Thanks, Tsula! After watching your vid, I ordered a SQM-L to measure my skies here in Northern New Mexico (which are generally Bortle 4 to 3), Moved here 3 years ago from the light pollution of Washington D.C., and I love being able to walk out my door and see the Milky Way again.
Thank you! I know what you mean. I live part of the year in the San Francisco Bay Area where I can't see anything and it really makes me appreciate it when I can come to my country home in Montana and walk out onto the driveway to see the Milky Way and lots of other wonderful things in the night sky. Cheers.
Hi Tsula, as ever, clear concise information. As someone who is dogged by light pollution and bad skies anything relevant to better seeing is of interest! I dream of moving to a dark sky area one day! I was shocked to read you’d had such a bad accident. I’m so glad you are alright, remember, equipment can be repaced….. you can’t be, so be sure to take care of yourself. I wish you well, what a year you’re having….stay positive, it can only get better! Here’s to dark skies for both of us! 🤗✨🌙
Linda: Thank you so much. I am so grateful that I was not seriously injured being such a horrific accident. Thank you and I wish you dark skies and may your dream come true one day of moving to a dark sky area! All the best.
The subtlety that is missed with the Bortle scale is that in the mid ranges of light pollution you almost never have a perfectly uniform sky brightness, it can mislead a lot of people. My personal experience living in a Bortle 5 is this. I live in the UK in a small-medium size village. North of me is a large town, to my east there are only a few houses, then there is the North Sea a few miles east. To my west I am looking through a bit of the village light pollution, then beyond that is the country side. Looking south is the same, the street lights of the village dominate, but beyond that is countryside. Only on the perfect nights is the zenith actually the darkest spot in the sky, usually for me it is looking east about 45-60 degrees up. I would imagine that is because it's the direction of the sea. The NELM for stars I can focus on and see as a pinpoint of light seems to be around 5.1-5.2. But on particularly clear nights, if I unfocus my eyes and take in a wide portion of the sky I can spot an uncountable amount of blurry very faint dots popping in and out of in my peripheral vision that once I try and look at them they disappear. Near the zenith If I'm lucky I can catch a quick glimpse of stars upwards of mag 5.8. It's a stark contrast to looking north and barely seeing mag 4 stars. On the best nights, the summer milky way only presents as a greyish fuzzy cloud that lacks any structure. The winter milky way is never visible.
very true i got used the LP maps before the bortle scale came out. In many of my videos i just used the color of the LP map. like what red orange, these are rough gauging but it just gives an idea. The Bortle rating was always wrong to me too BUT its what almost everyone is used to now so i now say. Iam located in a white zone or bortle 8, my country setting is a grey zone or a bortle 2 zone. That way most understand what iam talking about. Cheers
That's a good way to explain it with the colors. It seems the light pollution maps just use population statistics but they change so rapidly that the maps are often not accurate and underestimate the amount of light pollution. I think my country home in Montana will soon be a Bortle 4 even though maps list it as Bortle 3, for example.
@@tsulasbigadventures true thats wht they are just a gage and are not meant to be perfect or accurate but maybe getting one of those gadgets is good, however i never got one/.
To judge brightness limit with the naked eye you must have your eyes well dark adapted. They say takes about 40 minutes in complete darkness to have our eyes perfectly dark adapted. And then you would take your sight at the zenith without seeing absolutely nothing else. I agree, it’s time consuming as you say.
Thank you. You can also use it to track the light pollution in your area over time and submit the information to the International Dark Sky Association who keeps records of light pollution world wide.
speaking of sqm, in 1 month i'm going to head up to wyoming for 2 months, ungh, i need to put together a rig and work out it's kinks and quick if I'm going to get any imaging done while I'm there.
I live under a slightly awkward sky to measure.It's Bortle 6 on the map and on Clear Outside but is a sky of two halves as I'm by the sea so looking west inland the sky is grey but if I look east out to sea it's quite dark.I think that if I had an SQM meter I'd get a different reading west than east.I often use the box part of Ursa Minor as a test ,if I can see the whole 4 stars of the box the sky is quite dark,Bortle 4 down, but if I can only easily make out the 2 brighter stars of the box Bortle 5 up.
