Extremely High Horizon Refraction
[ version française du site EH2R ici ]

Description: Refraction of sun light due to cold dense polar air under warmer thermal layers causes an increase in brightness almost unknown within present physics literature. Global Warming may be seen by studying simple satellite picture archives. Low on the horizon polar sunsets have sun disks compressed into a line. Thermal Inversions cause equally an increase in brightness during twilight.

This page contains a vast database pertaining to temperate and polar sunsets. It also holds many differential refraction pictures, at multiple Zenith Angles. Recently conceived twilight brightness theory with respect to the Y-V Ulluq Q effects are presented. Extraordinary Moon shots show simple refraction. The data is there for you to study, the thoughts are progressive from February 2001 till today, they change according to knowledge acquired from this page and from other pages as referred to below. The data presented is quite accurate, calculations if any can be verified, while past thought mistakes are left untouched, in order to leave the examiner review a fascinating journey in science. Major paradigm shifts will be explained on each individual pages, they will be recognizable by the date they are written.

WD, December 2004

Atmospheric Refraction is very misunderstood or rather under-studied, it has enormous potential to solve apparently complex problems, like the true temperature of the troposphere. A landmark paper:

SUNSET SCIENCE. IV. Low-altitude refraction. By Andrew T. Young, Departnment of Astronomy, San Diego State University, Astronomical Journal, 127:3622-3637, 2004 June.

Proves without much doubt that Astronomical refraction is caused in the Troposphere. This certain fact can help ascertain key measurements, as used on this webpage, helping to calculate the temperature of the lower troposphere, without MSU doubts, such as radiometer microwave satellite readings which fail to distinguish the Stratosphere from the Troposphere.

Another important paper has shown the sun seen by explorers in 1597 at -5.7 degrees below the horizon. This record still holds to this date:

S. Y. van der Werf, G. P. Können, W. H. Lehn, F. Steenhuisen, and W. Davidson, "Gerrit de Veer's True and Perfect Description of the Novaya Zemlya Effect, 24 -27 January 1597 ," Appl. Opt. 42, 379-389 (2003)

Click here for Link

WD April 27, 2007

old description

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2013 Summer fall early winter projection

~ New forms of heat found, a new metric can be seen

First the success of last Fall's winter projection, lessons learned.

"1- Slow start of winter; Winter does not start at the solstice as tradition goes, it begins at various days about the fall equinox, when darkness hits the North Pole.

->This year winter started very late."

It did, but it had a twist, literally the circulation around the Pole was dominantly Anticyclonic. Very much opposite to previous winter of 2011-12.

"2- Sea ice thickness affects the enter circulation of cyclones about the Northern Hemisphere, very little thickness means the slow build up of winter.

-> Low pressure cyclones will easily penetrate the North Pole area same as last year, this means a warmer Arctic and somewhat cooler temperate zone, as opposed to a wide variation of very cold to cool temperate winter."

It was not quite so, the Pole area had an early starting anticyclonic build up directly above the remaining pack ice from the great melt of 2012. This was the dynamic genesis of the winter of 2012-2013. I identified this phenomenon early on but miss diagnosed its importance. Didn't think it would gave stayed after growing along with the recovering ice extent. Lows didn't penetrate the North Pole , despite thinner ice, primarily because the circulation around the Pole was clockwise. The flow basically kept Kara and Barents sea Cyclones to hover over these seas. Very unlike 2011-12 winter.

"3- Sea surface temperatures along with atmospheric temperatures are at all time highs

->Implying great moisture events throughout the winter everywhere influenced by sea evaporation."

That was bang on, great records of record precipitation was reported all over the world.

4- Cold Temperature North Pole locations, they have been varying for about a month

-> means not steady monotonous weather for the Northern Hemisphere."

Bang on varying Jet stream locations caused unusual weather patterns were witnessed pretty much everywhere.

…….."A warm wet winter for all. How warm depends on cloud extent, how wet depends on whether El-Nino will survive. And by wet, I mean when near 0 C with snowfall as well. Ireland and UK should have a reprieve in regular rainfall and more variable weather, North America will wonder where winter went again. The rest of The NH will enjoy warmer weather along with bitterly cold periods as Eurasia will cool down more than the Arctic."

