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ASTRO 101

ASTRO 101. Principles of Astronomy. Instructor: Jerome A. Orosz (rhymes with “ boris ” ) Contact:. Telephone: 594-7118 E-mail: orosz@sciences.sdsu.edu WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ Office: Physics 241, hours T TH 3:30-5:00.

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ASTRO 101

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  1. ASTRO 101 Principles of Astronomy

  2. Instructor: Jerome A. Orosz (rhymes with “boris”)Contact: • Telephone: 594-7118 • E-mail: orosz@sciences.sdsu.edu • WWW: http://mintaka.sdsu.edu/faculty/orosz/web/ • Office: Physics 241, hours T TH 3:30-5:00

  3. Text: “Discovering the Essential Universe, Fifth Edition”by Neil F. Comins

  4. Course WWW Page http://mintaka.sdsu.edu/faculty/orosz/web/ast101_fall2012.html Note the underline: … ast101_fall2012.html … Also check out Nick Strobel’s Astronomy Notes: http://www.astronomynotes.com/

  5. Astronomy Help Room No appointment needed! Just drop by! Where: Room 215, physics-astronomy building. When: • Monday: 12-2, 4-6 PM • Tuesday: 12-1 PM; 4-6 PM • Wednesday: 12-2, 5-6 PM • Thursday: 4-6 PM

  6. Homework/Announcements • Homework due Tuesday, October 9: Question 5, Chapter 4 (Describe four methods for discovering exoplanets)

  7. Next:Comparative Planetology • Outline and introduction to the Solar System • Planets around other stars

  8. Quick Concept Review • Some useful concepts: • Density • Albedo

  9. Density and Albedo • The concepts of density and albedo are useful in planetary studies. • Density = mass/volume • The density of water is 1 gram per cubic cm. • The density of rock is 3 grams per cubic cm. • The density of lead is 8 grams per cubic cm. • The density of an object can give an indication of its composition.

  10. Density and Albedo • The concepts of density and albedo are useful in planetary studies. • Albedo = % of incident light that is reflected. • A perfect mirror has an albedo of 100% • A black surface has an albedo of 0%. • The albedo of an object is an indication of the surface composition.

  11. The Planets • Why solar system planets are special:

  12. The Planets • Why solar system planets are special: • Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.).

  13. The Planets • Why solar system planets are special: • Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.). • You can also send spacecraft to visit them.

  14. The Planets • Why solar system planets are special: • Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.). • You can also send spacecraft to visit them. • Stars always appear pointlike, even in the largest telescopes.

  15. The Planets • Why solar system planets are special: • Planets are resolved when seen through telescopes (i.e. you can see the disk, surface features, etc.). • You can also send spacecraft to visit them. • Stars always appear pointlike, even in the largest telescopes. Also, they are so far away that we cannot send probes to study them.

  16. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc.

  17. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. • Do not confuse “solar system” with “galaxy”: • The solar system is the local collection of planets around the Sun. • A galaxy is a vast collection of stars, typically a hundred thousand light years across.

  18. The Solar System Census: • There were 5 planets known since antiquity: • Mercury • Venus • Mars • Jupiter • Saturn

  19. The Solar System Census: • There were 5 planets known since antiquity: • Mercury • Venus • Mars • Jupiter • Saturn • Since the 1600s (Kepler, Galileo, Newton), the Earth was considered a planet as well.

  20. New Members • Uranus: discovered in 1781 by William Herschel.

  21. New Members • Uranus: discovered in 1781 by William Herschel. • Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier).

  22. New Members • Uranus: discovered in 1781 by William Herschel. • Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). • Pluto: discovered in 1930 by Clyde Tombaugh.

  23. New Members • Uranus: discovered in 1781 by William Herschel. • Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). • Pluto: discovered in 1930 by Clyde Tombaugh. • Asteroids: thousands, starting in 1801.

  24. New Members • Uranus: discovered in 1781 by William Herschel. • Neptune: discovered in 1846 by Johann Galle (based on the predictions of John C. Adams and Urbain Leverrier). • Pluto: discovered in 1930 by Clyde Tombaugh. • Asteroids: thousands, starting in 1801. • Kuiper Belt Objects: Dozens, starting in the 1980s.

