h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Twilight - A3856250
Author: I am Donald Sutherland - U641020

Just something that has always facinated me. Reading a newspaper outside without any artificial light at 1 AM in the North of Scotland is a strange experience.

Hi there! Interesting topic for an entry.

Is the definition of civil twilight something that is UK specific, or is used everywhere?

Also, for this sort of entry the first person bits (where you say "I" or "me") need to be changed to 2nd or 3rd person to fit with the <./>WritingGuidelines</.>. Let me know if you have any questions about this.

More later.


Mikey

Interesting! I had no idea...

Me either! Very cool.

This is a damn fine entry Got some corrections for you.

There are a lot of words in the entry which don't need to be capitalised. For instance: Twilight, Eastern, West, Sun, Latitude, North.

"vampires stair from their sleep"
stir?

"Civil twilights begins"
twilight

"Civil twilights begins when the Sun is six degrees below the horizon at sunrise and ends when the Sun is six degrees below the horizon at sunset"
That almost suggests that twilight lasts all day long. If morning twilight begins when the sun is six degrees below the horizon, when does it end? And likewise, when does evening twilight begin?

"Between these time is considered light enough to work outside"
Aside from the grammatical problem with that sentence, it's rather vague. What kind of work? I used to work through the night delivering magazines, but I've no idea at exactly what point the sun was six degrees below the horizon nor how light it was at that moment. I just know that I hated the dawn cos I like going to bed when it's dark.

"It is still used today for work that needs to be done at quieter times of the day such as motorway maintenance"
Again, a rather vague statement. Motorway maintenance is done through the night with the aid of powerful lighting. Do you mean that they start and end their work at twilight? That would be difficult in the northern hemisphere winter since they'd be working through the rush hour.

There's a contradiction in the Civil Twilight section. If civil twilight *begins* at dawn and *ends* at dusk, it can't "last[s] all night during mid summer" because night is the only time there is no twilight.

It would be good not to forget the southern hemisphere, pole, and Antarctic Circle in this section.

"Nautical twilights begins"
twilight

"This is the time when the horizon is distinguishable at sea"
The horizon is distinguishable everywhere. Do you mean the *curvature* of the horizon? That too is said to be distinguishable from a number of very flat places on land.

"Nautical Twilight lasts all night during midsummer"
Again, if it begins in the morning and ends in the evening, how can it last all night?

"Astronomical twilights begins"
twilight

"observation if faint"
of

There is a deal of work to do here, but this has the makings of a really good entry

"The horizon is distinguishable everywhere"
Of course, I meant 'everywhere you've got a clear view of it' In other words, there are plenty of places on land where you can see it.

Mikey:

Civil Twilight as with all the others are an internationally recognised standards.

Oojakapiv:

Corrected the spelling and grammatical errors. Added to the civil twilight sentance to make it clear that it is without the aid of artificial light when light would be required to do the job.

Civil twilight doesn't begin at dawn. Dawn in when the sun rises. In UK latitudes twilight can begin over an hour before dawn and the further north you go, the greater the difference between twilight and dawn.

There is no official designation for when twilight ends except the one described. The transition from twilight to daylight and vice versa is of little interest to most people so there is no reason to make a designation for it. Anyone who is really interested will be using the times of sunset and sunrise. The time before dawn that twilight starts will vary depending on your latitude and time of year. In equatorial regions it is just a matter of minutes. In northern latitudes it can extend to hours.

Twilight can last all night during the summer months because the sun never goes far enough below the horizon in order to terminate twilight. The same same phenomenon that stops the termination of daylight for months at a time in polar regions.

At sea, at night, the horizon is indistinguishable - it is just one mass of black. On a bright starry night with a full moon it might just be possible to distinguish the horizon but it will not be sufficiently well defined to use a sextant which is what mariners are interested in.

Donald

Hi there!

Good, interesting, informative entry

Just a couple of typoos:

>long before then end of - the end of

>Between these time the horizon is distinguishable at sea. - times. I understand what you're saying but this sentence does sound a bit odd, maybe a bit of a re-phrase would help.

>the Norther Hemisphere - Northern

I agree that this is a fabulous topic for an entry .

On a quick read-through, this bit confused me:
Nautical Twilight differs slightly from the other two as it is the time of darkness between the end and the start of twilight when there is no light that interests astronomers.

Should that be Astronomical Twilight?

And another typo: quieter times of the day when there are no many people around >> are not or aren't

A fine entry, no doubt about it.

Just to internationalise it a little bit, would it be possible to add in a few well known placenames in Canada and the US? It does seem to be a bit too UK focused at present (with a bit of France thrown in for good measure).

Well done!

Woodpigeon

When I first saw that an entry called 'Twilight' was entered 16 hours ago I thought that the researcher who entered a poem also called 'Twilight' last week had resubmitted it.

To follow on from Miloso:

>>North of latitude 50 degrees, Nautical Twilight lasts all night during midsummer. Abbeville in Northern France is about 50 degrees North. Therefore it can be seen that Astronomical observations during midsummer in the UK can be rather difficult.<<

I think that "Nautical Twilight" should also be "Astronomical Twilight".

But that bit is in the Nautical segment, isn't it? I took that to mean casual observations by Everyday Joe, not precise observations by a professional astronomer. But as they're both included in the entry I can see where it would get confusing.

No, that's in the Astronomical Twilight section, second paragraph.

ok

Thank you all for your observations. Corrections made.


Milso:

You are right, it should be Astronomical Twilight, not Nautical Twilight.

Donald

A really fine Entry.

If I was forced to make a comment I would say maybe the title could be expanded to 'The definitions of Twilight' or something along these lines.

Other than that

HELL

Woodpigeon:

Inserted a few International places. They are all in Canada as the US/Canadian border is only 49 degrees North. In the Southern Hemisphere there is not a lot South of 50 degrees except ocean and Antarctica.

Donald

I always think of twilight as in the evening, rather than the morning.

As for car headlights, the Highway Code that I've got just says they should be on half an hour *after* sunset and half an hour *before* sunrise. Sidelights should be on *at* sunset until sunrise. There's no mention of headlights having to be on at sunset itself. My HC doesn't have a date in it, so that could have been updated since then. It was 99p if that helps to age it...

Talking in degrees has made this entry incomprehensible to me I'm afraid.

"Civil twilight doesn't begin at dawn"
That was bad wording on my part - I wasn't talking about any 'official' dawn. What I should have said was 'If twilight begins in the morning and ends in the evening, it can't last through the night'.

Which is still what the entry seems to be suggesting to me.

"Twilight can last all night during the summer months because the sun never goes far enough below the horizon in order to terminate twilight. The same same phenomenon that stops the termination of daylight for months at a time in polar regions."
Ah, with you now - that makes perfect sense If that's the reason why, it needs to be explained that way in the entry to avoid any confusion on the part of the reader.

"It is used today for work that needs to be done at quieter times of the day when there are not many people around."
This still means very little, and can even be contradictory - at certain times of the year twilight can fall during the rush hour - not a quiet time of the day at all. Work that needs to be done during quieter times is done according the clock, regardless of what time twilight happens, because the clock bears more relevance to how many people are around. In other words, at night, whether or not it's a time of the year that twilight lasts throughout the night.

You Highway code is probably more up to date than mine Mina. The last time a read the Highway Code it cost 6d. So it probably has been updated since then. I'll take that bit out.

Donald