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 Just been reading a thought provoking thread on another forum about the distance of the Andromeda Galaxy.  The OP asked, being as the galaxy is accepted as appearing as it was 2.5 million years ago, how much nearer to us is it now.  It appears that at its speed is 110 kilometres/sec it will be 917  light years nearer, in other words not a noticeable amount.  It was then said that if scaled down to the galaxy being equivalent to a human being  the distance would be 1/2" in 2.5  million years and the distance to the galaxy about 7.5ft.  A further thought was that due to its supposed diameter of 200,000 light years, light observed from its nearest edge reaches us 200,000 years sooner than light from its furthest edge.  Something to think about when you next observe it.      🤔

Edited by Peter Drew
typo
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Peter you got me thinking already...

It really is incredibly difficult to comprehend the time and distances involved isn't it?

Just flying to Pluto has taken space probes 10-12 years. Even at light speed it would take roughly 4.5 hours. In the grand scheme of things that's barely spitting distance. In fact more like a dainty throat clearance away.

 

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The thing that always makes me think, when you look into the night sky you're looking into a time-machine. Many of the things you see are no longer where you're looking and some may not even exist anymore. Equally, there's "stuff" that is there but you can't see it yet.

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That's really interesting and helps put the magnitude in perspective. 

So over the 2.5mil years the light has travelled, even at massive speeds of 110 km/s it has 'only' closed the distance by 0.004%. 

Incredible. 

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The science is awesome.

A couple of of nights ago, I was out looking at Taurus through a pair of if 8x42 binoculars. Crystal clear night but I do get light pollution. I was struck by the sheer mass of stars that could be seen, and I was thinking about how our ancestors, with no light pollution and no expensive binoculars mapped out constellations and created myths around them. Gemini was clear with Castor and Pollux and the Pleiades were beautiful. 

I admire the science of the universe, but we should never forget the staggering beauty of what we see in the night sky. 

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Carlo Rovelli’s Reality is Not What it Seems (or perhaps The Order of Time) is a superb mainly qualitative discussion of just this stuff. How a photon halfway from Andromeda is in Andromeda’s past but our future. How it’s possible indeed commonplace for any of us to time-travel forwards but not backwards. By far the best explanations of these mind-exploding things I’ve read, anyway.

Magnus

Edited by Captain Magenta
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I've always been fascinated with Andromeda being one of the furthest objects you can see with the naked eye. And despite this distance you can even resolve individual stars in this galaxy with fairly modest imaging equipment.

What hasn't been mentioned here but no doubt most will be aware of is the the Andromeda galaxy is in the Local Group, merely a stone's throw (or spitting distance) away from our own Milky Way. Compare that to other galaxies out there and beyond, think Hubble Deep Field and Hubble Ultra-Deep Field.

Those photons have travelled all that distance for so many years and then get squished on your retina or camera sensor like a bug on a windscreen.

 

 

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On 11/02/2021 at 22:30, Peter Drew said:

A further thought was that due to its supposed diameter of 200,000 light years, light observed from its nearest edge reaches us 200,000 years sooner than light from its furthest edge.  Something to think about when you next observe it.      

That's an interesting one to let the mind play with. I've just been reading that M31 has an estimated rotational velocity of 225 km/s  at 1,300 light years from the core, so things are never quite where we think they are to say the least. A "snapshot in time" and the idea of what we mean by "now" gets very blurry ... err ...I think. 

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