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Announcements

Announcements. Don’t forget the second project over something of historical importance to astronomy. Presentations will be Wednesday April 30, one week from today.

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Announcements

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  1. Announcements • Don’t forget the second project over something of historical importance to astronomy. Presentations will be Wednesday April 30, one week from today. • The last exam will be Monday May 5 @ 4:30pm. Covers Chapter 8 & 9. If there are any leftover presentations to be made we will do them first. • The last observing night is tonight. Last nights crowd wasn’t as big as expected so they may end up coming out tonight. Set-up starts at 7:30pm.

  2. The Structure of the Milky Way

  3. Hershel had used star counts and brightness to get the shape John Herschel went down to South Africa and did the same thing, coming up with the same result.

  4. Stephen Alexander suggested it looked like Lord Rosse’s spirals

  5. Others proposed a variety of structures Richard Proctor Wilhelm Struve Easton’s Milky Way

  6. J. C. Kepteyn suggest a plan of attack Basically Herschel’s method but with accuracy. Measure all the stars possible and plot them out. Assumes the space between stars is empty…bad assumption

  7. Harlow Shapley has a better idea…measure the globular clusters He uses the 60” at Mount Wilson, the largest telescope in the world at the time

  8. Shapley uses Miss Leavitt’s stars (Cepheid's) to measure the distance He makes a number of other assumptions about the size of the clusters and the brightest stars in them

  9. In 1918 Shapley announces his results The Galaxy is 300,000 lightyears across. He doesn’t claim to understand the structure, just how big it is. He is off due to obscuring dust.

  10. By 1900 long exposure photography is showing lots of nebulae

  11. E. E. Barnard publishes a collection of “dark nebulae”

  12. Really long exposures show stuff everywhere E. E. Barnard discovers lots of glowing gas all around the Orion constellation

  13. Robert Trumpler publishes the definitive study on obscuration in 1930 There is a lot of gas and dust out there. In the disk of the galaxy it cuts the magnitude by one every 5000 lightyears

  14. In 1938 the answer to the structure question is summarized by J. S. Plaskett By this time Shapley’s numbers had been corrected for obscuring dust. The galaxy is abut 100,000 lightyears across and the center is in the direction of Sagittarius about 30,000 lightyears away. It probably has a spiral structure

  15. The Spiral Nebulae

  16. Around 1900 most believe the spiral nebulae are in the galaxy William Huggins suggests they are solar systems in the formation process

  17. VestoSlipher starts taking spiral nebulae spectra At first he finds those on one side of the Milky Way are receding while those on the other side are approaching us at hundreds of km/s

  18. Heber Curtis determines that our view of the spiral nebulae is blocked in the plane of the galaxy

  19. AdriaanMaanen claims to have seen movement in the spiral nebulae

  20. The Great DebateWashington D.C. 1920 Harlow Shapley: The Milky Way is enormous beyond imagination and is the entire universe Heber Curtis: the spiral nebulae are “island universes” like the Milky Way.

  21. The domination of the Californians The 100” at Mount Wilson 60” at Mount Wilson

  22. Edwin Hubble uses the 100” to measure Cepheid’s in the Andromeda nebulae

  23. Hubble’s discovery is announced in 1925 The Andromeda “nebula” is almost a million lightyears away and is, therefore, an island universe like the Milky Way. His numbers are off because he is using the wrong calibration for the Cepheid’s he is observing

  24. Working with Hubble, Walter Baade finally figures out the errors in distance There are two types of stars. Type I stars are like the Sun with high “metal” content. Type II are low metal content and found in globular clusters and the galactic bulge

  25. The Expansion of the Universe

  26. In the late 1800’s something was amiss in physics Aspects of Maxwell’s electromagnetic theory hinted at non-Euclidian space and time. The precession of the perihelion of Mercury was not what it should be according to Newtonian gravity

  27. Michelson & Morley Michelson and Morley attempted to measure the Earth’s motion through the luminiferous aether. The aether was the medium through which light traveled. They kept coming up with a null result…no detectable movement.

  28. Albert Einstein came up with the Special Theory of Relativity to explain some of the problems In his theory Einstein linked the spatial dimensions to the temporal dimension and created space-time

  29. It took another decade for Einstein to come up with the General Theory of Relativity According to General Relativity (published in 1916), massive objects warp spacetime and other masses must move through that curved spacetime.

  30. Early solutions to GR suggested an expanding universe Wilhelm De Sitter, Alexander Friedmann and Georges Lemaitre did calculations using general relativity that indicated the universe should be expanding

  31. By 1925 Slipher had spectra for 45 galaxies They had star-like character and Slipher could identify absorption lines and thus get redshifts. They were large, several hundred km/s to over 1000 km/s

  32. Hubble gets Humason to measure more redshifts Hubble wants redshifts on even more distant galaxies. He stretches his own work on measuring distances to get the distance to the galaxies Milton Humason is measuring.

  33. In 1929 Hubble publishes his distance-redshift results

  34. From the plots, Hubble determines an “age” for the universe The problem is it is too small. Early estimates are an age of only 1.95 Gyr. By this time geologist are saying the Earth is 2 to 4 Gyr old. For most of the 20th century the Hubble constant will slowly creep down from 500 km/s/Mpc to around 75 km/s/Mpc. Current best estimate is 73.8 km/s/Mpc

  35. Chapter 9: Astronomy’s Widening Horizons

  36. The Californians continued their domination with the Keck's Completed in the early 1990’s, they are still among the largest telescopes in the world (for now). They only recently closed down the optical interferometry part of the Keck system…it was just too difficult

  37. Consortiums and international collaborations have broken the California domination Other telescopes like Gemini, CFH and Subaru have taken up residence on Mauna Kea Kitt Peak is operated by AURA: the Association of Universities for Research in Astronomy

  38. The southern hemisphere has gotten into the game Cerro Tololo and Cerro Paranal are home to 8.2 meter class telescopes

  39. The Australians built the Anglo-Australian Observatory in the 1970’s

  40. Photographic plates have been replaced with CCD’s The LSST CCD will be a 3.2 Gpixel camera. The computers that process the data will be capable of handling teraflops of data

  41. The difference between photographic plates and digital On the left is one of Hubble’s images of M31 taken with the 100” telescope. On the right is an image taken by an amateur with a 5.1” apo-refractor and a Canon 5D digital camera

  42. Even “amateurs” can do extraordinary work Mark Manner’s Spot Observatory near Bucksnort, TN (Hickman County ~45 miles west of Nashville)

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