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The Milky Way and the Three Brethren

I've set myself a bit of a challenge to photograph the galactic centre of our milky way. This is proving a bit difficult. It isn't possible see the core of our galaxy during the winter months - October to February - because it's on the other side of sun. The best time to see the centre is in northern hemisphere's summer but you need dark skies - so that rules out May to August for me living in Scotland. The best view on the planet is in the southern hemisphere during their winter. I'm told that the view from the Atacama desert in Chile with its dry air and high altitude is simply stunning. For me though, it leaves March/April and September/October. In March the core is visible before dawn and in the autumn it's after sunset . . . at a much more sociable time of day. In September from where I live near Edinburgh, the centre only just appears above the horizon for a few minutes between the start of astronomical dark (when all trace of sunlight has vanished) and the setting of the centre below the horizon and conversely in springtime you can see it rising just before dawn gets in the way at some ridiculous hour in the morning.

But there are other limitations. Strong moonlight will wash out the contrast in the sky, so you're restricted to a few days either side of the new moon or at least when the moon hasn't risen yet.

The lunar calendar for September 2020. The 17th would be a good day to photograph the milky way.

I might be getting a little obsessive about photographing the dead centre. After all the galaxy is pretty big so what's so special about the centre? But it's more than just a point in space. As well as being at the centre of 200 - 400 billion rotating stars it is also the home for a super massive black hole called Sagittarius A. It has a mass 4 million times that of our sun and is completely invisible to the human eye (it's a black hole). Observations using x-ray telescopes have determined that every galaxy has a super massive black hole at its centre. Also that the mass of the galaxy is always about a thousand times that of the black hole. So the question now is what drives that correlation? Is it the black hole that determines the mass of the galaxy, or the other way around?

This is a good point to ponder how lucky we are to be living on our small green dot orbiting a star that happens to be going around the galaxy in a relatively stable circular orbit. Our sun makes a single trip around the galaxy every 250 million years and maintains roughly the same orbital distance from the galactic centre all of that time. Not all stars are so lucky; some have very eccentric orbits that take them much closer to the galaxy core and so subject to higher levels of radiation and gravitational disturbances; conditions not favourable to life . . . or at least life as we know it.

But I digress. In summary, the further north you go, the less you see of the galaxy core region and the time window that it is visible above the horizon gets smaller until it just isn't possible to see it. But the galaxy is really big so you still get great photos. However, to really get the full view I'm going to have to travel much further south . . . somewhere like the Atacama desert in Chile would do nicely . . . one day . . . maybe.

But staying south in Scotland has the disadvantage of greater light pollution. I'm sure anyone looking down on the UK from the International Space Station would be able to pick out the central belt at night without any difficulty. This image is from the light pollution map available online at https://www.lightpollutionmap.info/.

Astronomers measure light pollution in a number of ways but one scale I frequently come across is the Bortle scale, named after John Bortle, which goes from 1 (proper scary dark) to 9 (Glasgow city centre night time and probably equally scary). As an astro-photographer ideally you want a Bortle scale of 1 (and no fear of the dark) and to get that I'd need to travel to the far north west of the Scottish mainland or onto the Western Isles or offshore (where I'd get seasick). Apparently if you can view the milky way in an area of Bortle 1, then the light of the galaxy casts a shadow . . . something I've yet to experience.

And then there's the weather - clear skies obviously help but in March it gets cold overnight and the best place to see big skies usually makes for a windy one too. A September late evening is usually at a more reasonable temperature and doesn't demand being awake into the small hours; I like September.

Taking all of the above into account I had pencilled in the week of 14th to 20th September 2020 as having a new moon and so kept an eye on the weather forecast. Perusing OS maps I wanted somewhere far enough away from towns and villages to have dark skies when pointing the camera to the south west, which is the direction where the milky way sets in September. I also wanted some interesting foreground and good views of the horizon which meant getting up high. The obvious choice is to head to the far north west where dark skies are aplenty but as I've explained, I wanted to maximise the amount of galaxy core in view. So I went south into the borders region. Looking at the light pollution maps you can find regions of Bortle 3 in this area - so not the best - but should be dark enough to capture something. So after much poring over of maps I selected the summit of the Three Brethren near Selkirk. Yes it's affected by light pollution from Selkirk, Innerleithen, Peebles and Galashiels but they are all north or east of the summit. In a south western direction, it's 45 km to nearest light pollution source of Moffat.

