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How to legally use or refer to images and content from this site
      Other than photographs and diagrams which are credited and/or linked to other sources, the contents of this site are the work of Courtney Seligman, and are copyrighted by him. No commercial reproduction of the contents of this site is allowed without the written permission of the author. Permission is hereby granted for commercial and non-commercial use of thumbnails similar to those found on Internet search engines (200 pixels or less in size), to direct others to images or pages on this site. Permission is also granted for use of any excerpt for non-commercial purposes, provided authorship is acknowledged (see the examples below). If an image has a link to another site, I cannot provide legal permission to use the image; in such cases, you should look for contact and copyright information at the link's target page (see the example for CFHT images below).

Crediting And Linking To This Site
      Excerpts, whether of text or images from this site, should be credited and linked to their source page(s) in a way which makes it clear to the user that they are from this site (e.g., "Excerpt/image courtesy of Courtney Seligman", "See cseligman.com/text/history/brahebio.htm for a biography of Tycho Brahe", or "There is a good discussion of Tycho Brahe on cseligman.com").

Example of External Copyright: CFHT Images
      Most of the photographs on this site are taken from NASA sites. In general, images produced by NASA are in the public domain and may be freely used by non-commercial sites such as this one, providing credit is given where credit is due (see NASA's site for restrictions on the use of such images). However, the presence of an image on a NASA site does not necessarily mean that it was produced by NASA, or is in the public domain. This is especially true of NASA's Astronomy Picture of the Day site (and various NASA collections of images from that site), which actually posts more copyrighted images than public-domain images.
      As an example, some of the images from the APoD site which are posted on my site were created and are copyrighted by the Canada-France-Hawaii Telescope Corporation. Unauthorized copies of those images are scattered all over the Internet, but that does not invalidate CFHT's copyright, and use of CFHT images without their permission is unlawful. I gratefully acknowledge CFHT's permission to use their images on this site, and recommend that anyone who wishes to use their images refer to the CFHT copyright page.