Mirage Of Astronomical Objects
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A mirage of an astronomical object is a
meteorological Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...
optical phenomenon, in which light rays are bent to produce distorted or multiple images of an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
. The
mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...
s might be observed for such celestial objects as the Sun, the Moon, the planets, bright
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s, and very bright comets. The most commonly observed of these are
sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...
and sunrise mirages.


Mirages versus refraction

Mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...
s are distinguished from other phenomena caused by atmospheric refraction. One of the most prominent features of mirages is that a mirage might only produce images vertically, not sideways, while a simple refraction might distort and bend the images in any way. The distortion in both images displayed in this section was caused by refraction, but while the image on the left, which is a mirage, demonstrates only vertical distortion, the image on the right demonstrates distortion in all the ways possible. It is easier to see the vertical direction of the mirage not even at the mirage of the Sun itself, but rather at the mirage of a
sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...
. As a matter of fact, it is at least a three-image mirage of a sunspot, and all these images show a clear vertical direction.


Inferior mirage of astronomical objects

Inferior mirage of
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
s is the most common mirage. Inferior mirage occurs when the surface of the Earth or the oceans produces a layer of hot air of lower density, just at the surface. There are two images, the inverted one and the erect one, in inferior mirage. They both are displaced from the geometric direction to the actual object. While the erect image is setting, the inverted image appears to be rising from the surface. The shapes of inferior mirage sunsets and sunrises stay the same for all inferior mirage sunsets and sunrises. One well-known shape, the Etruscan vase, was named by
Jules Verne Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...
. As the sunset progresses the shape of Etruscan vase slowly changes; the stem of the vase gets shorter until the real and the miraged Suns create a new shape – Greek letter omega Ω. The inferior mirage got its name because the inverted image appears below the erect one.An Introduction to Mirages
by Andy Young
Here's how Jules Verne describes an inferior mirage
sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...
. : On very rare occasions the mirages of astronomical objects other than the Sun and the Moon might be observed. An apparent magnitude of an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
should be low enough (that is, bright enough) in order to see it as not only a real object, but also a miraged one.


Mock mirage of astronomical objects

A mock mirage of
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
s is much more complex than an inferior mirage. While an inferior mirage of astronomical objects can produce only two images, a mock mirage can produce multiple miraged images. The shapes of the miraged object are changing constantly and unpredictably. In order for a mock mirage to appear, the cooler air needs to be trapped below the inversion. Several inversion layers produce multiple pancake-like shapes.Sunset Mirages
Les Cowley
It is possible that the
solar Solar may refer to: Astronomy * Of or relating to the Sun ** Solar telescope, a special purpose telescope used to observe the Sun ** A device that utilizes solar energy (e.g. "solar panels") ** Solar calendar, a calendar whose dates indicate t ...
anomaly mentioned in the
Book of Joshua The Book of Joshua ( he, סֵפֶר יְהוֹשֻׁעַ‎ ', Tiberian: ''Sēp̄er Yŏhōšūaʿ'') is the sixth book in the Hebrew Bible and the Christian Old Testament, and is the first book of the Deuteronomistic history, the story of Isra ...
may have been an example of a mock mirage. In that tale, Joshua launched a surprise attack on the Amorites following a night march, causing the Amorites to panic and flee as far as Beth-horon, but they did not find a safe haven there. "...they were more who died with the hailstones than they whom the children of Israel slew with the sword."The Book of Joshua 10.11
Joshua
Hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
stones are a rare event in
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
s and are a good precondition for creating a mock/superior mirage of the setting sun. Inferior mirage is the most common mirage in the
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
s. When the Israelites went from a hot desert to a hail-covered desert to fight the Amorites, the inversion layers could have created a mock mirage of the setting sun. To the Israelites, the sun would then have appeared to stand still. A poem is quoted from the
Book of Jasher Sefer haYashar is a reference to the Five Books of Moses, Joshua 10:13, see Targum Jonathan, "sifra d'oriaitho"; named on behalf of the Patriarchs who were call "Yesharim", see Numbers 23:10. Sefer haYashar (Hebrew ספר הישר) means "Book of ...
, which states that the sun stood still at Gibeon, and the moon in the valley of Ajalon, in order that Joshua could complete the battle.The Book of Joshua 10.13
Joshua

