Astronomy 10 Introduction to the Solar System

Transcription

1 Astronomy 10 Introduction to the Solar System

2 This is your source for all things in this class: 1. Grading policies. 2. What topics we ll covering. 3. How to reach me. 4. Reading assignments. 5. Lecture notes. 6.

3 A B C D

4 What we ll be talking about Motions in the sky The Sun The Planets How the Solar System formed Other planetary systems, and life in the universe

5 The SCIENCE of Astronomy Just what IS astronomy? Astronomy is a science, usually thought of as a branch of physics. But, it also involves chemistry, geology, meteorology, and some other areas that I didn t think of when writing this. This breadth of topics comes about because we deal with objects as small as atoms (or smaller!), and as large as the universe. In a sense, it is the oldest branch of science. We could say that it began as soon as people began looking upward, and wondering what was going on. and in a sense it is relatively new. The modern scientific method is actually a relatively new concept. Prior to this, astronomy, religion and mysticism were very much intertwined. We can certainly be accused of chauvinism, but astronomers like to think that theirs is the most fundamental science, in that it deals with the biggest and oldest questions that humans have been asking.

6 In astronomy, we must deal with a huge range of scales in terms of mass, length and time To deal with this, we typically invent units of measurement that give us convenient points of reference. You are already used to doing this. How would you measure your height, vs. the distance to Oakland? How would you measure the walking time to your next class, vs. your age? For masses, astronomers may use: Atomic mass units, equal to the mass of a hydrogen atom (much more convenient than kg). Solar masses, equal to the mass of the Sun (much more convenient than 2,000,000,000,000,000,000,000,000,000,000 kg). For distances, we may use Ångstroms ( m). Light years (9,450,000,000,000,000 m). Astronomical Units (150,000,000 km). For time, we typically stick to powers of ten times familiar units. For rapid, atomic-scale events, we may use nanoseconds ( s). For long term events, mega-years (Myr) or giga-years (Gyr) may be used.

7 Question: If Earth orbited the Sun in 730 days, how would this affect the length of the light year? a) It would be the same distance, in meters, as our current definition. b) It would be half as long. c) It would be twice as long. d) It would still equal one year.

8 Another way we can be lazy is to use scientific notation In scientific notation, 100 would be written as 10 2 This is a shorthand way of saying ten times itself. To convert to scientific notation, count the number of spaces to the left between the decimal point and the leftmost, nonzero number. What is 2,000,000,000,000,000,000,000,000,000,000 in scientific notation? 2x10 30 For numbers less than one, the exponent is negative would be written as 10-2, shorthand for saying one divided by ten twice. To convert to scientific notation, count the number of spaces to the right between the decimal point and the leftmost, nonzero number. What is in scientific notation? 1.66x10-27

9 Let s practice some scientific notation mathematics What is 6x10 23 times 3x10 56? How about 4x10-13 times 5x10 20? OK, now try =?

10 To try and get a feel for distances, let s build some scale models of the universe. Let s start by shrinking the Sun down to 6 cm in size Diameter of Planet (mm) Orbital radius of planet (m) Mercury Venus Earth Mars Jupiter Pluto The nearest star? 1,800 km away (near Denver) Size of Milky Way Galaxy? 68 million km! (near Mars)

11 OK, that didn t work too well for large distances. Let s shrink the Sun down to 2 mm in size: Pluto is now less than 9 meters away (of course, it s only 3 microns across) Nearest star is still 36 miles away (near Monterey) How about 0.01 mm (human cell)? Nearest star is now 300 m away. Edge of Milky Way is about 2,000 km away (Canada) Nearest large galaxy is about 60,000 km away (about five real Earth diameters)

12 How about time? Can we get a sense of scale for the history of the universe? Let s do a scaled time model. Start by shrinking the entire history of the universe down to a single year in length. On this scale, when would various interesting events occur?

13 3:30 am 1/1, recombination 2/17, 1st stars form in Milky Way January February March April May June July August September October November December 9/3, Sun and planets form 10/14, Earliest life on Earth 12/17, Cambrian explosion 12/30, Dinosaur extinction 12/31, 9 pm, 1st homonids. 11:58 pm, modern humans