Extraterrestrial skies
As the sky view is commonly referred to, which is an observer with a view of the surface of a celestial body, in the original sense of the earth, has to outer space. When an alien sky vision is this different from the earthly view for different reasons.
The most important factor for the appearance of the sky of a world is its atmosphere. Depending on the atmospheric density and chemical composition can the sky in any color spectrum represent. Is the world surrounded by clouds, they can appear in a variety of colors. However, many objects in the sky have no or only a very thin atmosphere, whereby an observer from there provides an unclouded view of the space. In addition, there are particular striking astronomical objects that define the sky a world like the sun, they orbiting moons, neighboring planet or possibly existing planetary rings.
Aliens sky visions are a field of astronomical phenomenology, which moves through space in their interest to include the same problems and celestial mechanics and in relation to atmospheric optics exactly determined as topocentric cases. Otherwise they are because so far no real accessible to a central subject of Space Art, as a popular scientific illustration.
- 3.1 Sun View
- 3.2 Earth view
- 3.3 Solar and Erdfinsternis
- 4.1 color of the martian sky
- 4.2 Sun View
- 4.3 Martian moons
- 4.4 Earth view and Venus view
- 4.5 The sky of the Martian moons
- 5.1 General
- 5.2 87 Sylvia and its moons Romulus and Remus
- 6.1 Jupiter's moons
- 6.2 The Heaven of Jupiter's moons
- 7.1 The Heaven of Saturn's moons 7.1.1 seen the rings of Saturn's moons from
- 7.1.2 titanium
- 7.1.3 Enceladus
- 9.1 Triton
Mercury
The sun closest planet Mercury has no atmosphere, so that his sky is black and does not differ from the view of space that opens up an orbit from the Earth. In principle, one could see the day stars and planets on Mercury as well. However, their light in the near sun outshines very strong, so that observation would only be possible if one were to shield the view of the sun and the blazing bright planet surface.
Mercury has a southern polar star, α Pictoris, of which the apparent brightness of 3.2 m, however, is weaker than the earthly Polaris ( α Ursae minoris ).
Sun view
On Mercury, the apparent diameter of the Sun is on average two and a half larger than on Earth, and their brightness is more than six times the value here. Due to the eccentric orbit of the planet along its orbit changes the apparent size and brightness that provides the sun on Mercury sky. So is the sun at aphelion size, the sonnenfernsten point 2.2 times the comparable Earth view, with their brightness reaches 4.8 times here in the sun near perihelion, however, it increases to 3.2 times the diameter of Earth view and their brightness value is greater by approximately 10.2- fold.
The Mercury runs in just 88 days around the sun with an orbital resonance of 3: 2 In other words, this means that the planet three times around itself rotates while he circled twice the sun in the same direction. On Mercury, takes a related to the fixed stars day - that is the time for a full rotation - about 58.7 Earth days, while related to the sun Merkurtag than the time between two meridian passages of the sun about 176 Earth days long.
A Merkurtag thus making it longer than the Merkur year between the Periheldurchgängen and it takes about twice that of a whole round. This leads to an unusual effect, in which it seems as if the sun reverses once within a year Merkur their usual east-west movement short. This phenomenon can be observed in different clarity, depending on where you are currently located on Mercury. During this phase, an observer can at certain points seen on the surface of the planet the sun rise, where it rises only to about the middle of the horizon, here its course reverses until she again goes before it, still on the same Merkurtag, again is ascending to see. This effect is due to the fact that exactly from about four Earth days before the perihelion, the angular velocity of the orbit of Mercury is its rotational speed is equal, so that the sun does not seem to continue their apparent motion; at perihelion, the orbital angular velocity of Mercury over again meets its rotational speed, which the sun moves seemingly declining. Four Earth days after perihelion will then continue their usual self-motion the sun. Due to its orbital resonance two sites on the surface of Mercury at perihelion are alternately facing the sun; one of these two points is the Caloris Planitia ( " heat - pool "). This level was so named because an observer in the vicinity of its center once per Merkurtag sees the sun draw a loop around the zenith of Mercury and thus makes the experience a in fact very hot day.
View of other planets
According to the Sun, Venus is the second brightest object in the sky Mercury. Venus appears much brighter than the case of an observer on the earth. This is justified by the fact that, when Venus is closest to Earth, it faces the sun and therefore a Erdbeobachter only gets to see their dark side. Although Venus is the brightest object in the sky of the earth (after the Sun and Moon), it is indeed so that you do not get more than a narrow crescent of her to see.
