An Introduction to AST 111 Our Solar System and Others

Transcription

1 An Introduction to AST 111 Our Solar System and Others

2 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 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. These new technologies have allowed us to understand where we came from, where we are, and what is happening around us. These are the subjects of AST 112, the other course.

3 The subject for this course, AST 111, is often called planetary science, but it covers more than planets. 50 years ago: telescopes were the only tool! Today: we have rovers on Mars, a spacecraft in orbit around Saturn, a spacecraft hurtling toward Pluto, and many, many others. The discoveries of the past century or two have revolutionized what we thought we knew. What do I mean? Let s take a look

4 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

5 Our view of the Solar System has changed

6 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.

7 It was thought that Earth was unique, the only world that had land, oceans, an atmosphere. Today, we understand that the Moon is Earth s sibling. It shared much of Earth s history and is affected by the same forces that shape Earth s surface.

8 We ve learned that Mars and Venus are rocky worlds like our Earth, but very different, too Mars, frozen desert world Venus, hellish volcanic world

9 The outer planets are not rocky at all, but giant, rapidly spinning worlds with huge atmospheres. Uranus Neptune Jupiter Saturn

10 Each outer planet is spanned by a ring system and a large family of moons. The largest moons are interesting worlds in their own right. Ganymede, larger than planet Mercury Io, volcanic moon Titan, only moon with an atmosphere

11 Many moons of the outer planets have water. Most are frozen, but a few sport geysers or possible oceans under their surfaces Enceladus erupts snow from cracks at its south pole Europa is thought to hide a global ocean much deeper than Earth s

12 In the past 15 years, we have even found the first planets orbiting other stars weird, oddball planets like nothing any one suspected. Gas giant planets that orbit so close to their star they boil away! Planets with orbits that last days, not years!

13 There are plenty of possible locations nearby, just look up on a summer night

14 We now recognize the Milky Way is a galaxy, a flattened, rotating group of 100+ billion stars, many of which are just like our Sun.

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

16 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?

17 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.

18 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 right here on Earth: Look for patterns in the natural world Apply those patterns to new situations Discover new information and new patterns This is science.

19 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 it does. Today, we understand that gravity can be applied to stars, galaxies, and to the Universe itself.

20 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.

21 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 the Universe.

22 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 Sun and its family of planets formed 4.6 billion years ago, from a flattened, spinning pancake of gas and dust. The last 50 years of research supports this extraordinary claim.

23 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.

24 Goals of a Science Course At the end of this course, you should be able to describe the Universe: What is a planet? Why are there two kinds? What properties are common to each? What makes planets orbit stars and not vice versa? What processes shape the surface of a moon or planet? How do the planets surfaces differ? How old is the Solar System? How did it begin?

25 Goals of a Science Course But you should also be able to say how we know about the Universe: How do we know what the planets are made of? How can we know a planet s temperature even if we can t touch it? How do we know Earth orbits the Sun? How do we know Mars was once warm and wet? How do we know the history of the Solar System?

26 Any questions???