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46-662: In dark, clear night skies , the rift appears as clear as the bright bulge of stars around the Galactic Center does to the naked eye or binoculars . The rift is largely between the Solar System (which is close to the inner edge of the Orion Arm ) and the next arm, inward, the Sagittarius Arm . The clouds are an obstruction to millions of the galaxy's stars detected at visible wavelengths , which compose

92-550: A bright hazy band appearing 30° wide and arching through the night sky. The clouds within our radial sector of the galaxy span about 800–1,000 parsecs (2,600–3,300  ly ) from Earth. The clouds are estimated to contain about 1 million solar masses of plasma and dust. To the naked eye , the Great Rift appears as a dark lane that divides the bright band of the Milky Way vertically. The Great Rift covers one third of

138-418: A combination of Rayleigh scattering and Mie scattering . As a ray of white sunlight travels through the atmosphere to an observer, some of the colors are scattered out of the beam by air molecules and airborne particles , changing the final color of the beam the viewer sees. Because the shorter wavelength components, such as blue and green, scatter more strongly, these colors are preferentially removed from

184-530: A decade. They tend to be visible only shortly before sunrise or after sunset because those are the times they are close enough to the Sun to show a tail. Clouds obscure the view of other objects in the sky, though varying thicknesses of cloud cover have differing effects. A very thin cirrus cloud in front of the moon might produce a rainbow-colored ring around the moon . Stars and planets are too small or dim to take on this effect and are instead only dimmed (often to

230-558: A distance from other objects because their navigation lights blink. Beside the Solar System objects changing in the course of them and Earth orbiting and changing orbits over time around the Sun and in the case of the Moon around Earth, appearing over time smaller by expanding its orbit, the night sky also changes over the course of the years with stars having a proper motion and changing brightness because of being variable stars , by

276-480: A dome. Orion is among the most prominent and recognizable constellations. The Big Dipper (which has a wide variety of other names) is helpful for navigation in the northern hemisphere because it points to Polaris , the north star. The pole stars are special because they are approximately in line with the Earth's axis of rotation so they appear to stay in one place while the other stars rotate around them through

322-451: Is about the size of a thumbnail at arm's length, and is readily identified. Over 29.53 days on average, the moon goes through a full cycle of lunar phases . People can generally identify phases within a few days by looking at the Moon. Unlike stars and most planets, the light reflected from the Moon is bright enough to be seen during the day. Some of the most spectacular moons come during the full moon phase near sunset or sunrise. The Moon on

368-446: Is brighter than the stars and often the only "star" visible near sunrise or sunset, depending on its location in its orbit. Because of its brightness, Venus can sometimes be seen after sunrise. Mercury , Mars , Jupiter and Saturn are also visible to the naked eye in the night sky. The Moon appears as a grey disc in the sky with cratering visible to the naked eye. It spans, depending on its exact location, 29–33 arcminutes – which

414-400: Is due to Rayleigh scattering by air molecules and particles much smaller than the wavelength of visible light (less than 50 nm in diameter). The scattering by cloud droplets and other particles with diameters comparable to or larger than the sunlight's wavelengths (more than 600 nm) is due to Mie scattering and is not strongly wavelength-dependent. Mie scattering is responsible for

460-561: Is followed by the nautical twilight , when the Sun reaches heights of −6° and −12°, after which comes the astronomical twilight defined as the period from −12° to −18°. When the Sun drops more than 18° below the horizon, the sky generally attains its minimum brightness. Several sources can be identified as the source of the intrinsic brightness of the sky, namely airglow , indirect scattering of sunlight, scattering of starlight, and artificial light pollution . Depending on local sky cloud cover, pollution, humidity, and light pollution levels,

506-401: Is instead lofted into the stratosphere (as thin clouds of tiny sulfuric acid droplets), can yield beautiful post-sunset colors called afterglows and pre-sunrise glows. A number of eruptions, including those of Mount Pinatubo in 1991 and Krakatoa in 1883 , have produced sufficiently high stratospheric sulfuric acid clouds to yield remarkable sunset afterglows (and pre-sunrise glows) around

