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Chapter 1 Here and Now

Chapter 1 Here and Now. Astronomy deals with objects on a vast range of size scales and time scales. Most of these size and time scales are way beyond our every-day experience. Humans, the Earth, and even the solar system are tiny and unimportant on cosmic scales. A Campus Scene. 16 x 16 m.

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Chapter 1 Here and Now

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  1. Chapter 1Here and Now • Astronomy deals with objects on a vast range of size scales and time scales. • Most of these size and time scales are way beyond our every-day experience. • Humans, the Earth, and even the solar system are tiny and unimportant on cosmic scales.

  2. A Campus Scene 16 x 16 m

  3. = 0.1 nm

  4. A City View 16 x 16 m 1 mile x 1 mile

  5. Pennsylvania 1 mile x 1 mile 100 miles x 100 miles

  6. Earth 100 miles x 100 miles Earth’s Diameter = 12,756 km

  7. Earth and Moon Earth–Moon Distance = 384,000 km Earth’s Diameter = 12,756 km

  8. Earth orbiting around the Sun Earth–Sun Distance = 150,000,000 km Earth–Moon Distance = 384,000 km

  9. Earth orbiting around the Sun In order to avoid large numbers beyond our imagination, we introduce new units: 1 Astronomical Unit (AU) = Earth–Sun Distance = 150 million km 1 AU

  10. The Solar System Approx. 100 AU Earth–Sun Distance = 1 AU

  11. (Almost) Empty Space near our Solar System Approx. 100 AU Approx. 10,000 AU

  12. The Solar Neighborhood Approx. 1,000,000 AU Approx. 10,000 AU

  13. The Solar Neighborhood New distance scale: 1 light year (ly) = Distance light travels in 1 year = 63,000 AU ~ 1013 km = 10,000,000,000,000 km (= 1 followed by 13 zeros) = 10 trillion km Nearest star to the Sun: Proxima Centauri, at a distance of 4.2 light years Approx. 16 ly

  14. Powers-of-ten notation 106 =10×10×10×10×10×10 =1,000,000

  15. Powers-of-ten notation 6.3 × 104 AU = 6 3 0 0 0 AU = 63,000 AU 1 2 3 4 5.43 × 10–4 m = 0.0 0 0 5 4 3 = 0.000543 1 4 2 3

  16. The speed of light • c ≡ 299,792,458 m/s, exactly. ( ≈ 3 × 105 km/s ) • The cosmic speed limit —You cannot go faster than this, ever! • 1 light-year (ly) = (speed of light) × (one year)

  17. 0.1 nm Table A-6, p. 447

  18. Extended Solar Neighborhood Approx. 16 ly Approx. 1,600 ly

  19. The Milky Way Galaxy Diameter of the Galaxy ~ 75,000 ly Approx. 1,600 ly

  20. The Local Group of Galaxies Diameter of the Galaxy ~ 75,000 ly Several million light years to the nearest large galaxies

  21. The Universe on Very Large Scales Clusters of galaxies are grouped into superclusters. Superclusters form filaments and walls around voids.

  22. For the units of physical quantities scientists use the metric system. • The basic units are the meter (length), kilogram (mass), and second (time).

  23. To conveniently express large (and small) numbers, astronomers often use the scientific notation, also called the powers-of-ten notation.

  24. The distance scale of the cosmos, from the smallest to the largest, involves a factor of 1040, or 1 followed by 40 zeros. To express large distances, astronomers use the astronomical unit (AU) and the light-year (ly).

  25. Science is a process in which conceptual models interact with observations to produce new pictures of reality.

  26. Science is about the cosmic order. Religion is about the cosmic purpose.

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