Chapter 1. The Galactic Center
1.1. Discovery of Sagittarius A*
1.2. Radio Morphology of the Central Region
1.3. X-ray Morphology of the Central Region
Chapter 2. The Radio Source Sagittarius A*
2.1. Position of Sagittarius A*
2.3. Structure as a Function of Frequency
Chapter 3. Sagittarius A*'s Spectrum
3.2. Linear and Circular Polarization
3.3. Infrared Observations
3.5. Observed High-Energy Characteristics
4.1. Short-Term Variability in the IR and X-rays
4.2. Long-Term Variability in the Radio
Chapter 5. The Central Star Cluster
5.1. The Stellar Cusp Surrounding the Black Hole
5.2. Stellar Constituents and Dynamics
5.3. Stellar Orbits and the Enclosed Mass
Chapter 6. The Four-Dimensional Spacetime
6.1. The Flat Spacetime Metric
6.2. Relativistic Transformation of Physical Laws
6.5. Particle Orbits and Trajectories
Chapter 7. Mass Accretion and Expulsion
7.1. Sagittarius A*'s Gaseous Environment
7.2. Bondi-Hoyle Capture from Distributed Sources
7.3. Accretion Close to Sagittarius A*
7.4. Magnetic Field Dissipation
7.5. A Compact Magnetized Disk
8.3. General Relativistic Flux Modulations
Chapter 9. Strong Field Physics
9.1. Spin-Induced Disk Precession
9.3. Imaging the Shadow of the Black Hole