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552-401: Is the overwhelmingly dominant source of light. In twilight, the period of time between sunset and sunrise, the situation is more complicated and a further differentiation is required. Twilight is divided in three segments according to how far the Sun is below the horizon in segments of 6°. After sunset the civil twilight sets in, and ends when the Sun drops more than 6° below the horizon. This

598-530: Is used to derive the time of sunrise and sunset, uses the Sun's physical center for calculation, neglecting atmospheric refraction and the non-zero angle subtended by the solar disc. Neglecting the effects of refraction and the Sun's non-zero size, whenever sunrise occurs, in temperate regions it is always in the northeast quadrant from the March equinox to the September equinox and in the southeast quadrant from

644-709: The Galactic Center ; essentially ending at Centaurus . One of the regions obscured by the Great Rift is the Cygnus OB2 association , a cluster of young stars and one of the largest regions of star formation within 2 kiloparsecs. Similar dark rifts can be seen in many edge-on galaxies, such as NGC 891 in Andromeda and NGC 4565 (the Needle Galaxy) in Coma Berenices . Dark zones obscuring

690-517: The International Space Station (ISS) and Iridium Satellites . Meteors streak across the sky infrequently. During a meteor shower , they may average one a minute at irregular intervals, but otherwise their appearance is a random surprise. The occasional meteor will make a bright, fleeting streak across the sky, and they can be very bright in comparison to the night sky. Aircraft are also visible at night, distinguishable at

736-462: The axial tilt of Earth, daily rotation of the Earth, the planet's movement in its annual elliptical orbit around the Sun , and the Earth and Moon's paired revolutions around each other . The analemma can be used to make approximate predictions of the time of sunrise. In late winter and spring, sunrise as seen from temperate latitudes occurs earlier each day, reaching its earliest time shortly before

782-516: The backscatter of sunlight by interplanetary dust . Shortly after sunset and before sunrise, artificial satellites often look like stars – similar in brightness and size – but move relatively quickly. Those that fly in low Earth orbit cross the sky in a couple of minutes. Some satellites, including space debris , appear to blink or have a periodic fluctuation in brightness because they are rotating. Satellite flares can appear brighter than Venus, with notable examples including

828-416: The geocentric model , which prevailed until astronomer Nicolaus Copernicus formulated his heliocentric model in the 16th century. Architect Buckminster Fuller proposed the terms "sunsight" and "sunclipse" to better represent the heliocentric model, though the terms have not entered into common language. Astronomically, sunrise occurs for only an instant, namely the moment at which the upper limb of

874-489: The morning , at the start of the Sun path . The term can also refer to the entire process of the solar disk crossing the horizon. Although the Sun appears to "rise" from the horizon, it is actually the Earth's motion that causes the Sun to appear. The illusion of a moving Sun results from Earth observers being in a rotating reference frame ; this apparent motion caused many cultures to have mythologies and religions built around

920-425: The rod cells without triggering the cone cells . If it is particularly dark and a particularly faint celestial object is of interest, averted vision may be helpful. The stars of the night sky cannot be counted unaided because they are so numerous and there is no way to track which have been counted and which have not. Further complicating the count, fainter stars may appear and disappear depending on exactly where

966-429: The summer solstice ; although the exact date varies by latitude. After this point, the time of sunrise gets later each day, reaching its latest shortly after the winter solstice , also varying by latitude. The offset between the dates of the solstice and the earliest or latest sunrise time is caused by the eccentricity of Earth's orbit and the tilt of its axis, and is described by the analemma, which can be used to predict

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1012-535: The "great river" (the Milky Way) and seen in silhouette. The classical Greeks sometimes described the Great Rift as being the path of devastation left by Phaeton , who tried to guide the chariot of Helios (the Sun god) across the sky before losing control, wreaking havoc, and finally being struck down by a lightning bolt of Zeus. Modern astronomy first began to notice the rift in the 18th century, but struggled to explain it until E. E. Barnard and Max Wolf in

1058-899: The Milky Way, and is flanked by strips of numerous stars, such as the Cygnus Star Cloud . West of the Cepheus Clouds , the Funnel cloud / Le Gentil 3 and the bordering North America Nebula , the Great Rift starts with the Northern Coalsack at the constellation of Cygnus , where it is known as the Cygnus Rift . The Great Rift stretches from there over the Serpens-Aquila Rift ; to Ophiuchus , where it broadens out; to Sagittarius , where it obscures