I know what you mean. There is a town west of my country home in Montana and there is significant light pollution coming from that direction. The sky quality from that area is bad but the rest of the sky is definitely Bortle 3. I think the Ursa Minor test is a good one.
I absolutely can see mag 6.5 stars in Bortle 4. I think his scale is very accurate, and have seen examples of all his classes. It is very well thought out. OTOH zenital brightness measurement is dependent on all sorts of extraneous factors, and the overall quality of the sky may be poor even though it is very dark near the zenith. In Bortle 3 I can easily see the spiral structure of M51 with direct vision, like looking at a book, with my 10".
I can see the pleadies from bortle 9, but it is tough. They look great in binoculars though. And don't forget that when the milky way is straight overhead, it can fool the sqm into giving a slightly worse reading. And sqms vary a bit unit to unit, so some will use 2 or 3 of them and average the results. When the milky way is at zenith, you can angle the sqm a bit to avoid it
I'm puzzled by this paragraph in the SQM meter's user guide: "TYPICAL READINGS: Magnitudes per square arc-second is a logarithmic measurement. Therefore large changes in sky brightness correspond to relatively small numerical changes. A difference of 1 magnitude is defined to be a factor of 100^1/5 [the number 100 lowered to the 1/5 power] in received photons. Therefore a sky brightness 5.0 mag/arc-sec² fainter corresponds to a reduction in photon arrival rate of a factor of 100." I'm not a mathematician, and I don't get this math at all. I understand why we're dealing with 100 instead of 10, because we're dealing with area instead of pinpoints. But how can a sky brightness five magnitudes dimmer be only 100 times dimmer? Is the 5.0 a typo for 1.0?
I can usually see to mag 6 or a little better in bortle 4 but I also have really good eyesight and am still young at 23. I have noticed my ability to see faint stars get slightly worse compared to when I was 18-20.
That's a good point. John Bortle complained that the NELM method relies on good eyesight but his scale does too in a way because the differences in between the levels are based in part on seeing various magnitude stars. That's pretty good for you to be able to see Magnitude 6 stars in a Bortle 4. I usually cannot see Magnitude 6 stars in my Bortle 3 country home but I am significantly older than you and my eyesight is failing as it inevitably does as we get older.
Are you sure it's not SMOKE Quality Measurement, Tsula? 😅 Thanks as always for a great and informative video! I'm glad you revisited your advice about judging sky quality using the Little Dipper. I use it all the time since you covered that last year (I think). Do you know if Astronomical Certificate Programs will accept a SQM using an iPhone app, e.g., Dark Sky Meter? Hope things are going well!
Thanks, Greg. The Astronomical League just requires you to convert your transparency into a scale from 1-7. They don't ask you how you arrived at your number. So, if you used SQM then you would just need to convert your numbers onto a 1-7 scale. Things are not going well! I had a horrific car accident, totaled my car, and the car partially submerged in water ruining much of my astronomy equipment I keep in CA including my Meade LX85, 8" SCT. I am fine physically but very shaken up. I hope things are going better for you.
@@tsulasbigadventures Oh, Tsula, I'm so sorry to hear all that! I'm very glad you're okay. That must have been a horribly frightening experience. I can only imagine. This certainly has been a rough year for equipment all around, hasn't it? I feel terrible for you.
@@tsulasbigadventures That's awful news about the accident, Tsula. I've been reading a little about SQM and have some questions to ask you, but I'll save it for the weekend. In the meantime, I'm glad you're OK.
I'm going to say something I'm sure you've never heard! :) I actually don't LIKE pitch black skies. It is almost overwhelming. It is always easier to observe when there is SOME skylight to deine the field stop in a medium power eyepiece. The best skies are ones where a high-power eyepiece - 0.5mm exit pupil, produces a black background, but a 1mm exit pupil allows the field stop to be clearly seen. Very little is lost - dim nebulae like the Horesehead and such. I have seen it so dark that every movement you risk tripping over your gear, and have to use the power LED to navigate - and it looks like a red lighthouse! I did not find this enjoyable at all once I got over the inital WOW factor. Reading maps, the handset etc blinds you for some time. I always have preferred Bortle 3 skies - more stars than appear in say Sky Atlas 2000, so many that constellations become hard to recognize from too MANY stars, but enough light to navigate in the dark.
