Submarines in the Winter Twilight

One of the more celebrated North Pole surfacings of the USS Skate happened today in 1959, see for more on that and several others.

Nearly a couple years ago at the ICCC in Chicago, Lord Monckton noted that at the time of this surfacing it was late winter and the Sun hadn’t risen. I’m not entirely sure why he mentioned that, but I wasn’t able to come up with a quick and accurate description of the lighting conditions. Let me do it now so I can get the issue out of my system. First, we need a submarine:

AGSS 569
The Albacore was a research submarine, and a convenient ship to view under lighting conditions similar to today at the North Pole.

I’m not about to spend my St. Patrick’s Day at the North Pole in hopes that a sub will surface, especially since there’s a perfectly accessible submarine in Portsmouth New Hampshire at Albacore Park. I go to an annual event in Portsmouth each February, which fit quite nicely into seeking photos set in an icy, snowy setting.

The rocket science part is to time the photo to match the Sun’s position below the horizon. At the North Pole the Sun rises in March and sets in September. The concept of a 24 hour day refers mainly to the longitude line the Sun is passing (it’s due south all “day” long).

Sunrise, by US Naval Office definition, is when the upper limb of the Sun touches the horizon. The USNO considers the horizon to be distant and the observer is close to land or sea surface. It’s fairly easy to compute the location of the center of the Sun relative the horizon as seen from the North Pole, it’s just the “declination,” which is the celestial equivalent of latitude. There are two significant effects to take into account. The obvious one is the Sun’s angular radius, which is about 16 arcminutes. The other is atmospheric refraction near the horizon. This is what makes the Sun and Moon look squashed when they are on the horizon. The refraction right at the horizon is about 34 arcminutes. So, sunrise occurs when geometrically the center of the Sun is 50 arcminutes (0.83°) below the horizon.

An aside – on the equinoxes, night and day are supposed to be equal. Not true! At most latitudes the time from sunrise to sunset is about 12h10m then. Today, for me, is the true clock time equinox.

Where were we? Oh yes. Some data from the North Pole on 1959 Mar 17, in degrees above the horizon:

1959 North Pole, Latitude    90.00  Longitude    0.00

  Date   Decln

Mar 15   -2.32

Mar 16   -1.93

Mar 17   -1.53

Mar 18   -1.14

Mar 19   -0.74

Mar 20   -0.35

Mar 21    0.05

It would be nice to know the hour, but let’s not be that obsessive. What does this tell us? First, the Sun will rise around the 19th. Second, Spring begins when the declination is 0°, and that will be on the 21st. On the 17th, the entire Sun is below the horizon and the upper limb is 0.70° below the horizon. This puts us well into morning twilight. Twilight – what’s that? Let’s take a look from a North Pole point of view, and start when it’s just plain dark.

Another aside – at the start of winter at the North Pole, the Sun is 23.44° below the horizon. However, the Full Moon will be between some 18° to 28° above the horizon. Yes, it’s nighttime, but not completely dark all the time.

If we discount the Moon and clouds, the sky is dark at the start of Winter with only stars providing feeble light. In late January, the Sun climbs above 18° below the horizon and we enter Astronomical Twilight. This is a period where there is enough light from the Sun that it interferes with seeing faint objects in the sky, especially those nearest the rising Sun. In mid February the Sun reaches 12° and we enter Nautical Twilight. Brighter, but mariners can still easily see the stars used for navigation. By early March the Sun reaches 6°, now the navigational stars are fading from view and we’re in Civil Twilight and people can get around pretty well without extra light. From the above, we can tell Civil Twilight will last a couple weeks and then daylight begins.

Now, let’s shift our point of view to Portsmouth. I’m also shifting to the evening because I took these photos after sunset. Civil twilight here lasts about half an hour, which fits in well with both our experience and state motor vehicle law that requires headlights to be on by half an hour after sunset.