1104-460: The Moon in the night sky has historically hindered astronomical observation by increasing the amount of sky brightness . With the advent of artificial light sources, however, light pollution has been a growing problem for viewing the night sky. Optical filters and modifications to light fixtures can help to alleviate this problem, but for optimal views, both professional and amateur astronomers seek locations far from urban skyglow . The fact that

1150-579: The September equinox to the March equinox. Sunrises occur approximately due east on the March and September equinoxes for all viewers on Earth. Exact calculations of the azimuths of sunrise on other dates are complex, but they can be estimated with reasonable accuracy by using the analemma . The figure on the right is calculated using the solar geometry routine in Ref. as follows: An interesting feature in

1196-496: The Sun appears tangent to the horizon. However, the term sunrise commonly refers to periods of time both before and after this point: The stage of sunrise known as false sunrise actually occurs before the Sun truly reaches the horizon because Earth's atmosphere refracts the Sun's image. At the horizon, the average amount of refraction is 34 arcminutes , though this amount varies based on atmospheric conditions. Also, unlike most other solar measurements, sunrise occurs when

1242-455: The Sun's upper limb , rather than its center, appears to cross the horizon. The apparent radius of the Sun at the horizon is 16 arcminutes. These two angles combine to define sunrise to occur when the Sun's center is 50 arcminutes below the horizon, or 90.83° from the zenith . The timing of sunrise varies throughout the year and is also affected by the viewer's latitude and longitude , altitude , and time zone . These changes are driven by

1288-416: The beam. At sunrise and sunset, when the path through the atmosphere is longer, the blue and green components are removed almost completely, leaving the longer-wavelength orange and red hues seen at those times. The remaining reddened sunlight can then be scattered by cloud droplets and other relatively large particles to light up the horizon red and orange. The removal of the shorter wavelengths of light

1334-452: The course of a night (or a year). Planets , named for the Greek word for 'wanderer', process through the starfield a little each day, executing loops with time scales dependent on the length of the planet's year or orbital period around the Sun. Planets, to the naked eye, appear as points of light in the sky with variable brightness. Planets shine due to sunlight reflecting or scattering from

1380-504: The dark adaptation. Star charts are produced to aid stargazers in identifying constellations and other celestial objects. Constellations are prominent because their stars tend to be brighter than other nearby stars in the sky. Different cultures have created different groupings of constellations based on differing interpretations of the more-or-less random patterns of dots in the sky. Constellations were identified without regard to distance to each star, but instead as if they were all dots on

1426-440: The dates. Variations in atmospheric refraction can alter the time of sunrise by changing its apparent position. Near the poles, the time-of-day variation is extreme, since the Sun crosses the horizon at a very shallow angle and thus rises more slowly. Accounting for atmospheric refraction and measuring from the leading edge slightly increases the average duration of day relative to night . The sunrise equation , however, which

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1472-537: The distance to them getting larger or other celestial events like supernovas . Over a timescale of tens of billions of years the night sky in the Local Group will significantly change when the coalescence of the Andromeda Galaxy and the Milky Way merge into a single elliptical galaxy. Sunrise Sunrise (or sunup ) is the moment when the upper rim of the Sun appears on the horizon in

1518-479: The distant stars. — Astrophysical Journal (1919) Night sky The night sky is the nighttime appearance of celestial objects like stars , planets , and the Moon , which are visible in a clear sky between sunset and sunrise , when the Sun is below the horizon . Natural light sources in a night sky include moonlight , starlight , and airglow , depending on location and timing. Aurorae light up

1564-480: The early 20th century, who produced the currently accepted explanation after careful photographic study. Of this, Barnard said: I did not at first believe in these dark obscuring masses. The proof was not conclusive. The increase of evidence, however, from my own photographs convinced me later, especially after investigating some of them visually, that many of these markings were not simply due to an actual want of stars but were really obscuring bodies nearer to us than

