APOD: Sunrise at the South Pole (2021 Oct 05)

[APOD Robot]

Sunrise at the South Pole

Explanation: Sunrise at the South Pole is different. Usually a welcome sight, it follows months of darkness -- and begins months of sunshine. At Earth's poles, it can take weeks for the Sun to rise, in contrast with just minutes at any mid-latitude location. Sunrise at a pole is caused by the tilt of the Earth as it orbits the Sun, not by the rotation of the Earth. Although at a pole, an airless Earth would first see first Sun at an equinox, the lensing effect of the Earth's atmosphere and the size of the solar disk causes the top of the Sun to appear about two-weeks early. Pictured two weeks ago, the Sun peaks above the horizon of a vast frozen landscape at Earth's South Pole. The true South Pole is just a few meters to the left of the communications tower. This polar sunrise capture was particularly photogenic as the Sun appeared capped by a green flash.

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[Ann]

Sunrise at the South Pole with a green flash. Image Credit & Copyright: Martin Wolf (U. Wisconsin), IceCube Neutrino Obs., NSF; ht: Alice Allen

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ESO staff Guillaume Blanchard was able to capture the rather rare blue flash while observing the sunset on Christmas eve from the Paranal Residencia. The image was taken with a digital camera attached to a telescope with a 480-mm focal length. The very intense blue seen on the image, as well as the purple edges, do not leave any doubt on the reality of the phenomenon. Please remember that looking at the Sun, especially through an optical device (camera, telescope, binoculars, etc.), is very dangerous, and could cause immediate blindness. Do not attempt to observe the Sun unless you know what you are doing. Credit: G. Blanchard/ESO

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Green flash? Pfft! Now a BLUE flash, that's something!

Ann

[asmallcorrection]

There is a typo in today's APOD: "peaks" should be "peeks" in the fourth sentence.

[RC Davison]

Since the sunrise takes weeks, does the green flash last proportionally longer?

[orin stepanek]

Awesome photo; I lost a ton of it making my background!

Kitten; kitty cat is adorable!

[diffeq]

Why is there a tower at the geographic south pole?

[Chris Peterson]

Since the sunrise takes weeks, does the green flash last proportionally longer?

Good question. Since the green flash is capturing a consequence of atmospheric dispersion when the Sun is just below the horizon, it should get easier and easier to see it as you get closer to the poles and the rate the Sun moves with respect to the horizon gets slower. Particularly near the equinoxes, I'd expect you could watch for minutes or hours as the green "flash" (or even Ann's blue flash) comes and goes with varying atmospheric conditions.

[neufer]

South Pole posts most severe cold season on record, a surprise in a warming world.
By Jason Samenow and Kasha Patel
The Washington Post, October 2, 2021

<<The average temperature at the Amundsen–Scott South Pole Station between April and September, a frigid -78 degrees (-61 Celsius), was the coldest on record, dating back to 1957. This was 4.5 degrees lower than the most recent 30-year average at this remote station, which is operated by United States Antarctic Program and administered by the National Science Foundation.>>

[neufer]

Why is there a tower at the geographic south pole?

The true South Pole is just a few meters to the left of the communications tower.

[Fred the Cat]

Same at our house. When it's hot upstairs it is very cold in the basement. My question is, "How did the photographer get the sun to tip its hat to Owlice?"

[neufer]

South Pole posts most severe cold season on record, a surprise in a warming world.
By Jason Samenow and Kasha Patel
The Washington Post, October 2, 2021

<<The average temperature at the Amundsen–Scott South Pole Station between April and September, a frigid -78 degrees (-61 Celsius), was the coldest on record, dating back to 1957. This was 4.5 degrees lower than the most recent 30-year average at this remote station, which is operated by United States Antarctic Program and administered by the National Science Foundation.>>

Same at our house. When it's hot upstairs it is very cold in the basement.

• Lack of circulation no doubt.

A summary of the path of the thermohaline circulation. Blue paths represent deep-water currents, while red paths represent surface currents

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<<The Thermohaline Circulation is a pattern of water flow through the world's oceans. Warm water flows along the surface until it reaches one of a few special spots near Greenland or Antarctica. There, the water sinks, and then crawls across the bottom of the ocean, miles/kilometers deep, over hundreds of years, gradually rising in the Pacific and Indian oceans.

Cold water is heavier than warm water. Salty water is heavier than fresh water. Water near the equator gets warmer, and near the poles, gets colder. Water near the mouths of rivers gets fresher, but water, where there's freezing or evaporating, gets saltier, because the salt is left behind. These, and other factors such as the shallow Bering Strait, combine to form this pattern of water flow.

The Gulf Stream is part of this circulation, and is part of the reason why northern Europe is warmer than it would normally be; Edinburgh has the same latitude as Moscow. The Thermohaline Circulation influences the climate all over the world. A shutdown or slowdown of the thermohaline circulation is a hypothesized effect of global warming on a major ocean circulation. A 2015 study suggested that the Atlantic meridional overturning circulation (AMOC) has weakened by 15-20% in 200 years.>>

[ta152h0]

And the Southern Cross is pointed right at it! pass the ice cold one.