Another aside – twilight is longest at the Summer Solstice, shorter at the Winter Solstice, but shortest near the equinoxes. If there’s interest, I’ll go into more details in the comments.

My intent was to photograph the Albacore in lighting similar to what there was for the Skate, i.e. when the Sun was 0.70° below the horizon. The math for this is a bit trickier, and entails messing with declination, right ascension, latitude, longitude, and Solar altitude to get the date and time. A fine approximation uses just the date (I was there on 2010 Feb 20) and some of this data:

2010 Albacore Park, Latitude   43.08  Longitude   70.76

  Date  Rise    Set  Civil   Naut  Astro    Decln

Feb 21  6:32A  5:22P  0:29   1:02   1:36   -10.43

At sunset, the solar altitude is -0.83°, we want the time when it’s about -1.53°. We know during Civil twilight the Sun will drop 5.16&deg, so interpolating, that’s about 4 minutes after sunset, and gee, there should be plenty of light. While the the visitor center and Albacore were locked, I could park there and walk around the trench used to bring in the Albacore. And indeed, there was plenty of light, as the photos prove.

Just one other thing – yes, black and white films in the late 1950s were plenty fast enough. The photographer probably used Tri-X (ASA 400) or Royal-X (ASA 1200). The latter was so grainy that it generally was only used in large format cameras. I had my camera set to a ASA 400 (or maybe even 100) equivalent.

Lord Monckton has probably figured all this out, but now we all know that there was plenty light and we know where to find a submarine in a snowy environment.

AGSS 569
Have you ever wondered how many photographs there are of submarines that have traffic lights in the background? No, neither have I.

The Albacore is an interesting vessel, several design experiments with it influenced the next generation of submarines.

Counter rotating prop
I'm always a sucker for interesting mechanical contraptions and this counter rotating screw caught my eye. I guess a sub with a single screw could have some interesting handling issues.
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March 17, 2012 1:00 pm

That’s a fake screw… the actual ones are classified…

March 17, 2012 1:23 pm

I am fascinated by submarines since watching Das Boot. 🙂

March 17, 2012 1:35 pm

I’ve been fascinated by submarines since before the first patrol I served on one…. 1974. Volunteered for subs in ’72. That “screw” is NOT fake. The Albacore was a 1950s experimental diesel powered sub. The testing of designs, including propellers, using it led to new shapes and applications that were utilized in the nuclear subs that were built in following years. The Albacore was decommissioned in ’72.

John Blake
March 17, 2012 1:37 pm

Why not favor us with the actual, classic photo of USS Skate riding comfortably at 90 North?
[Reply Originally I was going to, but between that photo having been used several times and there being such a good collection in that 2009 post I figured I’d add an extra photo of the Albacore instead. -Ric]

March 17, 2012 1:40 pm

What was the point of all that?

March 17, 2012 1:43 pm

“I’m not about to spend my St. Patrick’s Day at the North Pole in hopes that a sub will surface.” One less thing I have to worry about. 😉
[Reply: Yes dear. Sorry I haven’t done anything about dinner yet. I’ve been on the computer, but you knew that. -Ric]

March 17, 2012 1:53 pm

Contra rotating.
I believe that’s more for efficiency than steering.

March 17, 2012 1:54 pm

There are two in Holbrook NSW not far from one of the great pie shops of all time.

March 17, 2012 1:55 pm

lol, that’s good Ric, very detailed. Couldn’t you have just stated that it’s light outside right before sunrise and right after sunset?
At any rate, when Monckton seemingly throws in a off-hand comment like, when “Lord Monckton noted that at the time of this surfacing it was late winter and the Sun hadn’t risen.” I often attribute that to bait. It’s a great argument style, which, I employ at times.

kbray in california
March 17, 2012 1:56 pm

“That’s a fake screw…”
CAGW “science” is also in that category.

David, UK
March 17, 2012 2:12 pm

A very interesting read, thank you!

