HDTenEightyP/NetNews huggingface dataset:
From: gold@imp.sim.es.com (Bruce Gold)
Subject: Re: Blueness
Organization: Evans & Sutherland Computer Corp., Salt Lake City, UT
Date: Thu, 28 Jan 1993 17:10:31 GMT

moroney@world.std.com (Michael Moroney) writes:
|> Water isn't blue. The ocean appears blue because it reflects the sky.
|> (look at it on a stormy day, it's gray)
|> 
There is a lake straddling the border of Utah and Idaho; Bear Lake.  It is
locally noted because it is intensely blue even on steel grey overcast days.
What Mike says may be generally true, but I'll bet Bear Lake isn't the only
exception around.
-- 
				Bruce Gold
				   Utah
From: steveo@mel.dbce.csiro.au (Stephen Oakes)
Newsgroups: alt.folklore.science
Subject: Why is the sky blue?
Date: 22 Jan 93 06:05:02 GMT
Organization: CSIRO, Div. Building Constr. and Eng'ing, Melb., Australia

Why does the sky appear blue?  I have heard that it is because water
particles (or perhaps "air particles") have a slightly bluish tinge.
More importantly, if it were not so, what would we see when we look
skywards?

--
| Stephen Oakes      CSIRO Division of Building, Construction and Engineering |
|                    Post Office Box 56, Highett, Victoria, Australia   3190  |
| Internet: steveo@mel.dbce.csiro.au  Tel: +61 3 252 6000 Fax: +61 3 252 6249 |
|_____________________________________________________________________________|
Newsgroups: alt.folklore.science
From: moroney@world.std.com (Michael Moroney)
Subject: Re: Blueness
Organization: The World Public Access UNIX, Brookline, MA
Date: Wed, 27 Jan 1993 23:09:14 GMT

Water isn't blue. The ocean appears blue because it reflects the sky.
(look at it on a stormy day, it's gray)

-Mike
From: anno4000@zrz.tu-berlin.de (Anno Siegel)
Newsgroups: alt.folklore.science
Subject: Re: Boneheads was Re: Tapping soft drink cans
Date: 27 Jan 1993 11:32:16 GMT
Organization: TUBerlin/ZRZ
NNTP-Posting-Host: w172zrz.zrz.tu-berlin.de

In article <C1Es0L.DAv@gabriel.keele.ac.uk> csa09@seq1.keele.ac.uk (Paul Singleton) writes:
[deletions]
>
>I believe you can decork a wine bottle (eventually) by banging the bottle
>base on e.g. the ground.  I saw (and heard :-) this attempted as a student.
>I got fed up with the hammering from the kitchen, investigated, and helped
>them out with a screwdriver.  The cork had crept out somewhat.  Another
                 ^^^^^^^^^^^
>half hour would have done it ...
>PS

Hmmm... Maybe a screwdriver provides a method of opening a wine bottle
superior to banging it to the ground. A cork screw wold have been even
more helpful.
-- 
Anno Siegel              siegel@zrz.tu-berlin.de
c/o TU-Berlin/ZRZ        s=siegel ou=zrz p=tu-berlin a=dbp c=de 
*** Disclaimer disclaiming to disclaim the usual disclaimer ***
Newsgroups: alt.folklore.science
From: baylor@NEBULA.SSD.LMSC.LOCKHEED.COM
Subject: Re: Another UL dies, plastic verus wood cutting boards.
Reply-To: baylor@NEBULA.SSD.LMSC.LOCKHEED.COM
Organization: LMSC, Sunnyvale, California
Date: Thu, 28 Jan 93 17:42:49 GMT

In article <1k7egfINNpcb@fido.asd.sgi.com>, jojo@sandman.asd.sgi.com (jojo Wesener) writes:
>I recently read a report on a study which came to the conclusion
>that wood cutting boards were better than plastic cutting boards.
>Studies using salmonella and other harmful bacteria showed that
>when the bacteria was left on wood boards overnight, the bacteria would
>die.  When the same bacteria was left on plastic boards overnight, the
>bacteria counts would increase.