The Three Brethren cairns mark the boundaries of the estates of Buccleuch, Yair and Selkirk Burgh and are at a height of 465m. The first cairn was built by Alexander Pringle, Laird of Yair and Whytbank Tower in 1512. However, one cairn was considered to be insufficient and another two were built at a later date. We do know that the hill is named as the Three Brethren on General Roy’s military maps from the mid-1700s. Suffice to say they've been around a while and are indeed well built as you will see.

In Scotland we often get a week in September of fine weather, usually after a very soggy June, July and August. The forecast had been predicting clear skies for Thursday 17th September from several days out and it delivered. High pressure was established and so the weather settled down and behaved itself for a few days. Game on.

I parked up in the tiny village of Ashiestiel and loaded up the bike with photo and some camping gear. I didn't intend to stay overnight but with little wind I was expecting a midge nightmare and so I wanted a tent for refuge whilst I waited for darkness. I reached the summit after about an hour and one unplanned dismount due to a very sudden change of gradient and being in the wrong gear. Normally this isn't a problem, but due to the location of camera bags and tripods attached to the bike, dismounting quickly can be tricky. Luckily I landed on heather with nothing expensive broken.

The summit proved midge free - woohoo - but not flat - boo - which meant it was going to be tricky finding a pitch for the tent. But as I wasn't staying all night it wasn't a major issue. Of more concern was where to get the best composition for the milky way and the three cairns . This was further complicated by the appearance of two dirt bikes within minutes of me arriving. It became clear that the summit was a confluence of paths and tracks and so I needed to be mindful that a tripod might get in the way of passing traffic.

Indeed it got even busier. I was soon visited by a fell runner and two mountain bikers. Each required a bit of a chat - in fact I haven't spoken face to face with this many people in such a short time since the beginning of lockdown. It was great to be talking about non-Covid stuff and sharing the glorious views. I was soon alone again but not for long as I was then joined by Andre Hudson another astro-photographer but much more experienced than me who had similar plans to me to photograph the milky way. More chatting ensued and I soon realised how seriously and specialised some people get when it comes to astro-photography. I'm not in their league and unlikely to ever to join that level of specialisation as it involves some eye wateringly expensive kit and a particular liking for cold dark nights. As I've said before, I'm just dabbling in astro-photography and finding my way just now.

Waiting for the milky way. The tent wasn't really necessary due to the lack of midges. I had plenty of company including Rory and Luna who were out making the best of the weather.

Eventually I got on with the setup of the camera and tracker. According to the Photopills app I had 8 minutes when the core would be visible above the horizon. I had planned a sequence of shots, some using the tracker and others which were static. Once that sequence was completed I also wanted to light paint the three cairns which means opening the camera shutter and shining torch light onto the subject. This would give me an image with some detail in the foreground subject rather than just a black silhouette.

I did some test shots in the run up to my window to get the exposure verified and then ran through my sequence of shots. Operating a camera in the dark isn't easy. You need to be very familiar with the controls and menu system, especially if you've forgotten your glasses. Focusing is also tricky - forget autofocus - instead it's manual focus only and make sure you don't accidentally catch the focus barrel after it's set. I was using a manual lens Samyang 14 mm f2.8 on an Canon 5D II, a camera I've owned for over 10 years and am well used to but even so operating in the dark isn't easy. Of course, being unable to see what you're doing is usually easily resolved by use of a head torch but I was aware that Andre was shooting at the same time. I tried to avoid using my red head light and we checked with each other before switching on lights but I might have got it wrong a few times. Sorry Andre.

I also made a mess of the tracker shots. The tracked shot should have resulted in pin sharp stars and a blurred foreground. But I was getting the opposite. i.e. the tracker wasn't moving the camera. I concluded that something had failed and resigned myself to just getting the static shots. It was only later back home I realised I'd setup the tracker incorrectly - a combination of operator error and trying something new. I'll get it right next time.

I'm reasonably pleased with the result. I'm still getting light pollution - not exactly sure where from but could be Moffat which is over 45 km away. But actually I think it helps to isolate the cairns. There's clearly some haze on the horizon which is obscuring the centre. So I still haven't managed to photograph the galactic core region; I did say it was proving difficult.

The Milky Way and the Three Brethren. The Cairns date back 300 to 500 years but they're just babies compared to the light coming from the milky way core which is over 26,000 years old.

Tim Hodges - www.irisone.co.uk

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Tim Hodges
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