Mystery of the Missing Nebula

The weekend stargazing was wet work: unusual for the Anza Borrego Desert. However, a couple of wet storms had enough moisture to make it across the mountains and there were small pools of water in some places. Although the night promised to be dark and not too cold, but there were soon reports of relative humidity in the 90s and there were signs of dew on some surfaces.

We are so spoiled. Many deal with this – and much worse! – all the time. Indeed, we were lucky to have reasonable stargazing at all, as much of the nation seemed to be snow-bound.

We had a nice collection of scopes: a 15", 18", and 20".  Paul Alsing, as usual, pointed out a couple of special delights in Canis Major. First of all, there is the open cluster NGC 2362 that is dominated by a single star, the 4.35 magnitude Tau CMa, surrounded by circles of stars. A distinctive cluster. To the north is the double star h3945, which is often referred to as the "Winter Alberio." Up in the northernmost end of the constellation is NGC 2359, often referred to as "Thor's Helmet." This is a nebula showpiece that benefits greatly from both aperture and an OIII filter. I had viewed this long ago, as it was checked off on my first edition of SkyAtlas 2000.0, but it didn't make it into my collection of regulars. I'll fix that.

However, after the fact, this list me to an interesting mystery. The Pocket Sky Atlas shows a nebulous patch just to the east, IC 468. To my surprise, this is not on Uranometria 2000. The Night Sky Observer's Guide indicates it on Finder Chart 8-6, but is otherwise silent. In fact, I noted that it was plotted on my first edition SkyAtlas, but has disappeared on the second edition.

This leads me to conclude that IC 468 is an artifact of earlier databases that have since been more closely checked and it has been eliminated from them. I'm disappointed that the relatively new Pocket Sky Atlas let that error creep in, particularly since its goal is to display the more important objects.

When we woke up in the morning the temperature was in the high 20's and the dew had frozen on anything left out. I would have complained, but I knew the temperatures would be rising into the 80's: balmy weather for any time of the year, let alone February.