For an observer on Mercury, Venus, however, is then the next when it is in opposition to the Sun, which is why from here their whole disc is seen. The apparent brightness of Venus amounts to -7.7 m.
The Earth and its moon are very striking objects in the sky of the planet closest to the sun, as their apparent brightness values approx -5m and amount to -1.2 m, the apparent distance between the Earth and the moon is a maximum of about 15 arc minutes [B 1]. All other planets is around from the same visibility as seen from the Earth, where they seem a little less bright in opposition. In contrast, the zodiacal light is likely to occur more prominent than is the case on Earth.
Venus
The atmosphere of Venus has a completely closed, about 20 km thick clouds of sulfuric acid and other ingredients. Thus her daytime sky is relatively dark, despite their relative close to the sun, comparable to the brightness of a covered day on earth. The atmosphere is on the surface extremely dense and hot. The lander Venera 8 of the Soviet Venera mission measured a visibility of about one kilometer.
The sun can not be seen on Venus as a definable disc, and the stars at night remain entirely invisible. Color images of the Venera probes suggest that the sky on Venus appears orange and yellow-green to a different source. When the sun would be seen from the surface of Venus from that time would from one sunrise to the next (ie, a solar day ), take a total of 116.75 Earth days. Since the revolution of Venus is retrograde, ie opposite to the rotation of the earth, the sun goes with her in the west and set in the east under.
The upper atmosphere of Venus rotates differentially and near the equator around 60 times faster than Venus itself, an observer whose position is located high above the clouds of Venus, is thereby rotated in just four Earth days around the planet and sees a sky in which appear clearly and brightly the sun, the Earth and earth's Moon ( their brightness values are -6.6 m and -2.7 m ), particularly in opposition, when both planets are at a 180 ° angle to the sun and thus the point of their achieve maximum approach. Also, Mercury is the Venus sky fairly easy to discover, because it is closer to the planet and therefore to the order of -2.7 m is brighter than it appears from Earth. Moreover, its maximum angular distance from the Sun is here much larger ( 40.5 ° ) than from an earthly point of observation ( 28.3 ° ) from.
The Earth's Moon
Since the Moon, similar to Mercury, has no atmosphere, its sky presents solid black. However, the sun rises from the Earth's moon yet so bright that it is impossible to see stars during the day, unless the observer is shielded from both the harsh direct sun sight, and on the blindingly bright surface from its point of view. The moon has a southern polar star, δ Doradus, which has an apparent magnitude of 4.34 m. This is even better aligned than the Polar Star of the Earth, but it appears much weaker.
Sun view
The solar disk has on the moon the same size as on Earth. However, due to the lack of atmosphere and the resulting lack of atmospheric scattering and absorption, it seems a little brighter and a purer white. Apart from the sunlight on the moon with the measurable radiation in Earth orbit is identical.
A lunar day, so the time of a solar peak to the next, take a synodic month, about 29.5 days. Since the axial tilt of the moon is relative to its orbit around the sun is almost zero, the sun moves approximately in the course of a year always on the same path across the sky. As a result, obtain the craters and canyons near the poles of the moon never direct sunlight and on the other hand, there are some mountains and lunar craters, whose tips or crater rims never lie in the shade. (→ see mountains of eternal light ).
Earth view
Among the most prominent features on the moon sky belongs to the view of the Earth. Your visible diameter ( 1.9 ° ) is about four times as large as the diameter, the moon has in the firmament of the earth. Since the moon's orbit is eccentric, varies the apparent size of the earth in the sky by about 5 % ( between 1.8 ° and 2.0 ° in diameter). The earth shows how the phases of the moon, but they are time each opposite to the phases of the moon: So if you see from Earth, the full moon is for the lunar observer the earth in its dark phase and vice versa. The albedo of the Earth is three times as high as that of the moon and with the larger area, the earth takes on the full moon sky, this seems brighter than the full moon for the terrestrial observer at zenith over 50 times.
As a result, the bound rotation, which owns the moon towards the earth, one side of the moon is always turned towards the earth, while the moon back is never visible from the Earth. Conversely, this means that the earth can only be seen from this one side of the moon, while it remains always visible on the back.