March 17, 2012 2:17 pm

michaelpgoad says:
March 17, 2012 at 1:35 pm
I used to chase you around. Was in ASW (anti-submarine warfare) starting in 1969. P3’s & S3’s etc. Bubble head 🙂

March 17, 2012 2:18 pm

Counter rotating screws to neutralize the torque, I guess?

old engineer
March 17, 2012 2:22 pm

The wikipedia article on Skate is at:
Quoting from the article: “In early March 1959, she again headed for the Arctic to pioneer operations during the period of extreme cold and maximum ice thickness. The submarine steamed 3,900 miles (6,300 km) under pack ice while surfacing through it ten times. On 17 March, she surfaced at the North Pole to commit the ashes of the famed explorer Sir Hubert Wilkins to the Arctic waste. When the submarine returned to port, she was awarded a bronze star in lieu of a second Navy Unit Commendation for demonstrating “… for the first time the ability of submarines to operate in and under the Arctic ice in the dead of winter….””
There is also a picute of Skate surfaced “in the Artic” in 1959. Looks like plenty of light ot me.
Also a great picture of Skate surfaced at the North Pole in 1962 at:
However, according to the Wikipedia article, this would have been on August 2, 1962

March 17, 2012 2:25 pm

I had GREAT success pushing that to 1600+ with fantastic results when taking photos of sports inside a gym.

March 17, 2012 2:55 pm

This page can help you with the Arctic light question.
Click on March!

Ken Hall
March 17, 2012 3:00 pm

If any of you want to speak to experts on Submarines, get in touch with the Dock Museum, Barrow in Furness Cumbria UK.
We have been building world class submarines here for well over a hundred years. This town has marine engineering in it’s blood and almost nobody who believes in Catastrophic Anthropological Climate Change.

March 17, 2012 3:05 pm

I always thought submarine screws were designed to be as quiet as possible ?
So, with one post, Ric, has managed to combine submarines, astronomy and Lord Monckton.
I truly pity you, but you brought this upon yourself 🙂

Bill Yarber
March 17, 2012 3:22 pm

No, we’re all getting screw.. by the “science” of CAGW!

March 17, 2012 3:24 pm

Have to say I am a little confused about the point of your post. The stages of astronomical twilight and phases of the moon are fully monitored by submariners (and villains) all around the world.
[Reply: There’s really no central point. WUWT’s theme is Commentary of puzzling things in life, nature, science, …. If some people find concepts like a “day” at the North Pole to be a puzzle worthy of commentary, then great.]
I suspect, but I am no means certain that you believe Monckton was suggesting the photo a fake. No way would a crew of 100 plus sailors be able to do that. Jack does not do fake.
[Reply: Not at all. The closest thing to a “suspicion” is that Lord Monckton may not have noticed the surfacing was before sunrise until that day and hadn’t determined for himself how light it was. I could have come up with a decent estimate (e.g. light like within 10 minutes past sunset) but I had forgotten the date of the photograph. In case Lord Monckton sees this post, I figure my analysis had better be complete!]

March 17, 2012 3:30 pm

A fun and interesting post. The photo of a sub in a park is a hoot!
Thanks, Ric.

March 17, 2012 4:30 pm

I remember one captain who had spent years driving a bouy tender that had one screw. They retired that boat and he got its two screw replacement. He provided us with hours of mirth before he got the hang of the thing.
The most fun part was docking where there was a strong current. With the old boat he would nose into the dock and haul on the throttle and the stern would swing over real nice like. With the new boat … no docks were actually destroyed and the boat didn’t get any major dents.
Unless you could control them independently, the counter-rotating screws look like the worst of both worlds. The only way to steer the boat would be with the rudder.
Of course all this stuff about the boat is a red herring. The real deal is that there was enough unfrozen water at the north pole for a submarine to surface.

Dave Worley
March 17, 2012 4:40 pm

I don’t know this, but contra rotation would probably dampen noise. Run silent… deep.

March 17, 2012 5:02 pm

Just in passing, forget propellers look propulsors.