1610-403: The figure on the right is apparent hemispheric symmetry in regions where daily sunrise and sunset actually occur. This symmetry becomes clear if the hemispheric relation in to the sunrise equation is applied to the x- and y-components of the solar vector presented in Ref. Air molecules and airborne particles scatter white sunlight as it passes through the Earth's atmosphere. This is done by

1656-403: The horizon benefits from the Moon illusion which makes it appear larger. The Sun's light reflected from the Moon traveling through the atmosphere also appears to color the Moon orange and/or red. Comets come to the night sky only rarely. Comets are illuminated by the Sun, and their tails extend away from the Sun. A comet with a visible tail is quite unusual – a great comet appears about once

1702-403: The light scattered by clouds, and also for the daytime halo of white light around the Sun ( forward scattering of white light). Sunset colors are typically more brilliant than sunrise colors, because the evening air contains more particles than morning air. Ash from volcanic eruptions , trapped within the troposphere , tends to mute sunset and sunrise colors, while volcanic ejecta that

1748-487: The night-sky lighting mass of the bulk of the Milky Way in a dry atmosphere (or at long exposures) were recognized by many ancient civilizations in which a seasonally or regularly dry climate is a frequent feature. In South America, the Inca gave some patterns of darkness and stars names much as normal stellar constellations were, including a series of animals like llamas , a fox , toad , and others, thought to be drinking from

1794-466: The observer is looking. The result is an impression of an extraordinarily vast star field. Because stargazing is best done from a dark place away from city lights, dark adaptation is important to achieve and maintain. It takes several minutes for eyes to adjust to the darkness necessary for seeing the most stars, and surroundings on the ground are hard to discern. A red flashlight can be used to illuminate star charts and telescope parts without undoing

1840-403: The planets' surface or atmosphere. Thus, the relative Sun-planet-Earth positions determine the planet's brightness. With a telescope or good binoculars, the planets appear as discs demonstrating finite size, and it is possible to observe orbiting moons which cast shadows onto the host planet's surface. Venus is the most prominent planet, often called the "morning star" or "evening star" because it

1886-459: The point of invisibility). Thicker cloud cover obscures celestial objects entirely, making the sky black or reflecting city lights back down. Clouds are often close enough to afford some depth perception, though they are hard to see without moonlight or light pollution. On clear dark nights in unpolluted areas, when the Moon appears thin or below the horizon, the Milky Way, a band of what looks like white dust, can be seen. The Magellanic Clouds of

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1932-513: The skies above the polar circles . Occasionally, a large coronal mass ejection from the Sun or simply high levels of solar wind may extend the phenomenon toward the Equator . The night sky and studies of it have a historical place in both ancient and modern cultures. In the past, for instance, farmers have used the status of the night sky as a calendar to determine when to plant crops. Many cultures have drawn constellations between stars in

1978-435: The sky is not completely dark at night, even in the absence of moonlight and city lights, can be easily observed, since if the sky were absolutely dark, one would not be able to see the silhouette of an object against the sky. The intensity of the sky brightness varies greatly over the day and the primary cause differs as well. During daytime when the Sun is above the horizon direct scattering of sunlight ( Rayleigh scattering )

2024-444: The sky, using them in association with legends and mythology about their deities . The history of astrology has generally been based on the belief that relationships between heavenly bodies influence or explain events on Earth. The scientific study of objects in the night sky takes place in the context of observational astronomy . Visibility of celestial objects in the night sky is affected by light pollution . The presence of

2070-425: The southern sky are easily mistaken to be Earth-based clouds (hence the name) but are in fact collections of stars found outside the Milky Way known as dwarf galaxies . Zodiacal light is a glow that appears near the points where the Sun rises and sets, and is caused by sunlight interacting with interplanetary dust . Gegenschein is a faint bright spot in the night sky centered at the antisolar point , caused by

2116-515: The stars visible to the unaided naked eye appear as hundreds, thousands or tens of thousands of white pinpoints of light in an otherwise near black sky together with some faint nebulae or clouds of light. In ancient times the stars were often assumed to be equidistant on a dome above the Earth because they are much too far away for stereopsis to offer any depth cues. Visible stars range in color from blue (hot) to red (cold), but with such small points of faint light, most look white because they stimulate

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