Slashdot Mirror
"Perfect" Mirrors Cast For LSST
eldavojohn writes "The Large Synoptic Survey Telescope (which was partially funded by Gates & Co.) announced a world record casting for its single-piece primary and tertiary mirror blanks, cast at the University of Arizona. From the announcement: 'The Mirror Lab team opened the furnace for a close-up look at the cooled 51,900-pound mirror blank, which consists of an outer 27.5-foot diameter (8.4-meter) primary mirror and an inner 16.5-foot (5-meter) third mirror cast in one mold. It is the first time a combined primary and tertiary mirror has been produced on such a large scale.'"
asdf
Here's hoping that when they grind it, they account for gravity in the calculations.
grind it
don't mind it
figure it
Right value does it good
Apparently it was so awesome, they just skipped the secondary mirror and went straight to tertiary. :)
Man microsoft is trying to monopolize science. Fuck micro$oft and their evil ways. I hope Bill and Melinda Gates get brutally murdered tonight!
Let's hope the grinding is more accurate than the Hubble mirror.
http://www.newscientist.com/article/mg12717301.000-the-testing-error-that-led-to-hubble-mirror-fiasco-.html
If I had an Ass, I'd call it Fanny Bottom, then I could slap my Ass; Fanny Bottom, on the Arse.
Since the University of Arizona was made in China, I don't think USians can take credit for this one.
Kongratulations
That is da hoojest. I remember when the 200 inch Hale was the largest optical.
Holeey Frijkin haooY00j !!!
Kongratulations!
--Shaddup and support your local PBS station Plan for it
... perfection is only a limitation of the measurement process used to find flaws.
The last time I heard that we were talking about the mirrors for the Hubble.
community at FUCKING USELEES 3 simPle steps! Fly They looked
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I'm confused- I thought mirror arrays were far superior at least in part because they don't have sagging problems and can correct on the fly for atmospheric disturbances by actuating the segments of the mirror. It certainly is a hell of a lot cheaper; U Texas did it for one third the cost of this thing, and theirs is almost a meter larger in "effective" diameter.
In fact, there are 7 or 8 telescopes larger than this, and eleven if you widen it to "larger or equal to".
Obviously, they wouldn't have done something like this if it was inferior, unless this was just for PR/bragging rights. So, why? Is the image quality inferior?
Please help metamoderate.
how it was supposed in any way related lay down paper TRYING TO DISSECT
Science is metric you banana heads! What the hell is 51900 pounds in real money?
A mirror big enough for RMS, now if only we could get him to look into it each morning...
-- Sex is the antonym of pringles. Once you pop it's time to stop.
but the summary did say that Microsoft money (via a level of indirection) was involved, so "good enough" is in its genes.
"National Security is the chief cause of national insecurity." - Celine's First Law
so what happens when the site gets /.ed?
Microsoft products aren't worth buying until they get to the third release. So they just skipped straight to #3 this time.
Weaselmancer
rediculous.
i am sure Billy G was glad it wasn't a giant, perfect window!
I wonder how much that mirror will expand and contract with temperature changes. They would surely have to factor it in. Oh well, I guess they can always cut an expansion joint across the middle if it looks like cracking. :)
Why is the tertiary mirror larger than the secondary? That's not like any telescope that I'm familiar with.
Never shake hands with a man you meet in a fertility clinic.
The digital camera in this thing generates 15TB of data a day from its 3200megapixel camera. I'm assuming it has an array of sensors, but thats still a ridiculous amazing pixel count.
I am an astronomer at the UA and the mirror is a major feat of engineering. It will be the first telescope to have the tertiary and the primary mirror on the same piece of glass. They will have to grind both parts to be perfectly aligned (point to the same place) as well as make the transition area as small as possible. The secondary mirror is a doughnut shape that will be placed above the primary and will have the $100M camera behind it. The camera itself will be the size of a small car and will be as stated before a 3.2 Gigapixel ccd. It will have 200+ 4k by 4k CCD chips that will be read out in 2 seconds. This coupled with the fact it will image the night sky in 5 colors every week will lead to petabytes of data by the programs terminus. Its basically the coolest telescope that will ever be built. ESPECIALLY since the data is set to be public (for US residents) the moment it is processed each morning.
...all the ants on the planet screamed out in horror at the same time, then suddenly went silent.
"perfect" is a malleable term for "flawless within the constraints and granularity of one's ability to measure". It may be perfect on the molecular level, and on the atomic, but ... some of thoze particalzorz haz a deviant spin!!
Do not mock my vision of impractical footwear
Casting 8-meter-class blanks simply isn't that uncommon any more. The Large Binocular Telescope has a pair of 8.4-meter primaries; Subaru has an 8.3-meter; VLT has four 8.2-meter, Gemini North and South each have an 8.1-meter. Oh, and the Giant Magellan Telescope is planned to have seven 8.4-meter mirrors.
The LSST is unusual in that its light path is more "folded", hitting 3 mirror surfaces on the way to its primary camera, which means that relatively run-of-the-mill 8-meter-class blank has to be ground pretty uniquely. (And I wish them the best of luck with the process.)
Also, its secondary mirror is absofreakinglutely huge, at 5 meters. To put this in context, just ten years ago there was only one operational telescope in the whole world with a primary mirror larger than 5 meters.
And f/1.25 is crazy fast, yes. The newest, fastest survey scopes out there right now are VISTA at f/3.25 and Pan-STARRS PS1 at f/4. SDSS is f/5, and VLT is f/5.5.
So there you have it - what's really cool about LSST, from a guy who drives a boring old f/10 2.2-meter. ;)
51,900-pound mirror blank, which consists of an outer 27.5-foot diameter (8.4-meter) primary mirror and an inner 16.5-foot (5-meter) third mirror cast in one mold
I have no idea what that means, but I want one anyway.
Can someone explain why a mirror this size has to weight 25 tons? Aren't there lighter materials that could be used to support the mirrors surface?
Is your "f" notation here the same thing as for cameras? I'm used to SLRs, where "f" denotes the f-stop, the size of the lens aperture versus the focal length, with smaller numbers meaning a wider aperture, resulting in a greatly reduced depth of field (i.e., you have to be a lot more careful about focusing correctly), but also more light coming through and therefore shorter exposure times. Is this what you mean by "fast"? And why is this important? Does it allow for imaging of darker objects?
Curious,
"What in the name of Fats Waller is that?"
"A four-foot prune."
Yes, it's the same. A shorter focal ratio ("fast") allows for a larger field of view with the same size CCD-chip. The "side-effect" of this is that a larger bit of sky falls onto the individual pixels, which means you sacrifice resolving power for sensitivity.
I scrolled through these comments without finding a single "Real Genius" reference of question about using the mirror for making popcorn. For shame, slashdotters, for shame!
SJW: Someone who has run out of real oppression, and has to fake it.