This Unihedron Sky Quality Meter (Ser. No. 5739 / Mod. 2.17) has been used over a six-year period at various venues in South Africa. I noted that the first four to six readings in every series of measurements we took drifted lower before stabilizing. My revised operating procedure discards the first four reading in every series and this has virtually eliminated the initial drift of earlier measuring sessions. My results showed and still show inexplicable outliers which have a negative impact on the error profile of the results produced. By mounting the unit on a tripod and making sure it is level and exactly vertical instead of operating it while hand-held, I have reduced the number of outliers but not eliminated them.
The results of the first experiment were obtained at Bergwater Lodge (-33°39’47.06″, 20°00’44.13″, 501m) near Montagu. The objective was to see if the readings taken with the Sky Quality Meter at the zenith (0°) and at 30° and 60° down from 0°, toward each cardinal direction varied and, if they varied, by how much. In experiment 1 the meter was hand-held.
Results for Experiment 1.
Discussion of Experiment 1.
The results in Figures 1 to 6 show that the values given by the Sky Quality Meter do differ at the different cardinal points and also at 30° and 60 ° down from the zenith (0°). At both 30° and 60°, the readings were darker toward the west and east than at 0° and less dark toward the north and south.
In order to illustrate the differences more clearly, the Sky Quality Readings were calculated as a percentage of the value obtained for the zenith (0°) and these results are depicted in Figure 7 (above). Here it is clear that W30°, E30°, W60° & N60° readings were consistently darker than the readings at 0° (average -0.4222) while those for N30°, S30°, N60° & S60° were lighter by a larger margin (average 0.8175).
One set of results is not enough to draw any general conclusions from and I suspect the results will vary from site to site. In all probability, they will also vary from season to season for the same site as the position of objects in the sky changes seasonally. I will select a suitable site and repeat the test at three monthly intervals over the course of one year.
The values in the second experiment were obtained at the SAAO Hostel near Sutherland (-32°22’35.29″, 20°48’18.56″, 1703m). I wanted to verify that my Unihedron Sky Quality Meter’s readings were consistent at 0° when the instrument was rotated 90° between consecutive readings around the vertical axis. In experiment 2 the meter was tripod-mounted and the tripod was set to level and vertical using a spirit level.
Results for Experiment 2.
Discussion of Experiment 2.
From these results, it appears that the Unihedron Sky Quality Meter I use does, in fact, give different readings in the two 90° orientations around the vertical axis that were tested. Even if one takes into consideration the three outlier values the S/N values are consistently darker than the W/E values. It seems possible to produce quite different sets of values, and therefore draw different conclusions depending on how the instrument is orientated around the vertical axis.
I will repeat the test using all four possible 90° orientations around the vertical axis. On that occasion, it will hopefully have the time to take two or three sets of readings on the same evening and also to repeat all of them on two or more consecutive evenings.
Exploring the Astronomy Potential at Kopbeenskloof
This report is a bit late. I thought I had written it and obviously I hadn’t so now I have to write it and look as sheepish as possible about the fact that it’s so late.
In May Lynnette and I went of to investigate a place we’d had our eye ever since we’d visited Leeuwenboschfontein a few kilometres further down the road in 2012. Other than the ominous sounding name it has the added attraction of being situated at over 1200 m above sea level and that, makes it one of the highest farms in the Western Cape Province. For the astronomers who also hike or walk during daytime, there are lots of trails and hikes and the farm is also ecologically interesting as it straddles the transition from typical Renosterveld to the Cape Mountain Fynbos.
The farm is run by Wouter and Elsabé Stemmet and regularly hosts groups of up to 200 from various youth organizations such as the Voortrekkers and Land Care & Land Services. These groups make use of a number of very basic wooden chalets containing only bunk beds. For the chalets there are adequate ablution facilities and a large, well equipped kitchen as well as an outside braai area. Wouter and Elsabé also cater for large functions and large groups, if asked to do so.
A separate camping area for tents and caravans that has its own ablution facilities is also available.
There is a rustic cottage for four that has no electricity and one heats the shower water by making a fire, situated about 200 m from the main house and the chalets.
The guest house, that could sleep nine in three en-suite bedrooms with double beds and three single beds in open areas, is situated about two km away from the main house and the chalets. The house has a kitchen with a stove, microwave and fridge and also has a large inside fireplace suitable for having a braai, should the weather turn nasty. All bedding and towels are supplied and further details can be found on their website if you go here. One last thing is that mobile phone reception is limited to one spot in the garden of the main house and I do not know if one can get a signal for all three service providers there.
