Focus on…focusing

I’ve been ill for a while and unable to observe, but I took delivery of a Moonlite Focuser with a focus motor and controller. Since I drive a Mac, the provided ASCOM interface for the controller doesn’t work for my setup, and I spent a little time putting a program together to run the controller. Eventually I’ll get around to integrating it with other Mac telescope programs or roll my own automatic focusing software, but at least for the moment I can control the focuser from my laptop, which means I will be able to run it remotely. The current software is written in Applescript, but I will eventually rewrite in one of the C dialects which compile under Mac OS X Tools. I need to add a couple of features even now – a panic stop function, for example, to handle the (hopefully rare) condition where the focus motor is started but the associated stop command isn’t received correctly. While I can always pull the plug, I’d prefer to be able to tell the controller to stop and return to a wait state.

Blue snowball

The Blue Snowball is a little puffball of gas surrounding a central star in the constellation of Andromeda. In the New General Catalog it’s number 7662, so a short designation is NGC7662. It’s also C22 in Patrick Moore’s Caldwell catalog. You would never mistake this for a comet so it didn’t appear in Messier’s catalog (if he even saw it) and it looks distinctly star-like in a small telescope, except for the intense blue colour, which is quite startling to see when you come across it in a sweep of the sky.

blue snowball image

This is an image captured on 22 July and consists of 10 3-minute subframes combined in Nebulosity but without preprocessing for darks and flats. Skyfog was quite strong and removing it has muted the colours a little. This crop of the original image has been reduced to about 25% of full size, just to show the Snowball in context. Below, a closer look (a crop at 100%) reveals a hint of the structure which surrounds the 13th magnitude central star. That central star is comparable in brightness to the surrounding stars in the image, and the nebula rather overwhelms it in this picture. Alas, a larger scope than my 110 mm f/6.5 is needed to show any real detail – in this image the apparent size is about 35-40 seconds of arc, only about 18 – 20 pixels, depending on where you locate the edge of the Snowball.

blue snowball image

I can’t just blame the low resolution of the scope though, there is a bit of a focus issue here as well. I’m not at all happy with the size of the stars in the image as they are about 5 pixels wide instead of the 2 or 3 I am aiming for – but I will revisit the Snowball once I have achieved computer control (i.e., Mac control) of my Moonlite Focuser (but that’s a story for another day).