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NGC 7311 and NGC 7312 A Pair of Spiral Galaxies

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Old November 17th 17, 08:49 PM
WA0CKY WA0CKY is offline
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Default NGC 7311 and NGC 7312 A Pair of Spiral Galaxies

NGC 7311 and 7312 are two spiral galaxies seen against the distant galaxy cluster, Abell 2454. The field is "above" the neck of Pegasus the horse that flies upside down in our northern skies. The cluster is about 2 billion light-years distant while the two galaxies are much closer and unrelated to each other. NGC 7311 a blue spiral is only 190 million light-years distant while NGC 7312 is about twice as distant at 360 million light-years by redshift and 440 million light-years by Tully-Fisher measurement. Both appear about the same size in my image but due to distance differences that is only an illusion. I measure NGC 7311 as being about 100,000 light-years across and NGC 7312 as being 163,000 to 200,000 light-years across depending on which distance you use.

NGC 7311 was discovered by William Herschel on August 30, 1785. It isn't in either Herschel 400 observing program. NGC 7312 was discovered 76 years later by Albert Marth on October 30, 1863. A near Halloween galaxy. It is appropriately rather orange in color compared to NGC 7311.

Only a handful of galaxies in the Abell 2454 galaxy cluster had redshift data. All had only coordinate based names which I omitted as anyone can plate solve my image and get their coordinates if need be. All but one in the very lower right corner appear to be members of the Abell cluster. Are all those without distance data also members of the cluster? Abell didn't so much worry about distance. He assumed that those within a couple magnitudes of the third brightest galaxy he saw as a cluster were members. NED lists it as being some 20 minutes of arc across. With the center being toward the top of my 22 minute high frame I assume I caught all at the south end of the cluster but am missing many north of my image. In fact, NED lists several members out of my frame to the north. It is listed as morphology class III meaning it has no central galaxy or galaxies which is obvious with nothing around its core position which is just left of the label in my annotated image. It is a class II cluster. By Abell's system that means it contains 50 to 79 members that meet the brightness limits mentioned above.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

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Old November 28th 17, 10:03 PM
slilge slilge is offline
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First recorded activity by SpaceBanter: Aug 2008
Posts: 151

Nice detail in these small galaxies.

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