"This leaves El-Nino in a lynch , suspended animation, but nonetheless leaning on a come back summer 2013, because there is no mechanics in place fostering a deep La-Nina except for the Southern Hemisphere dominated by Antarctica and ozone holes,"

This has happened pretty much as expected. ENSO varied quickly towards La-Nina. Then re-trended towards El-Nino. The continents were much colder than the Arctic first. Early winter of 2011-12 was mild following the sea ice great melt.

"If La-Nina returns full blast, unlikely but if so, the melt in spring and summer time will crush 2012 great melt as a distant old record, the Pole will be sailable. If everything remains Neutral or warmer ENSO wise, the ice pack North Pole will be assailed once again by open sea water, 2012 record melt will be still exceeded. The big add on would be increased tornadoes (where they thrive) early in the season, its in the cards, a normal tornado season is not yet foreseen, by all accounts waiting for Polar stratospheric vortex to show itself last. wd December 2, 2012."

North American Tornadoes prediction was excessively precise. Once a rapidly building Polar Stratospheric collapsed in Late December Early January, the very early tornado season ended. ENSO has been very difficult to predict. But El-Nino trending from and almost certain pending La-Nina . Proved that ENSO had no real driver at the wheel, and seemed to languish without a sense of direction.
Over all I rate this past projection as fairly good. While I missed to extend what I detected with respect to sea ice build up reinforcing anticyclonic activity.

Sun Refraction data;

What is the score?

275 observations of differential sun disks; leading in averages percentages, 120 decimal levels from -1 to 10 degrees elevation

2010 and 2005 #1, 2011 #2 and 2013 #3.

February and Early March sun disks were very compressed, only to expand gradually, for the first time I measured many sun disks with strictly adiabatic profiles consistently at end of April. They revealed pure cold temperature refraction compressions. Not surprising, since captures were taken in the zone of cold temperature North Pole, an area where the densest coldest air existed. This zone was much reduced to the Northern part of the Arctic , the Northeast sector of the Canadian High Arctic. ECMWF 500 mb map captured this quite well, when eventually the 500 mb Low center in blue will disappear so will also winter, and this is projected to be so on May 8 2013. One would expect round sun disks when the temperature profile becomes purely adiabatic, it was so, even to the extent when green flashes were less numerous. But the disks were not compressed strangely similar to 2005 or spring of 2010, which were greatly expanded on a continuous way. So the habit of projecting the temperature trend for the Northern Hemisphere is the basis or the back bone for this seasonal long range forecast. Since we were in the Cold temperature North Pole region during literally the entire duration ob differential refraction observations, while coincidentally the rest of the Northern Circumpolar Hemisphere was not, it may be more suitable to predict 2013 as # 2 or 3 warmest year in history. From there we can likely reason out the outcome of the weather to come. The basic cold dense temperature centric idea is that the rest of the world weather circulates around this center. It becomes then important to know where the likely location of the cold temperature North Pole will be. Especially given the circumstances of a rather well established anticyclonic circumpolar flow over winter just past .

New method; Horizon refraction analysis finds more heat.

Particularly strikingly different than sun disk measurements is Horizon refraction, which can be analyzed even in darkness. These observations were compared to a database of past 3 years. Recent refraction analysis presented much stronger adiabatic tendencies. Last year 2012, had very similar effects especially compared to 2011 which had a strong polar stratospheric vortex. Any vortex once well established may trigger a great ozone depletion at its center, giving temperatures lower than -80 C. This great chasm in temperature affects even the surface values, but also the structure of the very lower temperature profile. Winter 2012 -2013 had a strong vortex short lived at end of December 2012, the vortex collapsed under its own oversized weight while some would say by a Sudden Stratospheric Warming, which may be part and parcel of its disintegration process. The vortex split in 2 in January. All during that period, there was very little strong refraction. This was an astonishing find. The Vortex split in 2, and there was 2 vortices more or less centered from ground up to stratopause , one over the Canadian Arctic Archipelago the other over Northern Russia.

2012-2013 summer projection.

Pre-summer Prognosis

ECMWF, the deep blue area at left comprises of the coldest air in the Northern Hemisphere, other lighter blue zones are mostly Cyclones. Winter essentially will vanish with the big blue. The larger question is how the circumpolar general circulation will be this summer? Cyclonic or Anticyclonic? In fancier terms

Arctic Oscillation Positive or Negative? After a winter of mostly anticyclonic weather, one should use the theory of persistence and say it will be anticyclonic. But that is too simple for a larger chaotic circulation system. The process of rapidly melting sea ice may give a different pattern all together, which is Cyclonic.

