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Sometimes, Size is Everything! (that new 39-meter European telescope)
Starts with a Bang ^ | 6/12/12 | Ethan Siegel

Posted on 06/13/2012 9:56:39 PM PDT by LibWhacker

“I went into a clothing store, and the lady asked me what size I was. I said, ‘Actual’. I’m not to scale.” -Demitri Martin

When you look out at the Universe, what you can see is limited, at the most fundamental level, by the size of what you look with. This is why you can see dimmer objects at night — when your pupils are dilated — than you can when your pupils are constricted.

Dilated Eyes

Image credit: National Institute of Health.

This same principle that applies to your eyes applies to telescopes as well. As telescopes have grown in size, so has our ability to see deeper into the Universe, as we can collect more light and view dimmer, fainter objects. Things that would have appeared imperceptible to us with less sophisticated equipment suddenly explode into view, brilliant and distinct.

A tiny area of the Milky Way



An even smaller area

Images credit: Mike Read (WFAU), UKIDSS/GPS and VVV, from VISTA.

In fact, as a consequence of telescopes getting larger, we can not only see deeper and farther, we can also see with higher resolution! These dim objects not only become visible to us, they also come into focus.

Binary Star Resolution

Image credit: Nick Stroebel, retrieved from Robert W. O'Connell's site.

The reason for this? Astronomically, the resolution you can see with is determined by how many wavelengths of the light you’re looking at can fit across your telescope! Scientifically, this is known as the Rayleigh Criterion, and it basically tells you that every time you double the diameter of your telescope, you not only quadruple your light-gathering power, you also double your resolving power.

Or, if you want to double your resolving power without building a telescope twice as large, you can look at shorter wavelengths of light!

Herschel 3 wavelengths.

Image credit: ESA / Herschel and the PACS consortium.

The shorter the wavelength of your light, the tinier the imperfections in your surface are allowed to be. For a gamma-ray telescope, the highest quality optics are demanded, while with a radio telescope, tremendous dishes (or arrays of dishes) are required to obtain even modest resolution, but the optical quality can be fairly lax. If the size of your telescope is fixed, wavelength is everything for determining resolution.

Wavelength is Everything

Image credit: NASA / JWST science team.

But if you’re determined to use a particular wavelength of light, then the converse is true: size is everything. For human beings, we’ve used visible light for far longer than we’ve had telescopes, and so that has a fixed wavelength. You want to get better at it? You build a bigger telescope. And for some time, that’s been exactly what we’ve been doing.

James Webb and Hubble Primary mirrors

Image credit: NASA, with the 2.4-meter diameter HST mirror and JWST's segmented 6.5-meter diameter optics.

While space has been the best environment for achieving these maximal resolutions, recent advances have allowed ground-based telescopes, despite having to contend with atmospheric distortion, to catch up. Most recently the 8-meter, ground-based Gemini Telescope has revolutionized adaptive optics so significantly that, for the first time, a ground based telescope has defeated the optical resolution of Hubble!

Hubble image of NGC 288.



Gemini image of NGC 288

Images credit: NASA / HST and Gemini Observatory / NSF / AURA / CONICYT / GeMS / GSAOI.

Well, if size is everything for optical resolution, the largest telescopes in the world — the 10-meter class giants — are about to have their hats handed to them. A new record-breaker, or I should say record-demolisher, was just approved by the European Southern Observatory consortium.

And, I promise you, you’ve never seen anything like it.

Construction of the E-ELT

Image credit: ESO / L. Calçada.

Sure, it may look like any giant, isolated telescope on the top of a high desert mountain, where the air is thin and rarefied, the skies are clear, and light pollution is virtually nil. But looks can be deceiving; this telescope is unique in all the world.

Artist's impression of the E-ELT.

Image credit: ESO / L. Calçada.

You’ve never seen this before: an observatory that’s literally the size of a football stadium! (Or, equivalently, a fútbol stadium.) But it’s the telescope inside — with a set of primary optics nearly 40 meters in diameter — that shatters all the records. Unlike Hubble’s single mirror, which is a bit larger than a human, or James Webb’s segmented design, with a honeycomb of 18 human-sized mirrors, this new telescope features a primary mirror made of 798 segments, each 1.4 meters across.

A reconstruction of the ESO's E-ELT.

Image credit: ESO / L. Calçada.

