Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared and ultraviolet light. On Earth, sunlight is filtered through Earth's atmosphere, is obvious as daylight when the Sun is above the horizon; when the direct solar radiation is not blocked by clouds, it is experienced as sunshine, a combination of bright light and radiant heat. When it is blocked by clouds or reflects off other objects, it is experienced as diffused light; the World Meteorological Organization uses the term "sunshine duration" to mean the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per square meter. Other sources indicate an "Average over the entire earth" of "164 Watts per square meter over a 24 hour day"; the ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D3 synthesis and a mutagen. Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun.

A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to the surface. Sunlight is a key factor in photosynthesis, the process used by plants and other autotrophic organisms to convert light energy from the Sun, into chemical energy that can be used to synthesize carbohydrates and to fuel the organisms' activities. Researchers can measure the intensity of sunlight using a sunshine recorder, pyranometer, or pyrheliometer. To calculate the amount of sunlight reaching the ground, both the eccentricity of Earth's elliptic orbit and the attenuation by Earth's atmosphere have to be taken into account; the extraterrestrial solar illuminance, corrected for the elliptic orbit by using the day number of the year, is given to a good approximation by E e x t = E s c ⋅, where dn=1 on January 1st. In this formula dn–3 is used, because in modern times Earth's perihelion, the closest approach to the Sun and, the maximum Eext occurs around January 3 each year.

The value of 0.033412 is determined knowing that the ratio between the perihelion squared and the aphelion squared should be 0.935338. The solar illuminance constant, is equal to 128×103 lux; the direct normal illuminance, corrected for the attenuating effects of the atmosphere is given by: E d n = E e x t e − c m, where c is the atmospheric extinction and m is the relative optical airmass. The atmospheric extinction brings the number of lux down to around 100 000 lux; the total amount of energy received at ground level from the Sun at the zenith depends on the distance to the Sun and thus on the time of year. It is 3.3 % lower in July. If the extraterrestrial solar radiation is 1367 watts per square meter the direct sunlight at Earth's surface when the Sun is at the zenith is about 1050 W/m2, but the total amount hitting the ground is around 1120 W/m2. In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared, 42 to 43 percent visible, 3 to 5 percent ultraviolet. At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet, with most of the extra UV consisting of biologically damaging short-wave ultraviolet.

Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiant flux. Multiplying the figure of 1050 watts per square meter by 93 lumens per watt indicates that bright sunlight provides an illuminance of 98 000 lux on a perpendicular surface at sea level; the illumination of a horizontal surface will be less than this if the Sun is not high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole. Dividing the irradiance of 1050 W/m2 by the size of the Sun's disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. Multiplying this by π gives an upper limit to the irradiance which can be focused on a surface using mirrors: 48.5 MW/m2. The spectrum of the Sun's solar radiation is close to that of a black body with a temperature of about 5,800 K; the Sun emits EM radiation across most of the electromagnetic spectrum. Although the Sun produces gamma rays as a result of the nuclear-fusion process, internal absorption and thermalization convert these super-high-energy photons to lower-energy photons before they reach the Sun's surface and are emitted out into space.

As a result, the Sun does not emit gamma rays from this process, but it does emit gamma rays from solar flares. The Sun emits X-rays, ultraviolet, vi


Dreamwaltzes is an orchestral composition by the American composer Steven Stucky. The work was commissioned by the Minnesota Orchestra for their annual Sommerfest series with support from the Jerome Foundation; the piece was completed in April 1986 and its world premiere was given by the Minnesota Orchestra under the direction of Leonard Slatkin on July 17, 1986. It is dedicated to the violinist Sonya Carl Pancaldo; the piece brought Stucky to prominence in the contemporary classical community and remains one of his most popular compositions. Dreamwaltzes is composed in a single movement and has a duration of 15 minutes. Stucky described his initial inspiration for the piece in the score program notes, writing, "Since the management of the orchestra suggested that the new piece have some connection with the Viennese theme of the Sommerfest concerts, I found myself daydreaming about the waltz, about Viennese composers like Schubert, Brahms and Berg, all of whom treated the waltz in their music."

He continued, "Dreamwaltzes is a public version of those daydreams: an orchestral fantasy of about fifteen minutes, based on fragments of real Viennese waltz music." Dreamwaltzes quotes three such waltzes in successive episodes. The first waltz referenced is one of Johannes Brahms's Liebeslieder Waltzes, Op. 52, No. 6. The second waltz is one of Brahms's Sixteen Waltzes, Op. 39, No. 8. The third waltz is from Richard Strauss's comic opera Der Rosenkavalier; the composer wrote, "From time to time these originals float to the surface. The three waltz episodes are surrounded by slower music forming an introduction, a coda. Stucky continued:But in Dreamwaltzes the past proves elusive; the point is clearest in the crucial third episode. Here, after a evolving, accelerating development, the orchestra seems just on the point of reentering the late nineteenth century in some grand, unrestrained waltz music—when the whole affair collapses, we are back in our own time. A composer in the late twentieth century can admire the waltz from a distance, but he cannot make it his own.

The work is scored for an orchestra consisting of three flutes, three oboes, three clarinets, two bassoons, four horns, four trumpets, three trombones, timpani, three percussionists, piano and strings. Dreamwaltzes has been praised by music critics. Reviewing the West Coast premiere by André Previn and the Los Angeles Philharmonic, Martin Bernheimer of the Los Angeles Times wrote, "Stucky stitched together some familiar hesitant phrases, a few recognized fanfares, motivic fragments made quizzical by unfulfilled harmonic allusions. Sometimes the wittily quoted sources proved self-explanatory. Sometimes they remained coy about their identity. In any case, the 15-minute exercise emerged as a clever, affectionate collage that puts some old stylistic skeletons through provocative new paces." He added, "Dreamwaltzes left little doubt that past-tense creativity, when applied with craft and imagination, can be amusing as well as engaging." Mark Kanny of the Pittsburgh Tribune-Review wrote, "It takes a familiar approach, seeing elements of old music through a modern lens.