Which will it be? An anticyclonic dominated circumpolar region would be a disaster for Arctic sea ice, the other way around would be better as was the case in 2012, imagine a 2012 greatest melt with clear air instead of clouds? How much more would sea ice have vanished? Nevertheless it turns out either way sea ice will melt further this summer.

The greatest puzzle to consider is why very weak refraction at the surface to air interface was observed? The answer is the sea was warmer. Because the over all thermal effect or long wave emission from the Arctic Ocean was strong this last spring and more so very strong particularly during the long night. Absent the sun, inversion effects were mostly rare, astounding considering past observations. These near surface lack of inversions were key, it stems from thinner ice or a warmer sea, perhaps both.

Projection scenario Neutral El-Nino

El-Nino does not seem to be making a come back. Although there was a time not long ago when it appeared that ENSO was becoming La-Nina, now re-trending towards El-Nino. ENSO is a major player with respect to cloud formations, even in the Arctic. A Neutral ENSO means worse conditions for sea ice than 2012. Therefore the sea ice melt of 2013 will be greater, with a great possibility of the Pole being free of ice and navigable by ordinary ships. Earlier on Adiabatic lapse rates enhance or bring up whatever is on the surface, open water would be a greater source of energy transferred to the atmosphere, therefore a great soggy wet summer for most of the Arctic. The mechanism is simple, an open spring lead usually spreads out its heat under a persistent inversion layer. The existence of the inversion layer literally surrounds the lead with very cold air. Eventually the lead freezes. The absence of boundary layer changes this scene. Adiabatic air likely draws more heat, which flows upwards. Since it is spring, sunlight

warms the darker water as well, the lead should remain open longer. This was observed particularly in 2010. While a same gap in the ice in 2011 was observed to last only a day.

General Circulation of the Arctic should be more Cyclonic, given the rather large influence of a more open Arctic Ocean, the already thinner ice is already favoring an early eradication of boundary layers. There should be lesser cloud coverage than 2012 for the circumpolar region because of Neutral ENSO conditions.

Further to the populated South will benefit from warmer weather with lesser harsh precipitation variances associated with El-Nino. Tornadoes should be less frequent than an average season less numerous than 2012. This would be nice if it was not for Neutral ENSO comes what should be a "normal" summer. This would be nice if it was not for Arctic sea ice disappearing greatly. The greater presence of much wider Arctic ocean water affects the very structure of jet stream circulations, making them lethargic or slow moving. A major omega block somewhere over the Northern Hemisphere, likely causing Central USA furtherance of drought and or Eurasian caucuses to dwell under similar conditions.

Extremes in precipitation will still exist, namely NW Europe especially by Greenland massive ice sheet placing the cold temperature North Pole near its NE shores.

WD April 28, 2013

Polar Tropopausic clouds

- Potential Proof of visible dark CCN's in the extreme lower stratosphere

Without further a due the evidence:

On this picture, the sun is well set, twilight is about to end, sun elevation is -6.36 degrees below the astronomical horizon, what appears to be a noctilucent cloud is likely a PSC , but Polar Stratospheric Clouds form at -78 C, there was no evidence of -78 C layer anywhere in the upper atmosphere throughout the entire Arctic. Furthermore the bright cloud appears lower, amongst what I call CCN layers which seed some scant Cirrus clouds just below. An approaching weather system from the Southwest moving NE (the picture is towards the SW), was likely bringing some moisture clashing with very cold high pressure air.

CCN black streaks were mixed with more liquid or ice crystal tropopause cloud, as they can be, there can be moisture in and just above the tropopause, in the middle are very visible small cirrus just under the the bright cloud, the cirrus was in the Earths shadow, the bright cloud wasn't. Furthermore the bright cloud disappeared shortly after, night set and no brightness was seen. Suggesting that this was a tropopause cloud 7.5 Km high which vanished along with twilight.

