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Presteigne and Norton were yesterday awarded dark skies community status by Dark Sky International. The BAA’s Commission for Dark Skies provided advice and guidance to the project during its early phases and remained engaged throughout. This is an important success story for Wales and England which provides a very good project template for other communities considering such an application. The application can be found here:
https://darksky.app.box.com/s/tq5x1e9xfp0svkw8rblpgi2131ax98i0
London Stratford Sphere proposal withdrawn.
What is the reason for the scepticism about the V-band measurements? Is the scatter not similar to AAVSO visual data, albeit for a different frequency of observation? Either way, a few days of continued observation should resolve the matter, should it not?
I looked at it two or three nights ago while searching for the comet and thought to myself “That’s dimmer than I remember” and then carried on without a second thought. There doesn’t appear to be any AAVSO data for two or three nights ago.
Hi Jeremy, not different plans as such but enjoying taking a closer look at the brighter objects. For example, attempting to split the trapezium in binoculars, observing Venus more closely than usual through the 10″ reflector, that kind of thing. I even managed to see the ISS a few times through the telescope the other night. Simple enjoyments.
At Uni I was given the hi-tech task of using a straight stick with a tiny disc stuck to it at right angles to measure the ellipticity of the Moon’s orbit. Observations involved pointing the stick at the moon and adjusting the position of the disc so as to cover the Moon precisely. From week to week the disc had to be moved up and down the stick to account for the change in apparent diameter of the Moon as a result of its elliptical orbit…. The same kind of measurement could be performed using a basic digital camera on max zoom. I think we also had a stick with an arc on the end so that we could measure the angular separation between the Moon and bright stars, presumably with the aim of working out other parameters of its orbit (memory is a bit hazy).
Hi Tony, low CCT seemingly comes with a price in terms of efficiency, hence the cash pressure is to install higher CCT lamps. The reduction in efficiency in moving to 3000K is said to be worth 15% or so. I haven’t studied this in detail and can’t yet confirm that % number, but it would explain the decisions being taken in this respect. Gloucestershire is the same; I’ve found out they installed 4000K as an optimum solution weighing efficiency against aesthetics.
I suppose what I’m saying is one should be cautious when specifying or referencing CCT unless one has the x, y data (or whatever standard is being applied) in their back pocket.
It has limitations in the sense that calculated or measured colour, expressed by two numbers, x and y, is instead represented by a single number, temperature. It is possible for different pairs of x, y values, i.e. different colours, to correspond to the same CCT.
Even so, I used to work in lighting and have performed x, y calculations in the past for LEDs based on measured spectra, rather than datasheets. I then measured the resulting chromaticity. For various combinations of LEDs (e.g. whites plus ambers) I tended to find good agreement between prediction and measurement for my prototype lighting fixtures 😉
It’s a straight forward calculation to do with a short computer program and I would invite somebody (not me) to do it for a representative white LED to confirm where it would be located in terms of x and y, and how this location compares to the locus for a blackbody.
If you search CIE colour space you’ll find all the maths for doing the calc. Wiki has a good page on the subject (could have saved my thumbs by pointing you there in the first place!).
Hi Robin, to predict the colour (chromaticy) of a source requires convolution of its spectrum with the colour receptor profiles of the eye (or equivalent standardised profiles, such as those of the CIE); two convolutions are required, the third can be found via normalisation, x + y + z = 1. This allows a plot of x and y, say, on a two dimensional ‘colour triangle’, with ‘red’, ‘green’ and ‘blue’ at the ‘corners’. A blackbody has a locus of x, y values running across the ‘triangle’. The method then boils down to matching the x and y values of the light source with those of a blackbody at a given temperature (as closely as the values allow). Chromaticy can also be measured using a chroma meter. Hope that helps.
Hi Robin, put simply, a blackbody of a given temperature will display a particular colour that is unique to that temperature. A general light source appearing to have the same colour as the blackbody is said to have a colour temperature that is equal to the physical temperature of the blackbody.
As a new CfDS committee member (and BAA member) I can confirm that the CfDS raises various issues surrounding light pollution, including ones not related to astronomy, with relevant government bodies (local and national), MPs, stakeholders etc., on a regular and frequent basis. I believe the message from us and our partners is getting through at the highest level, as evidenced by the Westminster Hall debate of late last year, held in relation to the dark sky status of Exmoor National Park. Nevertheless, lobbying by astronomers and other concerned persons will continue to be required in order to turn the tide.
LED technology, as with many technologies, comes with potential benefits and dis-benefits. One of the potential benefits of this technology is that its light output can be varied as required, as is done in Gloucestershire with regards to its recently installed LED streetlights.
However, it is undoubtably the case that the lighting of factory and business premises continues to be a significant, possibly the most significant, contributor to skyglow in general. Here too LED technology is becoming more widely used. However by my judgement, LEDs or not, the operating costs of external lighting must typically be ~30% greater than they need be because of the amount of mis-directed light emitted (wasted) directly into the sky. Why businesses (and ultimately customers) tolerate this unnecessary cost is presumbly because of a lack of awareness.
Individuals are of course free to raise this kind of issue, as well as ecological issues, astronomical issues etc., with such businesses, if moved to do so, and CfDS will support such individuals with evidence-based advice so far as time and ‘resource’ permits (one such request for support arrived in my in-tray just this evening). At the same time, CfDS will continue to make the case for darker skies to organisations that are in a position to influence the sitution for the better.
Regards,
Nick
Thanks Robin, spotted that paper. Looks like I missed the dip by half a day or so. Did anybody else here have luck with it?
How common are microlensing events of this brightness? I had no idea such things could be observed visually with a small-ish telescope (I hope to follow it down using my 10″ telescope). Thanks all for sharing – ditto BAAVSS notices.
Thanks Robin, I spotted something at that position tonight (~23:00 UT Nov 1st) with averted vision through my 5” reflector. I watched for about an hour but didn’t notice any change in brightness (conditions improved as the night went on, making everything slightly easier to see by the time I packed up).
Hi Robin, I see that GRB 080603 appeared at m~14 a few seconds after detection, a surprise to me having not looked into this kind of thing before. Would the position error reported within the GCN circular not present a problem?
Thanks Gary, looks like my reading is sorted for the rest of this week while I’m off work.