To get there one takes the R318 from the N1 and, after 26 km you turn left onto the Nougaspoort gravel road. After six km the turnoff to Kopbeenskloof is on your right and then you just follow the road to the main farm house, the chalets and the rustic cottage, or go past the house, keeping to the left and after two gates, you will be at the guest house.
The reason we went there was to try and evaluate Kopbeenskloof for future astronomy outings. It might work for a Star Party but the chalets are very basic and the area around the chalets does not really lend itself to placing telescopes and I can also see the astrophotography people experiencing problems with power. I think the chalets and the camping are too far apart to allow the groups to interact easily. I would, however, not rule the site out for Star Parties, as one could possibly overcome some of the perceived difficulties by negotiating with Wouter and Elsabé.
The rustic cottage could work for a small group with Dobbies, or even equipment that will run off batteries, which I am sure the owners would be more than happy to allow one to re-charge the next day.
The guest house is a suitable site for doing astronomy and astrophotography but obviously only for small groups. There are some limitations as the house has tall pine trees on both the western and southern sides. The trees are about 25 m from the house but the area other side the trees is open so one can put a telescope there. The areas north and east of the house are open but the house then creates a high horizon to either the south or the west. The site is dark but unfortunately when we were there the weather was not good and we had partially cloudy weather on the first two nights and complete overcast on the third night. One aspect of the site that needs mentioning is the very noticeable sky glow from Worcester if there is even the slightest hint of cloud along the western horizon.
Here are my Sky Quality Meter readings taken at the guest house on Kopbeenskloof.
Lynnette and I went off on another New Moon recce, looking for suitable venues at which to present either Southern Star Parties or Dark Sky events. Our first port of call was a farm in the Touw’s River area which belongs to an acquaintance of ours. The owner is not amenable to the idea of allowing people onto the farm for astronomy or any other activity, for that matter. We would like, nevertheless, to share our astronomy experiences there. The sky brightness reading was 21,53 MSAS.
Our next stop was Marion Maclean’s place in the Montagu area. She is situated in the same area as Bergwater Lodge but closer to the R318 and a bit further North at just over 400 m above sea level.. Marion has a spare room with a separate entrance that will sleep three and, at a push, four. You share her bathroom and kitchen but bear in mind she does not have a freezer, electric kettle or microwave and all cooking is on gas. Marion has expressed interest in having one or two people at a time there for Astronomy and also anyone interested in hiking, walking, birds, plants, insects, reptiles and small mammals – Evan take note. The average sky brightness reading there was 21,52 MSAS.
Marion’s place is certainly dark enough for Astronomy and, I think in particular for astrophotography. There might be a problem with the horizon, as that is quite high to the West and North. Astrophotographers can set up on the stoep right outside their room from where they have an excellent view from East, through South and round to South-West all the way up to the zenith. I do, however, doubt if more than two people could setup in the space available there. You could certainly set up a telescope on a tripod in front of and away from the house, but the surface is not level and setting up a Dobby there would present one with major problems.
We still have to negotiate the terms on which Marion is prepared to make her place available and, when that’s done, we will let everyone know. In the meantime, just take note that the place has potential for very small groups of astronomers.
The two other venues that we have already visited that might be suitable are Leeuwenboschfontein (average sky brightness reading 21,29 MSAS) and Kopbeenskloof (average sky brightness reading 21,29 MSAS) , both situated over 900 m above sea level. We intend organizing a visit to both these venues for interested parties at a date in the not too far distant future so I won’t say much more about them now.
For purposes of comparison the sky brightness reading at Kati’s Wine farm was 21,20 MSAS. My value for Night Sky is 21,58 MSAS and 21,54 MSAS for Bergwater.
We left Brackenfell on Sunday morning of the 25th of May, under threatening clouds and elected to take the longer route over Du Toitskloof Pass instead of using the Huguenot Tunnel. Lynnette was driving. I was checking out the scenery and Snorre was spread out on my lap. We negotiated the N1 and the multiple traffic lights at Worcester successfully and stopped for coffee at the Veldskoen Padstal north of De Doorns. We were very glad to find that the service there was as friendly and efficient as we remembered it from past visits. Back on the N1 we drove past the R318 turnoff so that I could take photos of the new 50 Mw solar installation nearing completion east of the N1 a few kilometres past the abandoned 1948 tunnel attempt. I only hope the designers have done their homework, otherwise northbound motorists are going to see a very sharp reflection in the late afternoon at certain times of the year.
