Posts Made By: Anthony Allsobrook

Hi Ron

When I enquired on Astromart a few days ago whether anyone had seen the moons of Mars I really didn't think that a 4" would manage it. Well, as Ed Hillary descended from Mt Everest, having climbed it 50 years ago, he gave us what is now his famous quote "We knocked the bastard off". Seems to be apt for the Light Cup and Deimos! So the Light Cup is no ordinary 4" - but we have always known that!!

One way to confirm your sightings is to make some measurements which will support a change in position of Deimos. A filar micrometer would do the trick nicely, but few of us have one of these. However, using a simple fine wire placed carefully across the field stop of your eyepiece and oriented North/South, switch off the RA drive and note the time as Mars, Deimos and at least two stars cross the wire. Repeat a short time later. And several times more. A pattern should develop!! You could even plot a graph showing the change of position with time!! That would be really neat!!! You will of course be measuring the orbital motions of both Mars relative to the stars and Deimos relative to Mars.

Thanks for the Mars applet - I wasn't aware of it. And as always, thanks for a really interesting read.

Best wishes from Downunder.

Anthony 41°S 175°E

Dear Light Cup

I bring you greetings from these islands in the Great Southern Ocean. Your master Ron has posted some queries on your behalf and I will endeavour to answer at least some of them.

<"My Light Cup curiously wondered why no observers of the past centuries ever called it "Gibbous Mars", "Full Mars" and "New Mars""> Well, the earliest treatise on Astronomy which I have in my library is the second edition of Thomas Keith's "A New Treatise on the Use Of Globes, or A Philosophical View of The Earth and Heavens" published by Samuel Wood and Sons, New York, 1826 A.D. On page 153 he writes, quote: "Mars, when viewed through a telescope, appears sometimes full and round, at others gibbous, but never horned. The foregoing appearances clearly show, that Mars moves in an orbit more distant from the sun than that of the earth." Unquote. So there you have it. Being a superior planet, Mars is never horned and can therefore never be "New" either (the logic being, that Mars would have to become "horned" as a prelude to becoming "New", if you see what I mean). ;-)

<"I wonder if the intense heat of the sun would melt the ice cap completely"> The southern "ice cap" is composed of carbon dioxide ice and not water ice. It is only the thickness of a very heavy frost (current speculation is that it is only a few inches thick). The atmospheric pressure on Mars is very low (below the "triple point" of carbon dioxide), and when the solid carbon dioxide ("dry ice") is heated by the sun it does not melt, but SUBLIMES i.e. passes directly from the solid state into the gaseous state, so that there is never any liquid present. Incidentally, WATER ice behaves similarly if the pressure of the gas above the ice is below the triple point of water i.e. the ice passes directly into water vapour without producing liquid water (incidentally, this is how freeze dried instant coffee is produced, although I suppose that Light Cups never partake of the quaint custom of consuming this beverage).

Well, dear Light Cup, I hope you will continue to delight us with the treasures of the Universe which you bring to our attention with your exquisitely fashioned cyclopaedian eye. If nothing else, you have shown us that size does NOT matter; what IS important is how (and how often) you use what you've got. ;-)

Yours in photonic brotherhood.

Anthony @ 41°S 175°E

Could someone who already owns a TMB80 please compare and contrast the relative advantages and disadvantages of the 480 mm and 600 mm models? It's a difficult choice and at $2000 not one I would like to get wrong!
Thanks
Anthony

Do away with nested adapters. 2" to 1 1/4" then to 0.965" is messy.

Fewer adapters = better alignment = higher quality image

Just one adapter 2" to 0.965" is the only way to go.

If you want to tweak the quality of your already excellent 0.965" Orthos, then please reply here and we can get a manufacturer to do a small run!!

Thanks

Anthony

Hi Floyd
What an interesting experiment!! In an effort to better UNDERSTAND what is happening to the image quality, may I suggest a further experiment. Replace the mask with the array of four inch holes with another mask with an array of as many 1 inch holes as you can fit onto the mask ... something like this if you see what I mean ...

ooo
ooooooo
ooooooooo
ooooooooooo
ooooooooo
ooooooo
ooo

Then you have 3 things to compare:
A. no mask
B. 4 inch mask and
C. 1 inch mask

And do this on at least two evenings. One evening with excellent seeing, and one evening with poor seeing. (You could even try transparent and poorly transparent sky as further variations ... but you don't want to introduce too many variables in the beginning or you many find the analysis gets too complicated. Remember KIS = Keep It Simple!)

And do of course DOCUMENT everything carefully just as any scientist would do ;-)

Hopefully you will give you a FEELING as to what is happening to the image when the holes are added. Then you can perhaps formulate a HYPOTHESIS (write it down) and then TEST IT by making another mask with, say, 1/2 inch holes. (Again, just like a scientist would do ...)

Thanks for an interesting thread ...
Best wishes
Anthony

Ron
Thanks for a really interesting report as always. I really like the way you focus on a small(ish) feature and then research it so thoroughly!!!

Best wishes and Seasons Greetings
Anthony

Very interesting report, Mike. We look forward to more photos and comments as the work progresses. Comments about problems encountered are especially useful!

Do you have a completion date in mind?

Many thanks
Anthony

Hi Russ

Here's my analysis.

1. Roll-off roof is easiest and cheapest to make, but equipment is exposed to the wind and cold. Your idea of a split roof sounds excellent, and Rick, I really like the idea of the internal gutter to catch the drips.

2. A dome provides protection from wind, dew and cold, but is difficult and/or expensive to make. Making the slit watertight is no mean task.

So why not combine them!!

I'm thinking roll-off roof with a very light weight dome inside!! The dome would be made of ribs covered with tent cloth - very light and easy to move. The slit would be permanently open so construction would be a breeze. It would provide protection from the wind, dew and cold. On good calm nights the tent cloth could be pulled off the ribs, and the ribs folded down to give an unobstructed view of the sky.

Alternatively, it could look something like the clam shell dome. When the roll-off roof is opened the clam could be erected if required ... remember that it has a permanently open slit.

Mark: I've followed your posts over the past year ... SUPERB ... this stuff inspires all of us to do even better!! Thanks!!!
Anthony

Mark, Nils, Markus

Many thanks for all the suggestions!!! I'll be following up on this and will post here from time to time.

Anthony