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Eroica
2004-Nov-16, 05:00 PM
The original Magnitude scale identified Magnitude 6 as being the faintest observable by the average human eye. As the scale has been revised, it is now commonly accepted that 5.5 is the faintest typically observed. These assume good health, 7.0mm entrance pupil, and excellent atmospheric transparency.
Is this accurate?

George
2004-Nov-16, 05:24 PM
The original Magnitude scale identified Magnitude 6 as being the faintest observable by the average human eye. As the scale has been revised, it is now commonly accepted that 5.5 is the faintest typically observed. These assume good health, 7.0mm entrance pupil, and excellent atmospheric transparency.
Is this accurate?

Nice site.

I would guesss the sky background is critical, as well as, eating carrots. :)

Surprisingly, the sky background can actually be additive to the light of the object being observed since this is the light your eye receives. Others should be able to address this better.

I was a little surprised with this one for surface brightness.

B = 10^0.4(9.5-M)/D^2
B = 0 for a mag. of 9.5. #-o

Harvestar
2004-Nov-17, 07:32 AM
My boyfriend and his friend can see down to 7th or fainter, depending on the site. yeah, I think they're not human too. ;)

No, he's not lying either. He's just got really sensitive eyes. (he really hates bright lights!)

Evan
2004-Nov-17, 07:57 AM
It really does depend on the site and your eye type. Blue eyes are much more light sensitive. I have blue eyes and when at the top of Mt. Kobau (6200 feet with NO light pollution) can easily see 7th. For a test there are several stars nearly exactly in line with the "lines" of the "dipper" of Ursa Major that range from 6 to 7 or so that are a good test.

Eye sensitivity (http://chaos.cpmc.columbia.edu/nyspi/askthedr/for_Pt/displayanswer1-sad.asp?Departments=sad&Controlnumber=1531)

George
2004-Nov-17, 02:10 PM
It really does depend on the site and your eye type. Blue eyes are much more light sensitive. I have blue eyes and when at the top of Mt. Kobau (6200 feet with NO light pollution) can easily see 7th. For a test there are several stars nearly exactly in line with the "lines" of the "dipper" of Ursa Major that range from 6 to 7 or so that are a good test.

My son has blue eyes and, at times, seems capable of telling me the alignment of Jupiter's moons. Their mag. is between 5 & 6, but the glare from Jupiter normally spoils them, I suspect, for most. Is his ability unusual?

Thanks for the 7th mag. test. I will use it when I get him south of town.

Evan
2004-Nov-17, 02:39 PM
Is his ability unusual?

No, not at all. The biggest problem most people have, including myself at age 55 is astigmatism. Even if your eyes pass the eye test and are deemed to be a "normal" 20/20 that does not take into account distortions in the lens and eye shape that only become apparent when the eye is fully dark adapted. Also, 20/20 is only an average deemed to be normal. Many people have better vision than that, especially when young. Your vision will usually vary from one eye to the other as well. When young my left eye was sharper than the doctors could test. It was at least 20/10 as I could read every line on the eye chart no trouble. 20/10 means that I could read at 20 feet what most people would have to be at 10 feet to see. I recall when in my twenties when I worked at an aircraft factory that I could read the clock across the shop floor 300 feet away. That was a standard clock face as found in a classroom. My vision isn't that sharp now and I sure miss it.

Some of the new eye laser surgery techniques are capable in some cases of giving "super vision" by exactly correcting lens shape.

George
2004-Nov-17, 03:04 PM
Is his ability unusual?

No, not at all. The biggest problem most people have, including myself at age 55 is astigmatism. Even if your eyes pass the eye test and are deemed to be a "normal" 20/20 that does not take into account distortions in the lens and eye shape that only become apparent when the eye is fully dark adapted. Also, 20/20 is only an average deemed to be normal. Many people have better vision than that, especially when young. Your vision will usually vary from one eye to the other as well. When young my left eye was sharper than the doctors could test. It was at least 20/10 as I could read every line on the eye chart no trouble. 20/10 means that I could read at 20 feet what most people would have to be at 10 feet to see. I recall when in my twenties when I worked at an aircraft factory that I could read the clock across the shop floor 300 feet away. That was a standard clock face as found in a classroom...
:o . Probably another reason you got into astronomy. :)

Thanks. Since they were visible by some, I wonder if anyone prior to Galileo made note of the moving white dots around Jupiter?

Evan
2004-Nov-17, 03:48 PM
BTW, I didn't bother mentioning presbyopia which is a given if you are over 45-50. That is the inevitable hardening of the lens that prevents accommodation, the ability of the eye to focus close. Everyone eventually has that eye problem. In otherwise normal eyes it doesn't affect long distance vision.

Evan
2004-Nov-17, 04:15 PM
The Chinese are credited with first spotting the Galilean moons by eye in 365BC.

http://www.psicopolis.com/timeline/astroltimeline.htm

Eroica
2004-Nov-17, 05:02 PM
The Chinese are credited with first spotting the Galilean moons by eye in 365BC.

http://www.psicopolis.com/timeline/astroltimeline.htm
I wonder how accurate that is. I heard that one Chinese observer, Gan De, spotted Ganymede, but not the other three.

frogesque
2004-Nov-17, 05:23 PM
This page (http://www-history.mcs.st-and.ac.uk/history/Mathematicians/Gan_De.html) seems to have a balanced view of Gan De's work and what little there is known about it.

badprof
2004-Nov-17, 06:31 PM
I guess it depends on what they mean by "average human eye". From my dark site in Australia, if the LM was not better than 6.5, it was not worth observing. An average night was mag 7 with the best I managed 7.4. This is despite 50 being a distant memory! :(

Yes I do eat a lot of carrots. :D

Cheers,

Maurice

Evan
2004-Nov-17, 07:22 PM
When I lived in Victoria on Vancouver Island in the early 70s I once took an 8 year old child who lived in the flat below us for a ride in my plane. He was very hyperactive so I gave him something to do. Since the air traffic in that area is fairly heavy I gave him the job of spotting aircraft in our vicinity. Well, that turned out to be an experience. He kept reporting traffic that I couldn't even see and my eyes were much better than most. He could even tell me what type of aircraft, high wing, low wing, float plane etc. Eventually it would come into my view and he would invariably be correct. I can't imagine how acute his vision was.