March 17, 2012 5:22 pm

CommieBob says
Of course all this stuff about the boat is a red herring. The real deal is that there was enough unfrozen water at the north pole for a submarine to surface.
Bob deems to have some resistance to the idea that ice floating on water moves around and that gaps open up that allow submarines to surface. No melting required. No low ice extent required.
Maybe the skate logs should be read to see if they had trouble finding openings through which they could surface. The probably even logged the ice thickness above them. If the ice on average was a lot thicker than today that would put paid to this stubborn belief in low ice in the 1950s.
In fact wasnt a book written about these expeditions?

March 17, 2012 5:22 pm

commieBob says:
March 17, 2012 at 4:30 pm
Of course all this stuff about the boat is a red herring. The real deal is that there was enough unfrozen water at the north pole for a submarine to surface.

Except of course there wasn’t, the Skate surfaced through a frozen lead.

March 17, 2012 5:27 pm

Ah yes here we are on Amazon:
Surface at the Pole: The Extraordinary Voyages of the USS Skate (Bluejacket Books) (Paperback)
James F. Calvert
It’s funny how you guys are always quoting from this book!!!!! Must be lots of refutations of the existence of lots of ice in 1950s Arctic in there.

March 17, 2012 5:32 pm

A brilliant post, with some really interesting info about subs and the Arctic – and on St Patrick’s Day! Who could ask for more? Thank you all!

March 17, 2012 5:51 pm

A picture of the USS Skate at the North Pole, Commander James F Calvert USN from his book “Surface At The Pole: The Extraordinary Voyages Of The USS Skate” first published 1966 .
Link : First edition
Link : Hard cover 2010 ;

March 17, 2012 5:56 pm

Phil. says:
March 17, 2012 at 5:22 pm
commieBob says:
March 17, 2012 at 4:30 pm
Of course all this stuff about the boat is a red herring. The real deal is that there was enough unfrozen water at the north pole for a submarine to surface.
Except of course there wasn’t, the Skate surfaced through a frozen lead.
BS, look at the picture, it was more than a lead.
The polar bears sniffing around the sub in another photo, shows a peak predator examining its prey.
[Reply: Apparently the polar bear incidents were not at the pole, at least not in these links:
In the first one, the bear tries to eat the rudder. Damage was said to be minor.
– Ric]

March 17, 2012 6:03 pm

From a review of James Calvert’s book at Amazon: “Nuclear subs do need to surface in an emergency (fire or power plant problems), to launch missiles or communicate so during the 1st cruise discussed, Captain James F. Calvert describes tactics developed for operating in the Arctic Ocean during the summer. These include locating melt pools (pond to lake-sized pools of water called Polynayas) dotting the arctic landscape and surfacing without the forward motion normally used to stabilize a submarine; there was to little space. There is an interesting account of how an arctic research station drifting 2-3 miles/day on an ice flow a few hundred miles from the North Pole was located. The USS Skate was able to surface in a polynaya within 50 yards of the camp. The crew greeted researchers that had been isolated for months (the summer ice was to thin and weak for a plane to land on).”
“the summer ice was too thin and weak for a plane to land on…” Hmmm

March 17, 2012 6:18 pm

u.k.(us) says:
March 17, 2012 at 5:56 pm
Phil. says:
March 17, 2012 at 5:22 pm
commieBob says:
March 17, 2012 at 4:30 pm
Of course all this stuff about the boat is a red herring. The real deal is that there was enough unfrozen water at the north pole for a submarine to surface.
Except of course there wasn’t, the Skate surfaced through a frozen lead.
BS, look at the picture, it was more than a lead.

But that isn’t a photo of the March 17 surfacing at the N Pole, this is:×383.jpg

March 17, 2012 6:46 pm

Phil. says:
March 17, 2012 at 6:18 pm
“But that isn’t a photo of the March 17 surfacing at the N Pole, this is:×383.jpg
Attribution much ?