For a cost of just over 1 billion Euros (it is an ESO project, after all), the European Extremely Large Telescope (E-ELT) will become the world’s largest eye on the sky. How much larger and how much more power will it have? In fact, the E-ELT will gather more light than all of the existing 8–10-metre class telescopes on the planet, combined.

But the first thing to be built won’t be even one of these giant segments; the first thing to begin construction will be the adaptive optics system; one of the most challenging bits. Remember how adaptive optics works?

You take what you see through the atmosphere — distortions and all — and, by focusing in on a “guide star” (or series of guide stars) whose properties are known, you build an “adaptive mirror” that literally un-blurs the image for you!

But how do you make a fluid-like mirror that can adapt in real-time to the changing atmospheric distortions? It isn’t that the mirror itself is fluid, it’s that it’s thin enough that it can be mounted on an electronically-adaptive system!

Adaptive Optics for E-ELT

Image credit: Microgate / ADS / ESO.

The flat mirror that rests upon this apparatus will be about 2.5 metres in diameter but just 2 millimetres thick, allowing it to be deformed like a flexible film. More than five thousand voice-coil actuators will flex the shape of the reflecting surface of the mirror up to a thousand times per second, precisely canceling out the distorting effect of the atmosphere. (See here for more details.)

M4 mirror; the adaptive optics system of the E-ELT

Image credit: Microgate / ADS / ESO.

The result is an adaptive mirror that gives us a final image that’s comparable to what we’d get from a space telescope, except getting a 40-meter-diameter telescope in space is a pipe dream at this point!

While a whole slew of revolutionary science will come out of this, including measurement of the first stars, the earliest galaxies, and unprecedented high-resolution imaging of pretty much anything you can imagine, the biggest victory will go to those on the hunt for exoplanets. Because with this new E-ELT, we’ll be able to directly image exoplanets as small as Earth around stars many hundreds of light-years away.

Artist's impression of Gliese 667C

Image credit: Artist's impression of Gliese 667C, ESO/L. Calçada

In just a generation, we’ll go from knowing just one star with exoplanets around it to direct imaging of thousands of Earth-sized (and possibly Earth-like) worlds around distant stars.

This is why we invest in science; this is what we can achieve.



TOPICS: Astronomy; Science
KEYWORDS: 39meter; eelt; european; telescope

1 posted on 06/13/2012 9:56:52 PM PDT by LibWhacker
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To: Lx; Verginius Rufus; Paradox; cripplecreek; Jonty30; BitWielder1; 21stCenturion; ...

Pinging Freepers who made substantive comments on the earlier thread about this telescope and who appeared to be genuinely interested in it. Don’t worry if you do not want to be pinged by me. This is only the second time I’ve done a group ping (small groups both times) in 15 years and it’s not likely to happen again. I just couldn’t resist this time, this article is so much fun! :-)


2 posted on 06/13/2012 10:05:42 PM PDT by LibWhacker
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To: LibWhacker

I.
Am.
Stunned.
!


3 posted on 06/13/2012 10:11:45 PM PDT by sauron ("Truth is hate to those who hate Truth" --unknown)
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To: LibWhacker

I.
Am.
Stunned.
!


4 posted on 06/13/2012 10:12:52 PM PDT by sauron ("Truth is hate to those who hate Truth" --unknown)
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To: LibWhacker

I love this stuff, thank you.


5 posted on 06/13/2012 10:15:53 PM PDT by Jonty30 (What Islam and secularism have in common is that they are both death cults.)
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To: LibWhacker

When I was a Boy Scout, I had a rare opportunity to visit the Palomar Observatory and spent a chilly night helping to take photos through the 200 inch; and like many in Southern California, I’ve been to the 100 inch at Mt. Wilson. I’m still amazed at the science behind observatories like the CHARA array, but this one goes that extra mile.. Adaptive reflectors have very long been the holy grail of reflective telescopes.

An adaptive field that big - wow, it is amazing. I remember some experiments in using liquids as an adaptive surface, but the reaction times were just too slow, or it created new problems in dealing with heat waves from the liquid.

But a billion dollars?? There’s some serious skimming in there for over-inflated salaries.

There’s a lot of very dedicated people out there - heck, Mt. Wilson’s Solar Telescope still draws sunspot activity by hand each day.


6 posted on 06/13/2012 10:27:02 PM PDT by kingu (Everything starts with slashing the size and scope of the federal government.)
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To: kingu
But a billion dollars??

Euros, actually. Does seem steep. But still, small government guy that I am, I nevertheless want us (Americans) to build something better and more powerful, even if it costs more.

