On Friday, it will be 70 years since the shipping forecast was first read out on the radio. A litany familiar to all, it remains mysterious to all but a few. Where is North Utsire? What does backing southerly mean? Would you fancy Finisterre? In 1992, the photographer Mark Power set out on an odyssey which will take him to all 31 sea areas. Outlook fair to good. Report page 26
Viking. Dogger Bank. Faeroes. Rockall. German Bight. Fred Astaire. Fred Astaire? I mean Finisterre, although these Gallic syllables sounded like the name of Hollywood's leading tap-dancer to me as a child, tucked up under the eiderdown on stormy nights, listening to the rain drumming, wind howling (or so it seemed) on my London window and the shipping forecast on the Home Service on the portable radio under my pillow.

The BBC has broadcast the shipping forecast with its risings and falls, goods and fairs, Forties and Finisterres since it first gained its charter in 1928. The forecasts actually began on 26 January, 1926, before the Beeb nannied the nation. Before then, gale warnings were tapped across Britannia's waves by Morse code. Essential information the shipping forecast, yet it needed no words. Seventy years on, we can hardly imagine a Britain, or a Beeb, without that lovely litany of late-night warning spoken still in perfect RP by the duty Radio 4 continuity announcer.

As David Chandler of the Photographers' Gallery writes in the preface to Mark Power's book of photographs of the places behind the names, "The shipping forecast... is at once familiar and obscure. For most people, those of us whose lives and livelihoods are not determined by the weather at sea, its coded messages are unintelligible, yet it resonates with a powerful mythic voice, conjuring dramatic seafaring imagery, the unremitting challenge of a sea that encloses us, that symbolically protects us and isolates the British isles, our group of old island nations, battered but surviving."

German Bight, Fastnet, Lundy and Malin exist not just on the edge of Britain's coastal waters, but also on the fringes of our imagination. For most of us, Fair Isle might as well be an offshore annexe of Narnia; Rockall, a goblins' fortress; and Forties, a film-noirish sort of place that most definitely roars.

It is something of a shock to see this world of uneasy dreams come to life in Power's potent photographs. Fortunately, no point on the shipping forecast map disappoints. Each is as bizarre and as unexpected as you secretly hope it will be; for the coast, its sea walls and promontories, lighthouses and prolific detritus, is host to some of the most unlikely buildings and groupings of people.

What Power believes he has caught are places where "existence is uncertain, contingent", places where "like patterns drawn in sand, life is subject to ebb and flow, the relentless turning of the tide and to forces beyond its control." His view is austere, bleak even, but with a salty beauty of its own. Because the pictures he has framed verge on the surreal, he does not tread on our dream of Britain's mythical shores in his quest for the real. Rockall, Finisterre, Fair Isle and Faeroes, despite Power's adventure, remain fabulous.

The shipping forecast itself remains real and in safe hands. Broadcast nightly at 48 minutes past midnight, after the regular rendition of "Sailing By" (by Ronald Byng), it reaches yachts and tankers by long-wave radio signals. The BBC has the sole right to long-wave broadcasting, which is why it has not yet been taken over by a commercial station. No law insists that Radio 4 broadcast the shipping forecast, but even the most iconoclastic, thrusting young corporate executive would think twice before pulling the plug on one of the most unexpectedly popular, delightful and - to sailors - vital British radio shows. Jonathan Glancey