Geometric calculations at the point where the cloud was recreate disappearing sun rays altitude by the Earth's shadow when the sun is 3 degrees below the Horizon (with no atmosphere). The distance of the bright cloud may be closely estimated since it was at 2.2 degrees above the horizon. Laser and Radiosonde results show the scant presence of a cloud 7.5 kilometers above ground, moisture mixing ratio was nowhere near capable of creating a cloud. This does not mean that other regions of the sky had higher moisture like where the bright cloud was, laser ceilometer likely back scattered the CCN's as no clouds were observed above. The CCN's cover the sky completely but were only visible just above the horizon. The more numerous CCN's are the more visible they become to cover a greater chunk of the sky from the horizon up to zenith. The bright cloud has a rare occurrence of moisture, not usually seen but happens when there was chemical reactions at extreme cold temperatures, or in this case, overshooting moisture from a thundercloud event further from the South which was quite intense. There may be another exlanation.

Part of identifying the altitude of the cloud must come from satellite photography:

Available NOAA Visible satellite February 20 2013 21:15 UTC. The arrow points to the likely band of clouds where the bright cloud was. Satellite brightness near the terminator may be in fact the cloud itself. Further to the South was a coming weather system from the North Pacific.

There is a problem, the cloud band was too close to meet the basic requirement, a theoretical 20 Km high Earth shadow exists, the cloud should not be bright by sun rays, only much more distant away. Unlike the satellite photo, the horizon picture above was taken at 23:36 UTC, the system clouds were even closer by 2 hours North Eastwards movement.

Arctic Atmospheric Refraction is interwoven with illusions, the sun appears where it shouldn't. Always further above than when there is no atmosphere. So the Earths shadow theoretically at 5 degrees was lowered by refraction by about 2 degrees. Refraction confirms the CCN's altitude, low along with the bright cloud, this suggests that the dark streaks are none other than drier Cloud Condensation Nucleii, the bright slightly yellowish cloud color was very similar to a sunset at 0 degrees astronomical elevation when observed at mostly pristine Polar air. Unlike in Southern locations, many with pollutants, normal sunsets appear bright white with a faint tinge of yellow in the cloudless Arctic sky.

Suggested reading: the Earth terminator shifting due to atmospheric refraction.

WD February 20-21, 2013

On Tornadoes and the Polar Stratospheric Vortex

As a matter of an attempt to see if there is a link between tornado frequency and winter buildup of Polar stratospheric vortex, I made predictions and waited for the results, sort of like a ball rolling down on a ramp in order to determine cause an effect, I explore to find if the vortex has any effect at all with Tornado activity way to the South.

The latest November 2012 prediction was bang on:

"About tornadoes, early in the season is not from January 1 onwards, but from December 21 and later, it is the real new year. So they have happened quite early as expected, Weather Underground reports he strongest outbreak for Christmas day ever. The link between the Polar Stratosphere Vortex and tornadoes is largely an hypothesis. A larger version version of the Lorenz butterfly wings, the chaos started way above seems to permeate well below to ground. Alabama's Christmas Tornado is a good example of very strong conflicting winds. 12/26/2012"

Late 2012 vortex was very intense, but collapsed in 2 distinct continental vortices early January literally changing the outlook of everything:

These high in the atmosphere vortices were amazingly in synch with the polar vortex below.

Accordingly NOAA Storm Prediction Center charted active Tornado Activity:

The greatest apparent link with respect to Tornadoes and PSV activity is made obvious here, the single vortex vanished and so did active tornado events. The link seems obvious and straight forward as was the weaker vortex of 2012 compared to 2011 having the most ardent PSV in memory. True enough there was a drought in 2012, as Dr Masters wrote, a drought is hardly conducive to violent thunderstorms. These recent records show tornadoes occur strongly in the spring, which preceded the drought, no doubt lack of moisture had an impact on thunderclouds, but a warmer troposphere helps drought conditions along, a non existent PSV should make the upper troposphere warmer. Warmer Upper Air is not friendly to convective activity. The question becomes larger, the drought itself is a part of the complex. In weather or climate, everything contributes to a single event.

What remains to be seen is whether the Vortex will reconstitute, it doesn't look so, but the signs are for a change from the Sudden Stratospheric Warming onwards:

The warming has stopped making way to a a weaker reconstituted vortex. Onto itself a pale fraction of 2011, tornadoes should be less frequent until the further news of a change way high in the Polar sky.

wd Feb 17, 2013

Atmospheric refraction, the curiosity which will become as important as the invention of the thermometer

~Few examples of density problems.

