June 22, 2004
towerspiraltelescope
A radio telescope - a tower with a bowl on top. (see May 24th 2004 entry).
The tower takes as it's starting point the Tower of Babel. Genesis 11 - "let us build a city, with a tower that reaches to the heavens". The story unfolds - God is not pleased and punishes the people by having them all speak different languages. No longer of the same tongue they can't understand one another. Babble. Radio noise.
Jump forward via Bruegal's painting to the late nineteenth century. Konstantin Tsiolkovsky, the father of space exploration, inspired by the Eiffel Tower, considers the building of a tower that will reach up into space where he imagined placing a "celestial castle" in geosynchronus orbit, at the end of a long long cable. A space elevator. A quarter of a century later, Vladimir Tatlin, designs another construction, a synthesis of the Eiffel Tower and the Tower of Babylon, The Monument to the Third International.
The spiral permeates the recurring towers through the centuries. The spiral, once one starts looking, is everywhere - from the pattern of seeds in a sunflower to the arc of a galaxy.
A satellite dish is a concave surface. A bowl. What falls in is gathered and focussed (as opposed to a convex surface which throws all that falls on it back out). Face a bowl to the sky and it will catch radio waves and focus them to a point. An antenna placed at the focus converts the waves to small electrical fluctuations which can be amplified. listened to, converted to visual maps.
Many designs for antennas are of a spiral shape. It's possible to make a radio telescope that is purely a wire tracing the path of a rising spiral.
Plotting hydrogen emissions - tune in on the 1420 Mhz waveband - reveals vast clouds of the gas, among them spirals, thousands, millions of light years across.