Sky at Night Magazine

[Stargazer357]

Hi,

Does anyone know where to get the parts for the artificial star build in the last two issues of the magazine?

[Aratus]

Unfortunately I came in after part one, but from the illustrations I can't see anything there you won't find at Maplins. Veroboard, leds and resistors, switches and case etc. Other hobby electronic outlets are available!

[Stargazer357]

Hi Aratus, thanks for your reply.

Unfortunately Maplin doesn't carry the 5mm White, 20000 mcd LED or the precision pinhole to produce the point source light from the LED.

Imho, the minimum the magazine should have supplied was a full parts list especially considering the specialised nature of some of the parts used in the build. A list of the suppliers they used to get their parts would have been helpful too. The parts list for the 'Part 2' build lists amongst other things: precision 10um pinhole in mount(?), project box - without dimensions - and a 5mm LED bezel mount - again without dims/type required.

[Aratus]

I just checked, and you are quite right. I put "20000 mcd LED 5mm white" into Amazon and a few came up. They are pretty expensive though. There are better prices on Ebay.

I didn't appreciate that the pin hole had to be specially manufactured
Some suggestions regarding sources wouldn't have gone amiss.

[Supercooper]

Hi again,

Yeah, it's me. On the subject of artificial stars. Using a pin hole would surely create an image instead of a point source (ie pin-hole camera acting as a projector?) But, I haven't seen the article, so forgive me if I've missed something.

In the old days they used to use a bulb (Substitute your LED) and have it shining on a highly polished ball-bearing. This produces a tiny regular point of light. I remembered the design being featured in a BAA Handbook from the '70s. See design pic.

If you want to get technical, the BB can be glued to the end of a bolt that passes through the back of the box ('top' as seen here). This allows a degree of fine-tuning of the exact position of the BB in the light-box.

This might be a means of improving the design and save time getting a precision made part where none is necessary?

Cheers, Barry

[Aratus]

I think this is why the pin-hole has to be manufactured rather than someone just poking a needle through. The article suggests widths of around 10 micrometres! About half the diameter of a human hair! Your design might be a great deal easier if pre-formed pin holes are hard to find.

[Supercooper]

Wow... That's a small hole indeed! Even in 1mm steel that would be a long tube! No pin-hole camera effect there then!

If you can get one, great. I was just saying, we always used ball bearings :o)

Cheers, Interesting thread, Barry

[Aratus]

That's the point the OP was making - he doesn't know where to get them from. I think they might be used for certain instruments, interferometry etc. Clearly the author of the article knows where to get them from, but I've not come across them.

Your idea with the ball bearing sounds a lot more feasible, and a great deal easier to obtain the parts. How it compares to the one mentioned in the article though, I couldn't say.

You can find ready made ones for about £60, but for best results they always recommend the telescope be about 100ft away from an artificial star. My back yard is just a little short of that.

[Supercooper]

It would be a bit tricky but you could use an optical flat mirror to fold the light-path in your garden. You might be able to get the necessary distance like that.

Edit:
And the best thing about that would be that you could have the telescope and the artificial star side by side - You wouldn't have to go running 100' down the garden when you wantet to make an adjustment!

Barry

[dave.b]

I read the article last night and was left wondering where to get the 10um pin hole from! As for the rest of the components try CPC, which I think is CPC.farnell.com.