This paper, originally published by F. Zwicky in 1933, provides an overview of the main characteristics of extragalactic nebulae and the methods used to explore them. The author discusses the redshift of these nebulae in detail, examines various theories that explain this phenomenon, and explores the potential importance of the redshift for studying penetrating radiation. The introduction highlights that extragalactic nebulae, which appear as fuzzy, self-luminous spots, are actually stellar systems similar to the Milky Way but located beyond it. These nebulae are homogeneous in both space and appearance, often appearing as individuals or clusters. The paper aims to describe the key features and methods that have enabled the exploration and understanding of these distant objects.This paper, originally published by F. Zwicky in 1933, provides an overview of the main characteristics of extragalactic nebulae and the methods used to explore them. The author discusses the redshift of these nebulae in detail, examines various theories that explain this phenomenon, and explores the potential importance of the redshift for studying penetrating radiation. The introduction highlights that extragalactic nebulae, which appear as fuzzy, self-luminous spots, are actually stellar systems similar to the Milky Way but located beyond it. These nebulae are homogeneous in both space and appearance, often appearing as individuals or clusters. The paper aims to describe the key features and methods that have enabled the exploration and understanding of these distant objects.