[Eclectic Man]

Since the sunrise takes weeks, does the green flash last proportionally longer?

Good question. Since the green flash is capturing a consequence of atmospheric dispersion when the Sun is just below the horizon, it should get easier and easier to see it as you get closer to the poles and the rate the Sun moves with respect to the horizon gets slower. Particularly near the equinoxes, I'd expect you could watch for minutes or hours as the green "flash" (or even Ann's blue flash) comes and goes with varying atmospheric conditions.

See: https://earthsky.org/earth/can-i-see-a-green-flash/

and https://en.wikipedia.org/wiki/Green_flash

"Green flash occurs because the atmosphere causes the light from the Sun to separate, or refract, into different frequencies. Green flashes are enhanced by mirages, which increase refraction. A green flash is more likely to be seen in stable, clear air, when more of the light from the setting sun reaches the observer without being scattered. One might expect to see a blue flash, since blue light is refracted most of all and the blue component of the sun's light is therefore the last to disappear below the horizon, but the blue is preferentially scattered out of the line of sight, and the remaining light ends up appearing green.

With slight magnification, a green rim on the top of the solar disk may be seen on most clear-day sunsets, although the flash or ray effects require a stronger layering of the atmosphere and a mirage, which serves to magnify the green from a fraction of a second to a couple of seconds."

Chris seems to be correct that at poles a green flash may last for some time:

https://www.aaas.org/catching-elusive-green-flash

"A mirage is also necessary for the phenomenon to be seen, because the flash is dependent on a variation in astronomical refraction near the horizon. There are actually four types of green flashes, each dependent on a different type of mirage:

The inferior mirage, or I-Mir, which is the type usually seen by the naked eye just as the last of the sun dips below the horizon (the same type of mirage that is seen over asphalt on a hot day);
The mock mirage, or M-Mir, which is caused by an atmospheric temperature inversion and looks similar to the I-Mir;
The sub-duct flash, where a mirage causes the setting sun to form an hourglass shape and turns the upper part green for up to 15 seconds; and
The very rare green ray, which is a beam of green light that shoots up from the green flash or is seen immediately after the sun sets. There is no known photograph of the green ray.

Although the green flash usually lasts between one and three seconds, it was observed on and off for a full 35 minutes on October 16, 1929 by Admiral Byrd's expedition at the Little America base on Antarctica."

[RJN]

In response to a valid criticism of the APOD explanation on APOD's Facebook mirror by Paul Schlyter, the text of the main NASA APOD has changed the wording "just minutes" to "hours". In this context, sunrise times include twilights like, for example, astronomical twilight.

[Jim Armstrong]

I hesitate to post here because it often gets lost., I'll try again.
Everyone knows, and it as been the basis for many riddles, that from the South Pole every way (direction) is north.
What I have never been sure of is how to grasp that every direction seems to also need another component.
These components might be "east-north" and "west-north" and ones in between.
So places around the horizon, including this sunrise, should have designators of some kind.
Maybe this is why my comments don't go through, but if there is enough here to answer, please do.
Jim Armstrong
Potter Valley, CA

[Chris Peterson]

I hesitate to post here because it often gets lost., I'll try again.
Everyone knows, and it as been the basis for many riddles, that from the South Pole every way (direction) is north.
What I have never been sure of is how to grasp that every direction seems to also need another component.
These components might be "east-north" and "west-north" and ones in between.
So places around the horizon, including this sunrise, should have designators of some kind.
Maybe this is why my comments don't go through, but if there is enough here to answer, please do.
Jim Armstrong
Potter Valley, CA

Every direction may be north, but every angle is defined by longitude. Anywhere you are, you can define a position on the horizon by an azimuth, most commonly where 0° is on the great circle passing through the poles. At the poles, azimuth is simply the longitude. 0° is in the direction of Greenwich.

[A few meters to the left]

I bet that there was a meeting to decide on where to put the communication tower, where someone suggested planting it right at the pole. However the Antarctic treaty has put nice people in charge of the place, who wouldn't do that to mother Earth; or maybe the pole is protected; or maybe there was an ugly fight between the communication tower people and some other group who wanted to stick their own gear. Anyone knows the real story? Anyway, the tower was put a bit to the side, and the pole was left alone. Unless it wanders under the tower, but that's the pole's business.

Partial victory anyway, because it seems there's no way to avoid seeing the tower when looking at the South Pole. Cue a chorus of "but there's nothing to see".

[ccsawyer]

Just north of Thule Greenland (where I spent a year) there were green flashes at the first sunsets ('midnight) of the summer. I could change the colour by walking up or down the hillside. The last colour after green was blue! The air was very clear.

[daddyo]

These Antarctic Film Festival videos are entertaining: https://www.wiffa.aq/en/station?tid=116

[Fred the Cat]

Not to anthropomorphize Earth but I think the pole has movements too.

