1. The Scale of the Cosmos “ The Universe is a big place. ” “ The Universe is a big place. ” Really big. Really big. Really, really big! Really, really big! You might be wondering… You might be wondering… How big is it?! How big is it?!

2. We ’ ll get to that… But first, let ’ s list some essential questions for Chapter 1.

3. Essential Questions Where and when are you in the universe? Where and when are you in the universe? How do astronomers express distance? How do astronomers express distance? Which objects are big and which are small? Which objects are big and which are small? How do scientists know about nature? How do scientists know about nature?

4. Starting at home The Earth The Earth The planet Earth is about 12,800 km across. (That ’ s about 8,000 miles for you non-metric folks.) The planet Earth is about 12,800 km across. (That ’ s about 8,000 miles for you non-metric folks.) How do you convert from km to miles? How do you convert from km to miles?

5. The Solar System The solar system contains: The solar system contains: The Sun The Sun The 8 Planets The 8 Planets Dwarf Planets, Asteroids, Comets, dust and gas. Dwarf Planets, Asteroids, Comets, dust and gas.

6. 3 rd Rock from the Sun The Earth is the 3 rd rocky (terrestrial) planet from the Sun. The Earth is the 3 rd rocky (terrestrial) planet from the Sun. The average distance from the Earth to the Sun is 150,000,000 km. The average distance from the Earth to the Sun is 150,000,000 km. This is called an Astronomical Unit (AU for short). This is called an Astronomical Unit (AU for short).

7. Table of Solar System Objects Object Distance in km Distance in AU Mercury Venus Earth150,000,000 1 AU Mars Asteroid Belt Jupiter Saturn Uranus Neptune Pluto

8. Scientific Notation Did you notice anything about the large numbers you used to fill in the table on the last slide? Did you notice anything about the large numbers you used to fill in the table on the last slide? A shorthand notation that astronomers and all scientists use for writing large numbers is scientific notation. A shorthand notation that astronomers and all scientists use for writing large numbers is scientific notation. Why don ’ t you practice with this now… Why don ’ t you practice with this now…

9. Light Years A light year is an even larger unit of distance than an astronomical unit. A light year is an even larger unit of distance than an astronomical unit. A light year is the distance light travels in one year. It is about 10 trillion km. A light year is the distance light travels in one year. It is about 10 trillion km. That ’ s 10,000,000,000,000 kilometers. Convert that to scientific notation and to miles please… That ’ s 10,000,000,000,000 kilometers. Convert that to scientific notation and to miles please…

10. Hey, how fast does light travel anyway? Light travels at 300,000 km/s! That ’ s how fast in miles per sec? Light travels at 300,000 km/s! That ’ s how fast in miles per sec? In one second light can travel around the Earth 7.5 times! It ’ s fast! In one second light can travel around the Earth 7.5 times! It ’ s fast! That being said, the universe is a big place…and light takes about 8 minutes to get from the Sun to the Earth. That being said, the universe is a big place…and light takes about 8 minutes to get from the Sun to the Earth.

11. How long does it take for sunlight to reach each planet in our solar system? Dig out your solar system chart and work with a partner and/or teacher to add a column entitled: “ Time for Sunlight. ” Dig out your solar system chart and work with a partner and/or teacher to add a column entitled: “ Time for Sunlight. ” Check you answers when you are done. Check you answers when you are done.

12. The nearest star… How far is the nearest star? How far is the nearest star? 1 AU of course, but seriously, the next nearest? 1 AU of course, but seriously, the next nearest? About 4.2 lightyears (ly). The triple star system Alpha Centauri. About 4.2 lightyears (ly). The triple star system Alpha Centauri.

13. Definitions: Planet—a small non-luminous body that shines by reflected light (non-technical definition) Planet—a small non-luminous body that shines by reflected light (non-technical definition) Star—a self luminous sphere of hot gas with a core undergoing nuclear fusion Star—a self luminous sphere of hot gas with a core undergoing nuclear fusion Galaxy–a great cloud of stars, gas, and dust bound together by gravity (they can contain >100 billion stars) Galaxy–a great cloud of stars, gas, and dust bound together by gravity (they can contain >100 billion stars)

14. The Milky Way

15. We live in a spiral shaped galaxy called the Milky Way (if you ’ ve ever seen it you know why). We live in a spiral shaped galaxy called the Milky Way (if you ’ ve ever seen it you know why). It ’ s about 80,000 ly across and contains about 100 billion stars! It ’ s about 80,000 ly across and contains about 100 billion stars! Our solar system is about 2/3 of the way out in one of the spiral arms. Our solar system is about 2/3 of the way out in one of the spiral arms.

16. The “Pinwheel” Galaxy M31

17. Structures larger than Galaxies: Only 100 years ago, astronomers thought the Milky Way was the entire universe. Now we know there are many more galaxies. Only 100 years ago, astronomers thought the Milky Way was the entire universe. Now we know there are many more galaxies. The nearest galaxy to our own is called the Andromeda Galaxy and is the only one visible to the unaided eye. The nearest galaxy to our own is called the Andromeda Galaxy and is the only one visible to the unaided eye.

18. The Andromeda Galaxy

19. The Local Group Andromeda is about 2.5 million ly away and is (along with the Milky Way) a member of about few dozen galaxies called “ The Local Group. ” Andromeda is about 2.5 million ly away and is (along with the Milky Way) a member of about few dozen galaxies called “ The Local Group. ” Ingenious name, don ’ t you think?! Ingenious name, don ’ t you think?!

20. Galaxy SuperClusters The Local Group is a member of a much larger group called a cluster or supercluster. The Virgo Supercluster to be exact! The Local Group is a member of a much larger group called a cluster or supercluster. The Virgo Supercluster to be exact!

21. One more note on units of distance… There is another unit of distance astronomers sometimes use based on the Earth ’ s orbital diameter and an angle measurement of 1 second (3600 hundred seconds in a degree). There is another unit of distance astronomers sometimes use based on the Earth ’ s orbital diameter and an angle measurement of 1 second (3600 hundred seconds in a degree). This measurement is called a parsec (pc) and is about 3.26 lightyears. This measurement is called a parsec (pc) and is about 3.26 lightyears.