March 17, 2012 7:28 pm

u.k.(us) says:
March 17, 2012 at 6:46 pm
Phil. says:
March 17, 2012 at 6:18 pm
“But that isn’t a photo of the March 17 surfacing at the N Pole, this is:×383.jpg”
Attribution much ?

Commander James Calvert, skipper of the Skate in his book “Surface at the Pole”!

Warren in Minnesota
March 17, 2012 7:45 pm

I think that just before the spring equinox at the north pole there would be no darkness as the sun would circle the horizon and be just below the horizon. The time would seem to not be important for lighting as it would always be dawn for several days just before the sun goes above the horizon.

March 17, 2012 8:31 pm

Contra-rotating screws are, indeed for quiet. Single screws on a shaft can and do “cavitate” (leading edge, low pressure, bubble collapse) making a ton of noise. Throttlemen on submarines have to be very careful about how quickly they open the throttles to avoid cavitation at shallow depths. Do not confuse single, twin and contra-rotating screws, please.

March 17, 2012 8:59 pm

Warren in Minnesota says: March 17, 2012 at 7:45 pm
I think that just before the spring equinox at the north pole there would be no darkness as the sun would circle the horizon and be just below the horizon. The time would seem to not be important for lighting as it would always be dawn for several days just before the sun goes above the horizon.
Ric is trying to replicate the lighting conditions while not being at the Pole, hence all that stuff he wrote.
A few years ago, before I began my climate science research, I did some research on calculating the time of sunrise and sunset from any position on earth. I found some code in basic that I converted into C# so I could make an app that would run on my pocket/mobile pc.
Some time afterwards I lost that work and the downloaded code in a rare triple failure of my hard drive in a parity raid setup as well as the backup. (warning, never use RAID as your only backup solution) .
I later decided that I would rewrite the code, without the help from someone else’s algorithm, especially after getting this email from the downloaded code location a few years after I had downloaded it:
“According to our records, you or your organization has downloaded the Solar Position Algorithm from   This algorithm is made available on our website without charge for non-commercial use only.   If you are interested in obtaining a license which would allow you to incorporate the algorithm into a product which you intend to sell,  please contact me at [redacted email].”
So began a long journey involving several years of studying calculus then getting side tracked by my climate science studies, and I still haven’t written any code to calculate sunrise/sunset. But I sure have learned a lot. (Note that I also began studying calculus to help me to both understand a book on “The Finite Element Method”, as well as to help me solve a computer programming problem related to physics).
I did find a good start to writing my own algorithm by downloading this text (ascii ?) file describing methods to use to do the calculations.
From my experience, Ric seems to have hit all the bases. The only thing missing perhaps is the mention of a “sidereal day” which might or might not be relevant.

March 17, 2012 9:05 pm

Mangled link, should be

March 17, 2012 9:18 pm

I think the hidden intent of Rics piece is to show his prowess mathematical skills and vast knowledge to shame that evil copper ‘You see your honor it was only 29 minets after twilight thus I was within the law not to have my headlights on’

March 17, 2012 11:50 pm

Navsource, in the Wayback machine, had it stated as March 17th 1959, just days before my original article. This is the April 18th 2009 snapshot from Wayback:
The caption then reads:

Skate (SSN-578), surfaced at the North Pole, 17 March 1959.

I remember checking NAVSOURCE for accuracy before publishing, my caption then says:

Skate (SSN-578), surfaced at the North Pole, 17 March 1959. Image from NAVSOURCE

History on that photo changed there at NAVSOURCE since then, probably due to alarmist pressure from Wiki etc. and other folks like Neven who went ballistic over the picture when I highlighted it. It is “inconvenient” in March (during peak ice season) but soothing for them in August (during near peak melt season).
The picture may have been taken a couple of days after the funeral photo in March alluded to upthread.
Se EM Smith comment in my original thread.

