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Cosmic_Barcodes_en.html
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<!-- saved from url=(0065)https://fuse.pha.jhu.edu/Graphics/scigraph/barcodes/barcodes.html -->
<html><head><meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Cosmic Barcodes</title>
</head>
<!--#include virtual="/web_includes/sidebar.html"-->
<body><center>
<table width="550">
<tbody><tr><td>
<img src="./Cosmic_Barcodes_en_files/emspect.gif" width="550">
<table cellpadding="5" cellspacing="5" width="550">
<tbody><tr>
<td valign="top" align="center">
<font color="#6666CC"><font size="+3">
<b>Cosmic Barcodes</b><br></font></font>
<p>
<img src="./Cosmic_Barcodes_en_files/bctop.gif">
</p><p>
</p><h4>Text by Ken Sembach and Bill Blair<br>
Graphics by Ken Sembach</h4>
</td>
</tr>
</tbody></table>
<img src="./Cosmic_Barcodes_en_files/emspect.gif" width="550">
<p>
Astronomers learn about the Universe by observing light from distant
astronomical objects, like stars or galaxies. Light contains <i>information,</i>
and since it is much easier to observe a star than it is to travel to one,
there is clearly a benefit to being able to understand what the light is
telling us!
</p><p>
One of the main tools for studying light is a device called a
<i>spectrograph</i>, which breaks light into its component colors, much
like raindrops refract sunlight to produce beautiful rainbows in the sky.
When attached to a telescope, a spectrograph becomes a powerful tool
for learning about the Universe.
</p><p>
Luckily for astronomers, this technique can be used with all kinds of light, not just
the visible light that our eyes are sensitive to. Different kinds of light, like infrared,
ultraviolet, X-ray light, etc., contain different kinds of information. The FUSE satellite
uses light in the far-ultraviolet spectral region,
light having wavelengths between 90 and 120 nanometers
(1 nanometer = 1 billionth of a meter!). For comparison, visible light ranges from about
400 to 700 nanometers (4000 to 7000 Angstroms).
</p><p>
In the absence of any intervening material, the light from a star
reaches us unobscured. When the light is dispersed into colors by
a spectrograph, it may look something like this <i>continuous spectrum</i>,
which has a smooth, gradual change of color, and no breaks or dropouts in
the intensity of the light:
</p><center>
<p>
<img src="./Cosmic_Barcodes_en_files/continuum1.gif">
</p><p>
</p></center>
However, if there are one or more gas clouds between us and the star, this <i>interstellar
medium</i> absorbs some of the light before it reaches us. Depending upon
what types of atoms or molecules are present in the absorbing gas clouds, a
number of dark features, or <i>absorption lines</i>, are superimposed on the
continuous spectrum emitted by the star, something like this:
<center>
<p>
<img src="./Cosmic_Barcodes_en_files/continuum2.gif">
</p><p>
</p></center>
These absorption lines contain information about the composition of the
clouds (the kinds and relative amounts of atoms and molecules in the gas). They also tell us
such things as how much gas is in the clouds, the gas density, the temperature of the
gas, how fast it is moving toward or away from us, whether there are cold regions
embedded in warmer material, and whether there are interstellar dust grains
mixed in with the gas. All this from analyzing the light!
<p>
These absorption features can be thought of as <i><b>cosmic barcodes</b></i>,
with each type of atom or molecule producing a different barcode signature.
One can then think of a spectrograph as a "barcode reader". Once the barcode
produced by a gas cloud has been read, astronomers can interpret what the
barcode means. Here are examples of the types of barcodes that are
produced by the FUSE spectrographs:
</p><center>
<p>
<img src="./Cosmic_Barcodes_en_files/barcodes.gif">
</p><p>
</p></center>
<b>Now it's YOUR turn!</b> <br>
See if you can guess which elements have left their mark on this spectrum:
<center>
<p>
<img src="./Cosmic_Barcodes_en_files/guesswhich.gif">
</p></center>
<p>
When you think you know, <a href="https://aibolem.github.io/dbrein/Cosmic%20Barcode%20Answer.html">check here for the correct answer</a>.
</p><p>
</p><center>
<img src="./Cosmic_Barcodes_en_files/emspect.gif">
</center>
<p>
Send mail to <a href="mailto:[email protected]">Dr. Ken Sembach</a> or <a href="mailto:[email protected]">Dr. Bill
Blair</a>.
</p></td></tr>
</tbody></table>
</center>
<!--#include virtual="/web_includes/lower_table2.html"-->
</body></html>