For instance, I'd LOVE to see us build a space-based optical interferometer, perhaps a few million miles across. But still doable with today's technology, not too expensive and serviceable. With such a telescope, iirc, we'd not only be able to image small planets out to several hundred light years, but rivers, lakes, forests and perhaps, animals, if those things exist that close to us.

7 posted on 06/13/2012 10:59:42 PM PDT by LibWhacker
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To: LibWhacker

My former girlfriend complained about the size of my telescope. Said it wasn’t big enough to explore the black hole.


8 posted on 06/13/2012 11:08:03 PM PDT by fieldmarshaldj (If you like lying Socialist dirtbags, you'll love Slick Willard)
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To: fieldmarshaldj

Oh, stop. You’re just trying to get on my next ping list. ;-)


9 posted on 06/13/2012 11:31:21 PM PDT by LibWhacker
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To: LibWhacker

Remember when we (the US) used to do stuff like this (build the best and biggest of everything)?


10 posted on 06/13/2012 11:32:14 PM PDT by aquila48
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To: aquila48

I do, indeed. Zero’s made us second rate in science overnight. Next to follow will be economic and military might.


11 posted on 06/13/2012 11:35:58 PM PDT by LibWhacker
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To: LibWhacker

“European Extremely Large Telescope”
That’s nothing compared to the Overwhelmingly Large Telescope:
http://en.wikipedia.org/wiki/Overwhelmingly_Large_Telescope


12 posted on 06/13/2012 11:39:36 PM PDT by Born to Conserve
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To: LibWhacker

Amazing. Add me to the list please.


13 posted on 06/13/2012 11:40:13 PM PDT by spetznaz (Nuclear-tipped Ballistic Missiles: The Ultimate Phallic Symbol)
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To: Born to Conserve

Wow, thx. Hadn’t heard of OWL.


14 posted on 06/13/2012 11:47:42 PM PDT by LibWhacker
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To: spetznaz

Hi, spetz... Sorry, I would be happy to add you if there were one. But this was only a temporary one-off deal.


15 posted on 06/13/2012 11:51:24 PM PDT by LibWhacker
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To: LibWhacker

Great post! Reminds me of a question on optics I had giving the optical dimensions of a camera. I had to figure out at what distance would you be able to determine that a blip in the distance was actually the 2 headlights of a car coming towards you. I actually measured the distance between the headlights on my car. Cool stuff with them Airy disks!


16 posted on 06/14/2012 12:20:38 AM PDT by gr8eman (Ron Swanson for President!)
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To: LibWhacker

“For instance, I’d LOVE to see us build a space-based optical interferometer, perhaps a few million miles across. But still doable with today’s technology, not too expensive and serviceable. With such a telescope, iirc, we’d not only be able to image small planets out to several hundred light years, but rivers, lakes, forests and perhaps, animals, if those things exist that close to us.”

Yep, send one telescope in one direction, send another in another direction and combine the imaging power of both together. Depending on how far you send them away - lol, you could image absolutely everything. ;)


17 posted on 06/14/2012 12:21:05 AM PDT by JCBreckenridge (Texas, Texas, Whisky)
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To: LibWhacker

The NIH images showing the operation of the dilated and undilated eye are incorrect.


18 posted on 06/14/2012 12:26:32 AM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: gr8eman
Cool stuff with them Airy disks!

On the Hubble, I think you need to call them vacuumy disks.

19 posted on 06/14/2012 12:44:52 AM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: Erasmus

How so?


20 posted on 06/14/2012 1:25:38 AM PDT by D-fendr (Deus non alligatur sacramentis sed nos alligamur.)
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To: aquila48
We actually did build one, and then two telescopes very much like this. Known now as the Keck telescopes at Muana Kea, they were designed at UC’s Lawrence Berkeley Lab, using the same stressed mirror technology. The Keck design is composed of 36 two meter segments, along with the active support mechanism which we called a “whiffletree” for what reason I don't recall.

Our problem was money, until the principle scientist, Jerry Nelson, whose alma mater was Cal Tech, found money from the Keck family. Polishing a mirror that large is a major problem because there are few vacuum chambers large enough to contain the 2 meter honeycombed structures. Vacuum chambers are necessary because measuring to enable the smoothing of the hills and valleys of the surface within less than a wavelength at the designed wavelength is done with laser interferometers, and normal air currents mean differences in temperature and pressure sufficient to diffract the laser to and from the mirror. Money allowed Jerry to farm the polishing out to a world famous optics house. That is probably why this new device uses 1.4 meter rather than 2 or more meter mirrors.