Joshua


Novaya Zemlya effect

Due to a normal atmospheric refraction, sunrise occurs shortly before the Sun crosses above the horizon. Light from the Sun is bent, or refracted, as it enters earth's atmosphere. This effect causes the apparent sunrise to be earlier than the actual sunrise. Similarly, apparent sunset occurs slightly later than actual sunset. In ordinary atmospheric conditions, the setting or rising Sun appears to be about half a degree above its geometric position. But sometimes, very unusual atmospheric circumstances can make it to be visible when it is really between two and five degrees below the horizon. This is called the
Novaya Zemlya effect The Novaya Zemlya effect is a polar mirage caused by high refraction of sunlight between atmospheric thermal layers. The effect gives the impression that the sun is rising earlier than it actually should, and depending on the meteorological sit ...
, because it was first observed in
Novaya Zemlya Novaya Zemlya (, also , ; rus, Но́вая Земля́, p=ˈnovəjə zʲɪmˈlʲa, ) is an archipelago in northern Russia. It is situated in the Arctic Ocean, in the extreme northeast of Europe, with Cape Flissingsky, on the northern island, ...
, where the Sun was seen when, according to astronomical calculations, it should have been two degrees below the horizon. However, due to changes in air pressure, relative humidity, and other quantities, the exact effects of atmospheric refraction on sunrise and sunset time cannot be predicted. Also note that this possible error increases with higher (closer to the poles) latitudes. Novaya Zemlya is a
polar region The polar regions, also called the frigid geographical zone, zones or polar zones, of Earth are the regions of the planet that surround its geographical poles (the North Pole, North and South Poles), lying within the polar circles. These high l ...
in Russia. The Novaya Zemlya effect is a
mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...
caused by high refraction of
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
between atmospheric thermoclines. The Novaya Zemlya effect will give the impression that the sun is rising earlier than it actually should or the sun is setting later than it actually should.
Fridtjof Nansen Fridtjof Wedel-Jarlsberg Nansen (; 10 October 186113 May 1930) was a Norwegian polymath and Nobel Peace Prize laureate. He gained prominence at various points in his life as an explorer, scientist, diplomat, and humanitarian. He led the team t ...
wrote It is possible to observe the Novaya Zemlya effect in any place, where the temperature variations are great enough to produce a high refraction.


Green flash

Green flash is a rare optical phenomenon that occurs during or shortly after set and during or before rise of a bright
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
, when a green spot is visible for a short period of time above a mirage of an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
or its set/rise point. Green flashes are enhanced by atmospheric inversions which increase the density gradient in the atmosphere, and therefore increase refraction. In other words, to see a green flash a mirage should be present.Explaining Green Flashes
by Andy Young
Jules Verne Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...
described a green flash. Many tend to believe that seeing a green flash brings good luck.K. Solarino : The Green Flash Collection Green flashes might be observed from any place with a low
horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
.
Desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
s, oceans and ice shelves are probably the best places to observe mirages and therefore green flashes. It is easier not to miss a green flash during
sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...
than during sunrise. It is especially true regarding an inferior mirage green flash, when the timing should be just right to capture it at sunrise. From the above observation it is clear that the author observed an inferior mirage green flash, when the much warmer surface of the
desert A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to denudation. About on ...
with the help of the rising Sun was fighting the cool morning air, producing in the process a green flash – one of nature's great spectacles. A green flash might be also seen with
rising or setting Moon.
br> In the right conditions it is common to observe multiple green flashes during one mock mirage sunset.
Some claim they saw a green flash from Venus. This may be true, but it might be that a color of the setting or the rising planet is mistaken for a real green flash that is a by-product of a
mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...
.


