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What is the recommended radiance level for stargazing?

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Hello, I am a fourth-year Interior Design Student. For my Final Major Project I am hoping to design an observatory and lecture space designed to encourage more people to engage with stargazing.

 I am currently researching the best location for this type of building. Naturally the darker the site the better it is for observing but I would like to know if there is a limit or maximum recommended level to the lighting radiance level or lux level of the surrounding area.

Attached is a photo of a lighting radiance key that may help to determine the answer to my question as it breaks the radiance levels down into sections.

I would be grateful for any opinions, knowledge or information relating to this J
Thank you in advance for your help


radience levels.jpg

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Since I have no correlation between the level given in term of radiance, this is going to be a bit of guess work and assumption. Will say that in astronomy people quote a NELM level and I have no idea what they are either.

For reasonable minimum I would say the darker green, 0.4 - 1.0. Reason for almost randomly selecting that one is that on some Ligh Pollution maps that green is the one that matches where I head to for a slightly darker site then where I live.

Now the other aspect. The most popular I know of is in a much worse radiance level, 3.0 - 6.0, I think, although equally may be 6.0 - 20.0. Again I am assuming that the colours correlate between the LP maps and your scale.

The popularity is simply the location, convenience and available facilities. Car parking, observing area, well presented and carried out. To get people interested it is likely not going to do a great deal to say drive 20 miles to a hard to find location, park your car on a verge then walk half a mile to join us stood in a field to look at the stars. It might be nice and dark and you will see more, but people are not going to do it.

To get people interested then look for a place with reasonable access, parking, then a not difficult route to an observing area or observatory. I find that many nature reserves sort of match this. The one I use is a small access road (tarmac) into an RSPB reserve. The car park there is actually surrounded by trees but that  access road has 3 passing points and I park up in one of those.

Little outside Leicester but Rutland Water is one sort of place. Have a meeting at one of the entry points there, Egleton entry hosts the annual Birdfair. Easy to find, defined road in, parking, fairly dark sky. It is a little out of many peoples limit, assume a 20-30 minute drive as the maximum, but there has to be something along those lines closer to the population centers.

Does Leicester Uni have any form of weekly or monthly observing? See they have an observtory at Oadby, which after all is close to Leicester, so not dark as in black or blue. But easy access.

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Welcome to the forums, and good luck with your project!

Light pollution is one of the biggest problems for astronomers. Ideally there is zero artificial light in the vicinity, hence top level research observatories are often in very remote places such as the Atacama Desert in Chile. However, this also means access is difficult for the general public. This picture gives an idea of the difference:



Amateur astronomers often use the relatively informal Bortl Scale to estimate light pollution: https://en.wikipedia.org/wiki/Bortle_scale

You need to minimise two types of light pollution - local illumination, such as street lighting, which can often be screened to an extent to reduce adverse effects, and the cumulative effects of large quantities of light, for example in an urban situation, and the best solution is really to move to a rural location.

It is worth remembering, too, that certain frequencies of light at low levels do not damage night vision. Red light for example is often used by astronomers, and there is some research suggesting other colours such as green may be advantageous. Something perhaps to think about when planning safe access for the public.

Night vision is also a gradual process - taking perhaps 30 minutes for our eyes to adapt after being exposed to any bright light. Hence it is important to avoid occasional exposure to bright light, for example a car arriving in a parking area during observation.

As I see it, the problem of determining exact light radiance levels is the variable of moonlight. Bright nights when the Moon is full are not ideal for many types of astronomical observation, but they are something we cannot control!


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  • 2 years later...

I agree with Bright Giant. I am fairly new to astrophotography and have also been looking into this. I see from various maps that the same Bortle zone can cover a large range of radiant light indices. As the Bortle scale seems to be defined by light at the zenith I am assuming that a low radiance value is important because this I presume is affecting viewing at lower angles, say 45 degrees , which will be important when viewing ,say, the Milky Way. I am thinking you would want a lowish Bortle Zone, say 3, but in the UK 4 is more realistically accessible and a low radiance value. The map I am looking at www.lightpollutionmap.info quotes these and whilst I don't fully understand the units it would appear that 0.18-0.3 is very dark, 0.4-1.0 is achievable in more accessible rural areas. I hope this helps but if I am talking rubbish feel free to tell me because it would help me as well ! 

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