Return to IndexA by-now-infamous programme which aired on BBC2 in February 2011 posed the question that is the title of this page. It considered many aspects of the relationship between the Earth and the Moon in order to give an answer. While it is clearly the case that fully detailed explanations could not be given in a programme of this type, unfortunately many of the simplified analyses it put forward were at best misleading, often confused and frequently just plain wrong! I thus engaged the producers in a lengthy discussion and managed to persuade them to correct some of the worst errors by the time the programme was repeated on BBC4 in May 2012, but not all. Unfortunately, the revised version (with its remaining errors) is still shown every so often, so I felt I should set about constructing a few paragraphs in order to set the record straight as concerns those parts of the programme dealing with "computational astronomy" and orbital mechanics. This is not to say that all the rest was correct of course (far from it!), but my field of expertise is primarily in these areas and so I felt I was best equipped to tackle the errors in these sections of the programme.
However, my studies soon revealed that to do these subject areas justice would require a very much fuller treatment than I had initially anticipated, and so the "few paragraphs" have turned into a set of articles of a complexity and depth comparable to any in these Theory Pages. The information presented goes way beyond anything that a popular science programme could possibly contemplate though and so I have also written a page giving the bare bones of the various discussions, at a level that the original programme could indeed have used with just a little more thought.
The description of the origin of the Earth's oceanic tides in the first version of the programme was, unfortunately, almost totally incorrect! About the only thing they got right was that the gravitational attraction of the Moon on the waters of the Earth causes them to rise up slightly under the Moon, to produce a "tidal bulge". At this point, the original programme said that as the Moon orbited the Earth the bulge was dragged round with it, producing the high and low tides - oh dear! This is patently absurd, as it would produce high tides monthly rather than daily.
What, for some unaccountable reason, was overlooked was that the Earth is itself rotating on its axis and so, because this rotation is much faster than the orbital rotation of the Moon, the Earth's land-masses would move through the [relatively speaking] stationary bulge thus experiencing high and low water, i.e. tides, each day. The much slower motion of the Moon would indeed drag the bulge round but this simply increases the interval between the daily high tides. This error was, fortunately, corrected in the revised version but the damage had been done.
When I started to look more deeply into the phenomenon of the tides, however, I soon discovered that the subject is far more complex than I expected, and would need an entire article to itself in order to do it justice. I thus set about the task, the result of which can be found by clicking here or as "The Tides" in the index of articles.
While the programme's description of the recession of the Moon was not entirely inaccurate, it did confuse Newton's Third Law ("to every action there is an equal and opposite reaction") with the Principle of Conservation of Momentum when attempting to explain why the Moon's distance is increasing as a result of the slow-down in the Earth's spin rate caused by tidal friction. It also offered us no means by which the angular momentum could be transferred from one to the other, completely overlooking the very important concept of "tidal lag" - the fact that tidal friction not only decreases the Earth's spin rate but also moves the tidal bulges slightly forward of the Earth-Moon line. They thus exert a gravitational force on the Moon, and this force is the agency which transfers energy and momentum: to omit this description therefore left out a very important part of the story.
The programme did identify that the tides and the Moon's recession are linked, however, and so it was inevitable that I would have to tackle the recession problem when describing the tides. This study threw up many complications though, and so the results of my research now constitute an entire article which can be found by clicking here or as "The Recession of the Moon" in the index. This article also contains, as a sort of "coda", a couple of sections exploring some consequences of lunar recession - the ultimate extinction of total solar eclipses and the change in the length of the day and lunar month over time.
The programme claimed that because there are more craters on the side of the Moon facing away from the Earth than there are on the side facing towards it, the Moon must therefore have intercepted the incoming bodies that caused the excess number of craters on the "far side", thus preventing them hitting the Earth and quite possibly wiping out all life, once and for all. Unfortunately, this line of reasoning is wrong at every point.
It is quite straightforward to show this, and so I could have done so as part of this page. However, as I have produced separate articles for all the other investigations connected with the programme, I have moved this discussion onto its own page also. It can be found by clicking here or as "The Moon as Guardian Angel" in the index.
Currently, the mean angle at which the Earth's spin axis sits with respect to plane of its orbit is 23 degrees 26 minutes and 20.4 seconds, or 23.439 degrees. This tilt, or obliquity to give it its formal name, is the reason we have seasons: when a given hemisphere is tilted towards the Sun it is summer there (and winter in the other hemisphere) and when it is tilted away the situation is reversed. In this section, the programme took as its premise the theory that, without the Moon, the obliquity would vary in a chaotic way over a very large range. This would clearly be highly detrimental to life, as the seasonal variation would be greatly exaggerated. There is, in fact, some theoretical basis to this idea but the explanation of the way the Moon probably stabilises the obliquity was wrong in all respects!
As with most of the other issues I am covering, when I looked into the subject in sufficient depth to enable me to give a scientifically accurate answer it became clear that I would have to write a full article on the subject which can be found by clicking here or as "The Stability of the Earth's Obliquity" in the index.
I have stated in a number of places in these articles that it would clearly not have been appropriate for 'Do We Really Need The Moon?' to have gone into even a fraction of the detail I have, as it would be way above the level of a popular-science programme. This begs the obvious question: what then should it have said? In this article I attempt to answer that question, by giving a "60 second summary" of the subjects covered in vastly greater depth in my other articles.
My version of what the programme should have said can be found by clicking here or as "What the programme should have said" in the index.