Kirjoittaja Aihe: Light pollution around Helsinki  (Luettu 15406 kertaa)

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Light pollution around Helsinki
« : 08-10-2009, 10:02:32 »
Hi all,
first of all, apologies for writing this in English, but my Finnish is not good enough for this :-)

I live in Helsinki, quite central, and as you know or imagine, the light pollution is quite bad. Does anybody know if there's a project similar to http://www.jshine.net/astronomy/dark_sky/ to find dark skies nearby?

Unfortunately I have found it very difficult to perform visual observations (no photography) because of the light pollution, and also because of the cold temperatures, which make everything more difficult.
How do you cope with observing when it's -15 outside? Sure I can wear enough clothes, but getting my gloves off and on all the time is really annoying :-)

Thanks everybody in advance for your answers :)

Salva.

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Vs: Light pollution around Helsinki
« Vastaus #1 : 08-10-2009, 10:18:38 »
I live in Helsinki, quite central, and as you know or imagine, the light pollution is quite bad. Does anybody know if there's a project similar to http://www.jshine.net/astronomy/dark_sky/ to find dark skies nearby?

Hi! I opened a discussion a while ago on this matter in this thread http://foorumi.avaruus.fi/index.php?topic=3063.0 (In Finnish, sorry  :azn:)

I'm not aware of light pollution map for Finland with the kind of accuracy as on the page you linked to. It would indeed be useful.
"In the beginning the Universe was created. This has made a lot of people very angry and has been widely regarded as a bad move."

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« Vastaus #2 : 08-10-2009, 10:40:53 »
Thanks, I've followed some links in that thread, and the situation looks pretty bad. It looks like there's no way to get a truly dark sky unless you go as north as Ivalo or something. That's really depressing.

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Vs: Light pollution around Helsinki
« Vastaus #3 : 08-10-2009, 10:50:28 »
I moved this thread to correct category (to "observing conditions" <--> havainto-olosuhteet)

In my opinion, moving away approx 30...50km from Helsinki center, will improve conditions for visual observations. But it still does not guarantee as dark skies as may be in the countryside, althought amount of light pollution is smaller.

My favourite place for observations has been Nuuksio nature park. It requires your own or colleagues car to get there. Some places are easy to access there, you can drive to parking place and put astro stuff there near to your car.

For cold winter night clothing, main rule is to keep "distant parts" of your body warm. Take special care to protect your head, hands and feet. If one (or more) of these gets gold, it begins to be annoying with observations. Some people can tolerate cold more than others... Also having layered clothing helps. And remember to eat well before observing session.

The model called "pilkkihaalari" is good point to start clothing (pants and jacket "integrated" together). Down filling in clothing makes them even warmer, but this will increase the price of clothing...

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« Vastaus #4 : 08-10-2009, 11:25:46 »
Thanks! Nuuksio is not that far away. Could you estimate the limit magnitude there in some nights you've been there?

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« Vastaus #5 : 08-10-2009, 11:46:11 »
A such dark skies you can find if you go little east or west from Helsinki, to Sipoo or Espoo or Kirkkonummi. The southern sky is guite dark also at Helsinki seashore.

At wintertime the clothing is the key to survive. Not necessary thick clothing but proper. Something warm and breathing under and then wind proof outerwear. Warm shoes and cap are important. You can also use mitten and the thin gloves under them. When you adjust your scope, just take the mitten off. I use an overall that has been made for ice-fishing. I have been out several hours without freezing myself, even it has been -25. If you have  a car, you can let it run every now and then and sit there warming a little while.

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« Vastaus #6 : 08-10-2009, 12:42:01 »
I live in Helsinki, quite central, and as you know or imagine, the light pollution is quite bad. Does anybody know if there's a project similar to http://www.jshine.net/astronomy/dark_sky/ to find dark skies nearby?

The light pollution in Helsinki is quite low compared to the really big cities and I've never seen the limiting magnitude drop below 5 even from the very heart of Helsinki. The best thing about Finland is that you don't have to drive/go too far to get to a fairly dark site. From Helsinki, go either east (Sipoo), west (Espoo) or south (near the sea or an island) and you have dark(er) skies. It is quite easy.

For a light pollution map, use Google Earth's light pollution layer. This is not very accurate but it gives you some ideas on where to observe.

How do you cope with observing when it's -15 outside? Sure I can wear enough clothes, but getting my gloves off and on all the time is really annoying :-)

If you get cold you don't have enough clothes on - it is quite simple :)

Thanks! Nuuksio is not that far away. Could you estimate the limit magnitude there in some nights you've been there?

The limiting magnitude in Nuuksio is at least 7. The number does not always tell the whole truth as you have to estimate transparency and background brightness for a start. My observing site in Sipoo has limiting magnitude of 6.5+ but it is very light polluted. The trick is to view objects near zenith and in the darkest part of the sky.

