<p>Most things in space move very predictably. For reasonably dense objects, like stars, planets or asteroids, gravity far outweighs all of the other forces acting on them, and it's not too hard to take account of gravity and predict their movements (if you have a powerful enough computer. For things like clouds of very thin gas it's a bit harder. So from the positions and movements of all the distant objects that we can see (at the time when the light we see them by left them), we can pretty accurately predict their movements a considerable way into the future, for instance up to possible collisions a few centuries out (for an asteroid) or a few billion years out (for Andromeda). </p>

<p>Of course there is a possibility of something unexpected happening -- between the light we see now being emitted and a possible future collision, a supermassive black hole travelling at close to the speed of light could pass through the Andromeda galaxy and scatter it, for instance, but we don't see things like that happening anywhere else in the universe, so it seems pretty unlikely to happen here.</p>

CC BY-SA 3.0
2018-04-17T09:28:18.043Z
2018-04-17T09:28:18.043Z
Steve Linton
<blockquote>
  <p>how can we confirm we are truly studying the actually position and everything of that object as we are seeing object from the past.</p>
</blockquote>

<p>We can't.</p>

<p>All astronomical observations are of things as they <em>were</em> at a time in the past that depends how far away the object is. We understand that. If we need to calculate the future behaviour of an object, then our extrapolation begins from that past point in time to work out a trajectory through time and space.</p>

CC BY-SA 3.0
2018-04-17T21:59:03.790Z
2018-04-17T21:59:03.790Z
ProfRob
<p>I think it's important to remember that we ONLY interact with objects in our past. If you're in the same room with someone, every foot distance between you is a nanosecond into the past -- in <em>exactly the same way</em> alpha centauri is 4 years in the past and Andromeda is 3 million years in the past.</p>
<p><em><strong>Everything with mass carries with its own &quot;right now.&quot;</strong></em></p>
<p>Because you're so close, your clocks are almost synchronized. But they're not exactly the same, ever.</p>
<p>Even when you touch something, you're really pushing against an electric field that was emitted by something a tiny distance away a short time in the past.</p>
<p>This is silly, irrelevant, or boring; but if you're going to think about space and time, you have to see interactions and distances in four dimensions, and this is the way you MUST  think about it if you want to understand what's going on.</p>
<p>EDIT: Oops, this was supposed to be a comment for @profrob, but I'll leave it as a poor answer.</p>

CC BY-SA 4.0
2024-07-04T04:04:27.767Z
2024-07-04T04:14:17.140Z
2024-07-04T04:14:17.140Z
Miss Understands
<p>Is it actually relevant to study objects that are light years far? Because in theories we are actually seeing the past as the light takes years to reach us.</p>

<p>Lets say we are studying a asteroid that is going to hit as after several hundred years how can we confirm we are truly studying the actually position and everything of that object as we are seeing object from the past.</p>

CC BY-SA 3.0
2018-04-17T07:12:54.520Z
An asteroid which is going to hit the Earth is likely to be very close (astronomically speaking) – mere light-*minutes* away instead of light-years.
Glorfindel
CC BY-SA 3.0
2018-04-17T07:29:09.147Z
Asteroid is just an example, lets take Andromeda - milky way collision. As Andromeda galaxy is about 2.5 million light-years far so actually the scientists concluded it is going to happen by studying things that are probably taken place years back. Right
Unnikrishnan R
CC BY-SA 3.0
2018-04-17T08:37:01.030Z
Well everything can be accounted for, at least for objects moving "around" us and for which a model considering expansion of the universe isn't necessary and won't be affected by change of cosmological model. Obviously the colliding Andromeda will have morphed into something different as compared to what we see. But knowing its "current" position and motion let us predict where it will be.
Alchimista
<asteroids><distances><space-time>
Are we really seeing the asteroids from the past?
Unnikrishnan R
# Are we really seeing the asteroids from the past?

(Asked by: username_0 on 2018-04-17)

Is it actually relevant to study objects that are light years far? Because in theories we are actually seeing the past as the light takes years to reach us.

Lets say we are studying a asteroid that is going to hit as after several hundred years how can we confirm we are truly studying the actually position and everything of that object as we are seeing object from the past.

**Tags:** asteroids, distances, space-time

> **Comments:**
> **username_1**: An asteroid which is going to hit the Earth is likely to be very close (astronomically speaking) – mere light-*minutes* away instead of light-years.  
> **username_0**: Asteroid is just an example, lets take Andromeda - milky way collision. As Andromeda galaxy is about 2.5 million light-years far so actually the scientists concluded it is going to happen by studying things that are probably taken place years back. Right  
> **username_2**: Well everything can be accounted for, at least for objects moving "around" us and for which a model considering expansion of the universe isn't necessary and won't be affected by change of cosmological model. Obviously the colliding Andromeda will have morphed into something different as compared to what we see. But knowing its "current" position and motion let us predict where it will be.  

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## 3 answers

### Answer by username_3 on 2018-04-17. Score: 5

Most things in space move very predictably. For reasonably dense objects, like stars, planets or asteroids, gravity far outweighs all of the other forces acting on them, and it's not too hard to take account of gravity and predict their movements (if you have a powerful enough computer. For things like clouds of very thin gas it's a bit harder. So from the positions and movements of all the distant objects that we can see (at the time when the light we see them by left them), we can pretty accurately predict their movements a considerable way into the future, for instance up to possible collisions a few centuries out (for an asteroid) or a few billion years out (for Andromeda).

Of course there is a possibility of something unexpected happening -- between the light we see now being emitted and a possible future collision, a supermassive black hole travelling at close to the speed of light could pass through the Andromeda galaxy and scatter it, for instance, but we don't see things like that happening anywhere else in the universe, so it seems pretty unlikely to happen here.


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### Answer by username_4 on 2018-04-17. Score: 2

> how can we confirm we are truly studying the actually position and everything of that object as we are seeing object from the past.

We can't.

All astronomical observations are of things as they *were* at a time in the past that depends how far away the object is. We understand that. If we need to calculate the future behaviour of an object, then our extrapolation begins from that past point in time to work out a trajectory through time and space.


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### Answer by username_5 on 2024-07-04. Score: -2

I think it's important to remember that we ONLY interact with objects in our past. If you're in the same room with someone, every foot distance between you is a nanosecond into the past -- in *exactly the same way* alpha centauri is 4 years in the past and Andromeda is 3 million years in the past.

***Everything with mass carries with its own "right now."***

Because you're so close, your clocks are almost synchronized. But they're not exactly the same, ever.

Even when you touch something, you're really pushing against an electric field that was emitted by something a tiny distance away a short time in the past.

This is silly, irrelevant, or boring; but if you're going to think about space and time, you have to see interactions and distances in four dimensions, and this is the way you MUST think about it if you want to understand what's going on.

EDIT: Oops, this was supposed to be a comment for @username_4, but I'll leave it as a poor answer.


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