March 18, 2012 1:24 am

Contra rotating makes the sound signature clearly known. And is not necessary.
That is why most submarines have only one screw, or rarely a pump jet.

March 18, 2012 2:18 am

Hit the Albacore Park Link. Fascinating story and I’d say the taxpayers got their money’s worth on that one.
Note the surface Navy considered the submarine arm as the enemy. I just read a book on John Boyd. Even during the cold war the USAF was the enemy in the Pentagon. I just got told this afternoon it isn’t much different between the RAAF and Australian Army at present.

March 18, 2012 2:22 am

u.k.(us) says:
March 17, 2012 at 5:56 pm
I can imagine the conversation with Mrs Polar Bear later. “You shoulda seen the size of that seal! And it got away!

j ferguson
March 18, 2012 6:31 am

The Albacore is an excellent thing to visit. We did in July a few years back. Maybe because there were two of us and we were adults, we were allowed in unaccompanied. I spent a couple of hours inside sitting in the various places where one could sit, admiring the X diesels, the gauges, the injector tester, and just generally absorbing the machinery. At the time, they had not public-proofed it. Maybe they still haven’t.
I loved it.
It seemed to me to be totally un-vandalized and very very complete, down to a typewriter in the radio room.
I don’t know what they do when kids are around, but…

March 18, 2012 7:32 am

The photo at Navsource is credited to Graham P. Davis and he had this to say about it Oct 30th 2011
“USS Skate did indeed surface at the North Pole but not until 17 March 1959. Ice conditions in August 1958 were too heavy at the Pole for the Skate to surface, as they were for the Nautilus some days earlier. The Skate did surface in several other leads and polynya that August, including one near Ice-station Alfa. The above picture may have been from one of those.
When the Skate sailed for the Arctic the following year, the sail had been strengthened to allow it to break through thin ice. At the Pole, they eventually found a small, refrozen lead, or skylight, and managed to break through it. Later, many of the crew gathered for a service at which the ashes of Sir Hubert Wilkins were sprinkled in the wind. The temperature during this service was -26F (-32C).”

March 18, 2012 8:28 am

Paul H is “fascinated by submarines since watching Das Boot. :-)”
in which case for you and those similarly afflicted you may be interested in following the exploits of the Gato Class US submarines in WWII operating out of Brisbane. It was the USS Guardfish that that dropped my Australian father among others to reconnoitre the Marine landing at Empress Augusta Bay on Bougainville-
He was a master gunner(shore battery in Suva) and surveyor stationed in Fiji with the Fiji Military Forces and as such had exactly the observational skills needed for the task, being right under the nose of US South Pacific Command in Fiji at the time (it was from Fiji that the first Marine landings of the war were launched upon Guadalcanal and the beginning of the Solomons Campaign)
The exploits of the Guardfish are documented by recall in the early 1980s here-
Should that whet your appetite for the Solomons campaign you might like to get hold of a copy of The Coastwatchers by Eric Feldt to put it all into perspective, particularly how instrumental submarines were in the crucial turning point of the Pacific War.
Then for an enthralling tale of submarine warfare from the other side you should read Iron Coffins-
You may find some uncanny similarity with that and Das Boot 😉

March 18, 2012 9:40 am

There were quite a few of them by the way and naturally some considerable logistics to keep them fighting-
bearing in mind they were mostly a bunch of 17-21 year olds.
I realized my father was only 19 when he signed up after I discovered a Soldiers Service Book tucked away in his personal effects upon his death and began piecing together some old war stories with the power of the internet.
He recalled the Fiji garrison(under NZ control then as Australians were busy in the ME) being called to action stations in expectation of a Japanes Fleet approaching Fiji but it was actually an American Fleet come to join the Pacific War in earnest after some argument in Washington that the European theatre should take precedence. A subsequent buildup of US forces occurred in readiness for a completely untried landing at Guadalcanal as described here-
Don’t be fooled by that understatement that- “One practice amphibious landing was made at Fiji, 28July, for about 1/3 of the 1st Marine division, to familiarize the troops with boarding landing craft and in unloading cargo. All accounts say the test was a failure.”
According to my father it was a complete disaster with swamped landing craft due to an intense tropical storm and no doubt some telegrams home were fudged as to how some young sons really died. No matter they were off to Guadalcanal to try and get it right the next time.
Lest we forget.