If the rotation of the Moon in perfect sync, the earth would make no noticeable movement in the sky the moon. In fact, the Earth seen from the moon performs a slow and complex wobbling motion ( libration ). For one month, the Earth describes a movement approximately oval with a diameter of 18 °. The exact shape and orientation of this oval depends on the location on the moon. For this reason, the earth is sometimes just below the horizon and sometimes just above it near the border region between the front and side of the moon.
Sun and Erdfinsternis
From time to time, are earth, sun and moon on a direct line of sight, which then a solar eclipse or a " Erdfinsternis " can be experienced at the moon sky. During the solar eclipse on the moon, the sun is obscured by the Earth. At the same time on earth is a lunar eclipse to observe the eclipse takes place not only in a narrow strip, but often on the entire front of the moon.
The end of the eclipse with its 4 contacts is from the moon, the same as seen from Earth. Since the apparent diameter of the Earth is four times larger than the Sun, the phase of the total solar eclipse can last over 2 hours, and the atmosphere appear at this stage as a reddish ring. It was originally planned to photograph such an eclipse of the sun by means of the Lunar Rover television cameras of Apollo 15. Unfortunately, the camera or the power source were already immediately after the astronauts were launched defective.
A " Erdfinsternis " is on the other side for a moon observer is not a very spectacular event, as the Moon's shadow to the earth narrowed considerably. Observers on the lunar surface is only the prospect to pursue with a telescope a small round, dark spot, which pulls on the Earth's surface away.
Mars
Mars has only a thin atmosphere. However, this is extremely dusty, so that much is scattered by the light that reaches it. Heaven thus appears during the day in full light and stars can not be seen. The north pole of Mars is aligned on the star Deneb, although the actual pole offset slightly pointing towards Alderamin. As Südpolarstern of Mars Kappa Velorum may be referred to.
Color of the martian sky
Surprisingly, it presents itself as a very difficult task to create accurate true-color images of the surface of Mars. One aspect of why this is the case, the Purkinje Effect: After it depends inter alia on the brightness of the ambient light on the way the human eye perceives color. For as soon as the surrounding brightness decreases, leaves the color perception of the human red objects appear dark quickly, while the color effect of blue objects decreases less rapidly. Besides showing the published pictures in the past large differences in the representation of the color of the sky. This is because many of the images filters were used to maximize the certain scientific aspects, without changing the representation of true color was the focus.
It is known that assumes a scarlet red or bright orange-red color during the Martian day the sky. During sunrise and sunset phase, the sky changes color pink, he said. Near the setting sun, as opposed to the familiar sight on earth appears blue At times, the sky takes on a purple color, which arises because the light is scattered by very small water-ice particles in the clouds. After the sun has set and before it rises, there is a long-lasting phase of Twilight. This is caused by the fact that the dust grains, which are found high in the atmosphere of Mars, scatter the light located behind the horizon and the sun light up the sky.
On Mars has the Rayleigh scattering, which is responsible among other things for the red color at dawn and sunset on Earth, usually a very weak effect. The red color of the sky is instead rather by, with iron ( III ) oxide enriched, causing dust particles in the air.
Sun view
The sun has seen from Mars just 5 /8 of the size it occupies on the Earth's skies (0.5 °). In this case, the planet reaches 60 % less light than our world, which roughly corresponds to the brightness of a low overcast afternoon on Earth.
A Martian day is almost the same length as a day on earth: 24 hours, 39 minutes and 35.244 seconds. This period is in English, called for example by NASA in connection with missions to Mars, also sol.
Martian moons
The Mars orbit two small moons: Phobos and Deimos. From the surface of Mars as seen from Phobos obtained between one third and about half of the angular diameter of the sun, whereas Deimos with only 2 ' angular diameter is little more than a point.
The apparent motion of Phobos is opposite due to its fast train speed of the movement of the sun, that is, it rises in the west and set in the east. This results from the fact that it orbits around the planet faster than this rotates about its own axis. Phobos is also close to such a low equatorial orbit, so the planet is so close to his round that he can no longer be seen above 70.4 degrees north and below 70.4 degrees south latitude. An observer positioned just below or just above the 70.4 ° visibility limit, sees a markedly smaller Phobos, because it is located farther away from him as an observer at the equator. The apparent size of the moon varies by up to 45 %. For an equatorial observer, however, Phobos appears on the horizon with an angular diameter of about 0.14 ° and reached its peak size of 0.20 °. It crosses the sky in about 4.24 hours and 11.11 hours appears all over again.
