Escape From Plato's Cave - The Milky Way and - Think Astronomy

Escape from Plato’s Cave

The Milky Way and the Galactic Coordinate System

Bill Tschumy© 2005 Think Astronomy

• Where is M13?

• How This Got Started

• Plato’s Cave Allegory

• Basic Facts About the Milky Way

• The Galactic Coordinate System

• A Galacto-centric Star Map

• Selected Objects and Where They Are

• Conclusions

Where is M13?

Where is M13?

Where is M13?

• Where is M13?







• Conclusions

How This Got Started

From the chapter: “The Structure of our Galaxy”

“Because we lie on the inner edge of our spiral arm, when we look at the winter Milky Way (away from the interior of the Galaxy) we are looking back into our own spiral arm, the Orion Arm. This is confirmed by all the relatively nearby open clusters, associations, and emission nebulae in the constellations form Perseus to Canis Major....

• Where is M13?







• Conclusions

• Where is M13?







• Conclusions

Basic Facts About the Milky Way

Artists rendering based upon a survey, conducted using NASA’s Spitzer Space Telescope. It sampled light from an estimated 30 million stars in the plane of the galaxy in an effort to build a detailed portrait of the inner regions of the Milky Way.


Artists rendering based upon a survey, conducted using NASA’s Spitzer Space Telescope. It sampled light from an estimated 30 million stars in the plane of the galaxy in an effort to build a detailed portrait of the inner regions of the Milky Way.





1,500 light-years

10,000 light yearsSun



• Approximately 100 billion stars.

• Mass uncertain but certainly greater than 200 billion solar masses: half of it in stars / half in dust.

• Total luminosity on the order of 10 billion times the Sun.


• Where is M13?







• Conclusions

Galactic Coordinate System• Established in 1958 by the

International Astronomical Union

• Spherical coordinate system with the galactic plane as the equator.

• Galactic latitude is the angle above or below this plane.

• Galactic longitude is measured along a line running through the Milky Way using 0º for the Galactic Centre in Sagittarius

Galactic Coordinate System

• Where is M13?







• Conclusions

A Galacto-centric Star Map


Stars from Yale Bright Star Catalog


Lines from PP3 database


Open clusters -- Saguaro Astronomy Club Database


Planetary Nebulae -- Saguaro Astronomy Club Database


Globular clusters -- Saguaro Astronomy Club Database


Galaxies -- Saguaro Astronomy Club Database


• Where is M13?







• Conclusions

• Where is M13?







• Conclusions

Conclusions

• The benefits of thinking in 3-D.

• Why has this been neglected for so long?

• Going forward...

Escape from Plato’s Cave

The Milky Way and the Galactic Coordinate System

Bill Tschumywww.thinkastronomy.com

The End

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Escape From Plato's Cave - The Milky Way and - Think Astronomy