[neufer]

In response to a valid criticism of the APOD explanation on APOD's Facebook mirror by Paul Schlyter, the text of the main NASA APOD has changed the wording "just minutes" to "hours". In this context, sunrise times include twilights like, for example, astronomical twilight.

• When I drag myself out of bed to watch a sunrise over the Atlantic, it
  • starts when I first see the sun and
    ends when I can see the full sun:

Code: Select all

Lat.	Spring Equinox "Sunrise duration"
............................
0	2.33 min
30	2.76 min
60	4.76 min
70	6.72 min
80	17.39 min
85	29.09 min
....................
90	30.7 hours

• I then go back to bed.

When you’re at the South Pole, the sun does not rise and set every day. It takes about two months to rise (August through October). It stays daylight from October through March. Then it takes another two months to set (March through May). Finally, it stays well below the horizon from May through August when Antarctica is in complete darkness.

The following quote describes what was probably the longest observation of a green rim, which at times could have been a green flash. It was seen on and off for 35 minutes by members of the Richard Evelyn Byrd party from the Antarctic Little America exploration base [78.2° S] in 1934. [On Aug.22, 1934, the sun rose & set over a 2.72 hour period [at 78.2° S] but never got fully above the horizon]:

• There was a rush for the surface and as eyes turned southward, they saw a tiny but brilliant green spot where the last ray of the upper rim of the sun hung on the skyline. It lasted an appreciable length of time, several seconds at least, and no sooner disappeared than it flashed forth again. Altogether it remained on the horizon with short interruptions for thirty-five minutes.
  
  When it disappeared momentarily it seemed to have been shut off by a tiny spurt, an inequality in the skyline caused by the barrier surface.
  
  Even by moving the head up a few inches it would disappear and reappear again and after it had finally disappeared from view it could be recaptured by climbing up the first few steps of the antanea [sic] post.

[bill ritchie]

Is not the "length of sunrise" the time between the appearances of the upper and lower limbs? At the 2021 Southward equinox, the Sun's apparent diameter was 31.8'. The Sun's declination (= the earth's tilt) was 0° 15.9' N at about 02:59 UTC on 22nd Sept, and 0° 15.9' S at about 11:41 UTC on 23rd Sept, so the length of sunrise at the South Pole was about 32 hours 42 minutes. That's assuming no atmosphere and an eye height of zero. Changes in any, or all, of these would not significantly affect the "length of sunrise".

Atmospheric refraction will advance the time of sunrise considerably. Being at an altitude of 2800m, with a temperature of -70°C, pressure of 675 hPa, and height of eye of 5m, standard formulae give an advance of about 37 hours, giving an upper limb rise on 20th Sept at about 14:00 UTC. There must be some phenomenally abnormal atmospheric effects to extend this to 14 days.

Re the mast, I hope arriving aircrew are well briefed on this hazard.

Regards,
Bill Ritchie.

[OgetayK]

In response to a valid criticism of the APOD explanation on APOD's Facebook mirror by Paul Schlyter, the text of the main NASA APOD has changed the wording "just minutes" to "hours". In this context, sunrise times include twilights like, for example, astronomical twilight.

This type of confusion is usually caused by vague definitions that we have to make. Popular science in nature has this reductionist behavior, otherwise, even if you just multiply two numbers, half of the people stop reading the rest. We have a similar situation with the definition of "sunrise" and "minutes/hours/weeks" here. Let's dig this a bit considering his valuable comment.

First of all, even I'm the type of person who likes the theoretical ways more, let's go with Stellarium and see what happens. When we do that for Sept 23, we see that Sun rises around 20 degrees per day -- it reaches 5 degrees around 13 days. Note that I'm still being vague by saying around, but I'm reducing the margin of error here. In this time interval, for 40 degrees latitude it takes around 30 mins --oops said around again!

Now let's turn back to his comment. His logic was there is a 1/365 ratio between these, but obviously, there is not, because of the assumptions made. Although that was a good first approximation, we see that for reaching 5 degrees there is a much more difference. 13 days is basically 13*24*2= 624 in terms of 30 minutes (each day has 24 hours so 24*2 30 mins). And weeks/hours is not an actual value, but an estimation. Also the sunrise. If you say 4 degrees or 7 degrees the results will change dramatically.

In conclusion, comparing his calculation and its margin of error to the previous text, there is not much of a difference. But as opposed to the claim, APOD changes its text when there is a valid criticism. In this case, it was the confusion it might possibly create, even though the results didn't change much.

For people who are enthusiastic about this, I suggest considering weeks as 2 weeks and 3 weeks or 1.5 weeks to see the difference. If you want to go even further make it two variables and change the sunrise definition too. When you have such inaccurate --or let's say vague-- definition, your margin of error will be so large that you can't be wrong. Or you will be wrong and correct at the same time!

From a scientific perspective, after spending more than 7 years on public outreach I can confirm that almost no one will remember that minute/hour/week detail. What people remember will be that there is a huge difference! If the physics is satisfied and makes sense, there should be no problem. And yes, we even do this for convenience in physics too.

[farlightteam]

Debe ser impresionante ver ese amanecer