Deimos goes, like a "normal " moon, in the east and sets in the west. His appearance at an angular diameter between 1.8 ' and 2.1 ' is more like that of a star. The brightness varies seen from Earth between the star Vega and the Venus. Since he also located relatively close to Mars, Deimos can not be seen from Mars widths above or below 82.7 ° north or south latitude. With about 30.3 hours, the orbital period of Deimos exceeds slightly the Mars rotation of approximately 24.6 hours. The moon therefore appears every 5.5 days for an equatorial observer and then remains visible for 2.5 days before he disappears behind the horizon. In a nutshell, that Phobos moves during a Deimosumlaufs almost 12 times over the Mars sky.
Phobos and Deimos, both cover the sun seen from Mars part, neither of the moon, however, is able to completely darken the sun's disk. In fact, more likely to be spoken by a sun passage as of a solar eclipse.
Earth view and Venus view
Earth interacts with its moon seen from Mars as a double star. The visible distance between Earth and the Moon is in the best case, ie at the inferior conjunction of the earth and the sun (for the terrestrial observer, this is the opposition of Mars and the Sun ) is about 25 arc minutes. In the vicinity of the maximum elongation of 47.4 ° earth and moon are seen in the apparent magnitude -2.5 m and 0.9 m.
The Venus lights seen from Mars near the maximum solar elongation of 31.7 ° with an apparent magnitude of about -3.2 m. This corresponds approximately to the value that reaches seen of Mars from Earth.
The sky of the Martian moons
From Phobos from Mars appears 6,400 times larger and 2500 times brighter than the full moon for a Erdbeobachter, where it occupies a quarter of the entire hemisphere. In contrast, the Mars Deimos appears still to 1000 times larger and 400 times brighter than our full moon and fills 1/11 of the hemisphere of the smaller satellites from.
Asteroids
Generally
Strictly speaking the asteroid belt is a sparsely occupied with objects area. Occasionally, " closer approximations " before, in which case but still are huge distances between the bodies. A realistic impression of the Asteroid Belt Space Odyssey again when the spacecraft encounters a lonely asteroid in a scene: Unlike other science fiction films is the 2001 movie.
Some of the asteroids that cross the orbit of a planet or other, can approach a planet or another asteroid occasionally. Then it is possible that an observer can see without the help of a binocular or telescope of this asteroid from the slice of a nearby object. In September 2004, the object ( 4179 ) Toutatis Earth approached, for example, to a distance of four times the distance from Earth - corresponded to the moon. At perigee, the Earth was viewed about to see from its surface with the same apparent size with which one can see the moon from Earth. The moon was just as much as a small disk in the sky of Toutatis visible.
Some asteroids have such an unusual path, that they offer a lot of material for fiction. Thus, for example, the asteroid (3200) Phaethon one of the most eccentric orbits of all known objects in the solar system. Its distance from the sun varies during its orbit from 0.14 to 2.4 AU. In the perihelion the sun appears more than seven times greater in his heaven as on earth, with its surface per unit area receives more than 50 times as much energy from her. In contrast, the aphelion sun absorbs less than half of its apparent diameter as seen from Earth, and from the object reaches only about one-sixth of the light that keeps it at the point nearest the Sun.
87 Sylvia and its moons Romulus and Remus
The asteroid (87 ) Sylvia is one of the largest asteroids in the asteroid belt and the first in whose conduct two moons could be observed. The moons Romulus and Remus about 18 km and 7 km in diameter. Romulus, the remote on, takes the sky the asteroid has an apparent size of about 0.89 degree angle, the smaller and more Remus about 0.78 °. As (87) Sylvia strongly deviates from the spherical shape, these values depending on the position of an observer on the surface to vary a little more than 10%. Since the two moons orbiting the celestial bodies almost in the plane of its orbit, it comes every 2.2 days mean that the one covering the other. Twice every 6.52 Sylvia years there is a solar eclipse, but due to the smaller apparent size of the Sun of 0.15 ° represents a much less spectacular event, as it ( 0.53 ° ) is the case on Earth. From Remus of view appears (87 ) Sylvia huge in the night sky, as it approximately 30 ° × 18 ° occupies here, while the adjacent Romulus between the apparent sizes of 1.59 ° and 0.50 ° varied. From Romulus from the asteroid has an angular diameter of 16 ° × 10 ° while Remus takes values between 0.62 ° and 0.19 °.
