# What is the current position of Andromeda?

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Can we predict where Andromeda is at the current time?

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#### MeteorWayne

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Yes we can look at it and measure it every night.<br /><br />The precise distance is not known, but it's about 2.2 million light years.<br />To be generous, +/- 200,000 light years.<br /><br />That means that traveling at 186,000 miles PER SECOND, the light takes 2.2 million years to get here.<br /><br />Take a few seconds and think about that.<br /><br />2.2 million years at the speed where it takes a second and a half for the light reflected off the moon to reach us.<br /><br />Even Pluto is only 4 1/4 hours away...Andromeda is 2.2 MILLION years away at 300,000 meters a second. <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>

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But when we look at Andromeda from a telescope today, we are actually looking at it as it was 2.2 million light years ago. So my question is, can we predict where the galaxy is right now?

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#### derekmcd

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In short, yes. By looking at the light and recognizing it is blueshifted meaning it is moving towards us. The current prediction is Andromeda colliding with the Milky Way in about 3 billion years. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

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#### MeteorWayne

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We are looking at the light from 2.2 million years ago.<br /><br />Based on it's motion at that time, we have a very good idea where it is now, since things go in the same direction unless acted on by an outside force. (see Newton's Laws <img src="/images/icons/smile.gif" /> ) There are no such forces that we can detect between here and there. <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>

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#### nexium

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So that means it will average almost 0.001c. (0.0007c) Do we expect Andromeda to accelerate to a bit more than 0.001c just before the merger? Is there a reasonable probability that only the outer edges of the galaxies will merge rather than a direct hit? The merger will last about 200 million years with only small changes in direction and speed if the central hubs miss each other. My guess is that is likely. Neil

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#### heyscottie

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We're actually not sure that there will be a collision, because we have not yet accurately measured the lateral velocity of Andromeda. It is certainly getting closer to us, but it may miss us to one side. I am not aware of what proposals may exist to determine said lateral velocity and answer the collision question conclusively.

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#### MeteorWayne

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It's very hard to get accurate lateral velocity on something 2.2 million light years away <img src="/images/icons/smile.gif" /><br />.00000000000000000000000000000001 arc seconds per millenium and all that <img src="/images/icons/laugh.gif" /> <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>

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#### alkalin

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We do not have much of a clue for itâ€™s precise location â€˜nowâ€™, because we do not have precise knowledge of where it was in the past as we see it now.<br /><br />Andromeda according to brightness data and especially Cepheid variables suggest it is over 2 M LYs from us. Some tend to think there is enough intervening IG gas that could produce a very incorrect distance, so they place the distance at about 1 M LYs. This is the view I take. Because of the methods of brightness measurement related to distance, intergalactic gases will always tend to lengthen the distance to very distant objects if there is absorption. This also helps explain some of the current mysteries of dark energy. The problem is that IG gas is not directly measurable, so it is for the most part ignored. But it is implied by polarization of EM energy.<br /><br />The light is blue shifted from Andromeda so it is moving in our general direction. I seriously doubt it is on a collision course with us, but maybe someday we might determine this a bit better.<br />

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