Basic question about spacecraft orbits

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>This is starting to make sense to me atleast on some basic level.If the space is bent due to gravitational wells everywhere, does this mean that the stars we see aren't actually quite there, but in reality reside someplace else? The path of the light being curved by gravities along the way? <br />Posted by aphh</DIV></p><p>That is correct. In fact the first proof of Einstein's space time bending was duringa total solar eclipse when the position of a star near the sun was measured and found to be out of place by the amount he predicted. The reason the sun was used is because it's the largest mass close to us; this made the effect large enough to be measured at the time. It was in the 1930's if I recall correctly, but I'm not sure of the date.</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[aphh]

<p>Excellent. Thanks again.</p><p>If I didn't have the ADD, I'd pull out the old physics book right now.&nbsp; &nbsp;</p>

 

[MeteorWayne]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Excellent. Thanks again.If I didn't have the ADD, I'd pull out the old physics book right now.&nbsp; &nbsp; <br />Posted by aphh</DIV></p><p>&nbsp;</p><p>Here's some links:</p><p>1919 Eclipse:</p><p>http://www.enotes.com/science-fact-finder/space/how-did-total-solar-eclipse-confirm-einsteins</p><p>1922 Eclipse:</p><p>http://www.asap.unimelb.edu.au/bsparcs/physics/eclipse.htm</p><p>&nbsp;</p><p>Sorry, my memory of it being in the 30's was defctive </p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[aphh]

<p>Would it be correct to say that spacecraft orbit is a demonstration of spacetime geometry of a given parameters?</p><p>Also, it seems to me that we know about gravity, we know it exists and can predict and calculate it. We just can't *hack* it at the moment? </p>

 

[spacester]

<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Would it be correct to say that spacecraft orbit is a demonstration of spacetime geometry of a given parameters?Also, it seems to me that we know about gravity, we know it exists and can predict and calculate it. We just can't *hack* it at the moment? <br /> Posted by aphh</DIV></p><p>Yes, exactly! Your intuition is very very good (unless of course you really already knew this stuff ).</p><p>An orbit demonstrates the curvature of space.&nbsp; This is precisely why it is called a 'well'.</p><p>Hmm . . perhaps a 'well' no longer conjures up an image for folks these days. I had a great demonstration of it in my youth - I fell into a well. No I didn't, just kidding. What I got to see was the fabulous 'Gravitram' at OMSI (Oregon Museum of Science and Industry), which was a very large contraption with large steel balls rolling on tracks made of brass rods. I spent hours watching it . . . anyway, at the bottom, after the balls finally made it down thru all the gizmos, they would come out on a large cone with a hole in the bottom. The ball goes roundy roundy in orbits (which decayed due to friction) until finally dropping thru the hole.</p><p>That cone is a great physical model for a gravity well. Actually, the shape should be more like a tornado's funnel cloud, but a cone is close enough for starters.</p><p>You are quite astute to mention the parameters. The shape of the curved cone depends on the parameters. In fact, the cone itself is defined by only one parameter: the mass of the planet/moon/star creating the gravity field. An orbit is a particular path on the cone, and for that, the primary parameter is the . . . wait for it . . . Bound Energy. </p><p>The math is done with geometric parameters, namely radius and semi-axis measurements, but to conceptually wrap your brain around it, I highly recommend thinking in terms of Bound Energy.</p><p>To shift the plane of an orbit, you need to make a whole bunch of energy, bound to the gravity field, change its binding. So you can readily see that this is going to take a lot of energy. On the other hand, if you just want to circularize your orbit from a too-eccentric one, you don't have to change the amount OR direction of your Bound Energy - just a little nudge of energy is all you need.&nbsp;</p><p>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>Also, it seems to me that we know about gravity, we know it exists and can predict and calculate it. We just can't *hack* it at the moment? </DIV></p><p>I think that sums up the situation quite nicely. In fact, I don't have anything to add!. </p><p>&nbsp;</p> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

<div class="Discussion_PostQuote">Also, it seems to me that we know about gravity, we know it exists and can predict and calculate it. We just can't *hack* it at the moment? </div><p>I think that sums up the situation quite nicely. In fact, I don't have anything to add!. >></p><p>I would point out that hacking it not an option. Gravity is the primal force of the Universe. We can find means to get around gravity, but I doubt we can ever eliminate it as a factor. Even a star light-years away has an effect on us, more minute then we can measure, but it all adds up. The Universe is constantly in motion.</p> <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

<p>A little anecdote from the March Discover (the special Einstein issue)</p><p>&nbsp;</p><p>" In the fall of 1919 Albert Einstein received an urgent telegram informing him that astronomers had observed the bending of light by the sun's gravity, validating a key prediction of his general theory of relativity. He handed the cable to a student who began congratulating him."But I knew that theory was correct" he interrupted. And what, she asked if the observations had disagreed with his calculations?</p><p>"Then I would be very sorry for the dear Lord" Einstein answered. "The theory is correct"</p><p>&nbsp;</p><p><img src="http://sitelife.space.com/ver1.0/content/scripts/tinymce/plugins/emotions/images/smiley-smile.gif" border="0" alt="Smile" title="Smile" /></p><p>&nbsp;</p><p>http://njaes.rutgers.edu/centers/quickinfo.asp?Snyder</p> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>