Except that if you were concerned about cleanliness, you'd
wash the boards rather than let them set out overnight.
Dishwasher-safe plastic would be better than wood.
From: cucem@uxa.ecn.bgu.edu (Chad Mattingly)
Newsgroups: alt.folklore.science
Subject: Re: Boneheads was Re: Tapping soft drink cans
Date: 26 Jan 93 21:15:35 GMT
Organization: Educational Computing Network
NNTP-Posting-Host: uxa.ecn.bgu.edu

In article <1993Jan21.144934.13509@newstand.syr.edu> pbwhite@rodan.acs.syr.EDU (White) writes:
>This is almost as dumb, and almost as widespread as the "Let's slap the bottom
>of the bottle of Snapple or Veryfine or whatever"
>People think this makes the bottle easier to open (like its a big chore any
>way).  It doesn't - and It doesn't "pop the top" either like a lot of 
>people think.  You can keep slapping the damn bottom all day if you like.
>Brian

I'm not so sure about slapping the bottoms of bottles making them easier
to open, but I DO know that you really can blow the bottom out of a 16
oz. returnable pop bottle by filling it almost full of water (leave ~1.5
inches of air at the top) and slapping the mouth of the bottle with the
palm of your hand. 


-- 
       ||||Chad Mattingly|||||||||||||||||INTERNET:||||||||||||||||||||
       ||||Eastern Illinois Univ.||||||||||||||cucem@uxa.ecn.bgu.ed||||
       ||||Charleston,Ill.|||||||||||||||||||||||||||||||||||||||||||||
       ||||||||||||||||||||||||||| Carpe Cyprinum! ||||||||||||||||||||
Newsgroups: alt.folklore.science
From: pbwhite@rodan.acs.syr.EDU (White)
Subject: Boneheads was Re: Tapping soft drink cans
Organization: Syracuse University, Syracuse, NY
Date: Thu, 21 Jan 93 14:49:34 EST

In article <mcampbel.727553725@eola.cs.ucf.edu> mcampbel@cs.ucf.edu (Mike Campbell ) writes:
>judson@watserv.ucr.edu (Mike Judson) writes:
>
>>Does tapping the top of soft drink cans really prevent them from "exploding"
>>when you open them, or is it a UL?
>
>I think this is pure poppycock.
>
This is almost as dumb, and almost as widespread as the "Let's slap the bottom
of the bottle of Snapple or Veryfine or whatever"
People think this makes the bottle easier to open (like its a big chore any
way).  It doesn't - and It doesn't "pop the top" either like a lot of 
people think.  You can keep slapping the damn bottom all day if you like.

Brian
From: carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Newsgroups: alt.folklore.science
Subject: Re: RADAR screens
Date: 26 Jan 1993 12:12:51 GMT
Organization: HST Wide Field/Planetary Camera
Distribution: world
Reply-To: carl@SOL1.GPS.CALTECH.EDU
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <1993Jan26.102335.6151@eng.ufl.edu>, george@epsilon.ee.ufl.edu (George L) writes:
>Well (not to get in the middle of this), but last time I checked, you had to 
>clear major sections (usually rectangular) of the storage tube at the same 
>time.

That was a result of the fact that terminals were intended to be refreshed in
that manner.  One could easily design a similar machine that could be cleared
radially (make the second grid radial, and apply voltage to the radii, instead
of to a rectangular section of the screen).

>Can you clear a storage tube in a cyclically rotating sweep pattern?

If you build the machine properly, yes.

>If you were using a storage tube, you would have to have it cleared in the 
>area just ahead of the rotating sweep.

It's doable.

>While you could probably use a storage scopein some sort of RADAR display, I 
>think the display the original poster refers to does indeed rely on a 
>persistent phosphor.

That may be.  However, the sweep line sounds to me an awful lot like clearing
the screen by energizing a radial grid.  Consider:  The sweep line is very
bright (as is the screen of a storage tube when you clear it), and from my
recollection of the old radar screens, it erases the images as it passes them.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
From: dam@dcs.glasgow.ac.uk (David Morning)
Newsgroups: alt.folklore.science
Subject: Re: The Tesla Unit
Date: 27 Jan 93 11:04:00 GMT
Organization: Glasgow University Computing Science Dept.

cannon@scs.unt.edu (Dustin Cannon (Lab 3460)) writes:


>	Hi everyone,

>	I have a question (my normal mental state).  I recently read a 
>biography on Nikola Tesla (Man Out of Time, Margret Cheney) and being a 
>physics major I know about the unit Tesla.  So here is the question: What 
>did Tesla do in magnetism that was so amazing that they named the unit 
>after him?

>        Does anyone know?  SHe didn't mention it in the book and I couldn't 
>find it in the library (not suprising)

From fuzzy memory, lots of developement work on high frequency, high voltage
alternators generating mega-big sparks.
He may well have been the man who actually invented the alternator as we know
it today but I can't be certain.
He's certainly an interesting character.

Dave
--
From: klaus@diku.dk (Klaus Ole Kristiansen)
Newsgroups: alt.folklore.science
Subject: Re: Why is the sky blue?
Date: 22 Jan 93 11:57:27 GMT
Organization: Department of Computer Science, U of Copenhagen

carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick) writes:

>In article <616@highett.mel.dbce.csiro.au>, steveo@mel.dbce.csiro.au (Stephen Oakes) writes:
>>Why does the sky appear blue?