A typical Finnish observing site where I observe from has a limiting magnitude close to 6 in the best direction. For example 10 km drive from Tikkurila to the east increases the limiting magnitude by 1 easily.

/Jaakko

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« Vastaus #7 : 08-10-2009, 12:51:52 »
The light pollution in Helsinki is quite low compared to the really big cities and I've never seen the limiting magnitude drop below 5 even from the very heart of Helsinki. The best thing about Finland is that you don't have to drive/go too far to get to a fairly dark site. From Helsinki, go either east (Sipoo), west (Espoo) or south (near the sea or an island) and you have dark(er) skies. It is quite easy.

A Bortle class of 6 in the center of Helsinki? Wow, I don't think so. I have observed from the Ursa observatory in Kaivopuisto, and looking south, where the sky is best, I don't think I've ever seen anything better than 4.5 magnitude. A Bortle class of 6 also means that the Milky Way is visible at the zenith, and I haven't seen it, even with perfectly adjusted vision.

Lainaus
The limiting magnitude in Nuuksio is at least 7.

Wow again. At least 7? I'm gonna have to go and check it out :)  That's a Bortle class of 2.

Thanks.

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« Vastaus #8 : 08-10-2009, 13:08:03 »
A Bortle class of 6 in the center of Helsinki? Wow, I don't think so. I have observed from the Ursa observatory in Kaivopuisto, and looking south, where the sky is best, I don't think I've ever seen anything better than 4.5 magnitude. A Bortle class of 6 also means that the Milky Way is visible at the zenith, and I haven't seen it, even with perfectly adjusted vision.

I wouldn't use the Bortle dark sky scale to estimate my skies even if it was the last and only way to do it.

Okay I do it but only with other details around, for example:
Bortle class: Class 4 (rural / suburban transition)
NE Lim.mag: 6.6m (east)
Background sky: 3
Seeing: 2
Transparency: 2
Weather: +9.0°C, humidity ~90%, air pressure 1022 HPa, no wind

It [Bortle] can be used only as a very rough way to measure the sky and it leaves no chance for variables such as weather/particles/airglow. The Milky way is probably invisible from the heart of Helsinki (with lights shining into your eyes and you never get night vision) but stellar bright points such as stars over 5th magnitude are mostly not. I've checked out the Kaivopuisto observatory only a few times in my life, it might be a good idea to do so again with SQM-L meter :)

Wow again. At least 7? I'm gonna have to go and check it out :)  That's a Bortle class of 2.

Like I said it isn't all about limiting magnitude and most certainly not about the Bortle classes. Background brightness counts the most at least when observing deep sky objects with the telescope/binoculars/naked eye. When near big cities you're bound to have reduced background brightness due to the light pollution - even if it is invisible to the naked eye.

/Jake

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« Vastaus #9 : 08-10-2009, 13:15:16 »
On my previous trips to Nuuksio, I had not made "exact investigations" for limit magnitude... Now I own SQM-L meter, so in next trips I could measure background sky brigness. I have seen Milky way many times in Nuuksio, even when the moon is brightening thew sky...

Here is sample image of my typical observation place at Nuuksio and Milkyway in the Moonlight:
http://timokuhmonen.smugmug.com/Nature/Astronomy/Milky-way/3460248_5dBhV#460232691_GFPih

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« Vastaus #10 : 08-10-2009, 13:17:09 »
http://timokuhmonen.smugmug.com/Nature/Astronomy/Milky-way/3460248_5dBhV#460232691_GFPih

Nice. I assume that the picture pretty much renders what you could observe with naked eye, otherwise why post it? :-) Thanks.

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« Vastaus #11 : 08-10-2009, 16:54:20 »
Lainaus
A Bortle class of 6 also means that the Milky Way is visible at the zenith, and I haven't seen it, even with perfectly adjusted vision.
At this autumn I have couple of times seen milkyway in Järvenpää (35km north from Helsinki) because the city wants to save money and turns the street lights off at midnight.
Other wise the limiting magnitude is somewhere between 4.5 and 5.

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« Vastaus #12 : 10-10-2009, 00:07:59 »
A Bortle class of 6 in the center of Helsinki? Wow, I don't think so. I have observed from the Ursa observatory in Kaivopuisto, and looking south, where the sky is best, I don't think I've ever seen anything better than 4.5 magnitude.

Right now the conditions are very good here in Helsinki with no clouds in the sky. I observed the sky in Katajanokka district in central Helsinki, and used Ursa Minor as a measuring stick. I could see all the stars in the "bowl" of the little dipper, and the faintest of them, Eta Ursae Minoris ( apparent magnitude 4.95 ) was right at the limit of my eyesight. So the limiting magnitude really was about 5, probably even better, as I'm quite an inexperienced observer so someone else might have seen even fainter objects. Of course that's close to zenith, but still it surprised me as I thought the light pollution was even worse here than it seems to be.

