APA (7th ed.) Citation

Wielen, R. (1979). The density-wave theory of spiral galaxies: Comparison between theory and observations. Stars and star systems.

Chicago Style (17th ed.) Citation

Wielen, Roland. "The Density-wave Theory of Spiral Galaxies: Comparison Between Theory and Observations." Stars and Star Systems 1979.

MLA (9th ed.) Citation

Wielen, Roland. "The Density-wave Theory of Spiral Galaxies: Comparison Between Theory and Observations." Stars and Star Systems, 1979.

Warning: These citations may not always be 100% accurate.