~The new ways to come.

Dr Jeff Masters recent article about Hurricane forecast prowess by European Center for Medium-Range Weather Forecasts , the ECMWF model, brings out a seldom mentioned fact that atmospheric refraction can be used to measure regional tropospheric densities.

"However, the ECMWF model's superior technique used to assimilate the initial data allows inclusion of data from a large number of polar-orbiting satellites, which the other models cannot do as well. Polar-orbiting satellites orbit Earth at an altitude of 540 miles twice per day, circling from pole to pole. Their data is difficult to use, since the it is only available twice per day at each spot on the Earth, and the time of availability is different for each location. According to an email I received from Jean-Noël Thépaut, the chief of the Data Division of the Research Department at the European Center for Medium-Range Weather Forecasts, the ECMWF model uses data from at least fourteen polar orbiting satellites: N-15, N-19, N-19, N-17 (ozone SBUV instrument only), Metop-A, AQUA, NPP (ATMS instrument only), AURA (ozone OMI data only), F-17, TRMM (TMI data), COSMIC, GRACE-A, TERRASAR, and the GPSRO data on top of METOP-GRAS. The data of most importance is the data collected in the infrared and microwave wavelengths, as well as atmospheric density data obtained via GPS radio occultation (as a polar orbiting satellite goes over the horizon, the GPS signals from the satellite get bent by Earth's atmosphere, with the amount of bending proportional to the density of the atmosphere. This GPS Radio Occultation data is gathered from eight polar orbiting satellites, and fed into both the ECMWF and GFS models.) You can find a nice summary of the impacts of polar orbiting satellite data on weather prediction models at this link.)"

Forecasting power found by using refraction is undeniable by the success from the work found here, an instant measurement of atmospheric density has a lot of meaning. Traditionally, density was usually integrated by radiosonde balloon sounding data, which only occurs twice a day in a not representative sampling at irregular locations of the entire Earth. The Oceans are largely not probed aside from the GPS method cited above. A simple measurement of the sun disk dimensions can determine the density of the air instantly. This method is very cheap, can be incorporated on sea ships, remote weather station locations anywhere on Earth. And is not necessarily limited by clouds.

It reveals the physics of invisible air if you know where to look:

This 2005 picture of a sunset demonstrates that the atmosphere can be highly stratified, its the way of hydrostatic equilibriums, perhaps unlike underwater sea thermal zones air thermal layers can be very thin. Less than 1/2 a meter or shallower. The sun can be replaced by a building, a lamp post, or anything opaque reflecting light. Terrestrial mirages can be used just as much.

The sun disk method has a simple rule, the greater the vertical sun disk diameter, the less dense the air is, largely roughly speaking this is the rule.

A simple sun disk picture can tell where it was taken anywhere on Earth- provided the sun elevation is known. Like the Arctic:

March 10 2006 through clouds, the surface based inversion was 3.3 C/100 m.

The measure of density is the sun itself, which if there was no atmosphere would be equal to 32 minutes of arc. Here it is 31.39' . Large despite sizable sea level pressure, but the shot was directed towards the Southeast from Cornwallis Island Canada. The all time spring average for this location was 31.4'. Summer Montreal all time average is 31.47' (at 100 meters above the Cornwallis observation site). The equipment used needs upgrades but the error rate is about .1 arc minutes, which is 6 seconds of arc.

Sun disk measurements were logged in the high Arctic and Montreal for more than 10 years. There has been a slow and gradual increase in sun disk sizes with the usual variances, when a hot year was ongoing like 2005, 2007 and 2010 the sun disks confirmed the temperature record very closely. Spring 2010 had all kinds of records broken, from 2005 to 2012, looking back at specific spatial locations in sun elevation the rank of warmest to coldest is:

#1- 2010 and 2005

#2- 2011

#3- 2012,2009 and 2006

#4- 2007

#5- 2008

Of which a neat cooling was noted in 2008 strongly linked with spring time clear air driven by La-Nina.

NASA GISS temperature record of the Northern Hemisphere ranked

#1 2005

#2 2010

#3 2006

#4 2012

#5 2008-2009

#6 2007

#7 2011

Vertical sun disk diameters from one location alone compared from one year to the next mirrored the temperature trend almost exactly. In other words, density of the atmosphere is a very important metric indicating Global Warming. Having density measurements taken from the entire Earth would be the most precise metric known.

