Why does the horsehead nebula always look the same?

[Saiph]

well...steve did start spelling out the acronyms in his post immediately after your request so neh! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[pioneer0333]

But why does it take so long? Just because it's big and vast? Because it seems to me that it should still change shape on a daily basis.<----solidsnake<br /><br /> You have to remember that space is beyond belief when it comes to size. Any change would take tens, if not hundreds of years to notice. <div class="Discussion_UserSignature"> </div>

 

[vogon13]

It does change shape on a daily basis. But the resolving power of even the Hubble Telescope (.1 arc second), is orders of magnitude too coarse to see it.<br /><br />Radio telescope arrays using very long baseline interferometry can achieve higher resolutions and have made observations of some distant astronomical objects internal motions on relatively shorter time scales.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[Saiph]

right, it's a matter of clarity as vogon says. Our sharpest images can only see so fine a detail (which varies in actual size depending on the telescope, camera, and distance to the object).<br /><br />Just for a scale here, one astronomical unit (~8 light minutes) spans 1 arcsecond of sky at 3.26 light years (defined as a parsec).<br /><br />So at 3.26 light years..which is closer than the nearest star, an object or change that's one light day in radius (so 2 light days in diameter) is 180 arcseconds across...or 0.1 degrees in the sky. And this is only at ~3 light years. Throw that out to over a thousand light years...and that angle gets much, much smaller.<br /><br />I chose 1 light day, because this is the furthest a change in an object can propagate in one day (with the change happening at the speed of light). I.e. a change on a daily basis is, at best, no larger than this.<br /><br /><br />So it's impossible for modern telescopes to resolve a change of that size. <br /><br />Throw in the fact that the changes aren't drastic (the subtle changes are likely to go unnoticed) and that the changes usually occur at a much slower rate, it it becomes even more impossible. (I.e. impossibler <img src="/images/icons/smile.gif" />) <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>

 

[newmoon]

New research indicates that the Horsehead Nebula is rotating, in such a way that the horse is trying to look our way:<br /><br />The Horsehead Nebula in Orion is rotating, say radio astronomers in France, Holland, and Germany. The centrifugal force the rotation has induced may account for the nebula's distinctive shape.<br /><br />More here.<br /><br />

 

[qso1]

In a few million years it will be known as the "Horse hiney" nebula. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[search]

They do change but as explained before only time and precision instruments allow us to see those changes.<br /><br />Horsehead Nebula<br /><br />http://www.glyphweb.com/esky/default.htm?http://www.glyphweb.com/esky/nebulae/ic434.html<br /><br />http://hubblesite.org/newscenter/newsdesk/archive/releases/2001/12/image/a<br /><br />Crab Nebula:<br />"The Crab Nebula is currently expanding outwards at about 1,500 km/s.[9] Images taken several years apart reveal the slow expansion of the nebula, and by comparing this angular expansion with its spectroscopically-determined expansion velocity, the nebula's distance can be estimated."