>Rayleigh (sp?) scattering.

>>I have heard that it is because water
>>particles (or perhaps "air particles") have a slightly bluish tinge.

>No.  It's scattering.  Nothing at all about a "bluish tinge" as in the
>particles having a color.

I once saw this very striking exhibit in the Tycho Brahe Planetarium.
A ray of white light was send into a glass cylinder, containing some
substance that scatters light much more than does ordinary air. The
cylinder looked blue near the lamp, green in the middle and yellow
at the far end. This is because short wave light scatters most.

This is what gives the sky its color. The blue light from the
sun gets scattered, and comes to you from all directions. When
the light has to go through a lot of air, that is when the sun is
near the horizon, all but the very longest light waves get scattered,
and the sun looks red.

Klaus O K
From: wingo@apple.com (Tony Wingo)
Newsgroups: alt.folklore.science
Subject: Re: Freeze Dry
Date: 22 Jan 93 17:22:35 GMT
Followup-To: alt.folklore.science
Organization: Apple Computer

In article <C17wDG.JF3@panix.com>, dannyb@panix.com (Daniel Burstein)
wrote:
> 
> In <1993Jan21.103724.28117@ozrout.uucp> stirling@ozrout.uucp (Stirling Westrup) writes:
> 
> >ppxpjr@unicorn.nott.ac.uk (P.J.Rodgers) writes
> >>I've got a question which is bothering people here - how do you freeze dry
> >>food?
> 
> >[...]
> 
> >>Finally have clean room facility in case of contamination problems.  We want to
> >>freeze dry Ice cream.
> 
> >Have you ever *tasted* freeze-dryed ice cream?  I have, and its not a
> >substance I would ever willingly reproduce.  Yech!
> 
> more to the point, how about freeze-dried water!  would certainly make
> storage and shipping simpler...

Actually, I always wanted freeze-dried beer for those long backpacking
trips.

-tony
From: csa09@seq1.keele.ac.uk (Paul Singleton)
Newsgroups: alt.folklore.science
Subject: Re: Boneheads was Re: Tapping soft drink cans
Date: 25 Jan 93 12:00:21 GMT
Organization: Keele University, England

From article <1993Jan21.144934.13509@newstand.syr.edu>, by pbwhite@rodan.acs.syr.EDU (White):

> This is almost as dumb, and almost as widespread as the "Let's slap the bottom
> of the bottle of Snapple or Veryfine or whatever"
> People think this makes the bottle easier to open (like its a big chore any
> way).  It doesn't - and It doesn't "pop the top" either like a lot of 
> people think.  You can keep slapping the damn bottom all day if you like.

I believe you can decork a wine bottle (eventually) by banging the bottle
base on e.g. the ground.  I saw (and heard :-) this attempted as a student.
I got fed up with the hammering from the kitchen, investigated, and helped
them out with a screwdriver.  The cork had crept out somewhat.  Another
half hour would have done it ...
PS
Organization: Carnegie Mellon, Pittsburgh, PA
Newsgroups: alt.folklore.science
Date: Sun, 24 Jan 1993 00:52:02 -0500 
From: David O Hunt <bluelobster+@CMU.EDU>
Subject: Re: Why is the sky blue?

My SO speaketh:

When my (then) four year-old daughter asked, I told her that when their
was a LOT of air, like in the sky, all of that air could act just like
water or glass and make a rainbow when the light struck it just right.
But, when light DOESN'T hit the air "just right", rather than a nice,
neat rainbow, you get all of the rainbow colors scattered everywhere.
The rainbow colors, all together, make, of course, white light. But the
color of the rainbow that's scattered most is the color we see: blue.

And, if some other color than blue were the one that scattered the most,
that's the color of sky we'd see. "Air molecules" (or the molecules/atoms
of those elements making up the atmosphere) have no color whatsoever, and
have absolutely nothing to do with the color of the sky other than in
their combined refractory abilities.