Surface temperature is not directly linked with vertical sun disk dimensions. March 7 2006 had a near average height.

While at the Equinox the vertical measure shrunk despite warmer surface weather. Higher pressure usually gives a smaller vertical sun disk size. Not in this case. The atmosphere is vast, especially horizontally. Therefore a sun disk measurement is very similar to a GPS satellite occultation. Except for the cost in acquiring it.

More to come.

WD Jan5, 2013

For past EH2R news:

The complete news for 2012

The complete news for 2011

The complete news for 2010

The complete news for 2009

The complete news for 2008

The complete news for 2007

The complete news for 2006

The complete news for 2005

Y-V Ulluq Q Phenomena (March 22 2005)

Star colors and waves as seen by ARCTURUS

SUMMER 2004 version 2


Mars EH2R link?

Winter 2004

Summer 2003

EH2R Introduction
Darkness and Brightness during Twilight - Compare examples of Y-V Ulluq Q

**UPDATED May 14, 2008**
Comparison gallery. And the 3 basic sunset science rules.
A big thermometer? Differential Refraction. UPDATED Feb 16, 2008
Polarization at the POLES. Sounds strange? It isn't!
The real argument Terminator! Showing that greater refraction exists at the poles.
Streaming over the moon
Double Sunset
Old pictographic archives; one with the sun 4 degrees below the horizon.
EH2r and how to prove Global Warming without waiting for the flood
The last "line" sunset of the season
Sunrise, effects caused by a warmer atmosphere.
One Polar Sunset Sequence
The latest EH2R data files ** UPDATED FEBRUARY 22, 2010 **
Homage to Gerrit de Veer, novaya zemlya effect. Gerrit de Veer proven! Please look at reference: http://aolp.osa.org/abstract.cfm?id=71002

Congratulations to Siebren Y. van der Werf and colleagues on this accomplishment.

EH2R Definitions                                                          EH2R discussion pages; no pictures just ideas

Text and photos by Wayne Davidson. Resident of Resolute Bay, Nunavut Canada.

To contact Wayne

EH2R credits:

Siebren van der Werf, from Holland, has finally a webpage including down loadable Journal links, also with programs capable of calculating sundisk sizes, along with sunset and sunrise shapes with a great deal of accuracy. He is one of the few top notch refraction expert of this world. Reading his material will make you nearly up to date with the latest cutting edge knowledge, including differential formulas, his works are required reading.

Ben Wheeler and Ethan Sollows.

Andrew T. Young's web page "An Introduction to Green Flashes" is essential to understand other refraction effects near the horizon. Dr. Young puts to rest many misconceptions which are still ingrained everywhere.

On his way to the North Pole, Gunther Kletetschka, a physicist, gave me a hand, pictures from his adventure can be found here.

Other related links:

Very important sunset sequences can be found at Tom Ruen 's web page. He's a Lake Superior expert on this subject. Some pictures resemble polar pictures, proving that Lake Superior is a cold lake indeed.

Zoltan Neda and other wrote 2 papers on the subject of sun flatness. Great pictures from space show a fantastic resemblance to pictures taken from Resolute Bay.

For a definition of a conventional sunset and sunrise, click here

For more Polar mysteries:

Sir John Franklin was here! : A human tragedy completely ignored and misrepresented.

The Red Star Project: Figuring out how much ozone you have above your roof without any instrument.

EH2r inspired research project:

Stonehenge Then: Many of the sun disk transformations found on this web page ressemble Megalithic structures found throughout the UK, Ireland and Northwestern Europe. Stonehenge Then is a web page designed to recruit more research in horizon observations at Megalith sites. It contains many theories which need field workers to confirm. These theories need to be checked out by hopefully volunteers, or eventually myself.


Global Warming

Visible Global Warming
Effects of cold air
Strong Refraction
Horizontal Refraction
Low horizon pictures
Sun pictures
Rectangular sun
Half sun
Red sun
Orange sun
Low Horizon
Rectangular sun
The Line
Novaya Zemlya effect
Ducting of sunlight
The Terminator
Satellite pictures
Visible light
Infrared sun
Sunset Phases
Ellipsoid sun
Arctic twilight
Red Twilight
Orange Twilight
Double sunset
GPS sunset
GPS errors
Sunset times miscalculated