After taking the photos, we turned back to the R318 and continued on that until we reached the turnoff for the Nougaskloof road. The gravel road was not as good as we’ve seen it in the past, but neither was it bad, considering the fairly heavy rain in that area in the recent past. At Kopbeenskloof, our first surprise was the flock of Emus grazing in a field. The owner, Wouter Stemmet met us at the house and then accompanied us to the guest house, a kilometre or so further on. We quickly settled in at the refurbished farmhouse which has all the necessary amenities and nice clean linen. The house can sleep up to 10 people and has three bathrooms but I think eight would be a more comfortable number. There is a small sunroom with a Queen Anne stove that would make nice focal point in chilly weather and the large indoor braai area with its huge fireplace has a great deal of potential.
After settling in, we set up the telescope and got ready for an evening’s viewing. The area around the house is clear, but the lines of pine trees on two sides of the house are a problem. From the front of the house one has a clear view all the way from the west to the southeast but, to work the sky from the southeast to the southwest one would have to set up in the road beyond the trees; a distance of about 25 metres from the house. What really surprised us was the amount of sky glow in the clouds to the southwest. This light pollution problem probably has its origins in Worcester but is no doubt helped by the lights of De Doorns and the new sodium lights along the Hex Pass. The more distant lights of Paarl and Cape Town also make a contribution. The seeing was quite good, but the general conditions did not favour observing. It was never entirely overcast, but there were always stray clouds moving across the sky which made observation for any length of time in any part of the sky impossible. Monday night was a repeat of Sunday night as far as the clouds were concerned.
On Monday evening Snorre disappeared into the surrounding veld and failed to reappear. I eventually set off with a headlamp in search of him and finally found him about 40 metres away from the house eating a mouse. My attempts to take him home before he had finished his meal were met with growls and flattened ears, so I just hung around until he sat back and very smugly started washing his face.
On Tuesday morning 27 May, we drove a few kilometres down the Nougaskloof road in the direction of Touws River to Leeuwenboschfontein. The place was under new management and we wanted to see what had been changed and discuss various possibilities with the new owner’s son, Johan Roux. The changes are all very positive and Johan is also open to discussions about concessions should we wish to use the place for stargazing in the future. We had the pleasure of bumping into Iain Finlay and Willem van Zyl while at Leeuwenboschfontein, where they had taken up residence in Willow Cottage for the week. After the discussions with Johan and coffee and snacks with Iain and Willem, we drove back to Kopbeenskloof to make lunch.
On Tuesday afternoon Wouter and Elsabé Stemmet showed us around the chalets and their other facilities. The indoor facilities are clearly intended for handling large groups and a visit to their website gives one a good idea of what they can do by way of arranging functions. The facilities would certainly be more than adequate for talks and presentations at a Star Party. The 20 chalets are very basic and can sleep up to 12 people per chalet on bunk beds. One does not have to put 12 people into each chalet, as they charge per person and do not prescribe a minimum number of occupants per chalet. There are sufficient toilets and showers and the communal indoor cooking facilities are quite adequate. In clear weather the outside braai area would be nice, but there is also an indoor facility should the weather turn nasty. Wouter and Elsabé regularly handle large groups of learners from youth organizations and do not seem daunted at the prospect of serving three meals a day to 200 odd hungry children.
That evening the clouds once again put paid to any ideas we might have had of doing any observing, but this time it was seriously overcast. Not wishing to load the Vito in the rain, Lynnette and I got as much as possible loaded before we settled down in front of a nice fire. The toasted cheese and tomato sandwiches grilled over the coals were excellent. It started raining later that night and on Wednesday morning 28 May we left in light rain; the gravel road to the R318 was already quite muddy in places. At the R318 we turned left and headed for Montagu.