Signed by Chari's Mommy
-------
David
From: carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Newsgroups: alt.folklore.science
Subject: Re: Another UL dies, plastic verus wood cutting boards.
Date: 28 Jan 1993 10:22:20 GMT
Organization: HST Wide Field/Planetary Camera
Distribution: world
Reply-To: carl@SOL1.GPS.CALTECH.EDU
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <1k7egfINNpcb@fido.asd.sgi.com>, jojo@sandman.asd.sgi.com (jojo Wesener) writes:
>I recently read a report on a study which came to the conclusion
>that wood cutting boards were better than plastic cutting boards.
>Studies using salmonella and other harmful bacteria showed that
>when the bacteria was left on wood boards overnight, the bacteria would
>die.  When the same bacteria was left on plastic boards overnight, the
>bacteria counts would increase.
>
>A news report was recently posted to one of the clarinet groups.  The
>researcher's involved couldn't find any studies which claimed plastic
>to be better than wood.  It all appears to be word of mouth, marketing
>propaganda.

Well, one possible explanation follows.  Wood is porous.  If you put a drop of
water on an unfinished wooden surface, it will (fairly) quickly be absorbed by
the wood, dispersed throughout that part of the surface near where the drop
started, and by virtue of the additional surface area of the moisture, dry out
pretty quickly.  Do the same on a plastic surface, and the water stays put and
evaporates rather slowly.  Many bacteria don't last long when dehydrated.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
From: carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Newsgroups: alt.folklore.science
Subject: Re: Boneheads was Re: Tapping soft drink cans
Date: 22 Jan 1993 09:53:05 GMT
Organization: HST Wide Field/Planetary Camera
Distribution: world
Reply-To: carl@SOL1.GPS.CALTECH.EDU
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <1993Jan21.144934.13509@newstand.syr.edu>, pbwhite@rodan.acs.syr.EDU (White) writes:
=In article <mcampbel.727553725@eola.cs.ucf.edu> mcampbel@cs.ucf.edu (Mike Campbell ) writes:
=>judson@watserv.ucr.edu (Mike Judson) writes:
=>
=>>Does tapping the top of soft drink cans really prevent them from "exploding"
=>>when you open them, or is it a UL?
=>
=>I think this is pure poppycock.
=>
=This is almost as dumb, and almost as widespread as the "Let's slap the bottom
=of the bottle of Snapple or Veryfine or whatever"
=People think this makes the bottle easier to open (like its a big chore any
=way).  It doesn't - and It doesn't "pop the top" either like a lot of 
=people think.  You can keep slapping the damn bottom all day if you like.

You're wrong (and have apparently never worked the safe side of a bar).  Take a
bottle containing a liquid and some gas.  Hit the bottom of that bottle.  If
you do it right, you can acheive a water hammer effect which will tend to
loosen the cap.  Just because *YOU'RE* totally uncoordinated doesn't mean that
everyone else is.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
From: carl@SOL1.GPS.CALTECH.EDU (Carl J Lydick)
Newsgroups: alt.folklore.science
Subject: Re: Freeze Dry
Date: 22 Jan 1993 10:30:20 GMT
Organization: HST Wide Field/Planetary Camera
Distribution: world
Reply-To: carl@SOL1.GPS.CALTECH.EDU
NNTP-Posting-Host: sol1.gps.caltech.edu

In article <1993Jan20.191142.12266@cs.nott.ac.uk>, ppxpjr@unicorn.nott.ac.uk (P.J.Rodgers) writes:
=
=
=
=I've got a question which is bothering people here - how do you freeze dry
=food?
=
=Do you need liquid nitrogen - cos we've got some and we want to use it?
=We also have high vacuum facilities - and these little suckers are just waiting
=to be put to a good purpose.
=
=Finally have clean room facility in case of contamination problems.  We want to
=freeze dry Ice cream.
=
=Thanks for your help

All you need is a freezer/pump combination that will drop the pressure and
temperature to the point that water sublimates instead of thawing and
evaporating.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.
From: prener@watson.ibm.com (Dan Prener)
Newsgroups: alt.folklore.science
Subject: Re: Coriolis (again!) on Pole to Pole
Date: 28 Jan 93 07:27:25 GMT
Organization: IBM T.J. Watson Research Center, Hawthorne, New York
Disclaimer: This posting represents the poster's views, not necessarily those of IBM

In article <1993Jan26.195224.25820@mnemosyne.cs.du.edu> bwatson@nyx.cs.du.edu (bruce watson) writes:

> On last night's Pole to Pole, part 5 with Michael Palin he has 
> gotten halfway to his goal of the south pole -- the equator.
> At the site of a burned out hotel, in Kenya, a man was
> demonstrating with a rectangular tub (about 0.3 meters widest)
> with a small hole at the bottom, that on one side of the equator
> it emptied swirling in one direction, on the equator no swirling,
> and on the other side swirling in the opposite direction.
> No one, including Michael, repudiated this nor was it endorsed.
> I'll have to rewatch the episode to see if they got the 
> directions right. I couldn't see him giving a little start
> to the process.

