Patrick Moore: Mapping the Moon

On the fourth anniversary of Patrick Moore's passing, we look back at his first ever feature written for BBC Sky at Night Magazine, in which Patrick describes his fascination with observing and mapping the Moon.

MoonMAIN

When I became fascinated by astronomy at the age of six (in 1929), professional astronomers paid little attention to the Moon, which was widely regarded as boring despite its undoubted beauty.

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This meant that available maps were chiefly the work of amateurs.

I started keeping lunar notebooks in 1932 and soon realised that I would have to learn my own way around the Moon.

I decided on the best way to do this: I saved for a telescope and acquired a 3-inch refractor, which I still have. It cost me the princely sum of £7.10s.

Though there have been no major structural changes on the Moon for at least a thousand million years, its appearance alters very quickly, due mainly to the changing angle of the Sun’s rays.

Some people are surprised to learn that a crater is not in the least like a steep-sided well or mine shaft.

Drawn in profile, it is more like a shallow saucer (not a flying saucer, I hasten to add).

When a crater lies at or near the terminator – the boundary between the sunlit and dark hemispheres of the Moon – its floor is largely or completely in shadow and the effect is spectacular.

When the Sun rises over it, the shadows shrink and the crater may become very hard to identify.

Near full moon there are almost no shadows at all and the whole scene is dominated by the bright rays or streaks coming from craters such as Tycho (craters are named after prominent people of the past – Tycho Brahe was the last great observer of the pre-telescopic period).

Anxious to observe

My plan was to take what was just about the only outline lunar map then readily available and to make three drawings, at different times, of every named feature shown.

It was a year before I was satisfied – the clouds seemed to cover the sky whenever I was particularly anxious to observe, but at the end of the series of observations I was confident that I really did know the lunar surface.

What’s more, I had no trouble in identifying the craters, mountains, ridges and minor features such as the crack-like features known variously as rills, rilles or clefts.

The drawings themselves were of no scientific value whatsoever, but that was not my reason for making them: I was now ready to attempt something which might possibly be useful.

My faithful refractor was joined by a 12.5-inch reflector.

I also had the occasional use of a 6-inch refractor.

I had learned how to avoid some elementary pitfalls of mapping.

For example, I never try to draw too large an area at any one time, because inaccuracies are bound to creep in straight away.

If I wanted to draw the 60-mile-wide (96km-wide) crater Plato I would make the crater at least an inch across.

Also, everyone has his own style of drawing and much of the result depends upon one’s artistic ability.

Illustrators such as David Hardy and the late Leslie Ball can make drawings which look completely realistic.

I, however, cannot, so I strive for accuracy, using pencil and, for shadows, Indian ink.

Between 1939 and 1945 my observing book was blank – I had other things on my mind! – but when I was able to return to observation I concentrated on the libration areas, which are carried in and out of view and are always foreshortened.

One could make interesting discoveries in those days.

In 1946, using my new 12.5-inch, I came across a large, complex crater right on the limb, which was not on the map.

I drew it and called it Crater X; it has now been named after Einstein.

Then, on 16 December 1948, while examining the terminator, I saw what I thought to be a small Mare.

I sketched it, and sent in a report to the lunar section of the British Astronomical Association, then directed by HP Wilkins.

He confirmed it and I suggested the name of the Mare Orientale or Eastern Sea, because it lay on what was then referred to as the eastern limb of the Moon.

What I did not know, and had no means of knowing, was that it is one of the most important of all lunar features – a huge ringed structure, almost all of which is permanently invisible from Earth.

I had been lucky enough to catch the tiny fragment which was available.

Years later, observers in the United States re-discovered it, but the name of the Mare Orientale was retained.

However the International Astronomical Union held a vote at a General Assembly, the idea being to follow the astronautical orientation and reverse east and west.

I was among those who opposed this proposition, but we were heavily defeated.

As a result, the Eastern Sea is now on the Moon’s western limb.

A great moment

During the 1950s it became clear that rockets to the Moon were imminent and, as a result, professionals began to give the Earth’s satellite their full and undivided attention again.

In 1959 the Russians sent their spacecraft Lunik 3 on a round trip and obtained the first views of the averted hemisphere which, predictably, turned out to be just as cratered and barren as the areas we have always known.