There are incident light measuring devices that calculate how much light is falling on the sensor. But they have a very wide field of view, and their measurements would tend to be ruined by any local or near horizon light sources. The SQM has a more narrow field of view and if pointed at the Zenith, it should not be able to see any of those local or near horizon light sources. The two devices would also be calibrated differently, and use different scales of measurement.
@@shubinternet I have only ever used the Unihedron SQM-L but another viewer said he has an app on his phone that measures sky quality. It probably works the same as the incident light measuring device you mentioned.
I suggest not using the SQM-L version. L stands for lens, it has a very narrow angle. The SQM version will give a better idea of the night sky brightness, as it measure more of the sky. The SQM-L will only measure a tiny part of the sky 'overhead', tells you nothing about the most of the sky.
Good video.., the “clear” verbal quality of your video is very good!
Thank you!
Thanks, Tsula! After watching your vid, I ordered a SQM-L to measure my skies here in Northern New Mexico (which are generally Bortle 4 to 3), Moved here 3 years ago from the light pollution of Washington D.C., and I love being able to walk out my door and see the Milky Way again.
Thank you! I know what you mean. I live part of the year in the San Francisco Bay Area where I can't see anything and it really makes me appreciate it when I can come to my country home in Montana and walk out onto the driveway to see the Milky Way and lots of other wonderful things in the night sky. Cheers.
Hi Tsula, as ever, clear concise information. As someone who is dogged by light pollution and bad skies anything relevant to better seeing is of interest! I dream of moving to a dark sky area one day! I was shocked to read you’d had such a bad accident. I’m so glad you are alright, remember, equipment can be repaced….. you can’t be, so be sure to take care of yourself.
I wish you well, what a year you’re having….stay positive, it can only get better! Here’s to dark skies for both of us! 🤗✨🌙
Linda: Thank you so much. I am so grateful that I was not seriously injured being such a horrific accident. Thank you and I wish you dark skies and may your dream come true one day of moving to a dark sky area! All the best.
The subtlety that is missed with the Bortle scale is that in the mid ranges of light pollution you almost never have a perfectly uniform sky brightness, it can mislead a lot of people. My personal experience living in a Bortle 5 is this. I live in the UK in a small-medium size village. North of me is a large town, to my east there are only a few houses, then there is the North Sea a few miles east. To my west I am looking through a bit of the village light pollution, then beyond that is the country side. Looking south is the same, the street lights of the village dominate, but beyond that is countryside.
Only on the perfect nights is the zenith actually the darkest spot in the sky, usually for me it is looking east about 45-60 degrees up. I would imagine that is because it's the direction of the sea. The NELM for stars I can focus on and see as a pinpoint of light seems to be around 5.1-5.2. But on particularly clear nights, if I unfocus my eyes and take in a wide portion of the sky I can spot an uncountable amount of blurry very faint dots popping in and out of in my peripheral vision that once I try and look at them they disappear. Near the zenith If I'm lucky I can catch a quick glimpse of stars upwards of mag 5.8. It's a stark contrast to looking north and barely seeing mag 4 stars. On the best nights, the summer milky way only presents as a greyish fuzzy cloud that lacks any structure. The winter milky way is never visible.
That is a good summary of one problem with the Bortle scale.
very true i got used the LP maps before the bortle scale came out. In many of my videos i just used the color of the LP map. like what red orange, these are rough gauging but it just gives an idea.
The Bortle rating was always wrong to me too BUT its what almost everyone is used to now so i now say. Iam located in a white zone or bortle 8, my country setting is a grey zone or a bortle 2 zone.
That way most understand what iam talking about.
Cheers
That's a good way to explain it with the colors. It seems the light pollution maps just use population statistics but they change so rapidly that the maps are often not accurate and underestimate the amount of light pollution. I think my country home in Montana will soon be a Bortle 4 even though maps list it as Bortle 3, for example.
