Everything relative to the earth...

[Mart]

I meant would some variant of epicycles have worked well enough for us to navigate spacecraft around the system.

 

It would depend on the variant. If it didn't allow us to discover/invent all the other necessary support then maybe not.

[Mart]

Huge difference between Periodic motion and SHM !

 

I don't know anything about this. What is the difference?

[-Demosthenes-]

But he had been silent since August till he began reposting on 11th January, so he was new to us.2u and I.

True, welcome back me.

 

Heres what I was thinking. Most of the time you see things relative to the earth, but when you're in a car you move relative to the car and the earth looks like its moving. But to someone standing normally it looks like you are moving. So everything depends on where you are relative to. I'm relative to the earth at the moment so I was wondering if you could see movement of other celestrial bodies in relation to the earth.

[JaKiri]

Orbital Motion isnt SHM its Periodic Motion !

Huge difference between Periodic motion and SHM !

 

It's a simple harmonic motion when referring to a 1 dimensional view of the orbit, technically it isn't of course.

[swansont]

Only if you define the positive direction as being 'Away from the sun', which seems silly. The earth's speed, ignoring tidal effects, friction and other such minor interactions, will remain fairly consistent throughout the year, or at least have a consistent cycle.

 

There will be some variation due to the eccentricity, but as that is small, so are the speed variations (which are periodic, as you say)

 

The earth is always accelerating toward the sun, and vice-versa. The magnitude of those accelerations are different by the ratio of the masses. If I've done my calculation right, the earth is accelerating at about 6 mm/s² toward the sun. The sun's acceleration will be almost six orders of magnitude smaller, and I'm ignoring the effects of other planets (which are cumulative, since a is a vector)

[JaKiri]

If I've done my calculation right, the earth is accelerating at about 6 mm/s^{2[/sup'] toward the sun.}

 

^{You have.}

[Sayonara]

Are we all eventually doomed?

[JaKiri]

Are we all eventually doomed?

 

If we weren't accelerating at that rate, we'd either be pulled into the sun or fly off at a tangent. It's the centripetal acceleration.

[Sayonara]

Bah.

[swansont]

Are we all eventually doomed?

 

Yes, of course we are. But not because of the acceleration we're discussing.

[-Demosthenes-]

Can I ask why?

[Sayonara]

It's fairly inevitable, given the heat death of the universe.

 

We've done this before.

[JaKiri]

It's also fairly likely in the short term unless a reliable and cheap antiagapic is discovered.