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A PHYSICIST WRITES . . .

(March 2011)

I hesitate to launch another column with a look at an edition of Top Gear on BBC2, but a note in Radio Times caught my eye: Jeremy Clarkson races the new Jaguar XJ against something even bigger and more powerful ó the rotation of the earth itself. Now the earth rotates from west to east, so evidently JC would be driving the other way and aiming to keep the sun steady in the sky.

But wait a minute: that means travelling at over 1000 mph, if you are on the equator. Even at our S of England latitude (on a smaller circle around the earth) itís 610 mph, and if he was heading up to northern Scandinavia for the race he would still need to average 360 mph to keep pace with the sun. This I had to see. But not the whole show, please, so like last time I viewed it on iPlayer.

What Clarkson announced was that he was going to drive from Landís End to Lowestoft (the western and eastern extremeties of England), starting at sunset and racing to arrive before sunrise. And ďto make it especially hardĒ, he would be doing this ďon Midsummer DayĒ (did he mean the night before, or the night after?) giving him just under seven hours to drive 432 miles, and requiring an average speed of 62 mph.

Do you follow: far from racing against the rotation of the earth, JC was going to be superimposing his own speed on it! Thatís a combined speed of more than 670 mph ó Iím surprised he didnít boast about this. The immediate question (to me) was why he didnít drive the route in the opposite direction: the earth would still be pulling him round from west to east, but more slowly, so he would have had an additional 80 minutes between sunset (at Lowestoft) and sunrise (Landís End). Though when you think about it, that would have meant no opportunity to film the low sun against wide dreamy sea-horizons, as we were shown at each end of the journey.

Anyway, Clarkson set off and was soon making unkind comments about a learner driver who was holding him up (was he never a learner himself?). Road works too had him fuming. Then I started to notice things: the camera car in front of him, or behind, or (dangerously) alongside. Scores of fixed-camera shots, from bridges and roadsides, of the Jaguar zooming past. A bright interior light on all the time, to make him visible as he pointed out to us (through the cameras mounted inside the car) its special features, from seat-massager to dynamic-mode engine control. His other hand lazily touching the wheel ... does the BBC have no Health & Safety Department with a duty to carry out a risk assessment, before a programme is authorized that includes the filming of a driver in action?

OK, I know about video post-production and editing, and obviously most of the fixed external shots were recorded at another time. But JCís chatter was plainly filmed as it happened ó I mean, as he drove at full tilt, peering out through the windscreen from light into darkness. Could this have been any more hazardous to life, limb and car? It was some relief that he didnít appear to have passengers aboard.

The journey from Landís End to Lowestoft did seem to be genuine and as described ... except that from the camera car, early on, we caught sight of the waxing moon, clearly just three-quarters full which, my research reveals, dates the filming (of the moon, at least) to a couple of nights or more before Midsummer Day. Also, the moon kept coming into view at intervals right up until just before the end of the journey at dawn, when it should have set three hours earlier. But thatís artistic and non-scientific video-editing for you!

And how better to round off quite an exciting drive than to show Clarkson apparently arriving in Lowestoft in perfect time for the sunrise, without (as far as we had been informed) exceeding the 70 mph limit anywhere. He zoomed to a halt on a large distinctively patterned circle, laid down I guess to mark the eastern-most point of England. Though when I found the spot in Google Street View and in those wonderful Birdís Eye angled aerial pictures on www.bing.com/maps, I observed that itís actually on the promenade, behind solid black bollards. Did someone phone ahead to get them unlocked and removed, or what?

There were other oddities too about the end of this long journey. JC climbed out of the car without a hint of tiredness or stiffness or needing a pee. He then stood looking at the sun as it appeared, and said not a word, just emitting a sort of triumphant gurgle. And back in the studio he hardly mentioned the Ďraceí at all, but focused on the Jaguar XKís characteristics (superb, he declared, except for its looks). But perhaps all this is in the tradition of Top Gear.

Changing the subject ó or rather, going back to the moon ó already, early in the month, Iíve seen news columns saying something like: ďLook up at the sky on 19 March, and you will see the biggest and brightest full moon of the year, in fact the biggest since 1993.Ē This does make me smile. The actual brightness of the full moonís surface doesnít change (except to us when cloud comes between), though thatís just a quibble.

Certainly the distance of the moon from the earth varies, by about 15%, as it follows its orbit. Hence the amount of light it reflects back to us when full (which happens at thirteen positions around the orbit through the year) can alter by over 30%. But the difference between this monthís full moon and last monthís, or next monthís, is less than 1% in distance, hence youíre highly unlikely to notice the change (and as for 1993, that full moon was probably only a few miles closer still).

The same thing happens with any slowly oscillating measurement: it approaches its maximum only gradually, and falls away likewise. For example, the (official) length of daylight varies by less than three minutes during a whole fortnight around Midsummer. So whichever night Jeremy Clarkson had chosen in that period, he would have faced pretty much the same Ďchallengeí!

Peter Soul

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