Bottom line: this instrument will be a wonderful tool, but it is a derivative design. Adaptive mirrors are fascinating, and have been used for more than fifty years in military optics long before the Keck became a reality, though some of the physicists and engineers at LBL had developed some earlier adaptive optic technology for use at the Lick Observatory and on at least one orbiting telescope. We used PDP-11’s for the adaptive focus elements on the “Ten Meter Telescope” - later named Keck. The difference today will be the advantage of faster processors and improved optical sensors. It is very doable, and I hope funding is a reality. These days it is not easy to justify a larger anything that does not generate revenue or promise employment except for a few dozen scientists and as many engineers and technicians.

21 posted on 06/14/2012 1:33:01 AM PDT by Spaulding
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To: LibWhacker

Wow. Able to directly image planets light years away....

Now, that beggars the question. If we, with 21st century equipment can now look directly at a planet, what can an advanced alien society do, say one that is just slightly ahead of us?


22 posted on 06/14/2012 1:48:52 AM PDT by Molon Labbie (Prep. Now. Live Healthy, take your Shooting Iron daily.)
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To: JCBreckenridge

An asteroid belt array should do it for now.

Then an Ort cloud array.


23 posted on 06/14/2012 3:29:26 AM PDT by cripplecreek (What does it profit a man if he gains the whole world but loses his soul?)
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To: LibWhacker
Photobucket
24 posted on 06/14/2012 3:30:43 AM PDT by cripplecreek (What does it profit a man if he gains the whole world but loses his soul?)
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To: Molon Labbie

Precisely! Also, the average star out there is one to two billion years older than the Sun. So, all other things being equal, the average technological civilization may be one to two billion years ahead of us. What can they do? And from how far away can they do it?


25 posted on 06/14/2012 5:09:00 AM PDT by LibWhacker
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To: LibWhacker

So many questions...Is the universe so vast that we have escaped notice for so long or are we truly alone, or (allow me a moment of grandeur) are WE, mandated by God, to “be fruitful and multiply” and the universe is ours to populate?


26 posted on 06/14/2012 5:58:41 AM PDT by Molon Labbie (Prep. Now. Live Healthy, take your Shooting Iron daily.)
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To: LibWhacker; kingu
Thanks for the ping LW.

But a billion dollars??

Well, that does include a mountain in Chile!

27 posted on 06/14/2012 6:20:51 AM PDT by Moltke (Always retaliate first.)
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To: fieldmarshaldj

oh my gosh. Can’t believe you would go there.

Well, we are often told that size doesn’t matter..............


28 posted on 06/14/2012 7:36:41 AM PDT by Dilbert San Diego
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To: D-fendr

The diagram shows the larger pupil (aperture) spreading the light out to a larger area of the retina, which is incorrect.

Instead, the light from the originating point gets focussed (ideally) to a point on the retina regardless of the pupil size.

It is the size of the base of the two light cones that meet at the pupil (one from the point on the object, the other to the point on the retina) that varies with pupil size, and thereby determines how much light reaches the point on the retina.


29 posted on 06/14/2012 7:54:55 AM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: D-fendr
After thinking about it, the diagram may not be technically incorrect for what it is, but it is not an illustration of how a larger pupil gathers more light for an image focussed on the retina.
30 posted on 06/14/2012 8:01:44 AM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: Molon Labbie
I hope it's the latter, though that may just as dangerous for us. Today, we can't even get along with humans who live a mere 12,000 miles away from us. How can we expect to see eye-to-eye with the descendants of human beings that we've had no contact with and who have been evolving in isolation from us, and us from them, for millions of years, and live halfway across the galaxy from us?

I read an interesting article on relativistic weapons a while back. A relativistic weapon is any kind of payload you can accelerate up to relativistic speeds, say 90% the speed of light. It could be a dense titanium rod the size of a telephone pole, a large ship, an asteroid, etc. The point is, once you can do that; i.e., once you become a space-faring civilization, you instantly become an immediate existential threat to any civilization within a few hundred light years of you, and they may decide to attack you first before you can attack them.

That's because a ten-pound dumbbell traveling at 90% the speed of light would deliver the same amount of energy to a target as a 200-megaton hydrogen bomb, much bigger than "Tsar Bomba." IIRC, a titanium telephone pole weighing a few tons would wipe out all life on earth, and an iron asteroid a hundred or two hundred meters across would melt the planet right down to the core, no warheads needed.