March 18, 2012 12:45 pm

A few weeks back in this thread there was this intriguing comment:

TG McCoy (Douglas DC) [March 1, 2012 at 10:28 am] says:
“Cousin’s husband was a young torpedoman on the Skate when they did that… there was a LOT of open water…”

Sounds like a possible primary source. If you are still reading this thread could you elaborate on his status? If he is still with us perhaps you might arrange for an interview of him on the record so he can at least get his important eyewitness experience documented! Maybe he has his own private photos.

March 19, 2012 1:51 am

Here is an article of Life Magazine form May 4th, 1959: This tells us a lot on the conditions when surfacing at the north pole
[Reply:Great find, thanks. The lead photo (split over two pages is one I hadn’t seen before.
The photo in the controversy is on page 135, and is identified as one of the 10 surfacings and clearly doesn’t match the conditions described in the article.]

March 19, 2012 3:25 am

Wow, I can’t believe I didn’t take the opportunity to mention that I worked for International Submarine Engineering for 6 years, when they made half of the total global underwater remotely operated vehicles (ROVs), as well as AUVs, USVs and other interesting projects, some classified perhaps 😉 .
The president, James McFarlane was in the navy before he started his company. I wonder what connections he still has.

March 19, 2012 5:45 am

The photo of the young sailor in the Bluenose ceremony from the Life Magazine article brings back memories. The missile sub I was on went north of the arctic circle twice. Being a missile sub on a cold war deterrent patrol, we didn’t go far north to go under the ice ( so far as I know).

March 19, 2012 8:43 pm

This thread (and the related one the other day) is so cool. It has everything – humour, pathos, bathos, history, geography, astronomy, physics, engineering etc, and lots of anecdotes, some of which may even be shaggy dog stories. What’s not to like?
Never being afraid to ask a dumb question, I will bite on this:
“Another aside – twilight is longest at the Summer Solstice, shorter at the Winter Solstice, but shortest near the equinoxes. If there’s interest, I’ll go into more details in the comments.”
A lot of interest here – intuitively it would seem that twilight (and the opposite in the morning) waxes and wanes with the solstices. Plus, anecdotally, where I live (about 35 degrees south) the night falls like a brick in mid winter, in a few minutes. Just now, near the equinox, there is still some twilight. But perhaps I have missed something in the definitions?

March 19, 2012 8:56 pm

On further thought, I am guessing that the point about twilights relates to longitude. They don’t have much at either end of the day near the Equator.

J Bowers
March 20, 2012 3:34 am

A photograph of the Skate during the actual event, takne by Commander James F. Calvert.

March 20, 2012 4:46 pm

Hmmm, I will just leave a few pictures from the NOAA North Pole web Cam, showing the actual lighting conditions and shadows, depending on the seasons, at the pole, under clear weather conditions.
How it works
The sun comes up each day because Earth rotates once on its axis every 24 hours or so. Seasons are a result of Earth being tilted 23.5 degrees on its spin axis coupled with the planet’s 365-day orbit around the sun.
The Arctic Circle, a line at 66 degrees north, marks the latitude at which the sun does not set during the summer solstice (when the top half of our planet is facing directly toward the sun), the longest day of the year, nor rise during the shortest day of the year, the winter solstice. The farther north you move from the line, the longer the period of night-less summer or sun-less winter. Ilulissat is located about 3 degrees north of the Arctic Circle, so residents spend the middle of winter without any sunlight.
At the North Pole, the sun rises only once a year — at the start of spring. It gets higher in the sky each day until the summer solstice, then sinks but does not truly set until late September, at the autumn equinox.

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