Class 8 Shock

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A
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Class 8 Shock

Post by A »

Hi

Just used the John Bortle light pollution scale to
give me some idea of how bad my local light pollution
is.
I live in a small rural town with open fields less than
a quarter of a mile away, the nearest city is a good
30 miles away. Just had a bit of a shock to see that I
have class 8 conditions, which is pants.

Looks like my location is not that much better than a city.
What do you guys have on the same scale.
jeff.stevens
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Post by jeff.stevens »

Hi A,

I seem to recall this article, from Sky & Telescope, explaining the Bortle scale. A fascinating read, but a strange classification. From my location I would expect to fall under Class 6, but based on his unaided eye limiting magnitude I'd say it's class 9.

It would have been good to have some examples of locations that fall within each category (even if US based), just to help put it into perspective a little more.

Jeff.
A
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Post by A »

Hi Jeff

Yes it would be nice to have some examples.

I have to admit that I am a bit shocked to see on the
Bortle scale that I have such poor sky conditions, as I spend
quite some time in areas (London) with much worse light
pollution than me. Yet on this scale, my skies are only slightly
better than those of the big smoke.

Perhaps we should all adopt the Bortle system for classifying
light pollution. Then when someone says that they have class 8
or 9 conditions, you are able to get a good mental picture of
what their conditions are like.

For example, how would people class conditions at Preston Montford,
or Kielder Forest based on the Bortle system.

Most people when talking about light pollution say things like 'the sky is bright 'or 'I cannot see the stars or deep sky-objects'. I have done
the same thing myself, yet I still struggle to get a good idea
of how bad their conditions really are from what is a rather general
statement.

It would be interesting to see people post their conditions based on the Bortle systems.
Cliff
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Post by Cliff »

Dear "A"
Although I think the Bortle Scale is interesting I am not sure if it will be of much value to many UK observers and will be of very little help as a tool to help fight light pollution.
Of course it is easy to be critical.
However, I personally think that the Philips Dark Sky Map covering the UK is a much more useful. From my limited observing travels around the UK I think the Philips Map very accurate. The great pity is that there are not a number of earlier editions of the Philips Dark Sky Map so that we have proper data that we can refer and can say with authority to what degree our night skies are deteriorating due to the increase in light pollution.
One thing that irritates me about the Bortle Scale is that his examples refer to using a 32 cm telescopes.
I do not do much serious visual deep sky observing because of local light pollution and I am now getting on a bit. Arguably it is impossible to get properly dark adapted in my garden because of various lights in my neighbourhood. On a decent night I reckon I can see stars of mag 4.3 in Ursa Major, sometimes not so good but very occasionally I can see fainter stars. Admittedly its going back some years, but I do claim to have observed Pluto from home and even Saturn's satellite Hyperion on one occasion using my 214 mm f7.6 newtonian. The Hyperion night was undoubtedly retty exceptional, I contacted a nearby acquaintance who is a keen deep sky observer using a 10 inch newtonian and he then observed Hyperion. I have never seen that satellite visually since, although I have CCDed it.
A year or two back Sky & Telescope had an interesting article about a light pollution meter device devised by two European astronomers. I thought it could be a useful tool but a pity it had not been brought out many years ago.
Best wishes from the Grumpy Old Codger Cliff
davep
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Post by davep »

jeff.stevens wrote:I seem to recall this article, from Sky & Telescope, explaining the Bortle scale. A fascinating read, but a strange classification. From my location I would expect to fall under Class 6, but based on his unaided eye limiting magnitude I'd say it's class 9.
Thanks for the link Jeff -- without it I wouldn't have had a clue about what this scale is.

I take it that this scale isn't something that you'd apply as a static measure of your skies ("the sky where I live is class X") but, instead, is something you'd try and apply each session? After a first read of the article I'm left thinking that atmospheric conditions will have quite an effect on the results.

Or am I missing something?
jeff.stevens
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Post by jeff.stevens »

Hiya Dave,
Dave wrote:I take it that this scale isn't something that you'd apply as a static measure of your skies ("the sky where I live is class X") but, instead, is something you'd try and apply each session? After a first read of the article I'm left thinking that atmospheric conditions will have quite an effect on the results.
I'd taken it to be used as a "general" basic assessment of the typical conditions for your site. However, I think there are some inconsistencies with it, and I'd love to see examples of the type of geographical areas that Bortle bases his location descriptions on.

Despite living on the outskirts of a city, without doubt the biggest headcahe for me are the effects of "local" light pollution. The effects on an observing session can range from subtle to significant. Usually this is directly related to the number of security lights or outside lights that have been switched off. Without a doubt, the best observing times for me (at this time of year) fall between 2:00am - 4:00am. I've never done a measured test, although I keep meaning to, but it can range from making an observing session pointless, to reasonably enjoyable. As ridiculous as this seems, but having read that this is a worthwhile technique, this week I finally resorted to placing a cover over my head to block out the extraneous local lighting. I have to say that on the one brief occasion I tried it, this made a huge improvement. Under conditions where I would normally have given up and gone inside, I was able to see some wonderful detail in M37, in Auriga, using my ETX 90.

Anyway, I digress. What fascinated me most about the Bortle scale, when I first read it, was where do you have to be to observe under class 1 skies - has anyone ever observed from a location such as this?

Jeff.
A
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Post by A »

Cliff wrote:Dear "A"

On a decent night I reckon I can see stars of mag 4.3 in Ursa Major, sometimes not so good but very occasionally I can see fainter stars.
Hi Cliff

I observe from countryside fields, away from security lights etc,
with the nearest city being 30 miles away. Yet, I dont see stars
any fainter than what you can see from light polluted Manchester.

On one or two occasions each year I see stars down to mag.6.0,
but just below magnitude 4.0 is the norm. I have given up on
observing DSO and comets.
I will buy a copy of the dark sky map (out of interest) and see
what it says about my location. It strikes me that the whole of the
UK including so called dark sites is pants.

This is why I was a bit shocked to see that my rural darker location
is only one step up (on the Bortle scale) from large light polluted
cities that I have worked in.

It would still be nice for someone who has observed from say
Keilder or that place out Norfolk way(sorry completely forgot the
name) to give us a rating based upon the Bortle scale.
Chris_Barlow
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Post by Chris_Barlow »

I think my location in Cheshire gets a 6 and my rural dark site may be down to a 5 on a good night.

That is mostly going off the descriptions of cloud illumination and the Milky Way. I can never see my equipment around me unless the moon is out though! :lol:
joe
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Post by joe »

90% of my observing has been in the 8 or 9 region and, like Jeff, have had to rely on blocking local light pollution to see anything slightly faint. This involved large sheets of plastic "board" hoisted up on poles to block lamps and fleeces over the head. I always try to go somewhere dark when on holiday and think I might have managed 2, possibly even a 1 when on a Scottish island, unfortunately without a telescope or binoculars.
200mm Newtonian, OMC140, ETX90, 15x70 Binoculars.
A
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Post by A »

Hi

Just got back from town with latest Sky at Night mag.
Just so happens to have an article about light pollution.
I had to laugh, as there is a night time picture of Europe.
My observing location is bang in the middle of one of the
darkest regions of the U.K.

Now I am even more shocked than before.
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