Light delay from habitable planets to earth

[DodgeDis]

<p>Hi all,</p><p>Forgive the question if it has been asked and answered before.&nbsp; I tried searching and came up with a zillion posts regarding my question.&nbsp; A link to a post that answers my question would be appreciated if you know where to find it. &nbsp;</p><p>Question:</p><p>Light from other planets and stars can take hundreds, thousands, even millions of years to get to earth so how are we supposed to find planets that are currently habitable or inhabited if what we are viewing can be millions of years old?</p><p>Thanks. </p><p>Floyd </p>

 

[robnissen]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Hi all,Forgive the question if it has been asked and answered before.&nbsp; I tried searching and came up with a zillion posts regarding my question.&nbsp; A link to a post that answers my question would be appreciated if you know where to find it. &nbsp;Question:Light from other planets and stars can take hundreds, thousands, even millions of years to get to earth so how are we supposed to find planets that are currently habitable or inhabited if what we are viewing can be millions of years old?Thanks. Floyd <br />Posted by DodgeDis</DIV></p><p><font size="3">We can see light from stars that are hundreds and thousands, but generally not millions of light years away.&nbsp; (I&nbsp;believe some of&nbsp;the largest telescopes can resolve stars in galaxies that are&nbsp;around a million light years away, but I am not certain.)</font></p><p><font size="3">But almost all exo-planets discovered to date are well within 1k light years.&nbsp; (There are a few around pulsars and a few others that are substantially more than 1k light year away.)&nbsp; Thus, at most we would only be looking back 1000 years in time.&nbsp; Unless their civilization collapsed in the last 1000 years, they would still be there.&nbsp; </font></p><p><font size="3">Also, even if we were to some day be able to image a planet on the other side of the MW, that is still only about 100K LY away -- the diameter of the MW.&nbsp; We won't be imaging planets in other galaxies any time soon.</font></p><p>&nbsp;</p><p>&nbsp;</p>

 

[DodgeDis]

<p>That makes a lot of sense.&nbsp; I've been thinking about that question for a few weeks now.&nbsp; Thanks a lot for the reply.</p><p>&nbsp;</p>

 

[derekmcd]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Also, even if we were to some day be able to image a planet on the other side of the MW, that is still only about 100K LY away -- the diameter of the MW.&nbsp; We won't be imaging planets in other galaxies any time soon.&nbsp;&nbsp; <br /> Posted by robnissen</DIV></p><p>Recent measurements place our solar system at 27,000 ly distance from the center.&nbsp; That would put the farthest edge of the Milky Way at ~77,000 light years distance.</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[robnissen]

Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Recent measurements place our solar system at 27,000 ly distance from the center.&nbsp; That would put the farthest edge of the Milky Way at ~77,000 light years distance. <br />Posted by derekmcd</DIV><br /><br /><font size="3">The farthest stars in the Milky Way are actually a little more than 100K LY from earth, because the galatic halo is abou 200k ly in diameter and earth lies close to the galatic plane and then add in the trigonemetric distance to stars at the outer limit of the galatic halo on the other side of the galactic center.&nbsp; But you are correct, my previous explanation was not accurate.</font>