Sky at Night Magazine

[david48]

I know there aren't really any canals on Mars.

But past observers such as Schiaparelli and Lowell reported seeing fine dark lines on Mars. These were evidently some kind of optical illusion. Is this illusion still seen nowadays? And what size telescope will show it?

The reason I ask, is that I was recently reading an old, 1956, edition of Patrick Moore's book "Guide To Mars". In an Appendix on observing Mars, PM says:

"Drawings of Mars made with small instruments, such as 3-inch refractors, must be rejected if they show fine details such as canals."

This implies that larger instruments will show the canals. It would be so fascinating to catch a glimpse of them, even if they are unreal!

I wonder, has any SaN observer seen the canals, and if so, what telescope was used?

[uea74]

Haven't looked at Mars, simply didn't have the right bits last year, have now.

A 3 inch refractor is still a fair instrument. What could be the reason for the statement is that some years back 3 inch refractors were not as high a quality as they are now, at least in general terms. However as with everything there will have been some 3 inch refractors that were well made and that, owing to chance, were better then average.

The 2 lenses ground were closer to the ideal then others, the lens complimented each other more, the alignment just that bit better, even the cementing was more even and each was centered to each other.

So 75mm at say f/10 is 750mm, if things fall right, you may have been able to get 120-150x out of some and still have a decently sharp image. F/12 or f/15 possibly more chance.

So I could see why some people were able to see fair detail on Mars with a 3 inch scope. Not everyone, but some I suspect would, and for the time the people would have had to pay proportionately more then now.

A cheap 75mm then would not, neither will a cheap 75mm now, but I sure hope my WO 80mm triplet does. Just 5mm more after all.

Edit to correct an inability to multiply by 10. [8|][8|][8|][8|]

[lancashire astroguy]

Hi David,

I've observed Mars with my Skywatcher 130mm reflector on the last couple of oppositions. My telescope was barely able to resolve surface features, but nonetheless I could just make out larger dark patches such as Syrtis Major. I didn't see any "canals" and I assume that the "canal" illusion only occurs once a great deal more surface detail becomes visible (perhaps at apertures of over 10 inches).

The illusion is fairly easy to understand. If you draw two blobs on a piece of paper close together and then look at them with your eyes de-focussed you will see a "bridge" linking the two blobs. Similarly, Schiaparelli et al thought they saw lines linking the fuzzy surface features they were straining their eyes to see on Mars. When you look at Schiaparelli's map however, it is clear that his imagination ran away with him. A case perhaps of the eye seeing what it wants to see. Nonetheless, canals excepted, his maps of Mars were amongst the best we had before the Space Age.

Regards,
James

[wilkibo]

Lowell is now thought to have suffered from an eye disease known as Lowell's syndrome which caused him to see canals on Mars and spoke-like features and a central spot on Venus.

[sftonkin]

A couple of decades ago, I attended a lecture, for Bristol Astronomical Society, by Prof. Richard Gregory on the Martian Canals. He talked a bit about what Lovell had seen and showed us a photograph from the era -- you could definitely see hints of canals. Then he talked about Schiaparelli, the Merkinese misinterpretation of "canali", and progressed onto Mariner and Viking stuff. At the end, he showed us another photo of Mars. Sure enough, no hint of canals. Then he showed us the first one again. It was the same photo!

Lesson (and the main point of the lecture): What we see is often determined by what we expect to see.

[david48]

This is a belated acknowledgement to uea74, LancashireLad, Wilkibo and sftonkin for your interesting and informative replies - thanks!

I've read a facsimile reprint of Lowell's 1906 book "Mars and its Canals". This has over 300 pages, crammed with data on the canals. There are graphs showing, eg, the development of the canal "Brontes" between Jan-Jul 1903. And tables showing the measured separation of double-canals, such as the "Phison", "Euphrates", "Thoth" ,"Nepenthes" and "Nilokeras I & II" . The measurements, in degrees and fractions of degrees, were made with a micrometer. Also full and detailed descriptions of the "oases", such as the "Fons Juventae", where two or more canals cross. Plus observational data on the "carets", small triangular marks, at the place where, for example, the canal "Euphrates" leaves the "Portus Signaei".

And all this mass of stuff[i] is based on sheer illusion[/i]. That's what makes the canals so fascinating and disturbing.

(I don't want to resurrect the thread - just remedying my discourtesy in not acknowledging replies)

[splog]

Sounds like a book I would love to read [:D] ..... Thanks for the info.

[mjpfc]

MGS and others including the rovers have uncovered No evidence at all of any Jet-ski owners on Mars.

This means either no canals or standing bodies of water or.....that the lifeforms there are reasonably
intelligent'

Mick.

[philip pugh]

Unfortunately, I did not have access to a digital camera in 2003. I saw (through a 5" Maksutov at about 300x magnification) what appeared to be some "lines" joining dark patches. What these really are are very long canyons which do not carry water, although it is possible that they may have done years ago before most life evolved on Earth. These lines are normally seen in instruments in the 5-12" aperture range, although I've seen photos taken through some larger instruments that would definitely suggest that they exist.

The problem with older planetary science was that even in the 1960s it was assumed that Mars was much warmer and wetter than it is and temperatures of 80 deg F were widely thought to be reached during summer.

So what may appear as lines connecting "vegetation" are either canyons or areas of rock and dust which are darker than the surrounding area. Without knowing that Mars was as cold and dry as it really is, one possible explanation would have been that the lines were either rivers or that intelligent Martians may have constructed canals covering large distances around the planet.

Remember also that in the 1960s, it was thought that life could be possible near the polar regions of Venus and that Pluto was larger than Mercury.