IOM Nordic Cup, race 2

Update: Thanks to Jorma Ojama for sending me some nice pictures from the first six races!

Race 2 of the IOM Nordic Cup (also known as the Scandinavian Cup, although that name is much longer and geographically incorrect) was sailed on 9 Aug 2008 at NJK Björkholmen. Only ten skippers showed up, probably partly because Helsinki/Finland is far away, but also because our own Finnish ranking series has seen a decline in participants this year (could smaller more readily available boats solve this?). 12 races in a shifting westerly wind were completed.

Results on iom-nordic.org

Race 3 of the series will be sailed on 20-21 September in Prestø, Denmark

Why can't AIP/Scitation do RSS feeds right?

I follow a number of scientific journals through their RSS feed of new articles. Google-reader makes it easy to stay on top of the 20 or so most interesting journals that each publish maybe 10 papers per week.

But now AIP and their website provider Scitation are messing it all up. They've decided to expand their archives and are putting scanned pdf articles from around 1979-1981 online. The trouble is these papers are showing up as new articles in the RSS feed! Not only that, but the text in the RSS feed shows the papers as appearing now, in 2008. It's only when you click through to the journal homepage that you realize the thing is 20+ years old.

This becomes very frustrating when suddenly APL or Rev.Sci.Instr indicates that they have 200 or more new papers! If they wanted to advertise to the world their 1980s physics they should do it with a different RSS feed.

I've emailed AIP and Scitation about this, but didn't get a reply. If you have the same problem I urge you to also email them and complain!

Rough grinding continues

Started out this evening with a 1 mm sagitta on the 240 mm mirror.

Started with no60 carborundum and ca. 20 + 30 min of grinding, which got us down to a 1.9-2.0 mm sagitta. The picture shows a 2.0mm drill bit under a steel ruler used for measuring the sagitta. The surface of the mirror is quite rough and appears white when dry.

Switched to no80 carborundum. Grinding is now much smoother with the mirror gliding easily across the tool with less sticking events. After about 30+30 min of grinding we are down to a 2.3 mm sagitta. A quick-and-dirty test shows around a 3 m radius of curvature. Surface now smoother to the touch, still white when dry.

Next stop: build a Focault-test/Ronchi-test jig to properly measure the focal length and the shape of the mirror (see for example plans here). Think about moving down to no150 carborundum.

Partial Solar Eclipse

Today's partial solar eclipse happened from 11:44 to 13:55 local time, so we combined observing the eclipse with a lunch-picnic for the whole lab.

One telescope with a 25mm positive lens at the eye-piece projected an image of the sun into a cardboard box. Another was used with a tracking mount and an OD=5 solar filter for visual observations and photography.

It was cloudy before the eclipse and rainy in the afternoon so we were lucky with the weather!

Variations on the same theme:

Mirror grinding

To keep the mirror edge from chipping and breaking we are putting a bevel on it. Most guides tell you to do that with a sharpening stone which is made from carborundum bonded into a stone-like material. I thought doing the bevel by hand with the stone was much too slow, so I tried it with a diamond-bit on a dremel:

This works much faster and a 1-2 mm bevel can be made in a few minutes. After the bevel grinding you see our 'grind-o-matic' machine. It's driven by a 90 W DC motor with a 30:1 gear-head connected to a 12 mm steel axle which supports an aluminium disk on which the mirror or tool sits. There's a sheet of plastic to keep the wood and floor dry.

After about 2 hours of grinding with nr. 60 carborundum we achieved 1 mm of sagitta. A drop of glycerol in the grinding slurry helps to avoid stiction between the mirror and the tool. For a 240 mm diameter F/6 mirror the target sagitta is 2.5 mm so there is still some work to do.

Starting to build a 240mm Newtonian

More aperture is better. I've started to build a 240 mm Newtonian with some mirror blanks from Tammilasi and knowledgeable help and grinding materials from Teknofokus.

The first task was to grind the 240 mm diameter (40 mm thick) borosilicate mirror blanks flat on each side. This took around 1.5 hours per side using 60-grit silicon carbide and grinding against a flat steel plate.

See also mirror grinding video by The Sky at Night/BBC.

Drama vid Skåldö färjan

En motorbåt körde på Skåldö färjans vajer ca 19:30 tiden. Alla ombord verkade ha klarat sig utan större skador och fördes bort med ambulans. Motorbåten satt fast i vajern och brandkår + färj-kapten försökte först få loss båten, men det slutade med att färjan togs loss från vajern och båt+vajer sjönk till bottnen! Färj trafiken löpte normalt igen ca 20:45.

Här en animation där man ser båten sjunka: farjan_animation2 (5 Mb AVI-fil)