## Re: DX-Atlas Twilight Setting

Expand Messages
• ... The short answer: it makes no difference. You should be interested in the actual time the sun is on the horizon, and you ll see this is constant for all
Message 1 of 4 , Oct 31, 2010
--- In dxatlas_group@yahoogroups.com, "db4iw" <db4iw@...> wrote:
>
> I wonder which setting for the twilight zone (civil, nautical, astronomical) would be the best for judging possible grey line conditions for MW and for the lower SW bands. Is there any suggestion or rule of thumb?

The short answer: it makes no difference. You should be interested in the actual time the sun is on the horizon, and you'll see this is constant for all 3 choices in DX Atlas. The 3 choices are actually showing the times after the sun sinks below the horizon by different amounts:

Civil: 6 degrees below horizon
Nautical: 12 degrees below
Astronomical: 18 degrees below

http://en.wikipedia.org/wiki/Twilight

I've been using actual sunrise/sunset times (not twilight) for 30 years and originally calculated them based on the formula in ON4UN's first 80m Dx-ing book (which had an error I discovered and corrected in a note to John).

If you use the actual sunrise/sunset times, you'll learn to judge the best time for propagation based on experience. For example, I learned that the best long path propagation on 80m usually comes with ~40 minutes of common darkness and the peak is usually half-way between (e.g. 20 minutes past my sunset and 20 minutes before DX sunrise). On 160m it's a bit more:

http://lists.contesting.com/archives//html/Topband/2002-02/msg00132.html

For short path propagation there's sometimes a very pronounced peak right at sunrise/sunset, or the best propagation may not begin until *AFTER* sunrise on the DX end (usually extending 15-20 minutes past his sunrise). Learning this is simply a matter of experience but you should always be looking at actual sunrise/sunset times so you can make accurate relative comparisons.

BTW actual sunrise/sunset times are those displayed by DX Atlas when you press Ctrl-D when a target location is highlighted (i.e. none of the "twilight" times).

73, Bill W4ZV (DXCC: 347 on 80m, 331 on 160m)
• Rod Serling was always Civil . ... -- ... If at first you don t succeed, then skydiving isn t for you. ... Bill H. in Chicagoland webcams at
Message 2 of 4 , Oct 31, 2010
Rod Serling was always 'Civil'.

On 10/31/2010 4:28 PM, bill_w4zv wrote:
>
>
>
> --- In dxatlas_group@yahoogroups.com
> <mailto:dxatlas_group%40yahoogroups.com>, "db4iw" <db4iw@...> wrote:
> >
> > I wonder which setting for the twilight zone (civil, nautical,
> astronomical) would be the best for judging possible grey line
> conditions for MW and for the lower SW bands. Is there any suggestion
> or rule of thumb?
>
> The short answer: it makes no difference. You should be interested in
> the actual time the sun is on the horizon, and you'll see this is
> constant for all 3 choices in DX Atlas. The 3 choices are actually
> showing the times after the sun sinks below the horizon by different
> amounts:
>
> Civil: 6 degrees below horizon
> Nautical: 12 degrees below
> Astronomical: 18 degrees below
>
> http://en.wikipedia.org/wiki/Twilight
>
> I've been using actual sunrise/sunset times (not twilight) for 30
> years and originally calculated them based on the formula in ON4UN's
> first 80m Dx-ing book (which had an error I discovered and corrected
> in a note to John).
>
> If you use the actual sunrise/sunset times, you'll learn to judge the
> best time for propagation based on experience. For example, I learned
> that the best long path propagation on 80m usually comes with ~40
> minutes of common darkness and the peak is usually half-way between
> (e.g. 20 minutes past my sunset and 20 minutes before DX sunrise). On
> 160m it's a bit more:
>
> http://lists.contesting.com/archives//html/Topband/2002-02/msg00132.html
>
> For short path propagation there's sometimes a very pronounced peak
> right at sunrise/sunset, or the best propagation may not begin until
> *AFTER* sunrise on the DX end (usually extending 15-20 minutes past
> his sunrise). Learning this is simply a matter of experience but you
> should always be looking at actual sunrise/sunset times so you can
> make accurate relative comparisons.
>
> BTW actual sunrise/sunset times are those displayed by DX Atlas when
> you press Ctrl-D when a target location is highlighted (i.e. none of
> the "twilight" times).
>
> 73, Bill W4ZV (DXCC: 347 on 80m, 331 on 160m)
>
>

--
---------------------------
If at first you don't succeed, then skydiving isn't for you.
---------------------------
Bill H. in Chicagoland
webcams at http://w9ol-towercam.webhop.org
weather at http://hhweather.webhop.org

[Non-text portions of this message have been removed]
• Back home from holidays in South Tyrolia/Italy I find your very enlightening and useful answer, Bill. Thank you very much! 73, Fritz
Message 3 of 4 , Nov 9 11:10 PM
Back home from holidays in South Tyrolia/Italy I find your very enlightening and useful answer, Bill. Thank you very much!

73, Fritz

--- In dxatlas_group@yahoogroups.com, "bill_w4zv" <w0zv@...> wrote:
>
>
>
> --- In dxatlas_group@yahoogroups.com, "db4iw" <db4iw@> wrote:
> >
> > I wonder which setting for the twilight zone (civil, nautical, astronomical) would be the best for judging possible grey line conditions for MW and for the lower SW bands. Is there any suggestion or rule of thumb?
>
> The short answer: it makes no difference. You should be interested in the actual time the sun is on the horizon, and you'll see this is constant for all 3 choices in DX Atlas. The 3 choices are actually showing the times after the sun sinks below the horizon by different amounts:
>
> Civil: 6 degrees below horizon
> Nautical: 12 degrees below
> Astronomical: 18 degrees below
>
> http://en.wikipedia.org/wiki/Twilight
>
> I've been using actual sunrise/sunset times (not twilight) for 30 years and originally calculated them based on the formula in ON4UN's first 80m Dx-ing book (which had an error I discovered and corrected in a note to John).
>
> If you use the actual sunrise/sunset times, you'll learn to judge the best time for propagation based on experience. For example, I learned that the best long path propagation on 80m usually comes with ~40 minutes of common darkness and the peak is usually half-way between (e.g. 20 minutes past my sunset and 20 minutes before DX sunrise). On 160m it's a bit more:
>
> http://lists.contesting.com/archives//html/Topband/2002-02/msg00132.html
>
> For short path propagation there's sometimes a very pronounced peak right at sunrise/sunset, or the best propagation may not begin until *AFTER* sunrise on the DX end (usually extending 15-20 minutes past his sunrise). Learning this is simply a matter of experience but you should always be looking at actual sunrise/sunset times so you can make accurate relative comparisons.
>
> BTW actual sunrise/sunset times are those displayed by DX Atlas when you press Ctrl-D when a target location is highlighted (i.e. none of the "twilight" times).
>
> 73, Bill W4ZV (DXCC: 347 on 80m, 331 on 160m)
>
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