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Date: Sun, 06 Dec 1998 23:48:39 -0500
From: "Jason M. Barton" <jason@icns.net>
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Subject: Re: night flying/currency flubup
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John Price wrote:

> Remember... Nighttime is sunset to sunrise... to carry passengers from 1
> hour
> after sunset to 1 hour before sunrise you must have made 3 takeoffs and
> landings
> to a full stop during those hours... Just doing 'em after sunset doesn't
> count!
>
> John

This is not accurate.  NIGHT (i.e., when you can log night time) is the period from
the end of evening civil twilight to the beginning of morning civil twilight.  This
"twilight" period, for practical purposes, is the time after the sun sets (or
before it rises) when it is still light out.  The amount of time it takes foe it to
actually get dark after the sun sets varies depending on latitude.  Near the
equator, the suns track across the sky is more perpindicular with respect to the
horizon than it is near the poles.  So when the sun sets near the equator it may
only take 25 minutes for the sun to set far enough below the horizon for it to get
dark enough for me to consider it night, while closer to the poles the sun's path
is not so perpindicular so it takes longer for it to get really dark.  Where I am
at (45 degrees north latitude) it takes about 40 minutes for "evening civil
twilight" to end.

Now, your landings for night proficiency must fall within the hours of NIGHT, not
simply between sunset and sunrise.  As you can see, there is a period of time after
sunset and before sunrise that is not night.

By the way, civil twilight is actually the point when the sun is within six degrees
of the horizon.  There are other terms used when referring to twilight.
"Astronomical" and "nautical" twilight are when the sun is within 18 degress and
three degrees respectively.

Information on the actual times of civil twilight are available at:
http://aa.usno.navy.mil/AA/data/

Jason Barton, CFII
New Haven Flight School
http://ic.net/~jason/
remove the NS from domain name to respond



