Re: Bright Events

Bjoern Gimle (b_gimle@algonet.se)
Fri, 12 Jun 1998 18:35:50 +0200

```Koos van Zyl wrote:
>>
>>One question! If I get one mag -8 Iridium flare per month,
>>am I lucky, or is that about normal?
>>
I wrote:
>...
>send two to the surface. If you have 90 passes, they are four degrees
>apart, on the average. This would be 445 km on the equator. Multiply
>by cos(latitude) When you are within about 10 km, the flare will be
>near max., so this ratio indicates the average frequency.
>...
>If there is a geometry where flares occur in your (wide) area, they are
>spaced by about 250 km * cos(Lat), so the chances are better than average,
...
I was too quick to let my arguments support Koos' supposed frequency.
The four degree spacing is for one orbital period, not a day, so the
frequency becomes about 1/3 days near the equator (twice at lat. 60).

Likewise, the 250 km spacing of a particular geometry is precisely that
- there are six planes * two directions, most of which should produce
flares, giving approximately the same results.

The 1/25 chance from the single geometry, is for e.g. a particular
orbit plane's evening twilight pass.

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