My first Magazine Sky & Telescope - 03.2019

Herschel Catalog to plan my program for the last 100+ Herschel objects. My conversations with Wolfgang and the recoating of my 16-inch and the 21-inch Manka scope encouraged me to go for it. pu FOUR PARTS TO A WHOLE The Trifi d Nebula (M20, NGC 6514), a star-forming region in Sagittarius, was initially assigned three entries by Herschel. He added a fourth des- ignation — in a different class — later (entries highlighted at right). However, some years ago I read that several amateur astronomers had actu- ally accomplished the feat of tallying all 2,500+ Herschel objects, including Sky & Telescope Contributing Editor Rod Mollise (see S&T: Aug. 2012, p. 60). Sue French also let me know by email that Larry Mitchell logged 2,508 Herschel objects. While I was corresponding with Jim Mullaney about these achieve- ments, he suggested that I contact deep- sky expert Wolfgang Steinicke about tackling the remaining objects in the Herschel catalogs. Wolfgang shared details with me on his observations of the so-called non- existent objects (largely open clusters) conﬁ rming to me that most of them did, in fact, exist. This left only a hand- ful of objects that have not been found, some of which may or may not have been comets. Once I knew how many galaxies, clusters, and nebulae deﬁ - nitely remained in my quest, I was able 34 M A RCH 2 019 • SK Y & TELESCOPE Confusion in transcribing across various catalogs has led to some objects being listed with wrong NGC numbers. Depending on the source, there are 36 to 50 duplicate observations by Herschel himself of objects that are listed under two or more Herschel numbers. The Triﬁ d Nebula and NGC 2264 together account for six Herschel numbers: Four numbers are assigned to sections of the Triﬁ d Nebula and two to NGC 2264, which consists of the Cone Nebula and the Christmas Tree Cluster. One example of an object listed under the wrong designation is NGC 5570. I tried to observe it one night in the spring of 2016 but couldn’t see anything at the location marked in Uranometria 2000.0. I did see other galaxies near that spot, but nothing where NGC 5570 was sup- posed to be as shown on the chart. As it turns out, NGC 5519, and not NGC 5570, is the true Herschel Class III object 12. One of the nonexistent objects that I was able to eliminate on my own is NGC 6847 in Vulpecula. I used the STScI page to scan the area near it and found that the planetary nebula NGC 6842 ﬁ ts the descrip- tion of Herschel Class II 202. The only objects that I consider truly non- existent are either NGC 420 or NGC 421 (depending on which of these two objects is taken to be the false detection), NGC 3401, and possibly NGC 5621 (but it may have been observed by John Herschel). Some might consider NGC 1908 to be non- existent, but I believe that the ﬁ eld of NGC 1908 does show a pattern of stars that could be mistaken for a cluster — and I was able to ﬁ nd it. I wanted to make sure that I had covered all possibilities and so I decided to observe other deep-sky objects in the ﬁ eld of view of Her- schel objects, in case one of them might be the object that Herschel actually observed. Another question- able object is NGC 4317, which is listed as a faint star. On the STScI image of the ﬁ eld of NGC 4317, I NSF; LONDON True Source or Not?

My first Magazine Sky & Telescope - 03.2019 | Page 36