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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. Homework/Announcements.

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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. Homework/Announcements • Homework due Tuesday, March 19: Question 6, Chapter 7 (What role did Charon play in enabling astronomers to determine Pluto’s mass?). • Tuesday, March 26: Wrap-up, review • Thursday, March 28: Exam #2

  4. Next: Chapter 7 (Dwarf Planets and Small Solar System Bodies)

  5. Pluto • Essentially nothing was known about Pluto until the 1970s. • It is far from the Sun (more than 40 times the Earth-Sun distance), hence it receives little sunlight. In turn, we see very little light reflected back. • The planet looks nearly pointlike owing to its large distance from us, so it was not possible to see surface features.

  6. Pluto’s Orbit • Pluto’s orbit is highly inclined relative to the orbits of the other planets.

  7. Pluto’s Orbit • Pluto’s orbit is also more eccentric than the orbits of the other planets. The period is 247.7 years

  8. Pluto’s First Moon • Pluto’s first moon was discovered in 1978. • The orientation of the moon’s orbit is such that during certain times, Pluto and its moon appear to pass in front of each other every 3.2 days as seen from Earth.

  9. Pluto’s First Moon • Pluto and Charon passed in front of each other in the late 1980s.

  10. Pluto’s First Moon • Pluto and Charon passed in front of each other in the late 1980s. • Studies of these events allowed astronomers to measure the masses and radii of Pluto and Charon. Images from Courtney Seligman (http://www.cseligman.com)

  11. Pluto’s First Moon • The masses can be deduced from Kepler’s Laws. • The radii can be deduced by looking at the total brightness over time.

  12. Pluto’s First Moon • Pluto’s mass is 1/500 of the Earth’s mass. • Pluto’s diameter is 2300 km.

  13. Pluto’s First Moon • Pluto’s mass is 1/500 of the Earth’s mass. • Pluto’s diameter is 2300 km. This is smaller than Jupiter’s large moons, and also Earth’s moon.

  14. More Moons for Pluto • Two additional moons were found using the Hubble Space Telescope in 2005.

  15. 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

  16. New Classification Scheme for the Solar System Many catagories overlap. For example, some asteroids are dwarf planets. In most cases, the distinctions between the catagories are not important for us.

  17. Dwarf Planets • Ceres was discovered in 1801 by Piazzi. • Its orbit lies between Mars and Jupiter. • Thousands of asteroids are now known to be in the “asteroid belt”. • Ceres was reclassified as a dwarf planet in 2006.

  18. Dwarf Planets • Since 2003, three additional dwarf planets have been discovered beyond the orbit of Pluto. • Eris, the largest one, is apparently composed largely of water ice. • Haumea appears to be slightly oval shaped.

  19. Dwarf Planets • Since 2003, three additional dwarf planets have been discovered beyond the orbit of Pluto. • Eris has a very eccentric and inclined orbit. The period is 557 years.

  20. Next: Small Solar System Bodies • Asteroids • Kuiper Belt Objects • Comets

  21. Small Solar System Bodies • The first asteroid, Ceres, was discovered in 1800 using visual observations through a telescope. • By the late 1800s, a total of about 300 asteroids were found. • The big breakthrough came in 1891 when photography was used...

  22. Small Solar System Bodies

  23. Small Solar System Bodies • As of September 2008, roughly 190,000 asteroids have been cataloged. • Only three asteroids have diameters larger than 300 km. The smaller you go in diameter, the more asteroids there are.

  24. Small Solar System Bodies • Most of the asteroids orbit between Mars and Jupiter. • Note the deceptive scale: the average spacing is 1,000,000 km between objects!

  25. Small Solar System Bodies • Most of the asteroids orbit between Mars and Jupiter. • Jupiter’s gravity causes the asteroids to gather into certain orbits.

  26. Small Solar System Bodies • Most of the asteroids orbit between Mars and Jupiter. • Some cross the orbit of the Earth. Asteroid 1994 XM1 was closer than the Moon on its nearest approach.

  27. Small Solar System Bodies • Most of the asteroids orbit between Mars and Jupiter. • Some have the same orbit as Jupiter, but either lead or lag the planet by 60 degrees.

  28. What Asteroids Look Like • Asteroids have irregular shapes, and typically have craters and other features.

  29. What Asteroids Look Like • Asteroids have irregular shapes, and typically have craters and other features.

  30. What Asteroids Look Like • A probe crashed into Eros on February 12, 2001.

  31. What Asteroids Look Like • A probe crashed into Eros on February 12, 2001. • The chemical composition of Eros is similar to that of old meteorites, indicating Eros contains “primitive” material.

  32. Comets and Kuiper Belt Objects • There are two main regions where the comets live: the Kuiper belt and the Oort Cloud. • The Kuiper belt extends roughly 30 to 50 AU. • The Oort Cloud may extend as far as 50,000 AU.

  33. Comets and Kuiper Belt Objects • There are two main regions where the comets live: the Kuiper belt and the Oort Cloud. • There are roughly 1500 known KBOs and counting. Most are a few tens of km in diameter.

  34. Comets and Kuiper Belt Objects • KBOs are extremely faint and must be observed with the largest telescopes.

  35. Comets and Kuiper Belt Objects • A few KBOs have diameters approaching 1500 km. Most are much smaller.

  36. Comets and Kuiper Belt Objects • Sedna has an orbital period of about 10,500 years. It is one of the most distant known solar system objects.

  37. Comets • When a comet comes close to the Sun, things get interesting…

  38. Comets • Comets are bright, fuzzy objects that appear relatively suddenly. • Most usually have a rather long, diffuse “tail”.

  39. Comets • Historically, comets were considered to be “bad omens.” • This tapestry depicts the appearance of Halley’s comet during the coronation of Harold as King of Britain on January 6, 1066.

  40. Comets • Historically, comets were considered to be “bad omens.” • This tapestry depicts the appearance of Halley’s comet during the coronation of Harold as King of Britain on January 6, 1066. The Norman invasion came later that year. • See http://www.bayeuxtapestry.org.uk/Index.htm

  41. Comets as Omens • The English word “disaster” has two roots:

  42. Comets as Omens • The English word “disaster” has two roots: • “dis”, a Latin term for “bad”.

  43. Comets as Omens • The English word “disaster” has two roots: • “dis”, a Latin term for “bad”. • “astro”, the Latin term for “star”.

  44. The Nature of Comets • In 1705, Edmund Halley applied Newton’s new theories of gravity and motion to the orbits of bright comets. He suggested that the bright comets that appeared in 1531, 1607, and 1682 were the same object. Also, the comet of 1066 is now known to be the same object.

  45. The Nature of Comets • Comets are objects orbiting the Sun.

  46. The Nature of Comets • Comets are gravitationally bound to the Sun. • The orbits can be highly elliptical (recall the orbits of the planets are nearly circular). • The orbital planes of the comets can be highly inclined with respect to the Earth’s orbital plane (i.e. the ecliptic).

  47. The Nature of Comets • The 8 planets orbit in nearly the same plane in space

  48. The Nature of Comets • Comets are gravitationally bound to the Sun. • The orbits can be highly elliptical (recall the orbits of the planets are nearly circular). • The orbital planes of the comets can be highly inclined with respect to the Earth’s orbital plane (i.e. the ecliptic).

  49. The Nature of Comets • Comets are gravitationally bound to the Sun. • The orbits can be highly elliptical (recall the orbits of the planets are nearly circular). • The orbital planes of the comets can be highly inclined with respect to the Earth’s orbital plane (i.e. the ecliptic). • The orbital periods range from a few years to thousands of years.

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