If I remember correctly, they did not get the directions right.
--
                                   Dan Prener (prener@watson.ibm.com)
From: chapman@u.washington.edu (Bruce L. Chapman)
Newsgroups: alt.folklore.science
Subject: Re: RADAR screens
Date: 27 Jan 1993 20:22:51 GMT
Organization: University of Washington
Distribution: world
NNTP-Posting-Host: 128.95.35.14

In article <1k39s3INN29k@gap.caltech.edu> carl@SOL1.GPS.CALTECH.EDU (Carl J  
Lydick) writes:

> bright (as is the screen of a storage tube when you clear it), and from my
> recollection of the old radar screens, it erases the images as it passes  
them.

Not on the airborne radar PPIs I stared at for many hours from 1975-1981; they  
did, indeed use a persistent phosphor. I would often adjust the beam intensity  
so I would have a faint ghost of the previous sweep displayed at the same time  
as the bright image from the current sweep --- this often proved handy for  
estimating the speed of the blip.

I'm sure one *could* design a storage tube to do the job, but persistent  
phosphors were quite adequate --- and much simpler, more reliable, and cheaper.

>  
------------------------------------------------------------------------------- 
-
> Carl J Lydick | INTERnet: CARL@SOL1.GPS.CALTECH.EDU | NSI/HEPnet: SOL1::CARL
> 
> Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.   
My
> understanding of astronomy is purely at the amateur level (or below).  So
> unless what I'm saying is directly related to VAX/VMS, don't hold me or my
> organization responsible for it.  If it IS related to VAX/VMS, you can try to
> hold me responsible for it, but my organization had nothing to do with it.

Bruce Chapman
Ya gotta be tough to fly the heavies.
Newsgroups: alt.folklore.science
From: rf@cl.cam.ac.uk (Robin Fairbairns)
Subject: Re: Celsius and Farenheit Scale Determination
Organization: U of Cambridge Computer Lab, UK
Date: Thu, 21 Jan 1993 16:31:40 GMT

In article <1jjnrvINN1tq@nanette.sto.pdb.sni.de>, sav@nanette.sto.pdb.sni.de (Dr.Savory) writes:
|> In <0iTgXB2w165w@cerianthus.pinetree.org> cowan@cerianthus.pinetree.org (Darin Cowan) writes:
|> 
|> >Most thermometers that you would use to measure body temperature are
|> >accurate to 3 digits anyway.
|> 
|> BULLSHIT: 3 digit accuracy implies 1 part per thousand.
|> 	  You might manage 1 part per 50 (ie 2%).
|> 	  This implies tenth of a degree over a 5 degree range (37 to 42C).

Err.  Isn't this 3-figure accuracy, in the scale we're using?
--
Robin (Keep Radio 3 != Classic FM) Fairbairns       rf@cl.cam.ac.uk
U of Cambridge Computer Lab, Pembroke St, Cambridge  CB2 3QG, UK
Newsgroups: alt.folklore.science
From: naran@fraser.sfu.ca (Travers Naran)
Subject: Re: Freeze Dry
Organization: Simon Fraser University, Burnaby, B.C., Canada
Date: Thu, 21 Jan 1993 22:32:28 GMT

dannyb@panix.com (Daniel Burstein) writes:

>more to the point, how about freeze-dried water!  would certainly make
>storage and shipping simpler...

But what would you add to it?

-- 
--------------------------------------------------------------------------
Travers Naran                                           | "We fear
Mail address: naran@fraser.sfu.ca or naran@sfu.ca       |  change. WHACK!
Simon Fraser University, British Columbia, Canada       | WHACK! WHACK!"
Cmpt. Science student wanna-be                          | -Garth 
Trekker, Leaper, Red Dwarf'er, Prober, etc.             |  "Wayne's World"
--------------------------------------------------------------------------
From: urban@sideshow.jpl.nasa.gov (Michael P Urban)
Newsgroups: alt.folklore.science
Subject: Re: Blueness
Date: 28 Jan 1993 15:43:12 GMT
Organization: Jet Propulsion Laboratory, Pasadena, CA
Reply-To: urban@sideshow.jpl.nasa.gov (Michael P Urban)
NNTP-Posting-Host: sideshow.jpl.nasa.gov

In article <C1JCBF.756@world.std.com> moroney@world.std.com (Michael Moroney) writes:
>Water isn't blue. The ocean appears blue because it reflects the sky.
>(look at it on a stormy day, it's gray)
>

Um, are you saying that when the Earth is viewed from space, the
oceans look dark blue because they reflect the sky?  I am having
trouble visualizing this process.



	Mike Urban

	urban@cobra.jpl.nasa.gov