Green rim

As an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
sets or rises, the light it emits travels through the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, which works as a prism separating the light into different colors. The color of the upper limb of an astronomical object could go from blue to green to violet depending on the decrease in concentration of pollutants as they spread throughout an increasing volume of atmosphere. The lower limb of an astronomical object is always red. The green rim is very thin, and is difficult or impossible to see with the naked eye. In usual conditions a green rim of an astronomical object gets fainter, when an astronomical object is very low above the
horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
because of atmospheric reddening, but sometimes the conditions are right to see a green rim just above the horizon. The following quote describes probably the longest observation of a green rim, which sometimes could have been a green flash. Members of Richard E. Byrd's party from the Little America exploration base saw the phenomenon on and off for 35 minutes (source for 30 versus 35 minutes?). Often the green rim of the setting Sun will change to a green flash and then back again to a green rim during the same sunset. The image to the right might accurately illustrate what members of Byrd's party from the Little America base might have seen. However, to see a green rim and green flash on and off for 35 minutes, there must have been some degree of mirage present. A green rim is present in every sunset, but it is too thin to be seen with a naked
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...
. The best time to observe the green rim is about 10 minutes before sunset time. However, the solar disc is too bright at that time to use
magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in siz ...
, such as
binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
or telescopes, to look directly at the Sun. Of course, a telescope or binoculars image can be projected on a sheet of paper for viewing. When the Sun gets closer to the horizon, the green rim gets fainter because of atmospheric reddening. Although a green rim is present in every sunset, and a green flash is rare because it requires a mirage to be present, it is actually more common for people to have seen a green flash rather than a green rim.


Not a mirage

The composite image on the left is made out of five frames of different
sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...
s. None of the images is a mirage. Frames # 1 and # 2 could fool even a very experienced observer. They do look like a mock mirage of the setting Sun, but they are not. Frames #3 and # 4 are clearly not a mirage. Frame # 5 is not a mirage and not even a
sunspot Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...
, it is a spider with the Sun as a background. The strange shapes of the Sun in this composite is due to vog and clouds. Numerous
atmospheric An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
effects, such as vog,
clouds In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may com ...
, smoke,
smog Smog, or smoke fog, is a type of intense air pollution. The word "smog" was coined in the early 20th century, and is a portmanteau of the words ''smoke'' and '' fog'' to refer to smoky fog due to its opacity, and odor. The word was then inte ...
and others could generate a mirage like appearance of an
astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
. Lens flares and ghost images also might be responsible for a false mirage or a false green flash.


See also

* Gravitational lens, which is believed to cause a similarly duplicate image of galaxies * Refraction * Atmospheric refraction * Looming and similar refraction phenomena


References


External links


All kind of mirages explained
Andrew T. Young's page with comprehensive explanations and simulations.

Andrew T. Young's page with comprehensive explanations and simulations.

explanations and image gallery, Les Cowley's Atmospheric Optics site.


Gallery

Image:Mock mirage sunset and brown pelicans.jpg, Mock mirage sunset with brown pelicans Image:Boiling sun new.gif, "Boiling" sun sunset Image:Sunset Mirage 03.jpg, Mock mirage sunset Image:Sunset mirage1231.JPG, Mock mirage sunset Image:Sunset mirage.jpg, Mock mirage sunset Image:GreenFlash.jpg, Mock mirage sunset with green flash Image:Mock mirage of the setting sun.jpg, Mock mirage sunset Image:Inferior mirage green flash.jpg,
Farallon Islands The Farallon Islands, or Farallones (from the Spanish ''farallón'' meaning "pillar" or "sea cliff"), are a group of islands and sea stacks in the Gulf of the Farallones, off the coast of San Francisco, California, United States. The island ...
and Inferior mirage green flash Image:Multiple green flashes on 101508.jpg, Sunset sequence with multiple green flashes
{{DEFAULTSORT:Mirage Of Astronomical Objects Atmospheric optical phenomena