How many stars can the unaided-eye see?

[Fr. Wayne]

Q: If you had good vision and could view both hemispheres (north and south) how many individual stars (nebula not included) could one person see?

[PhantomWolf]

At best about 12,500 with really good eyesight and clear skies.

[astromark]

Clear skies is an absolute must., and theres a few problems. Pollution and light being the first on the rank. Then theres the time factor. Earth is rotating, another problem. Build yourself a glass dome, with a grid on it to help your counting exercise. . . Better still, use a camera to capture the image for counting latter. What magnitude do you go down to? what can a well adjusted eye see from a truly dark sky site. Some of those bright dots in the sky are not stars. . . that one there is Saturn, and that bright one in the morning? I'll wager is Venus. Go buy Stary Night. They 've done all this.
But just for you I will help. . . .

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ----- Ummm, bugger!

1 2 3 4 5 6 7 8 9 10 eerr.. umm.. I'm going to bed.

[Fr. Wayne]

I was reading a very old book- over 100 years old- and it said:
By magnitudes:
I = 20
II = 70
III=220
IV=500
V =1400+
VI=5000+
totalling about 7185 stars. Is that still pretty accurate today?

[hhEb09'1]

I was reading a very old book- over 100 years old- On three different pages (pp. 108, 227, 242) in his (almost 4 years old) book, The Bad Astronomer says that there are about 10,000 stars visible with the naked eye.

[astromark]

Yes, the old book is still right today. The only real change might be that today our night vision is farther diminished by all that extra lighting that our larger cities and dirty air might present. The quoted book above ( The bad Astronomer ) is as you would expect, right on.
Get away from the lights of any nearby town or city and you will be surprised by just what you can see. From my inner city home, when I look at the Orion Group, Its just the brighter stars I see. Going out into the country side reveals a much richer field of stellar confusion. . .
Ask the question,. How many stars are mag 7 or better ( brighter ). I would think 10,000 - 12500 would be close enough a. . . .

[Eroica]

It depends on how good your naked eyesight is and how dark your skies are. According to Kaptain K there are people who claim to be able to see down to magnitude 7 (can't remember the exact figure he gave). That would surely put the number well past 10,000 (which is probably a good ball-park figure for the rest of us).

[Eroica]

The Yale Bright Star Catalogue contains 9110 entries of all stars brighter than magnitude 6.5. (http://www.alcyone.de/SIT/bsc/)

(That figure can be reduced to about 8404 if we exclude those fainter stars that slipped into the YBS catalog (http://cdsweb.u-strasbg.fr/viz-bin/VizieR?-source=V/50).)

[turbo-1]

Here in central Maine, mag 6 is a no-brainer on any decent night if your are not close to a big town. Get a few miles back into the woods (like at my house), and the sky explodes with stars. There is a place about 45 miles north of here where I go to fly-fish when the green drakes are hatching, and if the night is clear, I always stop at the log yard on the way back to look at the sky. I've got to bring Uranometria sometime, but intuitively I'm pretty sure that mag 7 is no problem from that site visually. I am no longer working as an optician, but when I see my opthalmologist (one of the doctors from the practice that I once worked for), he makes recommendations, but allows me to determine the amount of correction that I want, which he then prescribes. I routinely over-correct a bit for the glasses that I use at night, and gain a bit of acuity that way. The night sky north of Parlin Pond is gorgeous (and the fishing is pretty good, too).

[Fr. Wayne]

wow. 6.5! Now those are baby-blues. Eyes that is.

[Nereid]

Time for some nitpicking pedantry :)

What about variables? There are quite a few which are well and truly visible at maximum, yet well and truly invisible at minimum; then there are all those which are are marginal.

As has already been pointed out, the 'darkness' of your sky really does matter - what's 'visible' at one (dark) location may not be visible at another (even to the same person, under the same conditions). Which leads to ... what's the place on Earth with the 'darkest' night sky? What for each hemisphere?

Then there's your actual latitude ... in principle you can see both (celestial) poles from anywhere on the equator, but they're on (or very close to) the horizon, so the faintest visible star near there will be much brighter than the faintest star you could see at the zenith (all that airmass makes for quite a few mags of extinction).

While we're at it, there are doubles - does a close double which you can split but I can't count as one, or two stars?

And let's not leave 'nebulae' out, as if it's a simple matter of 'is this a nebula? if yes, it's out; if no, it's in'. How many 'nebulae' are there, visible to the naked eye by one criterion or other, which contain at least one 'star' which appears, in at least one sense, as a 'star'? To get technical, if the PSF of your eyes has a FMHW (full maximum half width) of 8', then any 'object' with an integrated mag of <6.5 within 8' and {insert some complicated spec re light distribution outside the central 8' here} would count as a 'star'.

