In 2011, astronomer Stephen James O'Meara published a list of 109 objects called the Secret Deep, documented in his excellent book of the same name. This list contains 109 interesting deep sky objects which are not included in the three popularly recognized lists - the famous list of 110 Messier objects (established in the 1700s), the list of 109 Caldwell objects (published in 1995), and the list of 109 Hidden Treasures (published in 2007). To think of these Secret Deep objects as the 329th to 437th "best" sky objects in the sky would be inappropriate in my opinion. These lists are very subjective and were developed primarily for visual observing, not astrophotography. I consider some of these objects, such as Thor's Helmet, to be among the best. The list consists of 23 open star clusters, 38 galaxies, 11 globular star clusters, 15 bright nebulae, 18 planetary nebulae, 1 asterism, 1 supernova remnant, 1 quasar and 1 black hole. I did not image the quasar (#59) or the black hole (#93), since there is not much to see of them. The first image below is a poster containing images of all of the objects, as well as a table which summarizes the key information for each object. After that, the Secret Deep objects are shown in order starting with SD1.
