
J002E3 - yread
http://en.wikipedia.org/wiki/J002E3
======
epochwolf
> One explanation could have been that it was a 30-meter-wide piece of rock,
> but University of Arizona astronomers found that the object's
> electromagnetic spectrum was consistent with white titanium dioxide paint,
> the same paint used by NASA for the Saturn V rockets.

I know this is a really old thing but the idea that we can determine
composition of the surface of an object from so far away simply by looking at
the light it reflects is absolutely incredible to me. Very science fiction. :)

~~~
jgrahamc
This is a pretty fundamental part of astronomy. Just look at what you can do
with Fraunhofer lines
([http://en.wikipedia.org/wiki/Fraunhofer_lines](http://en.wikipedia.org/wiki/Fraunhofer_lines)).
They are an almost steganographic signature written into the elements.

And more generally spectroscopy:
[http://en.wikipedia.org/wiki/Spectroscopy](http://en.wikipedia.org/wiki/Spectroscopy)

~~~
JonnieCache
Just to reinforce jgc's point: this object was not "far away" by spectroscopy
standards. You can use the same technique for looking at the most distant
stars and galaxies in the sky.

When people talk about Hubble (the guy, not the telescope) detecting the
expansion of the universe by looking at redshift from distant galaxies, what
he was actually looking at were spectral signatures. He saw all the patterns
he expected to see from burning stars, but the lines were smeared out. Because
he knew the patterns always form a consistent picture of the atomic structure,
and he understood the doppler effect, he was able to estimate the distances of
those objects quite accurately. Amazing stuff.

~~~
Karellen
Not quite. From the doppler-shifted spectrosocopy lines, we can figure out
what speed everything is moving relative to us, but that by itself doesn't
tell us anything other than their speed.

Noting that _all_ the doppler shifts of other galaxies are red-shifts tells us
that all the galaxies are moving away from us, but it still doesn't tell us
whether speed correlates to distance in any way.

Figuring out the distance of galaxies is a different matter entirely, and is
done with standard candles[0].

It's from the standard candles that we can measure distance, and only once we
know the distance that way can we make a correlation between speed and
distance, from which we see that the further away a galaxy is, the faster it
is receding.

Only once we have found that there is a speed/distance curve can we estimate
the distance to an object based on its doppler shift. We can't get it from the
doppler shift alone.

[0]
[http://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard...](http://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard_candles)

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lmm
Oh, for _fuck 's_ sake, mods. There was a useful, informative, uncontroversial
title here, and you've turned it into something meaningless. You've actually
made it _more_ clickbaity. Stop doing this, for the love of all that is good.

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ColinWright
Original title:

    
    
        J002E3 - piece of Apollo 12 returned
                 to Earth orbit after 31 years
    

That was much, _much_ more useful and informative.

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pwenzel
For those interested, NASA's Jet Propulsion Lab runs a telnet server that
provides information about objects like this via its HORIZONS system.

To avoid an onslaught of HN traffic to the telnet server, I will just say to
go to ssd.jpl.nasa.gov, and click through to find it. Once you're telnetted
in, enter J002E3.

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al2o3cr
My Kerbals will be honored to know that even NASA loses track of used stages.
:)

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helicon
Apollo 12 was struck by lightening shortly after launch. I wondered initially
if this was the reason for the "extra long burn of the ullage motors".

But according to the Apollo 12 wikipedia page: "a small error in the state
vector in the Saturn's guidance system caused the S-IVB to fly past the Moon
at too high an altitude to achieve Earth escape velocity".

[http://en.wikipedia.org/wiki/Apollo_12](http://en.wikipedia.org/wiki/Apollo_12)

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dokem
> ...the object's electromagnetic spectrum was consistent with white titanium
> dioxide paint...

Isn't this just a fancy way of saying that it was white?

~~~
Sharlin
No. It means it, spectroscopically, looked _specifically_ like titanium
dioxide paint, and not just any arbitrary white material. Its spectral lines
were consistent with titanium dioxide.

[http://en.wikipedia.org/wiki/Spectral_line](http://en.wikipedia.org/wiki/Spectral_line)

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_delirium
The see-also links below this article are pretty interesting too.

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micampe
Now this is a much clearer title!

~~~
ColinWright
Sarcasm?

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jerf
Godspeed, J002E3. Next time you come back around, we'll bring you home.