@@tsulasbigadventures true thats wht they are just a gage and are not meant to be perfect or accurate but maybe getting one of those gadgets is good, however i never got one/.
To judge brightness limit with the naked eye you must have your eyes well dark adapted. They say takes about 40 minutes in complete darkness to have our eyes perfectly dark adapted. And then you would take your sight at the zenith without seeing absolutely nothing else. I agree, it’s time consuming as you say.
That is correct. Thanks for bringing that up about the need to dark adapt as well.
Excellent and clear explanation for a key element of any astro activity.
Thanks.
Very enlightening and interesting video. Have taken all on board because you got it over so well. Thank you for sharing.
Thank you!
Your video was fantastic and I enjoyed it. I do need to get a Unihedron Sky Quality Meter unit. So much quicker and can be quantified. Awesome:)
Thank you. You can also use it to track the light pollution in your area over time and submit the information to the International Dark Sky Association who keeps records of light pollution world wide.
Thank you Tsula.
Thank you, Ron.
Thank you for making this very interesting video, I learned a lot Tsula!
Thank you. I'm glad to hear that.
Very well explained and presented. Thank you! 😎👍
Thank you very much.
Thank you
You're welcome. Thanks for watching.
speaking of sqm, in 1 month i'm going to head up to wyoming for 2 months, ungh, i need to put together a rig and work out it's kinks and quick if I'm going to get any imaging done while I'm there.
I live under a slightly awkward sky to measure.It's Bortle 6 on the map and on Clear Outside but is a sky of two halves as I'm by the sea so looking west inland the sky is grey but if I look east out to sea it's quite dark.I think that if I had an SQM meter I'd get a different reading west than east.I often use the box part of Ursa Minor as a test ,if I can see the whole 4 stars of the box the sky is quite dark,Bortle 4 down, but if I can only easily make out the 2 brighter stars of the box Bortle 5 up.
I know what you mean. There is a town west of my country home in Montana and there is significant light pollution coming from that direction. The sky quality from that area is bad but the rest of the sky is definitely Bortle 3. I think the Ursa Minor test is a good one.
I absolutely can see mag 6.5 stars in Bortle 4. I think his scale is very accurate, and have seen examples of all his classes. It is very well thought out. OTOH zenital brightness measurement is dependent on all sorts of extraneous factors, and the overall quality of the sky may be poor even though it is very dark near the zenith. In Bortle 3 I can easily see the spiral structure of M51 with direct vision, like looking at a book, with my 10".
Good for you. You must have good vision. Way to go.
I can see the pleadies from bortle 9, but it is tough. They look great in binoculars though.
And don't forget that when the milky way is straight overhead, it can fool the sqm into giving a slightly worse reading. And sqms vary a bit unit to unit, so some will use 2 or 3 of them and average the results. When the milky way is at zenith, you can angle the sqm a bit to avoid it
Thanks. I can see the Pleiades from the Bay Area but it doesn't look good. OK. I will angle the SQM if the Milky Way is at the zenith.
I'm puzzled by this paragraph in the SQM meter's user guide:
"TYPICAL READINGS: Magnitudes per square arc-second is a logarithmic measurement. Therefore large changes in sky brightness correspond to relatively small numerical changes. A difference of 1 magnitude is defined to be a factor of 100^1/5 [the number 100 lowered to the 1/5 power] in received photons. Therefore a sky brightness 5.0 mag/arc-sec² fainter corresponds to a reduction in photon arrival rate of a factor of 100."
I'm not a mathematician, and I don't get this math at all. I understand why we're dealing with 100 instead of 10, because we're dealing with area instead of pinpoints. But how can a sky brightness five magnitudes dimmer be only 100 times dimmer? Is the 5.0 a typo for 1.0?
So easy to lose your night vision in bottle 8 with all the street and security lights.gonna try the hoodie!
Agreed, BUT once I get up to bottle 10 it doesn"t matter anymore, I get to see many new constellations 😉
A blanket or hoodie is essential in a Bortle 8 because it's usually the localized lights that cause the most problems.
I can usually see to mag 6 or a little better in bortle 4 but I also have really good eyesight and am still young at 23. I have noticed my ability to see faint stars get slightly worse compared to when I was 18-20.