George
2004-Nov-17, 08:35 PM
Maybe it's the water. :)

That, IIRC, is the airport my grandfather told me about. Back in his prime, he missed a flight that had just taken off. He went to the tower and insisted they return the plane for him. Surprisingly, they were extemely courteous and radioed the pilot, who turned around and picked him up. Grandad was a little guy but nerves of steel. (slightly off topic, sorry)

Dgennero
2004-Nov-17, 09:26 PM
I heard about mag. 7.5 as a limit.
I once saw 9 of the pleiades instead of 6, but the difficulty with these is glare (Atlas drowns Pleione e.g.) and that they are close together, just like with the Jupiter moons, none of which I ever saw without having at least a 7x35 bino attached to my eyes.
To test mag. limitude, NOT resolution (as with eps 1/2 Lyrae) or the ability to overcome the glare of nearby objects, one should choose a field of widely apart faint stars near the zenith, memorize a pattern and compare with a good star atlas.
I haven't done that yet but it is a good idea for the near future.

P.S.: If you take the Pleiades as a test nevertheless, use this site to compare with what you see: http://www.ras.ucalgary.ca/~gibson/pleiades/

George
2004-Nov-17, 10:22 PM
Eroica, you might find this site helpful.... here (http://w1.411.telia.com/~u41105032/visual/Schaefer.htm)


The formula for visual limiting magnitude (from Knoll et al, converted from equations 2, 16 and 17) is:

Im=7.93 - 5 log(1 + 10(4.316-Ba/5))

It also provides a table listing the visual mag. limit based on background mag.

[edit - "Ba" is background mag. At 25 for Ba, you can see 7.95 mag! Of course, I can't :) :o ]

MrObvious
2004-Nov-18, 04:06 AM
It really does depend on the site and your eye type. Blue eyes are much more light sensitive.

What's that make me? Light green in the middle and brown on the outside..... :-?

I compared my pupils on a few occassions to others and for the same light level mine are about half the diameter of theirs. That could mean mine are either more sensitive and need to close up or I'm constantly in the dark. Ask anyone and they'll say its the latter :D

Would make an interesting study; pupil size variance for any given light intensity with eye color recorded.


Since they were visible by some, I wonder if anyone prior to Galileo made note of the moving white dots around Jupiter?


So does that mean it may be possible for some to see or detect the rings of Saturn?

Andromeda321
2004-Nov-18, 05:44 AM
I always do the Pleades test myself. Got down to 11 of them once in upstate New York, which was matched later on in rural New Hampshire. :)

Eroica
2004-Nov-18, 09:02 AM
Eroica, you might find this site helpful.... here (http://w1.411.telia.com/~u41105032/visual/Schaefer.htm)
Thanks for the link, George.

On the surface brightness thing, this is my own formula for calculating the SB from the Integrated Magnitude and Apparent Area:

SB = M + (logA/0.4)

SB = average surface brightness in magnitudes per square arcminuite
M = integrated magnitude
A = apparent area in square arcminutes
0.4 is the log of 2.51188.... (the factor by which magnitude steps differ)

Argos
2004-Nov-18, 01:59 PM
Last night I saw 10 Pleiades (wearing my - astigmatism - glasses). Nice for somebody who had retinal problems due to high blood pressure 2 years ago.

aurora
2004-Nov-18, 09:18 PM
the Bortle Dark Sky scale (published in 2001 in S&T magazine, IIRC)

http://www.meteorobs.org/maillist/msg21005.html

George
2004-Nov-19, 04:35 PM
Anyone know the the magnitude limit of the unaided eye for color vision?

[I have it, somewhere, based on power into the cones and their threshold limits. It would be nice to have more info specific to magnitudes.]

Crazieman
2004-Nov-19, 04:50 PM
Its amazing how much of the sky you guys can regularly see. There's so much light pollution here, I have to drive 40 miles to the west-southwest to see anything interesting. Its like an entirely different sky out there.

George
2004-Nov-19, 05:14 PM
Its amazing how much of the sky you guys can regularly see. There's so much light pollution here, I have to drive 40 miles to the west-southwest to see anything interesting. Its like an entirely different sky out there.

Here is an APOD view of the earth's light pollution.

here (http://antwrp.gsfc.nasa.gov/apod/image/0108/artificialnight_dmsp_big.gif)

Evan
2004-Nov-19, 06:32 PM
So what is the massive light pollution shown where the Falkland Islands are?

Dgennero
2004-Nov-22, 11:07 PM
BTW, you should never forget what I call the "schooling factor" - astronomers know what to expect, have seen it before under better conditions (binos, telescope), use averted vision, maybe know the exact position of a star in relation to neighbors, so it is pretty clear to me that an astronomer with 15/20 vision can "outperformance" the "guy next door" with 20/20.
A reality check is important - have we really seen what we claim to have seen - or just confirmed to ourselves what we know has to be there...