A couple of nights ago Milky-Way.kiwi was outside observing the night sky and tried to find the galaxy Centaurus A (in the above image which was taken by the author). This is no easy task in the central Wellington sky as it’s rather light polluted and can take a bit of effort. The galaxy was also quite low on the horizon so the conditions were far from ideal, but not being one to shy away from a challenge I thought we could persevere and try and see this, normally reasonably bright galaxy. It’s quite easy to find from Omega Centauri, just down a bit and to the left. This article is about our journey to try and see Centaurus A and some of the techniques you can use to see faint objects.
(Can we just make a small comment here to say that no matter how hard she tried, the other Milky-Way.kiwi -who is a relatively seasoned observer and not to mention telescope operator – just could not see the %#^ galaxy nor she’s ever seen it before through a telescope. So she could not even resort to expertise bias to resolve the situation.)
Adapting your eyes to the night sky
First you need dark adapted eyes, that means no looking at lights for about 40 mins, no checking your cell phone! It takes a bit of time for your eyes to start relying on the rods rather than the cones so you need to give it time for your eyes to adapt. Not much point in looking for really faint things until you have allowed your eyes to fully adapt to the dark. Try very hard not to hold it against your neighbour if they turn on their outdoor spotlight that ruins your dark adaption after 35 minutes, they have no idea what they are doing – breathe calmly and explain in a nice voice why you do not want them shinning that super bright light into your backyard. If you really have to use a light, make sure it has a red filter so you only see red light. This won’t hurt your night vision as. Much – blue light is very bad.
Humans are very good at seeing things in their peripheral vision, because we were used to being hunted and doing a bit of hunting we evolved to be able to detect movement really well that we weren’t directly looking at. This is quite good at night because most of the cones, which are used for colour, in your eyes are concentrated in the centre of the back of your eye whereas the further from the centre, the more rods there are, which are better for night vision. This is why you often can’t see colour in deep sky objects – they are simply too ain’t to register any signal in the cones in the back of your eyes. So at night you are more likely to see things if you don’t look directly at them – called averted vision. You only have to look away a few degrees in your field of view to get the view falling on more rods in the back of your eye and you’ll really notice the difference. Centaurus A was really tricky to find so was certainly made easier by using averted vision. Of course you need to know exactly where to point the telescope in these situations as often there’s no way you’ll even get a hint of the object in the finderscope.
Like I mentioned above, humans are very good at spotting movement – especially in the periphery of our vision so if you want to spot something faint it’s best to introduce movement into the field of view. The best way to do this is to wobble the telescope a little, it’s not enough movement to just have the view move with the Earth in the eyepiece – it needs to be fairly quick movement or your brain won’t register it. This was the most effective way to spot Centaurus A a few nights ago. The thing that jut popped out when I wobbled the telescope was the dust lane. Of course the moment you look directly at the detail it disappears again. So you have to get used to looking at things in the periphery of your vision. Wobbling the telescope will help you lock onto the detail in your periphery.
Detecting the subtle changes in background contrast
Often when looking at faint objects like galaxies, they are usually quite big so can almost entirely fill your eyepiece. This means that it can be quite tricky to detect the contrast changes in the background view as there’s no clean edge from the galaxy to space. Lucky for Centaurus A the galaxy has a big huge dust lane right through the middle of it which gives plenty of contrast. I remember looking at M33 a few years ago, which entirely filled the whole eyepiece and it took a while to realise that I had to move it the telescope around quite a bit to catch a glimpse of the dust lanes and subtle variations in the background which were the knots of star formation regions of this huge galaxy.
So there a few little techniques on trying to see faint staff in the night sky. Like everything, practice makes perfect so get out there and try to find really faint objects. It takes a while to get used to looking for these things but after a bit of experience you’ll be a professional and able to find the most elusive of night sky targets.