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While awaiting for the electrician at the Norman Lockyer Observatory recently, I had a few moments to browse through many of the old books we have in our Lockyer archive. I came across this wonderful paragraph written by Sir Robert Ball in “The Romance of the Sky” which I guess was written before the invention of radio.
“Shall we ever be able to communicate intelligently with people on other planets? Often has the question been asked. Mars is at times most favourably placed – can we direct the Martian’s attention to a code signal and elicit a reply? Perhaps! Say we get a giant flagstaff about 500 miles in length and attach thereto a flag about as large, say, as Ireland, find some means of waving the flag – then, should the Martian astronomers be possessed of instruments equal to our own, I fancy, I hear them saying: “What are they doing down there (or up); I thought I saw something twinkling.”
I guess that was written at a time when semaphore was the prime means of long distance communication. Anyone keen to fact check whether a flag the size of Ireland can be visible from Mars!
David
Well, if we take Ireland as being 500 km long and the nearest Mars comes to the Earth as 60 million km then the flag would subtend around 500/60E6 = 8 microradians or about 2 arcsec so a Martian Damian Peach would definitely be able to resolve it.
So maybe Damian Peach’s great grandson will be the first to verify this – an image of Ireland from Mars!
Thanks Nick!David
Well, if we take Ireland as being 500 km long and the nearest Mars comes to the Earth as 60 million km then the flag would subtend around 500/60E6 = 8 microradians or about 2 arcsec so a Martian Damian Peach would definitely be able to resolve it.
Or our Martin Lewis, for that matter, who quite often produces of images showing surface details on the Galilean satellites of Jupiter, all of which are less than 2 arcsec across.
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