On Jun 12, 9:32*am, dxAce wrote:
bpnjensen wrote:
On Jun 12, 5:08 am, dave wrote:
bpnjensen wrote:
On Jun 11, 1:40 pm, Bob *wrote:
bpnjensen wrote:

Metal Halide lamps, especially unshielded, are the pits. *Brilliant,
sky-obscuring, and hard to overcome with normal amateur filter
equipment.

I remember MHs as having a discontinuous spectrum
with about five distinct resonance points
so you would have to combine filtration,
unlike the monochromatic LPS lights.
They probably have some IR and UV too
but I only looked at the visible range in my spectrographic device..

--

Operator Bob
Echo Charlie 42

Thanks for this, Bob. *We have filters that can filter out more than
one wavelength, and we can stack filters up to a point - but none that
will cut all five of the spikes, and too many stacked means you also
lose precious desirable light. *We also have broader band filters
designed to cut general LP that would probably address all five, but
these filters are also weaker than the stronger line filters. *You are
right about LPS, it's a snap to filter - which is why it's been
encouraged for cities near major observatories, such as Lick, Mt.
Wilson (now pretty much useless) and Palomar.

Of course, just as in radio an RF quiet area is best, so in astronomy
nothing beats a good rural or wilderness *dark* sky.

Bruce Jensen
California

As Wilson is primarily a solar observatory these days, I doubt the gas
mixture in the street lamps is very important. *I am 18 miles NNW of
Wilson at 1,790', and I can see the Milky Way from my back yard.

That's why it's primarily a solar observatory - the LP from LA has
rendered it useless for dark sky astro. *18 miles can make a big
difference...but it takes a REALLY dark sky for the Milky Way to throw
shadows...

Might it be really dark when Arizona cuts off the juice?

dxAce
Michigan
USA

We can only hope - I'll move to LA if that happens!