  25. Pluto “Demoted”! • The definition of a “planet” was changed recently: • Planets: The eight worlds from Mercury to Neptune. • Dwarf Planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite."• • Small Solar System Bodies: All other objects orbiting the Sun. http://www.space.com/scienceastronomy/060824_planet_definition.html

  26. The Solar System • The planets orbit more or less in the same plane in space. Note the orbit of Pluto. • This view is a nearly edge-on view.

  27. Classifications of Solar System Objects

  28. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. • The scale of things: • It takes light about 11 hours to travel across the Solar system.

  29. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. • The scale of things: • It takes light about 11 hours to travel across the Solar system. This is 0.001265 years.

  30. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. • The scale of things: • It takes light about 11 hours to travel across the Solar system. This is 0.001265 years. • It takes light about 4.3 years to travel from the Sun to the nearest star.

  31. The Solar System • The Solar System refers to the Sun and the surrounding planets, asteroids, comets, etc. • The scale of things: • It takes light about 11 hours to travel across the Solar system. This is 0.001265 years. • It takes light about 4.3 years to travel from the Sun to the nearest star. • It takes light about 25,000 years to travel from the Sun to the center of the Galaxy.

  32. Scale Model Solar System • Most illustrations of the solar system are not to scale.

  33. Scale Model Solar System • Most illustrations of the solar system are not to scale. • Usually, the size of the planets shown is too large.

  34. Scale Model Solar System • Build your own scale model of the solar system: http://www.exploratorium.edu/ronh/solar_system/ http://pages.umpi.edu/~nmms/solar/

  35. Scale Model Solar System • Build your own scale model of the solar system: http://www.exploratorium.edu/ronh/solar_system/ http://www.umpi.maine.edu/info/nmms/solar/index.htm • Conclusion: the solar system is pretty empty.

  36. Scale Model Solar System • Most depictions of asteroids in the movies are wrong…

  37. The Scale Model Solar System • Most depictions of asteroid fields are also not to scale. Image from Star Trek Voyager.

  38. Two Types of Planets • Planets come in two types: • Small and rocky. • Large and gaseous. Or • Terrestrial • Jovian

  39. The Terrestrial Planets • The terrestrial planets are Mercury, Venus, Earth (and Moon), and Mars. • Their densities range from about 3 grams/cc to 5.5 grams/cc, indicating their composition is a combination of metals and rocky material.

  40. The Terrestrial Planets • The terrestrial planets are Mercury, Venus, Earth (and Moon), and Mars.

  41. The Giant Planets • The giant planets are Jupiter, Saturn, Uranus, and Neptune.

  42. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth.

  43. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth. • However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high.

  44. The Giant Planets • The radii are between about 4 and 11 times that of Earth. • The masses are between 14 and 318 times that of Earth. • However, the densities are between 0.7 and 1.8 grams/cc, and the albedos are high. • The planets are composed of light elements, mostly hydrogen and helium.

  45. The Gas Giants • The composition of the giant planets, especially Jupiter, is close to that of the Sun. • The internal structures of these planets is completely different from that of the Earth. In particular, there is no hard surface. • These planets are relatively far from the Sun (more than 5 times the Earth-Sun distance), so heating by the Sun is not a big factor.

  46. Next: • The formation of the Solar System

  47. Star Formation • The starting point is a giant molecular cloud. The gas is relatively dense and cool, and usually contains dust. • A typical cloud is several light years across, and can contain up to one million solar masses of material. • Thousands of clouds are known.

  48. Side Bar: Observing Clouds • Ways to see gas: • By “reflection” of a nearby light source. Blue light reflects better than red light, so “reflection nebulae” tend to look blue. • By “emission” at discrete wavelengths. A common example is emission in the Balmer-alpha line of hydrogen, which appears red.

  49. Side Bar: Observing Clouds • Ways to see dust: • If the dust is “warm” (a few hundred degrees K) then it will emit light in the long-wavelength infrared region or in the short-wavelength radio. • Dust will absorb light: blue visible light is highly absorbed; red visible light is less absorbed, and infrared light suffers from relatively little absorption. Dust causes “reddening”.

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