Fragments of waltzes by Johannes Brahms and Richard Strauss exist in a modern sound world. The old harmonies don't hold; the instrumentation has a modern edge in place of romantic plush." John Rockwell of The New York Times was more critical of the piece, remarking, "Dreamwaltzes belongs to that slightly tired notion of a look backwards from a modernist perspective - or, if you shuffle your categorical cards differently, a post-modernist perspective." Rockwell continued:In this case, Mr. Stucky has taken three Vienna-linked waltzes by Brahms and Richard Strauss and allowed them to color and peer through a veil of more contemporary harmonic texture; the trouble is - in comparison with other such works, like Jacob Druckman's Prism or, less familiarly, Pauline Oliveros's Bye Bye Butterfly - that the new material sounds anonymous and the older material remains too buried. The best bit came at the end, as Mr. Stucky played with Strauss's anticipatory fragments before the final, dreamlike duet in Der Rosenkavalier


Ü, is a character that represents a close front rounded vowel. It is classified as a separate letter in several extended Latin alphabets, but as the letter U with an umlaut/diaeresis in others such as Catalan, Galician, German and Spanish. Although not a part of their alphabet, it appears in languages such as Finnish and Swedish when retained in foreign names and words, Finnish and Swedish spells said letter and sound in domestic words as Y. A small number of Dutch words use this as a diaeresis. A glyph, U with umlaut, appears in the German alphabet, it represents the umlauted form of u. It can represent; the letter is collated together with U, or as UE. In languages that have adopted German names or spellings, such as Swedish, the letter occurs, it is however not a part of these languages' alphabets. In Swedish the letter is called tyskt y which means German y. In other languages that do not have the letter as part of the regular alphabet or in limited character sets such as ASCII, U-umlaut is replaced with the two-letter combination "ue".

Software for optical character recognition sometimes sees it falsely as ii. The letter Ü is present in the Hungarian, Turkish, Uyghur Latin, Azeri, Crimean Tatar, Kazakh Latin and Tatar Latin alphabets, where it represents a close front rounded vowel, it is considered a distinct letter, collated separately, not a simple modification of U or Y, is distinct from UE. In the Swedish and Finnish alphabets ü is alphabetized as y; this same letter appears in the Chinese Romanisations pinyin, Wade-Giles, the German-based Lessing-Othmer, where it represents the same sound: 綠/lü or 女/nü. Standard Mandarin Chinese pronunciation has both the sounds and. Pinyin only uses "Ü" to represent after the letters "L" or "N" to avoid confusion with words such as 路/lu and 怒/nu. Words such as 玉/yu or 句/ju are pronounced with, but are not spelled with "Ü". Although Wade-Giles and Lessing use Ü in all situations; as the letter "Ü" is missing on most keyboards and the letter "V" is not present in standard Mandarin pinyin, the letter "V" is used on most computer Chinese input methods to enter the letter "Ü".

As a result, romanisation of Chinese with the letter "V" representing the Ü sound is sometimes found. However, Ü sound should be represented by "yu" in Pinyin when it's difficult to enter Ü. For example, the surname Lü would be written as "Lyu" in the passports. Several languages use diaeresis over the letter U to show that the letter is pronounced in its regular way, without dropping out, building diphthongs with neighbours, etc. In Spanish, it is used to distinguish between "gue"/"güe" / and "gui"/"güi" /: nicaragüense, pingüino. In Catalan, "gue~güe" are ~, "gui~güi" are ~, "que~qüe" are ~ and "qui~qüi" are ~, as in aigües, pingüins, qüestió, adeqüi. Ü is used to mark that vowel pairs that would form a diphthong must be pronounced as separate syllables, examples: Raül, diürn. In French, the diaeresis appears over the "u" only rarely, in some uncommon words, capharnaüm, Capharnaüm/Capernaüm or Emmaüs. After the 1990 spelling reforms, it is applied like aigüe, ambigüe and argüer. In the Rheinische Dokumenta, a phonetic alphabet for many West Central German, the Low Rhenish, few related vernacular languages, "ü" represents a range from to.

The unique letter Ü and U-diaeresis were written as a U with two dots above the letter. U-umlaut was written as a U with a small e written above: this minute e degenerated to two vertical bars in medieval handwritings. In most handwritings these bars in turn nearly became dots. In modern typography there was insufficient space on typewriters and computer keyboards to allow for both a U-with-dots and a U-with-bars. Since they looked near-identical the two glyphs were combined, done in computer character encodings such as ISO 8859-1; as a result, there was no way to differentiate between the three different characters. While Unicode theoretically provides a solution, this is never used; the methods available for entering ⟨Ü⟩ and ⟨ü⟩ from the keyboard depend on the operating system, the keyboard layout, the application. Microsoft Windows – some keyboard layouts feature separate keys for ⟨Ü⟩ Using the Swiss French keyboard, ⟨ü⟩ can be entered by typing ⇧ Shift+È Using the US International layout, ⟨ü⟩ can be entered by typing AltGR+Y Microsoft Windows: with the Number Lock on, hold down the Alt key while typing on the numeric keypad the decimal value of the code point from the active DOS/OEM code page without a leading zero release the Alt key.