I well remember my excitement.

The Russians had asked me to send over all my charts of the libration areas – I hope some of the charts were mildly useful to them – and the images came through when I was actually presenting a live Sky at Night television programme.

It was a great moment.

Let me stress that I was a minor figure in a large team of observers and, compared with others, my contribution was infinitesimal.

Also, any work I did is now completely obsolete.

Today any well-equipped amateur, using modern electronic devices, can produce results completely beyond me, either then or now.

The amateur can still be a real help, but old-fashioned lunar sketching, with pencil and paper, is a thing of the past – except for giving the observer sheer pleasure.

One has to move with the times and I have to regard myself as something of an astronomical dinosaur.

All the same, I have an inward feeling of satisfaction when I see pictures of the Mare Orientale!

Patrick’s top tips

How to get the most out of your lunar observations

1

A closer look

Binoculars can give splendid views of the Moon and will show many of the features given in the outline map.

Of course, low-power binoculars (say x7) will show less detail, but are excellent for the Earthshine and lunar eclipses, though probably not for occultations of any but the brightest stars.

Higher magnifications give greater scope, but above about x12 the binoculars are so heavy that a neck mounting or a tripod has to be used.

2

It’s not the size of the scope…

One can now obtain small telescopes at low cost that will give satisfying views of the Moon – something that could not have been said a few years ago.

For specialised investigations, I would say that an aperture of 4 inches (10cm) for a refractor or 6 inches (15cm) for a Newtonian reflector is about the minimum requirement, and this does depend upon the quality of the optics.

3

The Moon’s definition

Filters are widely used and for some types of observations they are invaluable.

But as far as the Moon is concerned I have decidedly mixed feelings about them, because I always feel that they result in a slight loss of definition.

However, if you want to see a full or near-full Moon under a reasonably low power a filter will generally be an advantage, as it will cut down the light and prevent hopeless dazzle.

Otherwise, I prefer to use higher magnification.

4

The limits of magnification

Never use too high a magnification.

Generally, a power of about x50 per inch of aperture is the maximum, but if the image is even slightly blurred it is wise to change at once to a lower magnification.

The highest power eyepiece you have for your telescope will probably have to be reserved for nights when conditions are really excellent – and in Britain these nights do not happen too often.

5

Opportunities mist

A night that is slightly misty may be good for the lunar observer, though of course it is of no use for deep-sky objects such as nebulae.

Slight mist will often produce steadiness, and this is probably the main requirement for anyone observing the Moon.

However, any appreciable thickness of cloud will be fatal.

Do not try to carry on when conditions are poor, as errors will undoubtedly creep in.

6

Stop stopping

Stopping down is something I never do.

I know that Percival Lowell stopped down his 24-inch refractor to a mere 18 inches, and I have heard claims that in our climate no telescope of aperture over about 12 inches is suitable, but I disagree.

If you find that conditions are not good enough for you to use your telescope at full aperture, then give up until conditions improve.

7

On a budget

Good photographs can be taken with equipment that is not too expensive: webcams are affordable for most.

Electronics have largely taken over from photography and amateurs can match the best results obtainable from professional observatories only a few decades ago.

If you want to use this sort of equipment, it is wise to save up and buy something worthwhile. After all, it may well last you a lifetime.

8

Altitude

In general, the greater the altitude of the target object, the better the conditions will be, with less tremor and blurring.

This applies to the Moon, but during the slender crescent phase there is no alternative, and all one can do is wait for the best compromise between altitude and sky brightness.

Even when the sky is light, soon after sunset or before sunrise, conditions can often be tolerable.

9

Don’t wait

If you have been making a drawing of a lunar feature, do not wait for too long between checking at the telescope, as the shadows can cause marked changes in aspect over a short period.

Add the following data to an observation: date, time (GMT, never Summer Time), equipment used, and seeing conditions, usually on the Antoniadi scale.

10

Never send away an original observation.

Sooner or later something you really need will go astray in the post.

Keep your observation log and send away copies. Collaborate with other observers and join a society: the British Astronomical Association has a history and reputation second to none, but many local associations now have flourishing lunar sections.

The isolated observer will not accomplish much.


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This feature was originally published in June 2005 in BBC Sky at Night Magazine