Can someone settle a debate between my hubby & myself?

[bassetmamax2]

Knowing that the Earth's orbit has slowly expanded over eons, is it possible that the orbit has expanded, if just minutely, in the past 40 years (my and my husband's lifetime)?<br />There's no bet, just bragging rights to who's right and who's wrong. Thanks. <br /><br /><br />

 

[h9c2]

It may be possible that over the last 40 years the farthest distance from the sun (aphelion) that the earth reaches may actually have decreased, depending on whether earth's orbit is currently tending towards a circular or an eliptical shape <img src="/images/icons/smile.gif" />

 

[newtonian]

x-snipe - Can you link to those calculations?<br /><br />Is that a steady rate or is it accelerating?<br /><br />Where does that put earth when the sun reaches red giant phase - a safe distance perhaps?<br /><br />OK, 7 centimeters per year would be 7 meters in 100 years, 70 meters in 1,000 years, 70 kilometers in one million years, 700,000 kilometers in 10 billion years.<br /><br />That would not be a safe distance, assuming stellar evolution models are correct.<br /><br />However, I am aware of studies, though I lost links to them, that earth may be much further from the sun at red giant phase.<br /><br />And those studies assume zero mixing of solar core gasses with more hydrogen rich exterior layers - which assumption I doubt is correct since the magnetic dynamoes heating the solar corona show evidence of floating from core to surface, and that requires ions in motion, hence mixing.<br /><br />In the latter model, our sun would lose more mass before red giant phase than assumed, and the sun would also take much longer (perhaps billions of years longer) to reach red giant phase, and therefore earth will be even further from the sun at red giant phase.<br /><br />Since gravity decreases with the square of the distance, i assume the recession rate is accelerating?<br /><br />Tidal interactions would also lessen with distance.<br /><br />BTW - tidal interactions between earth and moon also cause the moon to recede from earth ever so slightly.<br /><br />While I know it is true, I still find the fact that these orbits are not decaying at all to be truly amazing - when compared with man-made satellites!

 

[newtonian]

x_snipe - Less effect is less gravity in this case - and to really define the effect one must do the math, or link to someone who has done the math.<br /><br />I was not talking about negligible mixing, btw.<br /><br />I forget the percentages, but I seem to remember something on the order of 90% of solar hydrogen not fused into Helium by red giant phase.<br /><br />If the mixing causes 50% of solar hydrogen to be fused over 50 billion years instead of 10 billion years (4 or 5 billion already past, btw), you see a very significant effect on earth's orbit will result.<br /><br />Clearly we will have to link to the math - but my time is limited as I am involved in Katrina relief here in SE Louisiana.<br /><br />I hope to look the studies up in the weeks to come.<br /><br />Feel free to get to it first!

 

[newtonian]

H9C2, you all - Any ideas as to whether earth's orbit is tending towards being either more eliptical or circular?

 

[h9c2]

I don't know. I believe that earths orbit is about as circular as it is going to get though. You can google "Milankovitch Cycles" and see what comes up.