APA (7th ed.) Citation

Hubble, E. Photographic investigations of faint nebulae.

Chicago Style (17th ed.) Citation

Hubble, Edwin. Photographic Investigations of Faint Nebulae.

MLA (9th ed.) Citation

Hubble, Edwin. Photographic Investigations of Faint Nebulae.

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