And we haven't even started to explore the variation between individuals of species Homo sap. ...

But I have a related question - how many nebulae are visible to the naked eye (same conditions as in the OP)?

Now for the real kicker ... setting your criteria as unambiguously as possible (and that means being quantitative), for as apparently a straight-forward question as this, is a very, very important part of the doing of astronomy (pedantry has its rewards :razz: ).

[Fr. Wayne]

winter time in the mohave is darkest I know. I just came from there. Not too much humidity either. As for variables at max but not at min I'd say 45 more than aren't visible at minimum. As for nebula? about 50 of the Messier objects (just under half and very determined by the visual capacities of observer to see with averted sight). Can anyone see any IC or NCG objects? I use Mizar, its 14" companion and Alcor as a test for separating doubles. So anything near 14" separation is totally exceptional for a human being. So maybe 100 more at best?

[cjl]

The darkest I've ever seen is in the mountains in Colorado (it's darn close about 11000 feet up Mauna Kea though). Both of those locations are easily dark enough to see mag. 6-6.5, and 7 is visible in some cases, largely depending on whether the moon is out or not.

[Fr. Wayne]

The darkest I've ever seen is in the mountains in Colorado (it's darn close about 11000 feet up Mauna Kea though). Both of those locations are easily dark enough to see mag. 6-6.5, and 7 is visible in some cases, largely depending on whether the moon is out or not.

truly better site but frickin freezin up there- in desert it's 50 degrees minimum and no wind.

[astromark]

On the back of the Moon. Away from the Earth shine. Thats the place for the best dark sky sight. Darkness lasts for...is it 12 days a month. No clouds. No lights. No pollution. No kids......

[Eroica]

Which leads to ... what's the place on Earth with the 'darkest' night sky? What for each hemisphere?
I'm gonna guess Mount Everest and Aconcagua! :)

[Nereid]

winter time in the mohave is darkest I know. I just came from there. Not too much humidity either. As for variables at max but not at min I'd say 45 more than aren't visible at minimum.The GCVS (http://www.sai.msu.su/gcvs/gcvs/) has approx 38k designated variables, of which approx 2000 have (listed) maxima brighter than 7, and ~1500 of these have minima brighter than 6.5.

Approx 130 would clearly count as 'must consider how to count in any list if stars visible to the unaided-eye' (max <6.5, min >7), and another ~200 would be marginal. In addition, there are some 60 or so (non-recurrent) novae and
supernovae.

Doesn't affect the number (8400, 9100, about 10,000, ...) much, but combined with discussion on whether the faintest is 6.5 or 7, and the trend evident in Fr. Wayne's data, you can see how just a small change in definition can produce a big change in 'the answer', because the fainter you go, the more stars there are (or, a little more accurately, for each extra magnitude, the number of stars now added is more than the previous total of all stars).
As for nebula? about 50 of the Messier objects (just under half and very determined by the visual capacities of observer to see with averted sight). Can anyone see any IC or NCG objects?Well, there are the two 'biggies' - the Magellanic Clouds (but they have 'nebulae' within them, do they count separately?).

The southern hemisphere is a good place to 'cheat' wrt Messier objects, NGC5139 (http://www.seds.org/~spider/Spider/MWGC/n5139.html) (aka OmegaCen), and NGC104 (http://www.seds.org/messier/xtra/ngc/n0104.html) (47Tuc) are just two examples. (do these two count as 'stars'? or are they clearly extended objects, to the unaided eye?).

And how do we 'count' the Milky Way, in terms of 'nebulae'? And what of 'dark nebulae (such as the Coalsack (http://www.seds.org/messier/xtra/ngc/coalsack.html))?

[Fr. Wayne]

Your updated material on variables is I'm sure better. It is fascinating to think about your many questions and I will ponder them more. Let's assume that 6.0 is a good border (there will always be exceptions). Once a star/nebula is 6.0 or fainter then to most observers what they are looking at is questionable, let us say. So my question is now how many natural objects in the night sky can the average human being count if they had the time and location to map it all out themselves? My preliminary estimate is 2500 MAX. (including nebula of all sizes, variables that even temporarily are visible, and binaries with at least 14" separation (Using MizarB as standard) (side note: under 5.0 is less than 900 total- rounded off to avoid nit-picking)

[ToSeek]

http://www.sciencecartoonsplus.com/gallery/astronomy/astron16.gif

[Celestial Mechanic]

http://www.sciencecartoonsplus.com/gallery/astronomy/astron16.gif

They had to count them all,
Now they know how many shine down on the Albert Hall.
:)

[farmerjumperdon]

I believe it's:

Now they know how many stars it takes to fill the Albert Hall,
I'd love to turn you on . . .

Woke up, fell out of bed, dragged a comb across my head, . . .