Commercial certificate question

And it is not end of twilight, it is end or beginning of civil twilight.

Is there another kind of twilight?

Jose
--
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Yes, there is nautical twilight and astronomical twilight, and then just
plain old everyday "generic" twilight that we refer to in everyday speech.
The former ones and civil twilight have precise definitions based on how far
the center of the sun's disc is below the horizon, thus being useful for
regulatory purposes. Generic twilight is defined in a usual dictionary but
is not precise.


"Jose" wrote in message
...
And it is not end of twilight, it is end or beginning of civil twilight.

Is there another kind of twilight?

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Yes, there is nautical twilight and astronomical twilight

As Spock would say - "fascinating". What is the reason for all these
different twilights? (never mind, if the FAA can have two different
definitions of night, I might as well just go google myself.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Jose wrote:
different twilights? (never mind, if the FAA can have two different
definitions of night, I might as well just go google myself.

three definitions actually if I understood the AOPA article correctly;
(seems that the difference between day or night special VFR uses
yet another definition -- but then, I might just be confused about it
all) :-)

--Sylvain

Jose wrote:
And it is not end of twilight, it is end or beginning of civil twilight.


Is there another kind of twilight?

I believe that twilight in and of itself is a fairly subjective
description. Civil twilight, however, has been more rigorously defined
and thus is more precise. I don't recall exactly, but it is something
like the time when the center of the disk of the sun is so many degrees
(6 sticks in my mind, but is just a recollection) below the horizon with
respect to the point of the viewer.

There are tables available to give you this time at pretty much at point
on the earth.

Matt

Matt Whiting wrote:
Jose wrote:

And it is not end of twilight, it is end or beginning of civil twilight.



Is there another kind of twilight?


I believe that twilight in and of itself is a fairly subjective
description. Civil twilight, however, has been more rigorously defined
and thus is more precise. I don't recall exactly, but it is something
like the time when the center of the disk of the sun is so many degrees
(6 sticks in my mind, but is just a recollection) below the horizon with
respect to the point of the viewer.

There are tables available to give you this time at pretty much at point
on the earth.

Matt

For twilight definitions, see
http://aa.usno.navy.mil/faq/docs/RST_defs.html.

--

Tauno Voipio
tauno voipio (at) iki fi

Nautical twilight had a practical purpose when we depended on celestial
navigation. That was the period when it was dark enough to see the stars
and light enough to discern the horizon. That's the only time you can
"shoot" stars unless you use a leveling device.

"Jose" wrote in message
...
Yes, there is nautical twilight and astronomical twilight

As Spock would say - "fascinating". What is the reason for all these
different twilights? (never mind, if the FAA can have two different
definitions of night, I might as well just go google myself.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.

Well, there is sunset/sunrise, but that does not fall exactly within the
discussion of twilight definitions.

The FAA uses three different types of "non-day" for different purposes:
after sunset, after civil twilight, and more than one hour after sunset, and
the corresponding morning times.


"Sylvain" wrote in message
t...
Jose wrote:
different twilights? (never mind, if the FAA can have two different
definitions of night, I might as well just go google myself.

three definitions actually if I understood the AOPA article correctly;
(seems that the difference between day or night special VFR uses
yet another definition -- but then, I might just be confused about it
all) :-)

--Sylvain

And, as we have said for a number of years, none of these "non-day" times
have a legal definition within the FAR.

Jim



"Stan Prevost" wrote in message
...
Well, there is sunset/sunrise, but that does not fall exactly within the
discussion of twilight definitions.

The FAA uses three different types of "non-day" for different purposes:
after sunset, after civil twilight, and more than one hour after sunset,
and the corresponding morning times.

And, as we have said for a number of years, none of these "non-day" times
have a legal definition within the FAR.

Well, I don't know about that. "one hour after sunset" is used thusly
in the FARs and and is therefore a kind of "non-day" that is defined in
the FARs, though a name isn't given to it.

Jose
--
Money: what you need when you run out of brains.
for Email, make the obvious change in the address.