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« Vastaus #13 : 10-10-2009, 00:50:30 »
I have mapped Helsinki city centre area last spring in both How Many Stars and
GLOBE at Night light pollution mapping projects.  Check results from the project
sites:

http://hms.sternhell.at/hms.php
http://www.globe.gov/GaN/

Find result maps and zoom to Helsinki area.

Some results:

  • The limiting magnitude is mainly 4 mag (!)
  • In Railway Station Square, 3 mag (!)
  • In some places, eg. at the sea, I reach even 5 mag

I agree the result 5 mag in good conditions, but 6 mag, no way!  At least with
my eyesight.  You, who have extreme good eyes, don't keep it as a average
standard!

I welcome also other Metropolitan area observers to mapping city light pollution. 
Don't forget The Great Wide Wide Star Count project, running on 9-23 Oct.

IYA 2009 Light pollution projects in Finnish: http://www.ursa.fi/wiki/Keli/IYA-projektit





Sama myös kotimaisella:

Olen kartoittanut Helsingin keskustan valosaastetilannetta How Many Stars ja
GLOBE at Night -projekteissa.  Linkit yllä. Katsokaa projektien karttasivut ja zoomatkaa
Helsingin keskustaan.

Muutama tulos:

  • Valtaosaltaan keskustan rajamagnitudi on 4 mag
  • Jopa Rautatientorilla pääsee 3 magnitudiin
  • Paikoitellen, esim. meren rannassa, pääsee jopa 5 magnitudiin

Olin juuri työporukan kanssa juhlimassa Sörnäisissä, ns. tukkualueella olevalla Agroksen-
mäellä, ja sielläkin pääsi 5 magnitudiin.

Allekirjoitan, että 5 magnitudiin paikoin pääse hyvällä säällä, kunhan ei häikäsyvalo
haittaa.  Helsingin keskustassa on kuitenkin vaikea päästä kunnon adaptoituneeseen
hämäränäköön, jota 6 mag vaatii.  Minusta niiden, joilla on hyvä harjaantunut näkö, ei
pitäisi tyrkyttää omia tuloksia keskimääräiseksi standardiksi.  Ainakaan minun on ollut
mahdoton saavuttaa tuollaisia tuloksia omilla silmilläni ja uskoisin olevani kohtalaisen
kokenut havaitsija.

Olisi tervetullutta, jos pääkaupunkiseudulta löytyisi lisää havaitsijoita valosaatetta
kartoittamaan. Saisimme varmaan vuoden loppuun mennessä jo komean kartan alueesta.

IYA-vuoden valosaasteprjektit: http://www.ursa.fi/wiki/Keli/IYA-projektit
Älkää unohtako The Great World Wide Star Count -projektia, joka on juuri menossa.
Alkoi tänään.  Kirjoitin siitä toiseen viestiketjuun.
« Viimeksi muokattu: 10-10-2009, 01:04:36 kirjoittanut VeikkoM »
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Vs: Light pollution around Helsinki
« Vastaus #14 : 10-10-2009, 11:56:46 »
  • The limiting magnitude is mainly 4 mag (!)
  • In Railway Station Square, 3 mag (!)
  • In some places, eg. at the sea, I reach even 5 mag

Several things come to mind. Did you have night vision? How was the weather? Clouds, cirrus? I have personally logged mag 4 skies maybe 4-5 times in my 10 year career (and I've seen a lot of horrible places). It doesn't happen very often here in Finland and when it does the sky is covered in cirrus/ice crystals or huge amounts of particles.

In the Railway station square I don't doubt the limiting magnitude is 3 with all those lights shining into your eyes but in my mind that doesn't count. Keeping away from lights is the key factor. So, yes granted limiting magnitude 3 but with a little effort (hide behind a building, keep even a poor night vision) you can go a lot deeper. I remember logging magnitude 5 stars (I often use Pleione) behind the National Theater hiding in the shadows. I have seen mag 4 skies only in London and compared to Finland that is quite a bit bigger. Apparently it is time for another "observing" run in Helsinki and with a SQM meter.

Lainaus
I agree the result 5 mag in good conditions, but 6 mag, no way!  At least with my eyesight.

With a "normal" eye sight magnitude 6 is not difficult from a selected region. From the Metropolitan area - yes of course. Santahamina has "good" skies as does southern tips of Vuosaari/Kallahti. Most of the observing sites in the suburban Helsinki area with a sea horizon have limiting magnitude close or above 6.

Lainaus
You, who have extreme good eyes, don't keep it as a average standard!

Same works both ways. Limiting magnitudes are estimates -  at best - between two observers. This is very easy to notice at the regular meetings when one observer lists limiting magnitude as 6 and other 7 and at the same time.

/Jaakko