Down through the Koo and the Keisie and then through Montagu to Kati’s Wine Farm
It really is a delightful drive down Rooihoogte into the Koo and then down Burgers Pass into the Keisie. The scenery is magnificent and varies continuously as one drops from more than 1200 metres at the top of Rooihoogte to just over 500 metres at the lower end of Burgers Pass in the Keisie. In Montagu we stopped off to buy some of the famous Montagu Muscadel and then took Snorre to Dr Marina le Roux, the vet, for his check-up and inoculations. After that we had coffee and lunch and a long chat with Christine, who is no longer at Bergwater after the recent ownership changes there. Then we were off to meet Katica Palic at Kati’s Wine Farm between Robertson and Bonnievale. To be more exact, the place is almost on the dot six kilometres down the R317 after one exits the big traffic circle on your way out of Robertson on the way to Bonnievale. After being shown to our room and making sure Snorre was out of reach of the local canine, Biscuit, we went looking for Kati. Biscuit, by the way, is encouraged to see cats off the premises in the interest of the safety of Kati’s Amazon Green Parrot who is free on the back stoep.
Kati is Croatian but speaks fluent German and her English has a strong German flavour. Her son and daughter are in a local school and speak fluent Afrikaans and English and Kati speaks to them in German. Kati is a very energetic person and during the whirlwind tour of her premises, it soon became clear that she has lots of ideas for the place and the energy to make them work too. What surprised us most, was that she had identified a potential stargazing area. I say surprised, because when we checked it out later that evening and took a set of sky brightness readings, it turned out to have a lot of potential.
We had supper with the family and went to bed fairly early after taking the sky brightness readings. The next morning 29 May, after a delightful breakfast next to a blazing fire to keep the early morning chill at bay, we went off to Bonnievale to say hi to Inus and Elsophie van Staden who were day visitors at the previous Southern Star Party. Their son, also Inus, has resurrected an old telescope and is very keen that we should come back and show him the ropes. After coffee we went off to Parmalat’s cheese shop in Bonnievale and then headed back to Kati’s place where she had organized that I would give a talk on astronomy and, weather permitting, also do some stargazing with the 12-inch Dobby in her stargazing area. The show also inaugurated her very innovative sleeping dormitory in the old 18th century wine cellar. In attendance were the Tourism people from Robertson as well as the local press, her staff and other guests from as far afield as Montagu. The talk went well and the weather cleared sufficiently to give us time to do a quite a good astronomy show-and-tell-session.
The next morning 30 May we departed for the Night-Sky Caravan Farm. Lynnette pointed out earlier to me that I have been calling it a Caravan Park when it is actually a Caravan Farm. I shall mend my errant ways.
Night-Sky Caravan Farm
The Weather at Night-Sky was not good during our stay. By day we had such strong winds that it was quite unpleasant to be outside, but every evening the wind died down and by 19:00 it was almost completely wind free. The clouds were a different matter and I do not think we had more than two hours cloud free at stretch on any given night. In fact, two hours might be stretching it quite a bit.
On Saturday evening Wilhelm de Wet and his son Christian paid us a visit. Christian’s mother, Helena, phoned me after the previous Southern Star Party in March, expressing interest in Astronomy and asking that we get in touch when we were in the Bonnievale area again. We did that and the outcome was this visit. Christian is a very talkative and knowledgeable lad and we spent some time discussing what we could see and pointing out interesting features between the clouds before doing some telescope viewing of Saturn, the Jewel Box and various other well known objects, as allowed by the clouds.
Sunday, Monday and Tuesday were pretty much repeats of the other days, but each evening the clouds were a little more persistent and the wind a bit stronger during the day. Snorre decided that sleeping on a chair in front of the fire covered with his blanket in the evenings was the only place he wanted to be. Finally, on Wednesday, down came the rain, lots of it, and even though it looked as if it was clearing late in the afternoon, the showers persisted, interspersed with short periods of being able to see a few stars. Lynnette and I once again loaded as much of our gear as possible on Wednesday afternoon during a break in the weather so as to make life easier the next morning.
On Thursday morning 5 June, there were still intermittent showers of rain as we had expected but we managed to finish the loading in good time. We said our goodbyes to Gesina and then left for Montagu where we stopped off for a bottle of Red Jeripigo, before proceeding along the R318 via the Keisie and the Koo to the N1.
We were hoping there would be snow on the road between the Koo and the N1. Half way up Rooihoogte we pulled off because we thought Snorre needed a toilet stop. After walking round the Vito twice and inspecting the area in general he decided it was far too wet and way too cold, so we got back into the vehicle and set off again. At the top of Rooihoogte (1234 metres) the temperature had dropped to 2.5° Celsius but the only snow was far way on the high mountains to the west and south. There was even a light dusting of snow on the mountain behind Kopbeenskloof and also on the mountain to the west of Leeuwenboschfontein, but nothing closer. There were little bits in amongst the Renosterbos next to the road, but certainly nothing to get excited about. From the N1 we headed home down the N1, once again taking the scenic route over Du Toitskloof Pass instead of through the tunnel. Back home in Brackenfell we discovered that the hail that had fallen there earlier in the day and on the previous day, had knocked several holes in the roof of our car port and back stoep. The unloading was delayed several times by showers of rain, but eventually it was all done and Lynnette and I went off to the Old Oak Diner for a well-earned plate of fries and a vegetarian pizza. Back home we did some serious catching up on e-mails before bedtime.
