16 January 2019
A variable ... nebula? Well, not really, the nebula is just a cloud of dust and gas. The cloud is the same, but the star that shines on it suddenly brightens every so often.
McNeil's Nebula is right next to M78, which is in the constellation or Orion. What's weird about it, is that it was only noticed in 2004 - and by an amateur astronomer using a 3-inch scope in his back yard. (Yes, there's hope for us yet!)
Further searching in the archives turned up images showing the nebula from 1951. What had happened was the variable star at the bottom end of the nebula brightened suddenly, and we could see the surrounding dust. The star is just visible in the first photo below, marked with a big yellow arrow.
It looks like someone shining a torch around inside a cave. You can see small areas of the cave walls when the torch is close, but normally everything is dark.
The final chapter in the story is that the star has now become so dim that the dust cloud isn't visible at all any more. We'll have to wait for the next outburst before we can see McNeil's Nebula. Just when that's going to be is anyone's guess.
ASV member Steven Mohr has been taking pictures of M78 for a while, and has got one with - and now one without - McNeil's Nebula. Great photos, Steven!