which later subdivided into galaxies. Galaxies are divided into three types. - **Spiral galaxies**, like the Milky Way, have long spiral arms reaching out into the universe. Because of the enormous gravity needed to keep the stars in position, scientists have concluded that at the center of these galaxies is a supermassive black hole. - **Elliptical Galaxies** are made out of old stars. For this reason, they are dim compared to spiral galaxies. Elliptical Galaxies range enormously in size. The smallest are only about one-tenth the size of the Milky Way while the largest can be more than a million light-years from one side to the other and contain more than ten trillion stars. - **Irregular Galaxies** are neither Spiral Galaxies nor Elliptical Galaxies. These galaxies do not have a particular shape and are among the smallest galaxies in the universe. They are full of gas and dust which means that they are creating a lot of new stars and are therefore very bright. Galaxies often collide. Our own galaxy is on a collision with the nearby Andromeda Galaxy. There's no need to panic though. Because of the large distances between stars, galaxies often pass through each other without any stars smashing into each other. ## Stars Stars are the building blocks of the galaxies as well as being factories that manufacture the elements that make up the planets and life as we know it. Stars are giant balls of burning gas made up mostly of hydrogen and helium. What makes them so hot and bright is the process of nuclear fusion by which they turn the hydrogen into helium. There are many types of stars, but astronomers usually classify them by their color and size. - The color tells us how hot a star is. Blue stars are the hottest, followed by white stars, yellow stars, orange stars and finally red stars. - Size is often measured in solar masses i.e. the mass in comparison to the Sun, the Sun being one solar mass. Depending on their size, stars are known as dwarfs, giants, or supergiants. - Our own Sun is a **yellow dwarf**. Yellow dwarfs make up about 10 percent of all the stars in the universe and have a lifetime of between 4 and 17 billion years. - **Red dwarfs** are the most common stars in the universe because of their long lifetime which can be anything from 73 to 5500 billion years. - **Blue giants** burn hot and fast. They can be anything up to 250 solar masses and last as little as 3 million years. - **Red Supergiants** are in the later stages of their evolution. Betelgeuse, a red supergiant in the constellation of Orion, is an example of one of these. If Betelgeuse were in the place of the Sun, it would reach all the way to Jupiter. ## The Life Cycle of a Star - Stars start off as a nebula, a huge cloud of dust about a 100 times the size of our Solar System. Gravity compacts the dust which becomes hotter and hotter until the center becomes hot enough for nuclear fusion to take place. - Once it is a star, it will continue to shine for billions of years. It will stay at this stage for the majority of its life. There is good balance between gravity which tries to compact the star and heat which tries to expand it. This time of a star's life is called the main sequence and lasts until it runs out of hydrogen. - When the star runs out of hydrogen, it cools and expands and becomes a red giant. - The core of the star continues to cool and begins to form iron and then collapse. When this happens the smaller stars will become white dwarfs and larger stars will explode into a supernova which in turn will become a neutron star or a black hole. ## Planets Planets are formed from elements in the same dust cloud that formed the star they revolve around. Particles in the nebular that is spinning around the forming star clump together as gravity brings them together. Planets near the star are usually formed with elements with a high melting point such as iron and calcium. These planets are rocky and relatively small. Planets farther away from the star, where it is cooler, are comprised mostly of hydrogen and helium. These planets are gaseous and a lot larger than their rocky counterparts. The star and the planets, moons and other objects that revolve around it is known as a solar system. ## Our Solar System Our solar system id divided into two parts that are divided by an asteroid belt. - The inner solar system includes the four rocky planets; Mercury, Venus, Earth and Mars. - The outer solar system includes the four gaseous planets; Jupiter, Saturn, Uranus, and Neptune. Astronomy has come a long way since Galileo, on a small planet called Earth, turned his telescope to the heavens. However, the more astronomers find out about the universe, the more mysteries there are to be resolved.