What can be seen with the unaided eye

[tdvance]

Not sure the best fit for this topic (Astronomy? Observations? Maybe even a question?)---but Bad Astronomy did have a chapter on seeing stars in the daytime, so...

in my local astronomy club meeting, two members claimed that many times, they have let a child look at Jupiter and its array of moons in their telescopes, only to have them look out at the sky and say, "so, why are the moons going the other way in the scope from what they are in the sky?"

Now, I know children see better than adults, usually, but it still sounded fantastic enough that, though I do not doubt the club members at all, I thought perhaps several children decided to play a prank on the amateur astronomers.

So, I mentioned it to a mathematician who was interested in stargazing since childhood, and he said, "no, it's not a prank. *I* used to be able to see the moons of Jupiter with the naked eye!"

Ok, that is amazing and noteworthy--it seems human beings with good eyes can see Jupiter without the aid of a telescope. I have to admit, it's the glare of Jupiter, not the dimness of the moons, that is the problem with seeing the moons. Children probably have good lenses in their eyes so the glare is not amplified and distorted so much.

That then brings the question--why did we not know of Jupiter's moons before Gallileo? The mathematician and I talked about it for a minute and decided that the children assumed they were stars, nothing was actually recorded, and if they said anything to the adults, the adults didn't find anything worth recording and checking up on at later times.

But still, this can be added to the list of things a society without a telescope could discover (along with Uranus, a few galaxies and globular clusters without knowing what they are exactly, and so on).

Now, the mathematician said, "think anybody could see the rings of Saturn without a telescope?"

My guess would be, no. Even in my 9x63 binoculars, which clearly show the four brightest moons of Jupiter, all I get is a slight elongation of Saturn with no gap between ring and planet. At best, perhaps children thought Saturn egg shaped at one time, I figure.

Todd

[Ronald Brak]

I think the asteroid Ceres can have a magnitude as high as 7 so is it possible for someone with keen eyes to spot it? Or is seven magnitude too faint even for a young person with excellent eyes?

Going the other way, there are cells that can be seen with the naked eye, so I imagine cell theory could have come about sooner than it did.

[tdvance]

I think the asteroid Ceres can have a magnitude as high as 7 so is it possible for someone with keen eyes to spot it? Or is seven magnitude too faint even for a young person with excellent eyes?

Going the other way, there are cells that can be seen with the naked eye, so I imagine cell theory could have come about sooner than it did.

Magnitude 7 is theoretically visible with good eyes under very good conditions. In fact, Sky and Telescope had this article about light pollution that dealt with limiting magnitudes:

http://skyandtelescope.com/printable...article_84.asp

If Ceres were noticed by ancients, it would probably be a planet today!

Todd

[Ronald Brak]

I know that short sighted people can sometimes see details close up that normal sighted people would need a magnifying glass to see, so I wonder if some long sighted people have the opposite ability? (Although I'm not talking about longsightedness that naturally comes with age.)

[01101001]

I know that short sighted people can sometimes see details close up that normal sighted people would need a magnifying glass to see, so I wonder if some long sighted people have the opposite ability?

Well, some people have better than average acuity at distance, like 20/15 -- around the best possible for a human -- instead of "normal" 20/20 (6/6 metric) and near-sighted, say, 20/40. Other than that, they don't have, like, telescope eyes, able to gather way-above-average extra light.

(Although I'm not talking about longsightedness that naturally comes with age.)

Presbyopia, not a misfocusing of things like near- and far-sightedness, is the inability to alter focus and isn't necessarily far-sight.

[ToSeek]

Moved from "Bad Astronomy: the Book" to "Q&A" in the hopes of broadening the discussion.

[antoniseb]

I think the asteroid Ceres can have a magnitude as high as 7 so is it possible for someone with keen eyes to spot it?

I have the impression that Vesta can be seen on some occasions at 5.5 or there abouts. I'll have to look it up, but I recall it from some old Sky&Telescope articles.

[aurora]

It would have been possible for the ancients to have noticed that Uranus is a planet, but they never did.

[mugaliens]

While it may have been possible for children to see Jupiter's moons, there's no way they'd have detected planetary motion.

Their attention span isn't long enough!

[tdvance]

Other than that, they don't have, like, telescope eyes, able to gather way-above-average extra light.

Definitely nothing like what even a mediocre pair of binoculars can gather. But--I do remember reading that an iris can expand up to 9mm for a young person with good eyes, but for most people, the limit is closer to 7mm. That does mean about 60% more light collected by the eyes, making the difference of a sizeable fraction of a magnitude. Combine that with a perfectly clear lens in the eye, and one that accomidates well (i.e. focusses properly)--that should reduce glare. So, it can be enough to make the difference for seeing the moons of Jupiter, or seperating Alcor from Mizar in the handle of the big dipper.

Actually, I think color vision in faint light is better for children--I seem to remember seeing more colors in stars then than now! (But I don't recall seeing the moons of Jupiter).

I wonder what a good pair of glasses can do to stargazing ability...right after getting the eye exam so the eyes don't have time to change from the prescription.

Todd

[Kaptain K]

As has been mentioned, the asteroid Vesta and the planet Uranus can reach naked eye visibility (when we were younger, my brother and I saw Uranus without optical aid).
There are reliable reports of people being able to see the cresent of Venus with the naked eye.
On a night of exceptional seeing, I once was able to count 11 stars in the Pleiades!

[Casus_belli]

In exceptional viewing conditions and far from any light pollution I once saw one of jupiters moons with the naked eye. When I checked with binoculars it was there. This was in 1984 or 85 near the Falklands so also well clear of any atmospheric pollution too.

