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Story: My boss dropped this off on my desk. The astronomers just received this message from a nearby galaxy. I need to decipher it and get a response drafted asap.

Message: AqgEUFASIiWVVVJAAAAAAYAADQAAGgAAVAAA+AAAAAYcYYgAMhoxhr7774AAABAABAAAACAAD8AB8AAAGGHGICAIaGOa++++AAAAQMAQAYAAgwA/BgfADAAQCAQQMBAYYEAMQwABmAAxDAGGBAQIBBAYBEAwCIAgIICAgIAGAMAwBHWACAgAEHwAIXS2BOT+4cG4AoOyBQfkCgwINgAAAAA4IAB1FVTgCqAAFAAPgAB/wAOA4AwAYDQBYMwGYRQUQiRIgEUQAIQgAQBAAJQAefTw

What is this message saying?

What is an appropriate response?

Please include which hints/resources were used with your answer:

1)

It is a fairly well known message, but not in this format.

2)

It was originally sent via radio waves. (~2375 MHz at 1000 kW)

3)

It was originally 1679 bits (There is an extra 0 bit on the end to make it fit base 64)

4)

Put the Binary data in rows of 23 bits.

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It's

the Arecibo message.

It shows

the numbers from 1 to 10 in a slightly weird version of binary, followed by some cryptic information about DNA, followed by a picture of a DNA double helix, etc. See that Wikipedia page for all the details. It's meant to be Homo Sapiens 101 for aliens.

It is

very unlikely that it came from a different galaxy.

An appropriate response might be either

Ha ha, very funny

or perhaps

Oh, it seems there's an enormous mirror 21 light years away.

Since the questioner asks: I read all the hints (I always do), though I've no idea what a question less than half an hour old is doing with four hints already. I don't think I'd have needed them, though #4 saved a minute or two dragging the right-hand edge of a text-editor window around. I didn't remember the name in my first spoilered paragraph above so I googled for

73 alien message

which of course turned it up immediately.

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  • 3
    $\begingroup$ I got the same answer by searching "1679 bits". $\endgroup$ – f'' Aug 17 '16 at 19:18
  • $\begingroup$ Yep! but it should be the whole message, not just the beginning (I mis-typed the hint switched the number of rows/columns). I used conv.darkbyte.ru to convert. I'm fairly new to this stackexchange, this is my first puzzle. Is it normal to add hints over time? How quickly are hints usually added? $\endgroup$ – 182764125216 Aug 19 '16 at 15:17
  • $\begingroup$ Sorry, yes, it's the whole thing. My mistake. $\endgroup$ – Gareth McCaughan Aug 19 '16 at 15:36
  • $\begingroup$ You should try to make your puzzle solvable in principle without any hints, given infinite intelligence. Then add hints only once you have good reason to think that other p.s.e participants aren't likely to make progress without them, which means waiting long enough that you'd expect to see answers (or some other evidence of progress) if there were any. Maybe a day or thereabouts; exactly how long depends on the puzzle. $\endgroup$ – Gareth McCaughan Aug 19 '16 at 15:40

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