Definition of Night

[3142]

Hi.

Night?

At what time the night begins and ends?

Is it at Sun set and Sun rise?

What about the twilight (corrected spelling?), can it be used for day VFR?


Many thanks.:cool:

[northwing]

I believe there is a legal definition of night but I can't remember what it is. There is sunset, then there is at least one type of twylight which is called nautical twylight, and night officially starts so many minutes before or after one of the official twylights. Try some sort of almanac. Sorry I can't be more precise.

[Captain Airclues]

Night is the time between the end of evening civil twilight and the beginning of morning civil twilight. As far as the UK is concerned, this is taken to be 30 minutes after sunset to 30 minutes before sunrise. I believe that the official definition of civil twilight is when the sun is between 0 degrees and 6 degrees below the horizon. Nautical twilight is when the sun is between 6 degrees and 12 degrees (or is it 0 and 12?) below the horizon. However, it is 36 years since I sat in my groundschool class learning that, so perhaps someone with more recent knowledge can correct me.

Airclues

[northwing]

Captain Airclues, you pipped me at the post! Having made the reply above yours I ran a Google search which revealed the following facts:-

1. You and 3142 can spell twilight and I can't.

2. You are absolutely correct in your definition of night as being between the end of evening civil twilight and the beginning of morning civil twilight.

3. There is also Astronomical Twilight which is defined by the refracted centre of the sun being more than 18 degrees below the horizon.

Actually, looking back at what has been written above there is a discrepancy.

Civil twilight starts when the (refracted) centre of the sun is MORE than 6 deg below the horizon. Hence 0 to 6 deg is still legally daylight.

[Captain Airclues]

No Northwing, civil twilight is when the sun is between 0 and 6 degrees, whether it is rising or setting. As far as the Rules of the Air are concerned, the twilight hours are considered to be daylight as the CAA do not have any 'twilight' regulations. So therefore, in answer to 3142's question, it is possible to fly a day VFR flight during civil twilight.

Airclues

[ROB-x38]

The length of the 'twilights' depends on your latitude.

At mid-latitudes the sun rises at about 90 degrees to the horizon, giving the shortest time between beginning of daylight and sunrise.

At higher latitudes the sun rises at a more oblique angle to the horizon and morning / evening civil twilight is longer.

24 minutes is a good starting point (4 minutes per degree).

[RUDAS]

in south africa it is 15 min before/after sunrise/sunset.seems we think night is different to that in the uk.

[square leg]

RUDAS boet,

The UK is further north than SA is south, dus die verskil in die lengte van civil twilight;)

But I know that you knew that. All the best for your training!:ok:

[3142]

'Day' means the time from half an hour before sunrise until half an hour after sunset (both times exclusive), sunset and sunrise being determined at surface level;


I got this from the air navigation order 2000. The times of Sun set and rise can be calculated of surfed in the net or look up on the Jeppessen manual.

It is also clearly writen on the uk aip gen 2.7.


Many thanks to all.



DOES THIS DEFINITION APPLY FOR THE REST OF EUROPE AND THE USA?

[aerolearner]

I throw in my $0.02.

Straight from ICAO Annex 6 - Operation of Aircraft
"Night. The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period between sunset and sunrise, as may be prescribed by the appropriate authority.
Note.— Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the morning when the centre of the sun’s disc is 6 degrees below the horizon."

In Italy, the following rule applies:

From AIP-Italia, page RAC 1-36
"Night VFR flights are those operated in the period from SS+30' until SR-30' according to ephemeris of the locality concerned."

I hope this helps.