That's a good point. John Bortle complained that the NELM method relies on good eyesight but his scale does too in a way because the differences in between the levels are based in part on seeing various magnitude stars. That's pretty good for you to be able to see Magnitude 6 stars in a Bortle 4. I usually cannot see Magnitude 6 stars in my Bortle 3 country home but I am significantly older than you and my eyesight is failing as it inevitably does as we get older.
Are you sure it's not SMOKE Quality Measurement, Tsula? 😅 Thanks as always for a great and informative video! I'm glad you revisited your advice about judging sky quality using the Little Dipper. I use it all the time since you covered that last year (I think). Do you know if Astronomical Certificate Programs will accept a SQM using an iPhone app, e.g., Dark Sky Meter? Hope things are going well!
Thanks, Greg. The Astronomical League just requires you to convert your transparency into a scale from 1-7. They don't ask you how you arrived at your number. So, if you used SQM then you would just need to convert your numbers onto a 1-7 scale. Things are not going well! I had a horrific car accident, totaled my car, and the car partially submerged in water ruining much of my astronomy equipment I keep in CA including my Meade LX85, 8" SCT. I am fine physically but very shaken up. I hope things are going better for you.
@@tsulasbigadventures Oh, Tsula, I'm so sorry to hear all that! I'm very glad you're okay. That must have been a horribly frightening experience. I can only imagine. This certainly has been a rough year for equipment all around, hasn't it? I feel terrible for you.
@@tsulasbigadventures I'm glad you're okay, Tsula. Insurance fixes stuff; people, not so much.
@@tsulasbigadventures That's awful news about the accident, Tsula. I've been reading a little about SQM and have some questions to ask you, but I'll save it for the weekend. In the meantime, I'm glad you're OK.
@@tsulasbigadventures Bummer! Hope things get better soon,
Thank You. I can't wait to get to a true Dark Sky location so my little 400mm focal length telescope can shine
Walter, I hope you make it there soon. Everything looks better in a dark sky location. You won't believe it.
I'm going to say something I'm sure you've never heard! :) I actually don't LIKE pitch black skies. It is almost overwhelming. It is always easier to observe when there is SOME skylight to deine the field stop in a medium power eyepiece. The best skies are ones where a high-power eyepiece - 0.5mm exit pupil, produces a black background, but a 1mm exit pupil allows the field stop to be clearly seen. Very little is lost - dim nebulae like the Horesehead and such. I have seen it so dark that every movement you risk tripping over your gear, and have to use the power LED to navigate - and it looks like a red lighthouse! I did not find this enjoyable at all once I got over the inital WOW factor. Reading maps, the handset etc blinds you for some time. I always have preferred Bortle 3 skies - more stars than appear in say Sky Atlas 2000, so many that constellations become hard to recognize from too MANY stars, but enough light to navigate in the dark.
To each his or her own. I prefer pitch black like the Indians saw it.
What about using a normal external light meter used in photography ?
I'm not sure a photography light meter can measure to infinity.
There are incident light measuring devices that calculate how much light is falling on the sensor. But they have a very wide field of view, and their measurements would tend to be ruined by any local or near horizon light sources. The SQM has a more narrow field of view and if pointed at the Zenith, it should not be able to see any of those local or near horizon light sources. The two devices would also be calibrated differently, and use different scales of measurement.
@@shubinternet I have only ever used the Unihedron SQM-L but another viewer said he has an app on his phone that measures sky quality. It probably works the same as the incident light measuring device you mentioned.
Sky quality is not just darkness (SQM), but seeing as well. How will you measure seeing?
I made an entire video about seeing. You can watch it here:
th-cam.com/video/oQVyRURxI7s/w-d-xo.html
I suggest not using the SQM-L version. L stands for lens, it has a very narrow angle. The SQM version will give a better idea of the night sky brightness, as it measure more of the sky. The SQM-L will only measure a tiny part of the sky 'overhead', tells you nothing about the most of the sky.
Thanks for the tip.
I'd chuck that silly box and just use the phone app.
I think I'll keep it.