5 ms·

> 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 spect

> 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. :)

userbinator 12y ago
It's not completely accurate, however; this one was also thought to be a rocket from its spectrum: http://en.wikipedia.org/wiki/2006_RH120 http://en.wikipedia.org/wiki/2006_RH120
- mturmon 12y ago
  Nice catch. Here's a link to some positional data collected from that one: http://www.skyandtelescope.com/astronomy-news/earths-other-moon/ http://www.skyandtelescope.com/astronomy-news/earths-other-m...
jgrahamc 12y ago
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 12y ago
  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 12y ago
    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_candles http://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard...
- keithpeter 12y ago
  Might be worth mentioning the use of doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of e.g. a star being observed. https://www.e-education.psu.edu/astro801/content/l4_p7.html https://www.e-education.psu.edu/astro801/content/l4_p7.html
- keithpeter 12y ago
  Might be worth mentioning the use of Doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of e.g. a star being observed. https://www.e-education.psu.edu/astro801/content/l4_p7.html https://www.e-education.psu.edu/astro801/content/l4_p7.html Hyperfine splitting of spectral lines in hydrogen gas caused by the interaction between electron and neutron spin allows you to map the hydrogen in our local Galaxy. http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html As parent post says this is pretty standard astrophysics, just find any reasonable text in your local library. Or just Google 'astronomy .pdf' for a huge range of handbooks and presentations.
Sharlin 12y ago
Spectroscopy is pretty much the reason we have been able to infer as much as we do about stars, their lifecycles, and what happens inside them.

userbinator 12y ago

It's not completely accurate, however; this one was also thought to be a rocket from its spectrum: http://en.wikipedia.org/wiki/2006_RH120 http://en.wikipedia.org/wiki/2006_RH120

mturmon 12y ago
Nice catch. Here's a link to some positional data collected from that one: http://www.skyandtelescope.com/astronomy-news/earths-other-moon/ http://www.skyandtelescope.com/astronomy-news/earths-other-m...

jgrahamc 12y ago

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 12y ago
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 12y ago
  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_candles http://en.wikipedia.org/wiki/Cosmic_distance_ladder#Standard...
keithpeter 12y ago
Might be worth mentioning the use of doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of e.g. a star being observed. https://www.e-education.psu.edu/astro801/content/l4_p7.html https://www.e-education.psu.edu/astro801/content/l4_p7.html
keithpeter 12y ago
Might be worth mentioning the use of Doppler shift of the known patterns of spectral lines associated with elements to get information about radial velocity of e.g. a star being observed. https://www.e-education.psu.edu/astro801/content/l4_p7.html https://www.e-education.psu.edu/astro801/content/l4_p7.html Hyperfine splitting of spectral lines in hydrogen gas caused by the interaction between electron and neutron spin allows you to map the hydrogen in our local Galaxy. http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html As parent post says this is pretty standard astrophysics, just find any reasonable text in your local library. Or just Google 'astronomy .pdf' for a huge range of handbooks and presentations.

Sharlin 12y ago

Spectroscopy is pretty much the reason we have been able to infer as much as we do about stars, their lifecycles, and what happens inside them.