Bill W4ZV said
>Why is W6ELProp so far off? Probably because he uses
>a different definition of sunrise and sunset. I believe most
>of the others use 0.75 degrees below the horizon since
>the atmosphere refracts the light and makes it appear the
>sun comes up earlier and sets late than is actually the
>case.
>
The official defintion of sunrise and sunset is when the center of the
Sun is 0.8333 degrees below the horizon (for the reason Bill stated).
W6ELProp uses 0 degrees (I don't know why - that's what the manual says
and it gives the differences cited by Bill).
IMHO the small differences in the tabular data that Bill gave are not
important. These are ground level sunrise and sunset times at your QTH
based on the above definition. What's important is when the Sun
illuminates the various ionospheric regions. Depending on the elevation
angle involved, this could be several hundred km down the road from your
QTH. On 160m, D region illumination is probably the most important, and
the illumination of the D region starts before your ground level sunrise
and the illumination does not stop until after your ground level sunset.
Additionally, at sunrise the ozone layer can delay UV from illuminating
the D region, so that adds another day-to-day variable (ozone
concentration) into the big picture.
What I think this all means is that it's best to use the sunrise and
sunset times as times to bracket your operations around due to the
issues mentioned.
A good example of this is the ST0RY DXpedition in March 2003. Of the
week and a half or so that they were operating, I had two days of
significant signal enhancement on 160m at my QTH in Ft Wayne. They both
occurred from about 0320 to 0340 UTC. This was quite a bit before ST
sunrise (around 0400 UTC) and well after my sunset (around 2347).
The point here is to not just focus on the sunrise and sunset times - of
course you should know them, but you better be on for some time period
before and some time period after to allow for real world issues.
Carl K9LA
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