Street lights as artificial stars

[Wonderweb]

Hi.

I have been trying to get my rc6 collimated as well as possible and am looking at different methods of producing artificial stars so I can spend cloudy nights getting it set up properly to maximise my image capture time when its clear and I was wondering if it was possible to use very distant street lights for this purpose? I am able to see street lights at a distance of around 10 to 15 miles. Is this far enough to work?

Thanks

 

[Clarkey]

I have used headlights on the M6 about 6 miles away for my RC8 and this along with a Reego (for the secondary only) gets pretty close. It still needs a star test to get the final result.

I should add I am still trying to get the collimation 'perfect' on my RC8. I am getting pretty close but the star shape in the OAG are not good enough yet.

[wimvb]

Street lamps are not point sources, ie they have a form and size. For proper collimation you should ideally use a light source that is a point source in order to resemble a star. One way to do this is to use a reflecting sphere near the light source, and use the reflection as the artificial star. A disassembled ball bearing or christmas ornament will do fine. Chrome details on a parked car will also work.

[vlaiv]

For simple collimation you don't need perfect point source, but just for argument sake, let's examine what would be needed size of street light in order to represent point source for a telescope.

In order for source to be enough point like - it needs to be some fraction of airy disk size of your telescope.

6" has size of airy disk of about 1.7 arc seconds. We could say that we want something like 1/6th of that diameter, so roughly around 0.3" diameter of light source.

You say that you have access to light sources that are 10 miles away? Let's say that it is roughly 16000 meters the distance.

Question is - how large something needs to be to subtend 0.3" angle at 16000m away?

Result is 2.3cm.

Street lights are considerably larger than that, but simple incandescent light bulb would be very usable point source as its filament is about 2cm long.

Having said all of that - small type of street light farther away will do for collimation purposes.