Book contents
- Frontmatter
- Contents
- Acknowledgements
- 1 Introduction: The Luminous Pathway
- 2 The Discovery of the Milky Way Galaxy
- 3 The New Physics
- 4 Parting the Veil with Radio Astronomy
- 5 The Violent Universe
- 6 New Windows on the Galactic Center
- 7 The Milky Way as a Barred Spiral Galaxy
- 8 The Evolving View of Active Galactic Nuclei
- 9 The “Paradox of Youth”: Young Stars in the Galactic Center
- 10 Stellar Orbits in the Galactic Center, QED
- 11 Black Holes Here, Black Holes There…
- 12 Traces of Activity: Past, Present, and Future
- 13 After Words: Progress in Astronomy
- References
- Index
13 - After Words: Progress in Astronomy
Published online by Cambridge University Press: 05 December 2013
- Frontmatter
- Contents
- Acknowledgements
- 1 Introduction: The Luminous Pathway
- 2 The Discovery of the Milky Way Galaxy
- 3 The New Physics
- 4 Parting the Veil with Radio Astronomy
- 5 The Violent Universe
- 6 New Windows on the Galactic Center
- 7 The Milky Way as a Barred Spiral Galaxy
- 8 The Evolving View of Active Galactic Nuclei
- 9 The “Paradox of Youth”: Young Stars in the Galactic Center
- 10 Stellar Orbits in the Galactic Center, QED
- 11 Black Holes Here, Black Holes There…
- 12 Traces of Activity: Past, Present, and Future
- 13 After Words: Progress in Astronomy
- References
- Index
Summary
It is remarkable that a mere one hundred years ago most astronomers thought that the Universe was the Galaxy, a large flattened system of stars with the Sun near the center and various fuzzy objects scattered around it. This was the view supported by the systematic study of the positions and motions of stars began here in Groningen by Jacobus Kapteyn, a view that turned out to be wrong because no correction was made, or could made at that time, for the obscuration of star light by interstellar dust particles. The true scale of the Milky Way and the position of the Sun in the system became evident only after the pioneering work by Harlow Shapley on the spacial distribution of globular clusters in the halo of the Galaxy, work in turn based on the fundamental discovery of the period-luminosity relation for Cepheid variable stars by Henrietta Leavitt.
But Kapteyn's precise measurements of positions and motions of stars turned out to be extremely useful for his student, Jan Oort, who used the data to support the idea of Galactic rotation and accurately described the scale of the Milky Way and the Sun's true place, not in the center but on the outskirts of this vast system of stars. Oort, more than anyone, discovered the Center of the Galaxy – its direction and distance. Through radio astronomy and the 21-cm line of neutral hydrogen he and his students discovered the center of rotation, that there were expanding gas features moving away from that center, and that the center coincided with the source of continuum radio waves, the brightest radio source in the constellation of Sagittarius.
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- Chapter
- Information
- Revealing the Heart of the GalaxyThe Milky Way and its Black Hole, pp. 177 - 184Publisher: Cambridge University PressPrint publication year: 2013