Ive also seen (I persume) both Venus and Jupiter in broad daylight at the same time. This was in Dumferline in 1986 late summer/early autumn at about 2pm

[Romanus]

It is definitely possible to see Jupiter's moons--Ganymede and Callisto, anyway--with the naked eye. IIRC, there is at least one or two verifiable reports of seeing them unaided in the pre-telescopic era.

As to why they weren't known earlier, the answer is the same as that for why Uranus wasn't discovered long ago: it's difficult to see them. Children with keen eyesight are unlikely to take notice, and even if they do, who would've believed them in pre-telescopic days?

[Jens]

While it may have been possible for children to see Jupiter's moons, there's no way they'd have detected planetary motion.

Their attention span isn't long enough!

I was thinking the same thing first, but it's possible they meant something else. Like, "in the sky, there are two on the left side and just one on the right, but in the scope there are two on the right and one on the left." Otherwise, it's true, you can't see the movement.

[TheOncomingStorm]

Never seen jupiters moons with naked eye but seen andromeda a few times though.

[ozark1]

I think that the record for DSOs with the naked eye is M81 at 12 Mly. Its faint at 6.9 magnitude so you need a seriously dark sky and teenage vision.

[Nereid]

How far away could a supernova be seen, with the unaided eye?

On the one hand, at their brightest, supernovae reach the same magnitude as a big spiral galaxy, so if you could see M81, you could see a supernova at approx the same distance.

On the other hand, hypernovae and (maybe) GRBs can be (intrinsically) much, much brighter ...

[antoniseb]

sn1987a was visible to the unaided eye, but wasn't an especially bright star. It got to slightly better than 3rd magnitude. That was about 160,000 LY. If it were ten times as far away (say just this side of M31), it would be five magnitudes dimmer (not visible).

[BigDon]

I was thinking the same thing first, but it's possible they meant something else. Like, "in the sky, there are two on the left side and just one on the right, but in the scope there are two on the right and one on the left." Otherwise, it's true, you can't see the movement.

I was thinking the same thing Jens.

[Denis12]

How far away could a supernova be seen, with the unaided eye?

On the one hand, at their brightest, supernovae reach the same magnitude as a big spiral galaxy, so if you could see M81, you could see a supernova at approx the same distance.

On the other hand, hypernovae and (maybe) GRBs can be (intrinsically) much, much brighter ...

What are hypernovas and GRb,s?

[Nereid]

sn1987a was visible to the unaided eye, but wasn't an especially bright star. It got to slightly better than 3rd magnitude. That was about 160,000 LY. If it were ten times as far away (say just this side of M31), it would be five magnitudes dimmer (not visible).

Hmm ... a quick skim of A Comparative Study of the Absolute-Magnitude Distributions of Supernovae, by Dean Richardson, David Branch, Darrin Casebeer, Jennifer Millard, R. C. Thomas, and E. Baron, seems to show that the 1987 SMC SN was rather sub-luminous (M_B, the B band absolute magnitude, only ~-14), whereas Type 1a SN, the standard candles, it is at least 5 mags brighter (between -19 and -20). That suggests that a 'normal' SN would be easily visible in any galaxy in the Local Group (unless heavily obscured by dust), at its peak ... and that such SN would be barely visible if they were ~15 to 20 million light years away.

[Kaptain K]

What are hypernovas and GRb,s?

Some (many?) supernovae are not spherically symetrical. If the progenitor star is rotating rapidly, the supernove can blow out through the poles, resulting in narrowly focused jets. When seen from the axis of the jet, it is orders of magnitude brighter than it is off axis - a hypernova.

GRB = Gamma Ray Burst.

[John Mendenhall]

With respect to the crescent Venus, my oldest had very acute vision as a youngster. While casually observing Venus one evening, I thought to follow a Sky & Telescope suggestion and asked if he could see a crescent. He said "Yes, just barely." Next question was "Which way do the horns point?” followed by a quick trip inside to retrieve the latest issue of S&T and check the direction. He was right, and I don't think he had any knowledge beforehand that there even was such a thing as a crescent Venus.

[DaveC426913]

While it may have been possible for children to see Jupiter's moons, there's no way they'd have detected planetary motion.

Their attention span isn't long enough!

You can see obvious lunar motion around Jupiter in the space of 24 hours easily. You can theoretically see movement over the course of an hour.

[DaveC426913]

I confess, when I first got into astro, I was astonished at how "close" Jupiter and its moons are (to us). I spent much time trying to determine how "wide" the system is to the naked eye, and came to the conclusion that it is indeed large enough to be seen as separate entities.

The only reason why you can't see the moons with the naked eye is that they are a little too dim.

It never occurred to be though to take it one step further and deremine how much too dim, and whether someone with really good eyes could see htem.

[hhEb09'1]

It never occurred to be though to take it one step further and deremine how much too dim, and whether someone with really good eyes could see htem.

Aren't they about mag. 5, on a good night? So, maybe just walk them over to the edge of a building, so Jupiter's "glare" doesn't overpower them?

[Aries_7]

Going the other way, there are cells that can be seen with the naked eye, so I imagine cell theory could have come about sooner than it did.

WHICH CELLS CAN BE SEEN BY THE NAKED EYE?????

[Aries_7]

[QUOTE= Going the other way, there are cells that can be seen with the naked eye, so I imagine cell theory could have come about sooner than it did.[/QUOTE]

WHICH CELLS CAN BE SEEN BY THE NAKED EYE?????

[Noclevername]

The people who saw them would not have been able to identify them as cells, just really tiny moving things. The concept hadn't been invented yet.

[Amber Robot]

If Ceres were noticed by ancients, it would probably be a planet today!

Ceres was a planet for a while.