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Alien astronomer?

crabbiT Scot

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crabbiT Scot

crabbiT Scot

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Ok, so I was sitting in the back garden last night, viewing M81 and M82, both galaxies, and lets say for arguments sake, 12 million light years away. My mind started wandering (tends to happen when I'm relaxing :o ).

If there is a guy sitting in his back garden 12 millions years from now, on a planet orbiting one the of the stars in M81 or M82, and he had an amazing telescope that could see people on Earth, would he be able to see me looking at him 12 million years ago??? :D:icon_scratch::o

Maybe a really stupid question??? :)

Thanks anyway :(

Scott

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Stephen

Stephen

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I think i saw one of those telescopes advertised the other other day

THE CELESTRON 1MILLION " SCT :D

Am i right in saying that the alien wouldn't see you because humans

dont give off light ?

Oh now you're just letting physics get in the way! :)

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sammy1404

sammy1404

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if you were looking right now and he was looking right now in 12 million years then yes this astronomer would see you. Wierd right lol so if we see people on other planets now then thats what they were like x time ago. So imagine how much they may have evolved in that time span!

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NickMilner

NickMilner

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So we're all conversant with the fact that looking outward is the same as looking backward in time, right? The light from an object 12 million lightyears away has taken 12 million years to get here, so we're seeing what it was like 12 million years ago.

If you could instantly jump from here to there you'd see earth as it was 12 million years ago, and if you had a sufficiently powerful telescope you'd be able to watch history unfold and answer all the questions we ever had about the past!

But of course there's a law that prevents us from doing this. A law that prevents us from "time travel" in this way. And that law is, of course, the speed of light itself. :) It's impossible to instantly jump 12 million light years away because we are bound to travel at a speed less than light (because we have mass).

It's quite beautiful, when you think about it. :)

(Sorry if this was obvious and old hat to you - but I love it!)

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Rosanella

Rosanella

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...., and he had an amazing telescope that could see people on Earth, would he be able to see me looking at him 12 million years ago???....

Where's that telescope? I want one and possibly the portable version :)

Ok, so if the alien astronmer is looking back in time and suddently both of you are staring at each other through the 'scopes but he's 12 million years ahead, then we on Eartch are behind in time. So, he's looking at his past while you're looking at his future. WoW! It's fenomenal :) ... and mind bending

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NickMilner

NickMilner

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Where's that telescope? I want one and possibly the portable version :)

Hmm, maybe if we had a supermassive black hole as an objective (now that's what I call an aperture!) Light from earth would be sucked into it when it finally arrived, but some wouldn't pass over the event horizon and would therefore bend around (gravitational lensing). So, you place an artificial body on the far side of the hole at the focal point - using the black hole as a giant refractor - and sit there, possibly with a 25mm Plössel and a 2x Barlow! :) (it's all complete BS, of course!)

Ok, so if the alien astronmer is looking back in time and suddently both of you are staring at each other through the 'scopes but he's 12 million years ahead, then we on Eartch are behind in time. So, he's looking at his past while you're looking at his future. WoW! It's fenomenal :) ... and mind bending
But remember, it takes 12 million years for the light to travel between us, so you're not looking at his future, you're looking at what he was doing 12 million years ago. Also, since he's looking at what we were doing 12 million years ago we couldn't get into this situation, unless...
  1. We start looking through our telescope
  2. 12 million years later the alien looks through his super scope and sees us start to look through ours
  3. 12 million years after that we would be able to see him start to look through his scope

Therefore, we have to look through our scope for 24 million years before we could see each other (and it would always be a view of 12 million years ago). That's going to give anyone a sore neck!

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FraserClarke

FraserClarke

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If there is a guy sitting in his back garden 12 millions years from now, on a planet orbiting one the of the stars in M81 or M82, and he had an amazing telescope that could see people on Earth,

As a mental exercise whilst cycling, I worked out you'd need a telescope with a primary mirror ~1 light year in diameter to get enough resolution to "see" a 2m high person in M81. So, for an f/5 telescope, you'd be looking 12 millions and 5 years into the past by the time the light got to the eyepiece :)

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crabbiT Scot

crabbiT Scot

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As a mental exercise whilst cycling, I worked out you'd need a telescope with a primary mirror ~1 light year in diameter to get enough resolution to "see" a 2m high person in M81. So, for an f/5 telescope, you'd be looking 12 millions and 5 years into the past by the time the light got to the eyepiece :)

Lol that's brilliant :) Unfortunately, I don't think FLO stock them yet :)

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acey

acey

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The alien astronomer 12 million years from now would see you looking up in their direction from the dark part of a crescent Earth so wouldn't have much of a view of you, and would need an image intensifier as well as a humungus telescope. Try putting a big sign on your lawn that they can see in daytime.:)

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FraserClarke

FraserClarke

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Yet more, quite possibly dodgy, maths fun for M81.

Mr and/or Mrs Alien Astronomer with their 1 light year across telescope trained on the Earth would be able to detect your neighbours 500W security lamp (making the completely fair assumption that it is radiating isotropically, and not shielded from the sky in any way what-so-ever). In fact, they'd be able to detect ~2500 photons per second from said light. Which interestingly is about the same brightness as a 13th magnitude star seen through a 6-inch reflector... (i.e. faint, but detectable if you've got a good dark parsec or two around you).

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