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Forecasting the real state of the galaxy
Since the light from deep sky objects takes thousands, and sometimes
millions of years to reach our eyes I was wondering if anyone is doing any research into forecasting what the actual sky looks like right now (imagine the speed of light was infinite - how would the sky actually look?) Taking the current position and structure of say, the Andromeda Galaxy, attempt to create a forecasted image of what it actually looks like at the moment in terms of its structure, and what its 'real' position in the sky is (how that has changed over the course of 2 million years) This could be quite a difficult task, since every object is at a different distance from Earth and therefore must be forecasted ahead by different amounts. Is there a name for this area of research? Okay, question two. Kind of related to the above. Andromeda is 200,000 light years in diameter. We are viewing it almost 'edge on'. Therefore the light from the edge closest to us is 200,000 years 'ahead' of the light from the furthest edge. Therefore, how can what we see in the sky be an accurate representation of the real structure of Andromeda? - It's as if the image gets more 'lagged' as we move further from the leading edge. The edge furthest away shows us what it looked like 2,200,000 years ago, the light from the leading edge showed what it looked like 2,000,000 years ago (approx) Could this actually be distorting our view of the galaxy to make it look more spiral-shaped than it actually is? John. |
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"John Honan" wrote in message ...
Since the light from deep sky objects takes thousands, and sometimes millions of years to reach our eyes I was wondering if anyone is doing any research into forecasting what the actual sky looks like right now (imagine the speed of light was infinite - how would the sky actually look?) Not much different than it does now. The speed of light, while finite, is much much faster than the relative velocity of most of what we can see (until you get very far away -- it turns out that much of what we can see at the edge of the universe is by now past our event horizon, i.e. they'll never see the light that's currently coming from us). Taking the current position and structure of say, the Andromeda Galaxy, attempt to create a forecasted image of what it actually looks like at the moment in terms of its structure, and what its 'real' position in the sky is (how that has changed over the course of 2 million years) Again, not much. It's a hundred thousand light years across, but the stars in it only move at hundreds of miles per second, whereas light travels at almost two hundred thousand miles per second. So it doesn't change much at the scale we're talking about. This could be quite a difficult task, since every object is at a different distance from Earth and therefore must be forecasted ahead by different amounts. Is there a name for this area of research? Other that "cosmology", I'm not aware of any. But it's essentially not a big enough difference to matter at any but the most distant scales, and even then it's only that the most distant (and fastest-receding) stuff has actually left our "universe" by now. Okay, question two. Kind of related to the above. Andromeda is 200,000 light years in diameter. We are viewing it almost 'edge on'. Therefore the light from the edge closest to us is 200,000 years 'ahead' of the light from the furthest edge. Therefore, how can what we see in the sky be an accurate representation of the real structure of Andromeda? - It's as if the image gets more 'lagged' as we move further from the leading edge. Yes, and the part moving toward us is blueshifted, which is one of the ways we can tell the direction it rotates. But again, it's not moving fast enough for this to distort the image in any really significant way. The difference is less than one part in a thousand -- and we know the direction it's moving, anyway. The edge furthest away shows us what it looked like 2,200,000 years ago, the light from the leading edge showed what it looked like 2,000,000 years ago (approx) Could this actually be distorting our view of the galaxy to make it look more spiral-shaped than it actually is? No; it doesn't actually work that way. There are lots of spiral galaxies that are face-on to us (the Whirlpool, for example, as the brightest and clearest one). John. Good thinking; unfortunately it doesn't really have much of an effect. |
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"eyelessgame" wrote in message
om... "John Honan" wrote in message ... Taking the current position and structure of say, the Andromeda Galaxy, attempt to create a forecasted image of what it actually looks like at the moment in terms of its structure, and what its 'real' position in the sky is (how that has changed over the course of 2 million years) Again, not much. It's a hundred thousand light years across, but the stars in it only move at hundreds of miles per second, whereas light travels at almost two hundred thousand miles per second. So it doesn't change much at the scale we're talking about. You're right. I did some rough calculations today basing the speed of light on 300,000Km/s, and the speed of the stars moving at 100km/s, the diameter of Andromeda is 200,000 light years, and Amdromeda is 2,000,000 light years away from us. In the course of 2,000,000 years, a star in Andromeda will only have moved 1/300th of the way across the galaxy. (As you pointed out, not much change at the scale we're talking about) Thanks for the feedback. John. |
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