page_title: Atlas of Peculiar Galaxies
section_title: Spiral galaxies with one heavy arm
hierarchical_section_title: Atlas of Peculiar Galaxies / List of galaxies in the catalog / Spiral galaxies / Spiral galaxies with one heavy arm
caption_attribution_description: English: constructed by Renseb, images of the individual colours were taken with the en:Isaac Newton Telescope on en:La Palma and the en:WIYN 0.9m telescope on en:Kitt Peak.
context_page_description: The Atlas of Peculiar Galaxies is a catalog of peculiar galaxies produced by Halton Arp in 1966. A total of 338 galaxies are presented in the atlas, which was originally published in 1966 by the California Institute of Technology. The primary goal of the catalog was to present photographs of examples of the different kinds of peculiar structures found among galaxies.
context_section_description: The spiral arms in these galaxies have an asymmetric appearance. One spiral arm may appear to be considerably brighter than the other. In the photographic plates produced by Arp, the bright arm would look dark or "heavy". While most of these galaxies (such as M101 and NGC 6946) are simply asymmetric spiral galaxies, NGC 6365 is an interacting pair of galaxies where one of the two galaxies is viewed edge-on and just happens to lie where the spiral arm for the other face-on galaxy would be visible.
caption: NGC 6946 (Arp 29) spiral galaxy
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