NLC geometry - range

[malcolmp]

If an observer sees an NLC overhead how far away will that cloud be seen ?

I realise that if observer1 sees some NLC then that is fair warning that conditions are right that observer2 may also see some NLC, but I bolded the above so that you could help me with the maths - range of a specific cloud case?

thanks,
Malcolm.

[Bill W]

Hi,
Somewhere in the general nlc posts is a graphic I produced a while back to give a guide to the range. However if the NLC is genuinely at 90 degrees, then it is 82km (+/- a little) above your head.

So if someone has it over their head it can be seen about 1100 km away right on the horizon, more or less, as it has to do with great circles and a lot of other spherical trig stuff.

For my own part I take it to be around 600km so that there are a few degress elevation and it makes actually spotting it a possibilty.
Bill.

PS I meant to add, these numbers are failry stable because NLC always appear at around 82km up.

[malcolmp]

Thanks Bill,
thats great reply, gives me a feel for reports from Cumberland wrt me, and for any of my reports ( I live in hope lol!) for Chris down in Torbay

Noted on reasonable range/elevation.

Would be interested to see your graphic if it ever emerges from the archive, I have been working back thro', not seen it, saw some posts by Markt ( I think it was '09) about a UK north pointing NLCwebcam but not seen a followup

that is a prob with blogs and fora, so much gets buried in the mists of time compared with structured websites dont get me started

[Bill W]

Hi,
If you look back to page 3 (this section), third posting from the top, "Range guide", that has the graphic.
The server I use was offline over the weekend, that may be why you couldn't find it.
Cheers,
Bill.

[malcolmp]

Thanks Bill I see it now, very interesting.
I will have to think a bit about how to convert those slant ranges into the case I was thinking about ie. observer to observer distance,
iow. sub-NLC point to me.
I now realise that I asked my orig. question rather imprecisely, when I said
"If an observer sees an NLC overhead how far away will that cloud be seen ?"
I meant how far away from that observer will that cloud be seen, the ground range.

Meanwhile I'll take your 600k as a working practical case.

Also now that the matter of great circles passing thro' two observers but not thro' the pole is introduced, , I'm off to scratch the gray matter well it's cloudy out there so a little thinking will not go amiss to while away the hours

Ta,
Malcolm.