BBC4’s Spectacular Vista of our Voyage to Neptune and Beyond.

For a long time in the 20th cen­tu­ry it was wide­ly believed that we would nev­er be able to trav­el through space fur­ther than to our near­est neigh­bour, Mars. The fuel need­ed to counter the grav­i­ta­tion­al pull of the sun and plan­ets would make that impossible.

But when a bril­liant PhD stu­dent solved one of the great maths’ prob­lems, the whole of the solar sys­tem sud­den­ly opened up.

The prob­lem being; how do you work out a space ship’s tra­jec­to­ry when its posi­tion is being con­stant­ly affect­ed by the huge grav­i­ta­tion­al pull of the sun to one side, and an enor­mous plan­et to the oth­er? Every new posi­tion will then be dif­fer­ent­ly affect­ed by both, and in con­stant­ly vary­ing ways.

Once that had been solved how­ev­er, they sud­den­ly real­ized that you could use that mas­sive grav­i­ta­tion­al pull as a las­so to fling your space craft off in any direc­tion you liked. Fur­ther­more, you’d be able to do so with­out using up any fuel what­so­ev­er. Your momen­tum could pro­pel you indefinitely.

Then anoth­er grad stu­dent spot­ted that the four biggest, out­er plan­ets, Jupiter, by far and away the biggest, Sat­urn, Uranus and Nep­tune (Plu­to was re-clas­si­fied as a dwarf plan­et in 2004) would all be aligned between 1975–7. We would have to wait anoth­er 200 years for the next chance. 

So in 1977 the two Voy­agers, I and II were launched. And over the next 12 years they sent back extra­or­di­nary data and pho­tographs of our four biggest gas plan­ets and their cou­ple of hun­dred moons.

When Voy­ager II even­tu­al­ly arrived at Nep­tune, some 3 bil­lion miles away, they need­ed to be able to cal­cu­late the pre­cise moment it passed the plan­et’s North pole, to with­in one, sin­gle sec­ond! The pho­tographs that result­ed were spectacular.

And that it was thought was that. But then Carl Sagan, Nasa’s de fac­to spokesman had an idea. Why did­n’t they get Voy­ager I, as it sped away from us, to turn around and take a pho­to­graph of us from the edge of our solar sys­tem. The result is a pho­to­graph with the Earth seen so small that it takes up less than a sin­gle pix­el (see below).

On the one hand, it’s a time­ly reminder of how insignif­i­cant we are in the grand scheme of things. But on the oth­er, it’s a cel­e­bra­tion of how extra­or­di­nary we are. We sent a machine near­ly four bil­lion miles and 13 years into the future to take a pho­to­graph and send the infor­ma­tion back to us, so that all of us can have a look at it today. 

Voy­ager I is 11 bil­lion miles away as we speak and has just reached the out­er reach­es of our solar sys­tem. It’s still send­ing back data, which it does using a mil­lionth of a bil­lionth of a watt. And the data that it sends takes 15 hours for the speed of light to reach us.

And all of it built in 1977. That, by the way, was the year Apple was launched.

BBC4’s Voy­ager: to the final fron­tier is yet anoth­er in what is fast prov­ing to be a gold­en age of sci­ence pro­gram­ming from the BBC (see for instance their recent doc on the Antikythera mech­a­nism, The 2000 Year Old Com­put­erhere.)

It struck exact­ly the right bal­ance between calm­ly pro­vid­ing the facts, and qui­et­ly look­ing up in awe. And if at all you can, watch it.

Sign up for a sub­scrip­tion right or below, and I shall keep you post­ed every week on All the Very Best and Worst in Film, Tele­vi­sion and Music.

The Earth seen from Voy­ager 1.