Part 5

Data captured over multiple nights

One thing that happens a lot in astrophotography is the collection of data over multiple nights; particularly with targets that are very faint. These targets require hours of data to achieve a suitable image.

So how do we process data that we capture over multiple nights or where multiple filters were used? The easiest way that I have found to do this is to simply use a Siril front-end called ‘Sirilic’ to all the hard work for me.

Part 4

Processing of astro images is more an art than a science. Two people can process the same data and end up with two completely different results.

One thing I’ll say is to beware of YouTube videos - those guys make it look stupidly easy to get fantastic results. I’ve found that it’s not easy!

Processing Workflows

When it comes to processing the stacked and pre-processed images, the workflow I use for a star cluster is different to what I use for a nebula. Generally, a star cluster doesn’t have colour gradients and swathes of shadows and highlights to deal with - it’s stars on a dark background. Nebulae are the opposite.

Part 3 - Image Processing

Now that the telescope is all packed away and we have our image data, how do we turn it into an image we can display?

If you’re using a DSLR to take wide-frame night view images, you can pretty much pick the best image, work on it with a suitable image editing program and call it finished.

However, I’m using a dedicated astro camera, have taken dozens or hundreds of images and now need to turn those gigabytes of data into an image. The image collection doesn’t stop with the data images - also called ’lights’. (We also use the term ‘subs’ (short for sub-frames) when referring to these images. I’ll try to be consistent with the terms I use.)

Part 2 - Software

Before we get too far into this section, I’ll point out that I use a Linux laptop with Kubuntu installed to drive my rig. If you’re a Windows user, there are many options out there for you - chief being NINA, Sequence Generator Pro and Astro Photography Tool. I have no knowledge of these programs, so you are going to be on your own if you use them.

Why I’m writing this

About a year ago I gave a presentation on astrophotography to my team at work. It was a “Get to know your co-workers better” session where we explained one of our hobbies over the course of lunch. After working on it for a couple of weeks, I ended up with a presentation of about 35 slides and talked for just under an hour.

When I have a new image (or two) ready, I share them with the team. I don’t think they quite understand just how much work goes on ‘behind the scenes’ to arrive at the final image, and that I merely point the camera at the sky and out comes an image.

Aside from my first trip to the ASV’s Dark Sky site when there was a large number of astro enthusiasts present; I’ve never attended a real ‘Star Party’ where people get together under the night skies and spent a night (or more) imaging and observing.

So I had expectations for a good turn-out to the inaugural ‘Gippsland Star Party’ held over the weekend of March 15th to 17th. The location (Stockman’s Camp, Buchan South) promised very dark skies, far away from the light-dome of the city.

Nights when I’ve been able to get the rig out and imaging have been few and far between recently. Sometimes I have other things on that prevent me from getting out under the stars, but mostly it’s been the weather.

Of course, there have been nights when I’ve checked the cloud forecast and stayed inside, only for there to be pristine skies above me. I’m now getting to the point of (mostly) ignoring the forecasts and using my pair of Mk I eyeballs and seeing for myself what the conditions are like.

I had originally set out to image NGC 3576, “The Statue of Liberty Nebula”, but mixed up the NGC numbers. Thankfully, these two emission nebulae are right beside each other. I ended up capturing my original target, but not without a few tense moments when I realised I had the wrong target.

Wikipedia says:

NGC 3576 is a bright emission nebula in the Sagittarius arm of the galaxy a few thousand light-years away from the Eta Carinae nebula. It is also approximately 100 light years across and 9000 light-years away from Earth. It was discovered by John Frederick William Herschel on 16 March 1834.

Wikipedia says:

NGC 2516 (also known as Caldwell 96) is an open star cluster in the southern sky in the constellation Carina discovered by Abbe Lacaille in 1751-1752. It is also called Southern Beehive or the Sprinter.

This bright cluster itself is easily visible with the naked eye as a hazy patch, but is resolvable into stars using binoculars. It contains two 5th magnitude red giant stars and three main visual double stars: HJ 4027, HJ 4031 and I 29. A small telescope would be required to split the double stars, which are all pairs of 8-9 magnitude and 1-10 arcseconds separation.

I was “wandering” around the sky map in Telescopius, looking for something interesting to image, when I stumbled across something unusual. A large DSO that wasn’t in any of the catalogues I looked at. I had the co-ordinates, but nothing matched it. How unusual. There were plenty of NGC entries all around it, but this one didn’t have an NGC identifier.

I asked the question on IIS - “What is this DSO?” and whilst I waited for people to answer, added the co-ordinates into my custom catalogue in KStars, got the rig outside and running.