Determining Night

[Cloud Watcher]

Hello everyone,

I have a question regarding when night officially begins. After a recent interaction with a flight instructor, I have found myself questioning when night truly begins.

It is not the definition of night that I am struggling with, but rather determining the actual time that night begins. According to the AIM, "Night is legally defined in aviation as the period of time that starts at the end of evening civil twilight and ends at the start of morning civil twilight." Then goes on to state, "In the evening, civil twilight ends...approximately 25-35 min after sunset." One instructor said to simply add 30 minutes to the sunset time and also directed me to use this website: https://nrc.canada.ca/en/research-devel ... alculator/. Using the website, either method for determining night (civil twilight or the 30-minute method) works just fine, which is what I had been doing for some time.

However, while going over my night cross country plan with another instructor, he mentioned that my departure time would not be late enough to be considered night. I had intended to depart in just under an hour, and even I was a bit surprised at how light it still was despite calculating my flight to leave a few minutes after legal night. This interaction left me second guessing how to actually determine night.

I would greatly appreciate some clarification (Was I doing it correctly in the first place, or is there another way?) as I would like to avoid accidentally logging my flight time incorrectly.

[ruffdeezy]

if you are following the legal way - 6 degrees below horizon between end of evening civil twilight and morning civil twilight - and you verified with the website then you are doing it right. Doesn't have to be too complicated, 30 min guideline sounds fine.

[NotDirty!]

Don’t forget that the NRC website gives times in “Standard Time”, so during daylight saving time you have to adjust the times by one hour.
So if the sunset time shows 20:30 EST, that is 21:30 EDT.

[digits_]

I don't know of anyone who would object to 30 min post sunset till 30 min pre sunrise.

Note, if it isn't night, that also means you don't need a night rating to fly in the conditions. You'll see that might change people's definitions quickly as well!

[Cloud Watcher]

Don’t forget that the NRC website gives times in “Standard Time”, so during daylight saving time you have to adjust the times by one hour.
So if the sunset time shows 20:30 EST, that is 21:30 EDT.

Haha of course, that's nearly caught me a few times before! Luckily it mentions that on the website itself, so I usually catch myself

[Jester123]

When I crack open that beer.

[Fly0nTheWall]

I had intended to depart in just under an hour, and even I was a bit surprised at how light it still was despite calculating my flight to leave a few minutes after legal night. This interaction left me second guessing how to actually determine night.

Ya, sounds like you're doing it correctly. Civil Dusk (start of legal night) is significantly brighter than both Nautical Dusk (12 degrees below horizon) and Astronomical Dusk (18 degrees below horizon). No one really cares about the latter two though in aviation. But suffice to say your point is valid....there's still a little bit of light left at the start of civil twilight.