So, as soon as we get close to accomplishing interstellar flight, we may find ourselves the object of a vicious, unprovoked attack from out of the blue. And guess what? Relatively speaking, we are close.

31 posted on 06/14/2012 9:07:35 AM PDT by LibWhacker
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To: LibWhacker

I can do that with the + symbol on my picture viewer!


32 posted on 06/14/2012 9:26:44 AM PDT by US_MilitaryRules (Unnngh! To many PDS people!)
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To: US_MilitaryRules
Sure ya' can. Kind of like this?


33 posted on 06/14/2012 9:34:14 AM PDT by LibWhacker
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To: LibWhacker

LOL


34 posted on 06/14/2012 10:22:52 AM PDT by US_MilitaryRules (Unnngh! To many PDS people!)
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To: Dilbert San Diego; LibWhacker

Hey, I told her she didn’t complain about the size when I used it to explore Uranus.


35 posted on 06/14/2012 11:39:06 AM PDT by fieldmarshaldj (If you like lying Socialist dirtbags, you'll love Slick Willard)
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To: Erasmus
Thanks. I was thinking of using some of this information in a class and very much appreciate your reply. Here's the graphic:

It does seem to be leaving off the lens part, the focusing, thus:

But I *think* this illustrates that light reflected at different angles - from the same subject point - are bent to hit the same point on the focal plane.

But this happens for every point of the subject and across the area of the sensor/retina:

So I think the article graphic is saying a larger pupil/aperture results in a larger image on the retina, more data points or information.

As you say, it is obvious that a larger opening allows more light, but the article graphic is about another variable, retina area.

I'm not at all sure about this, I looked twice at the graphic also. Appreciate your response or anyone else who cares to weigh in.

thanks again.

36 posted on 06/14/2012 11:56:39 AM PDT by D-fendr (Deus non alligatur sacramentis sed nos alligamur.)
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To: D-fendr
In regard to the second image, your surmise is correct. It goes hand-in-hand with my previous verbal description. Just imagine the lens being of varying diameter, but the same focal length. The rays emanating from a single point on the subject (at left) which make it through the lens will then converge on the single corresponding point on the image plane.

It's just a matter of how wide a cone of rays--how many rays--radiating from a given point on the image will make it through the aperture; this is determined of course by the area of said aperture.

The third image shows a single ray from each of two points on the subject (namely, the one in each case which passes through the center of the lens) and finds its way, along with others not shown, to the corresponding point on the image plane. Because the particular rays shown pass through the center of the lens, their path is not disturbed by it; a pinhole would work the same.

Now as to your conjecture that "a larger pupil/aperture results in a larger image on the retina," it doesn't do that. If the lens were just a blank hole of varying size (which the original illustraton essentially shows), you'd get more light from a larger hole but it would just be a blob on the retina. Reduce the size of the hole and you get less light but also the beginnings of an image, until you get to a very small aperture where you have a dim image being produced by a pinhole.

With a lens there, however, you get a focussed image regardless of the size of the aperture; a larger aperture doesn't change the size or magnification of the image, just its brightness.

Of course, aperture size does affect the range of distances that are essentially in focus (called "depth of field), but that's a different can o'"worms.

37 posted on 06/14/2012 6:03:04 PM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: LibWhacker

Here’s something cute to think about.

Consider that particular star out there, twinkling in the sky. It’s a few quadrillion to a quintillion miles from your eyeball.

Imagine that it’s sending visible photons evenly distributed onto a hypothetical sphere a quintillion miles in radius. How many square millimeters of area does that sphere possess?

Now, your eye’s pupil happens to be on the surface of that sphere. How many sqare millimeters is that?

The ratio of those two numbers is the fraction of visible photons that your eye is collecting from that star. And yet that fraction of its total output still amounts to a few hundred or a few thousand photons every second.

Now multiply that, oh, thousand photons per second by the ratio of the area of that big sphere to the area of your pupil.

To paraphrase Winston Zeddimore, “Tha’s a big number.”


38 posted on 06/14/2012 6:12:55 PM PDT by Erasmus (BHO: New supreme leader of the homey rollin' empire.)
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To: kingu
But a billion dollars?? There’s some serious skimming in there for over-inflated salaries.

The James Webb scope will be at least 8 times worse.

39 posted on 06/14/2012 6:21:13 PM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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