An Introduction to AST 112 Stars, Galaxies, and the Cosmos

An Introduction to AST 112 Stars, Galaxies, and the Cosmos

What is Astronomy? 50 years ago, astronomy was the study of everything outside Earth s atmosphere: the planets, the Sun, stars, galaxies, the Universe, In the last 50 years, we have begun to explore the Solar System: rovers on Mars, spacecraft in orbit around Saturn, spacecraft hurtling toward Pluto Today, the study of the Solar System is usually called planetary science or solar physics. These topics are the subject of AST 111 Intro to the Solar System. Everything else is the realm of AST 112, this course.

In those 50 years, we have gathered a wealth of information about the Universe. (By we, I mean humans. You have participated, too.) Telescopes sit atop mountains around the world and orbit Earth. This new technology has allowed us to understand where we came from. With these discoveries, the cozy Universe of the past has given way to a strange and beautiful Universe of today. What do I mean? Let s take a look

An Extremely Brief Tour of the Universe A 1000 years ago, the Universe was thought to contain Earth and its Moon, the Sun, planets, and the stars. The entire volume was thought somewhat larger than Earth. Sun Earth Ptolemaic Model of the Universe

Our view of the Solar System has changed

We ve looked back at the Sun s family of planets from our distant robot explorers. Solar System family portrait Taken by Voyager 1 in February 1990 when it was 4 billion miles from Earth and nearing the edge of the Solar System. All of human accomplishment, triumph, and misery is located on that pale blue dot.

The ancient Greeks knew of methods for determining the distances to the stars. Their attempts to use these methods failed. They took this failure to mean the stars were fixed on the sky, unmoving, painted onto the celestial dome overhead. It was not until 1838 that Friedrich Bessel measured the first distance to a nearby star and found it to be 11 light-years away.

What is a light-year? Despite the name, a light-year is a distance not a time. A light-year is the distance light travels in one year: 9.5 trillion kilometers. A light year is also about 63,000 times farther than the distance between Earth and Sun. For comparison, the Earth-Sun distance is about 8.5 light-minutes. So how old is the sunlight you see?

Our telescopes have provided measurements of the distant stars and shown they are the Sun s kin. The Sun epsilon Indi, a smaller orange star Proxima Centauri, a tiny red star

We ve learned that the Sun is an average star, surpassed in size and brightness by other stars. The Sun Large blue star theta Orionis 1-C (central star of the Orion Nebula)

We can watch as stars are born The Great Orion Nebula This stellar nursery glows from the reflected light of 4 large blue stars, including theta Orionis 1-C. The region is home to several thousand newborn stars. And portions of the giant cloud is fragmenting into smaller clouds that will form more new stars.

and the explosive ends of stars lives. Crab supernova remnant The Crab supernova was recorded by Chinese astronomers in July 1054. Today, the remnant of the star is visible expanding into the space around the original star.

even peek at the weird beasties inside. Crab pulsar and wind nebula The Crab pulsar rotates 33 times per second, is about the size of downtown Phoenix, but has more mass than the Sun. The intense magnetic field combined with the pulsar s rapid rotation produces a wind of subatomic particles that flow outward at 1/3 rd the speed of light.

If you look up at the summer sky far from city lights, you see the Milky Way

A century ago, the Universe was thought to be synonymous with the Milky Way Galaxy. By 1900, the size of the Universe was thought to be no larger than a few thousand lightyears in size. SUN William Herschel s model of the Milky Way

We now recognize the Milky Way is a galaxy, a flattened, rotating group of 100+ billion stars.

We can look a few million light-years away at neighboring galaxies Andromeda galaxy

Or out at the nearby galaxies a spiral galaxy viewed edge on a spiral galaxy viewed at an angle a giant elliptical galaxy

Or farther still to see colossal galaxy clusters. Each yellow smudge in this image is a galaxy composed of billions of stars. There are only two stars in the foreground visible. Can you spot them?

Or, most recently, we can peer into blank stretches of sky to reveal the depths of the Universe. Hubble Ultra Deep Field This image was created by staring for 11 days at the same blank patch of sky. The HUDF contains galaxies more than halfway back to the first starlight, almost 6 billion years ago. There are 4 foreground stars in the image. Every other smudge of light is a distant galaxy.

Understanding the Universe How do we begin to grasp a Universe that is so large, so old, and so beyond human experience? The same way we try to understand the everyday world around us: Look for patterns in the natural world Apply those patterns to new situations Discover new information and new patterns This is science.

Science is a Tool What goes up must come down is a rule everyone learns. About 300 years ago, Isaac Newton developed a set of rules (logical and mathematical) for why this happens. He called it gravity. He applied these rules to the Moon, explaining why it orbits Earth at the speed that it does. Today, we understand that gravity can be applied to stars, galaxies, and to the Universe itself.

Science is a Tool But Einstein came along in 1905 and found that Newton wasn t quite right. Einstein called his new rules for gravity general relativity. With them, he could explain newly discovered aspects of the motion of the Sun and planets and of light itself. In science, rules and patterns are called laws or theories. They represent our best ideas of how nature works.

Science is a Tool Just as Newton and Einstein improved our ideas about gravity, all scientific ideas are challenged and modified over time. Science is not a list of facts. It is a tool for learning about the natural world. Science is a set of rules to help us discover the natural world without biases, preconceptions, or moral judgments. It is the most powerful method we have for learning about how the Universe behaves.

The Ground Rules 1. Claims require evidence. You can claim the Sun is made of iron. But if measurements of the Sun show otherwise, your claims are only so much hot air. 2. Extraordinary claims require extraordinary evidence. Astronomers claim to know the Universe began 13.5 billion years ago, infinitely hot, perfectly smooth, and expanding rapidly. The last 50 years of telescope observations support this extraordinary claim.

Goals of a Science Course In this course, we will focus on 3 broad topics: 1. What we know facts, figures, concepts 2. How we know technology and theories 3. What we knew the ideas that formed the basis for what we know today (what we know today forms the basis of what we ll learn tomorrow) These three topics are equally important. What we know today is useful, but it is also changing. Knowing how to find new patterns is the key.

Goals of a Science Course At the end of this course, you should be able to describe the Universe: What is a star? How long will the Sun shine? What is a pulsar? How is one born? How big is a galaxy? What is the Milky Way? How old is the Universe? How did it begin?

Goals of a Science Course But you should also be able to say how we know about the Universe: How do we know the distance to nearby stars? How do we measure the temperature of a star? How do we know galaxies rotate? How do we know the Universe is expanding? How do we know it started with a hot Big Bang?

Any questions???