A mathematician required

[wilderness]

My other hobby is astronomy

I have an 8" Newtonian reflector using a Dobsonian mount. The mount is pushed around by hand to wherever you want to look. No computerised "goto" for me.

However, I want to make the 'scope a bit easier to use by having scales on the horizontal and vertical axes. Objects in the sky can be found by knowing their altitude (vertical) and azimuth (horizontal) at a specific moment in time. The vertical one I've sorted with an electronic inclinometer.

For the horizontal axis I need a 360 degree "ruler" to go round the base.

The base has a diameter of 56.3cm hence the circumference is 176.87cm. So each 10 degree division has to be 49.13mm.

The picture is not of my Dob as it has a square base. My base is circular.

Anyone any ideas how I can print an accurate "ruler" with the divisions at exactly 49.13mm?

 

[BKF Admin]

Gingernut is a gazer..

 

[Russel]

Have you tried Google SketchUp?

 

[wilderness]

Hi Russel,

No. Does it produce scale drawings?

 

[Russel]

It's main function is 3D modelling and lot of woodies use it for drawings, so I asume that it could?should do. I'm sure someone more informed will be along soon and tell you otherwise.

 

[Brosville]

Here's a nice big 360 image -

 

[For want of a better word]

could you not go to a bigger diameter to get a less awkward scale to work to ?

 

[RoofTops]

I assume you are after a linear scale you can wrap around the base? If this is the case, on the assumption you won't have a printer big enough to print it out in one go you could use a word processing package like Word. Switch to landscape format and then draw a table with two rows and 5 columns across the page. Word has a feature where the column widths can be spread evenely so use this if the columns are not even.

Print off the page and measure the column width, then by trial and error adjust the overall size of the table until you get as close to the 49.13mm width as you can get. You would be best to print off enough so you can check it wraps around the base perfectly. You can alter the size of the table in Word by just grabbbing a corner and moving it.

When you have the size of table you want add 45 more columns and distribute them evenly. You could then merge the cells in the upper row so it gets back to 5 columns with the 50 columns in the lower row. The top row is in 10 degree sections, individual degrees in the lower row.

This should then be a strip of paper, after you have printed of off and cut out the table, which shows 50 degrees. Do a few more and stick them together until you have the full 360.

 

[wilderness]

Bros, where did you get that image? Is it scaleable? I guess I could stick it on the top of the base.

Rooftops, yes I'm looking for a linear scale. I'm having a look at Google Sketchup to see what that can do for me but I like your thinking.

Thanks all for your suggestions so far.

Bros, found the article on iceinspace - thanks

 

[roche]

So would a sheet of A3 printed with lines 49.13mm apart be what you're after? I can do that. Might be better to print onto film though, or a metallic sheet, for stability. I have some self adhesive printable metallic sheets, but only in A4. Cut it to width for the base...

 

[Adam]

If you don't have a really large printer, but can get the image as a jpg or suchlike, there are quite a few places that will print really large photos, or plot it for quite a reasonable fee. You can find them on google with search times like "poster photo" etc etc.

Adam

 

[wilderness]

Sorted

Hi all,

I used RoofTops idea of using MS Word and tables. There is the facility to draw tables to specific dimensions. The printer also has to have the "shrink to fit" unchecked.

It's taken me all day to get something that looks right and is accurate. I'll do a sticky backed plastic job on it for now and let you know how it works.

Attached is page one

Roche, if the experiment is successful, I'll get in touch about a more permanent solution.

Now if only this fog would lift ......

 

[RoofTops]

I'd forgotton you can alter the column width to a specific size in table properties. Better than my trial and error approach!