2. In this lecture… What is Astronomy? Where we are in the Universe Distances and Orders of Magnitude
3. What Is Astronomy? Astronomy: The scientific study of stars, planets, galaxies, and other celestial bodies NOT to be confused with astrology, which is the attempt to explain earthly events based upon the positions of objects in the sky (such as zodiacal signs and horoscopes, predictions based on celestial “alignments”, etc.
4. What’s Great About Astronomy? Astronomy is one of the oldest sciences, reflecting humanity’s fascination with the heavens since the beginning of time. The Dunhuang Star Map, from the Chinese Tang Dynasty, approximately 700 A.D.
5. Edwin Hubble at Palomar, 1949 (Caltech) (NASA) (D. Kasen et al.) Andromeda Galaxy in multiple wavelengths (mixed sources) We live in a very exciting era in astronomy, in which our knowledge and understanding of the universe beyond our atmosphere has advanced rapidly in the past hundred years.
6. Astronomy is a hobby as well as a science. Incredible astronomy is done by many talented and dedicated amateurs, in addition to professionals.
7. Do You Know Where You Are? You Are Here Take a moment to consider – if someone asked you your position in the universe, what would you say? Try to be as specific as you can.
8. Do You Know Where You Are? We live on the planet Earth… The “Blue Marble” image of our home planet. For this and other pictures of Earth, see http://visibleearth.nasa.gov
9. Do You Know Where You Are? which is part of the solar system…
10. Do You Know Where You Are? in the Orion Arm of the Milky Way galaxy
11. Do You Know Where You Are? which is part of a galactic cluster called the Local Group… image from Wikimedia Commons, created by Andrew Colvin
12. Do You Know Where You Are? which is part of the Virgo supercluster… image from Wikimedia Commons, created by Andrew Colvin
13. Do You Know Where You Are? which is just a small piece of the current observable universe. image from Wikimedia Commons, created by Andrew Colvin
14. Our Place in the Universe A Brief Tour of the Larger Universe http://www.youtube.com/watch?v=17jymDn0W6U You’ll notice this video indicates distance in terms of light travel time. This is like the way in which we often refer to distances here on Earth in terms of how long it takes to drive there, assuming a reasonable speed in a car. Light speed = 300,000 kilometers per second Light travels 9,500,000,000,000 kilometers in one year
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19. Kiloparsecs (1 kpc = 1000 pc) are useful for measuring distances to further parts of the galaxy or to nearby galaxies.
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21. The Universe in Powers of 10 We notice different structures and features as we examine maps of the universe at various scales, multiplying by 10 each time. Take some time to explore how the universe looks as you change scales by powers of 10 at http://www.atlasoftheuniverse.com/
22. Powers of 10 We can use negative powers of 10 to describe small numbers: 10-1 = 1/10 = 0.1 10-2 = 1/100 = 0.01 10-3 = 1/1000 = 0.001 10-4 = 1/10000 = 0.0001 The negative number tells you that you’ve divided by that many powers of 10; gives the position of the 1 after the decimal point. Remember 10o = 1!
23. Powers of 10 Powers of 10 are used in scientific notation to keep track of the accuracy of large and small numbers. 3.6739 x 105 = 367,390 In this case, the additional digits tell you that this is a number known to a very high precision – there may be a reason these numbers are important enough to be specified. 3.7 x 105 = 370,000 In this case, the lack of additional digits tells you that further precision is not necessary with this number.
24. Keeping a Perspective The power of 10 of a number also helps us to quickly judge what will and will not produce a significant change or effect. Consider: A person standing on the floor is trying to read a paper on the ceiling. They climb a 5 foot ladder to get a closer look. Will this be helpful? A person standing on the ground trying to see a detail on the surface of the Moon. They climb a 5 foot ladder to get a closer look. Will this be helpful?
25. Using Powers of 10 Numbers can be quickly compared using powers of 10. Example: The planet Mercury is approximately 5.8 x 107kilometers away from the Sun, while the planet Neptune is 4.5 x 109 kilometers away from the Sun. Mercury: power of 10 is 7 Neptune: power of 10 is 9 Neptune’s distance is two powers of 10 larger 102= 10 x 10 = 100 So Neptune is 100 times further away from the Sun.
26. Try it Yourself Mass of planet Mercury = 3.3 x 1023 kilograms Mass of planet Jupiter = 1.9 x 1027 kilograms Identify the power of 10 in each planets mass: Mercury: 23 Jupiter: 27 How many more powers of 10 does Jupiter’s mass have? Jupiter’s mass is 4 powers of 10 larger Using the powers of 10, how many TIMES larger is Jupiter’s mass than Mercury’s? 104 = 10 x 10 x 10 x 10 = 10,000 times larger
27. Orders of Magnitude Astronomers often use the term “order of magnitude” to refer to the power of 10 of some number. From our previous examples: Distance from Sun to Mercury is 5.8 x 107kilometers, or 7 orders of magnitude in kilometers. Distance from Sun to Jupiter is 4.5 x 109kilometers, or 9 orders of magnitude Can say that Jupiter is 2 orders of magnitude further from the Sun. 2 orders of magnitude further = 2 powers of 10 further = 100 times further.
28. Final Comments Make sure you read the “Preview” chapter in your textbook and learn the basic vocabulary terms Complete this lecture’s related activity, using powers of 10 to learn about the sizes and locations of various astronomical objects.