Carol Botha is a member of ASSA (Cape Centre) and also of the Orion Observation Group (OOG). She is also an accomplished Deep-sky observer and can regularly be found lurking in dark places with her telescope, appropriately cloaked (Ninja-style). Carol is also an active campaigner against light pollution which, for obvious reasons, is an absolute pain in the posterior for astronomers . She also touches on the role light pollution plays in crime prevention and energy wastage. Cities are often identified as the main transgressors but there is hardly a town, even the one-horse variety ones, that does not have this problem. A problem which humans are not aware of, but which ongoing research is showing to be very important, is the environmental effect of light pollution on migratory birds and the disruption it causes in the lives of nocturnal birds, animals and insects.
Here is Carol’s very informative coverage of the subject.
Since the dawn of human history, people have been attracted to the splendour of the night sky. To appreciate and study the universe we need dark skies at night.
The invention of artificial light brought great benefits. Astronomers were among the first to become aware that artificial light also had adverse effects as it became more and more difficult to see the stars in urbanised areas. Satellite images of Earth at night have become a wake-up call of how much artificial light is polluting our environment.
Light pollution has become a global problem and has reached such high levels in certain countries that steps have been taken by various organisations to address the problem.
When it comes to alternate and anti-light pollution solutions, South Africa is ahead of most African countries, but lagging far behind developed countries. In an effort to save energy, mercury vapour bulbs in street lights are currently being replaced by high pressure sodium vapour bulbs in cut-off fixtures which comply with international standards. Factors taken into account are cost, luminous efficiency, colour rendering and typical life (hours). The resulting orange sky glow over urbanised areas is of minor importance at this stage.
Excessive and obtrusive lighting interferes with astronomical observatories, is particularly annoying for astronomers affecting their ability to dark adapt, obscures the stars in the night sky for city dwellers, has an adverse effect on human health, poses a threat to wildlife, disrupts ecosystems and is a waste of energy.
Potential sources of light pollution are streetlights, exterior and interior lighting of buildings, floodlights, billboard advertising, illuminated landmarks and illuminated sports stadiums. Industrialised and densely populated areas are affected most severely.
Forms of light pollution include:
• Light trespass which occurs when stray light illuminates an area other than that which it was intended for;
• Over-illumination is the excessive use of light;
• Glare is categorized into blinding glare (which can lead to temporary or permanent visual impairment), disability glare (which can lead to temporary but significant visual impairment), and discomfort glare (which is annoying and irritating; extended periods of exposure can cause fatigue);
• Light clutter refers to excessive groupings of lights which can cause confusion or distraction;
• Sky glow is caused by the combination of all unshielded, stray and reflected illumination shining up into the sky, which is then redirected back to the ground by the Earth’s atmosphere.
Light pollution can be reduced with available, inexpensive technology. Each of us can contribute towards the preservation of dark skies by installing lights that are efficient and do not create stray or excessive illumination.
(1) Use the lowest intensity light for the desired effect; (2) Turn lights off using a timer, sensor, or manually when not needed; (3) Improve lighting fixtures, so that light is directed to where it is needed; (4) Use energy efficient lamps; and (5) Evaluate existing lighting plans.
Lighting and crime
Fear of crime is a significant concern when it comes to reducing illumination but dark skies do not mean dark ground. Effective lighting improves night-time visibility, safety and security.
Blinding light impairs night vision. Human eyes take 20–30 minutes to fully adapt to darkness and become much more sensitive.
Bad lighting creates dark shadows where criminals can lurk and could contribute to a less safe environment.
Continuous lighting is actually beneficial to criminals. Installing motion detector security lights not only save energy but are more effective and cause less light pollution if directed downwards.
The ASSA Dark Sky Section aims to educate, create awareness, and campaign against the misuse of artificial light. The ongoing loss of the dark night sky is of major concern. The over illumination of cities needs to be addressed and Dark Sky Sites need to be respected, protected and preserved for posterity.