From: Cedric Chang <cc@nope9.com>
> On Aug 6, 2007, at 12:16 PM, David VanHorn wrote:
> > I hope they remember to travel not just back to the appropriate when,
> > but also the appropriate WHERE.  It would be inconvenient to discover
> > the planet a few million miles away.
> 
> Maybe about once per year would be about right

Not really. The sun is moving through space, too.

The earth's surface at the equator moves about 0.46 km/sec because of
rotation.

The earth's movement along its orbit is about 30 km/sec.

The sun's movement along its orbit within the Milky Way galaxy is on
the order of 210 km/sec.

The Milky Way is moving at 552 km/sec relative to the cosmic microwave
background.

The question really is, to what inertial frame of reference (if any) are
you "anchored" when time-travelling?

-- Dave Tweed
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