{"id":376,"date":"2007-10-28T15:41:32","date_gmt":"2007-10-28T15:41:32","guid":{"rendered":"http:\/\/perezmedia.net\/beltofvenus\/2007\/10\/28\/17p_holmes_illu\/"},"modified":"2007-10-28T15:41:32","modified_gmt":"2007-10-28T15:41:32","slug":"17p_holmes_illu","status":"publish","type":"post","link":"https:\/\/perezmedia.net\/beltofvenus\/2007\/10\/28\/17p_holmes_illu\/","title":{"rendered":"17P \/ Holmes &#8211; Illusion of Annularity"},"content":{"rendered":"<p>Visual observations of the comet have been giving me the strong impression that there is a slightly brighter, ring-like structure along the outer edge of the coma. Photographs were showing the same effect, but along with other observers, I was wondering if this was a real feature or perhaps an illusion. I used Photoshop to measure the Luminosity values of one of the images posted at CloudyNights.com on Friday to see if the effect was real. I measured the image along an axis through the center of the bright fan-like structure, as well as another axis perpendicular to this.<\/p>\n<p>The results showed no drop in brightness inside the edge of the coma. Instead, there was a plateau in brightness. My guess is that our eyes and brain see the steep rise in brightness both at the edge of the coma and around the pseudo-nucleus and this plateau comes out looking like a dark region.<\/p>\n<p>Below is a chart showing the values I measured. I haven&#8217;t received permission from the imager to post his image for comparison. But there are certainly enough images posted to <a href=\"http:\/\/www.cloudynights.com\/ubbthreads\/showflat.php\/Cat\/0\/Board\/planets\/Number\/1933504\/page\/0\/view\/collapsed\/sb\/5\/o\/all\/fpart\/1\" target=\"_blank\" rel=\"noopener\">this thread<\/a> at Cloudy Nights to see that the illusion is rather strong. Tom Polakis made similar measurements via the R G B channels of a photo he shot, and his clear presentation can be seen <a href=\"http:\/\/members.cox.net\/tpolakis\/astro\/holmes_photometry_20071028.jpg\" target=\"_blank\" rel=\"noopener\">here.<\/a> His results got me off my rear end to go ahead and post this without the reference image. As Tom said, &#8220;Don&#8217;t believe everything you see.&#8221;<\/p>\n<p style=\"text-align: center\"><a href=\"http:\/\/www.perezmedia.net\/beltofvenus\/archives\/images\/2007\/img2007102603_17PLumilg.gif\" target=\"_blank\" rel=\"noopener\"><img decoding=\"async\" src=\"http:\/\/www.perezmedia.net\/beltofvenus\/archives\/images\/2007\/img2007102603_17PLumi.gif\" border=\"1\" color=\"ffffff\"><\/a><br \/><i>Click image for larger version.<\/i><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Visual observations of the comet have been giving me the strong impression that there is a slightly brighter, ring-like structure along the outer edge of the coma. Photographs were showing the same effect, but along with other observers, I was wondering if&hellip;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-376","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","jetpack-related-posts":[{"id":377,"url":"https:\/\/perezmedia.net\/beltofvenus\/2007\/10\/28\/image_processin\/","url_meta":{"origin":376,"position":0},"title":"Image Processing and Artificial Details","author":"jperez1690","date":"October 28, 2007","format":false,"excerpt":"Image Processing and Artificial Details","rel":"","context":"In &quot;Tools and Techniques&quot;","block_context":{"text":"Tools and Techniques","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/tools-and-techniques\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":378,"url":"https:\/\/perezmedia.net\/beltofvenus\/2007\/10\/29\/17p_holmes_oct_3\/","url_meta":{"origin":376,"position":1},"title":"17P \/ Holmes &#8211; OCT 28, 2007","author":"jperez1690","date":"October 29, 2007","format":false,"excerpt":"17P\/Holmes 20071028","rel":"","context":"In &quot;Comet&quot;","block_context":{"text":"Comet","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/comet\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":486,"url":"https:\/\/perezmedia.net\/beltofvenus\/2009\/09\/20\/m88_ngc_4501\/","url_meta":{"origin":376,"position":2},"title":"Messier 88 (NGC 4501)","author":"jperez1690","date":"September 20, 2009","format":false,"excerpt":"M088","rel":"","context":"In &quot;Deep Sky&quot;","block_context":{"text":"Deep Sky","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/deep-sky\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":327,"url":"https:\/\/perezmedia.net\/beltofvenus\/2007\/04\/28\/comet_2006_m4_s\/","url_meta":{"origin":376,"position":3},"title":"C\/2006 M4 (SWAN) &#8211; OCT 28, 2006, 01:50 UT","author":"jperez1690","date":"April 28, 2007","format":false,"excerpt":"C\/2006 M4 SWAN 20061028","rel":"","context":"In &quot;Comet&quot;","block_context":{"text":"Comet","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/comet\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":476,"url":"https:\/\/perezmedia.net\/beltofvenus\/2009\/05\/29\/messier_98_ngc\/","url_meta":{"origin":376,"position":4},"title":"Messier 98 (NGC 4192)","author":"jperez1690","date":"May 29, 2009","format":false,"excerpt":"M098","rel":"","context":"In &quot;Deep Sky&quot;","block_context":{"text":"Deep Sky","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/deep-sky\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":114,"url":"https:\/\/perezmedia.net\/beltofvenus\/2005\/03\/10\/m108\/","url_meta":{"origin":376,"position":5},"title":"Messier 108","author":"jperez1690","date":"March 10, 2005","format":false,"excerpt":"M108","rel":"","context":"In &quot;Deep Sky&quot;","block_context":{"text":"Deep Sky","link":"https:\/\/perezmedia.net\/beltofvenus\/category\/deep-sky\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/posts\/376","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/comments?post=376"}],"version-history":[{"count":0,"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/posts\/376\/revisions"}],"wp:attachment":[{"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/media?parent=376"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/categories?post=376"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/perezmedia.net\/beltofvenus\/wp-json\/wp\/v2\/tags?post=376"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}