APA (7th ed.) Citation

Zekl, H., Klare, G., & Appenzeller, I. (1981). Optical brightness variations of BL Lac objects. Astronomy and astrophysics, 103, .

Chicago Style (17th ed.) Citation

Zekl, Hans, Gerhard Klare, and Immo Appenzeller. "Optical Brightness Variations of BL Lac Objects." Astronomy and Astrophysics 103 (1981).

MLA (9th ed.) Citation

Zekl, Hans, et al. "Optical Brightness Variations of BL Lac Objects." Astronomy and Astrophysics, vol. 103, 1981.