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Mars
2004-Mar-10, 12:53 AM
From what I understand of the expanding nature of the universe is that we are always moving. When there was evidence presented of a galaxy that was found originated 13.2 Billion light years away, when the two galaxies were a mere 2 Billion light years away I got to thinking.

Can we gage the speed at which we are moving in space within a galaxy?

If so can we take this movement into account when launching space craft, or is it's effect even noticeable?

If we are moving at such a speed already, couldn't we launch a probe towards the center of the universe and use this movement to our advantage to get a probe closer to an oncoming galaxy, kind of like using the Earth's rotation to fly places?

AGN Fuel
2004-Mar-10, 01:32 AM
From what I understand of the expanding nature of the universe is that we are always moving. When there was evidence presented of a galaxy that was found originated 13.2 Billion light years away, when the two galaxies were a mere 2 Billion light years away I got to thinking.

Can we gage the speed at which we are moving in space within a galaxy?

If so can we take this movement into account when launching space craft, or is it's effect even noticeable?

If we are moving at such a speed already, couldn't we launch a probe towards the center of the universe and use this movement to our advantage to get a probe closer to an oncoming galaxy, kind of like using the Earth's rotation to fly places?

Measurements of H(naught) are made on a megaparsec level. On a local scale within a galaxy, gravitational effects will swamp expansion effects.

Launching a probe toward the centre of the universe could also be a little difficult.... :o

Mars
2004-Mar-10, 01:36 AM
From what I understand of the expanding nature of the universe is that we are always moving. When there was evidence presented of a galaxy that was found originated 13.2 Billion light years away, when the two galaxies were a mere 2 Billion light years away I got to thinking.

Can we gage the speed at which we are moving in space within a galaxy?

If so can we take this movement into account when launching space craft, or is it's effect even noticeable?

If we are moving at such a speed already, couldn't we launch a probe towards the center of the universe and use this movement to our advantage to get a probe closer to an oncoming galaxy, kind of like using the Earth's rotation to fly places?

Measurements of H(naught) are made on a megaparsec level. On a local scale within a galaxy, gravitational effects will swamp expansion effects.

Launching a probe toward the centre of the universe could also be a little difficult.... :o

That makes sense.

Tim Thompson
2004-Mar-11, 03:19 AM
Can we gage the speed at which we are moving in space within a galaxy?

Yes. The speed of rotation of the Milky Way, at our distance from the center of the galaxy, is approximately 200 km/sec (124.3 miles/sec; Milky Way Rotation Curve (http://nedwww.ipac.caltech.edu/level5/March01/Battaner/node9.html)). That's the speed of the solar system with respect to the center of the galaxy.

The mean orbital velocity of Earth around the Sun is 29.78 km/sec (18.5 miles/sec; Earth fact sheet (http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html)). That's the speed of Earth with respect to the sun, the center of the solar system.


The speed of a point at the equator of Earth, as it spins, is just the circumference divided by the sidereal length of day, or 1040 miles/hour (0.289 miles/sec). That's your speed with respect to the center of the Earth, if you happen to be on the equator. If not, then your speed will be slower by about a factor of the cosine of your latitude.

But we can also tell what our relative speed is, with respect to things outside the galaxy. For instance, our own local group of galaxies, which includes the Milky Way and M31, is moving towards the Virgo cluster at about 200 km/sec (I've seen numbers from about 180 km/sec to 220 km/sec).

We can measure the speed of Earth with respect to the putative rest frame of the universe, which is the rest frame of the cosmic microwave background, by virtue of the strength of the dipole anisotropy. That relative velocity of Earth is about 369 km/sec (229 miles/sec; Cosmic Microwave Background Anisotropy (http://www.astro.ucla.edu/~wright/CMB-DT.html)).

The universe has no center, at least not in 3 or 4 dimensions, but if it did, our speed relative to the cosmic microwave background would be as good a guess at our speed relative to the center as one might get.

But sending a spaceship is a forlorn hope. The Voyager II spacecraft is on its way towards Sirius. It will pass within 4.3 light years of Sirius, but it won't do that for another 269,000 years. But take heart. The Voyager I spacecraft will need only 40,000 years to get within 1.6 light years of the obscure star AC+79 3888 (Voyager interstellar Mission (http://voyager.jpl.nasa.gov/mission/interstellar.html)). And those are the trip times to the nearby stars. If the voyager spacecraft were going in the right direction, and if they don't slow down, they would reach M31 in 46 billion years (ignoring the fact that m31 is moving this way much faster, and will slam into the Milky Way full tilt, in about 5 billion years or so).

I don't think Congress will fund a multi-billion year research project, but you can always try!