Jupiter
Although never before pictures were taken from inside the Jovian atmosphere, go artistic representations typically assume that the sky appears blue gas planet. However, it is likely that he has a duller blue than the Earth's skies, since the sunlight, at least not at the top of the atmosphere is 27 times weaker than Earth's average. Viewed from Jupiter from the sun has only an extension of 5 minutes of arc, which is less than a fifth of what it takes Earth's skies. The near- rings of the planet are probably slightly visible above the equator. Deeper in the atmosphere, the sun appears, however, through clouds and fog probably in different colors and takes up mostly blue, brown and red tones to the deeper one penetrates into the planet's atmosphere, darkening quickly. Currently, various theories about the cause of these colors will be discussed, but there is as yet no exact answer to this question.
Moons of Jupiter
Apart from the sun are the four Galilean moons, the most striking objects in the sky of Jupiter. Io, which is the planet closest to acting, slightly larger than the full Earth's moon in the sky, but here they appear less bright Despite the larger albedo of the second closest moon Europa creates this it to outshine because of their greater distance to Jupiter is not, Io. In fact, it is so that the low solar constant (3.7 % that of Earth's surface ) ensures by the distance from Jupiter to the sun is that none of the Galilean satellites appear as bright as the full moon on the earth. From Io on Europa and Ganymede to Callisto be the apparent magnitudes of the moons. -11.2 M, -9.7 m, -9.4 m and -7.0 m [A 1]
Ganymede, the largest and third closest of Jupiter's large moons, is almost as bright as Europe, but appears only half as large compared to Io on Jupiter sky. The more distant Callisto, however, has only a quarter of the apparent size of our full moon. All four Galilean moons have it as compared to Earth's moon a larger web speed, which is why they move much faster on the Jupiter sky as the moon on the Earth's skies. Each of them is also large enough to cover the sun during a solar eclipse in full.
The smaller inner moons of Jupiter appear as star-like points, while most of the outer moons to the naked human eye are no longer visible.
The sky of Jupiter's moons
None of the moons of Jupiter has more than at most a trace of atmosphere, so that their skies are entirely or almost black. For an observer on one of the moons is the most prominent feature of the sky apart from the sun, of course, the Jupiter. On Io, the planet located closest large moon, Jupiter has an apparent diameter of about 20 °. This is equivalent to 38 times the visible diameter of our Moon, which he occupies 1 % of the sky of Io. For an observer on Metis, the innermost moon, the apparent diameter increases to a value of 68 ° or 130 times the apparent diameter of our Earth's moon, so a total of 18 % of the sky of Metis are taken from the planet. A " full Jupiter" on Metis shines with about 4 % of the brightness of the sun, whereas our full moon lights up only 400,000 times weaker than the sunlight.
Since the inner moons of Jupiter have a synchronous rotation of the planet, it always appears at almost the same spot in the sky (Jupiter " wobbles " due to a small eccentricity, however, a bit ). Observer on the side facing away from Jupiter sides of the Galilean moons get the planet, however, never to be seen. Of these moons of Jupiter from the eclipses caused by it are very spectacular, because an observer can see the circular shadow of the respective moon pull on the surface of Jupiter slowly.
Saturn
The atmosphere of Saturn has in the upper layers probably a blue color, although the predominant color of the clouds suggests that they appear further down rather yellowish. The rings of Saturn are here, at the top of its atmosphere, certainly clearly visible, although they are so thin that they are almost invisible from a certain position on the equator of Saturn, because it only looks here on the edge of the rings. From anywhere else on the planet but they can be seen as a spectacular arc which extends over half of the celestial Saturn hemisphere.
See Saturn's moons in his heaven, however, is not particularly impressive, since most are relatively small and the biggest draw their orbits far from the planet. Also Titan, the largest moon of Saturn, appears only half as large as the moon in the Earth's skies. Subsequently, the approximate angular diameter of the main moons are indicated ( in comparison, the Earth's moon a angular diameter of 31 '): Mimas: 5-10 ', Enceladus: 5-9 ', Tethys: 8-12 ', Dione: 8-12 ' Rhea: 8-11 ', Titan: 14-15 ', Iapetus: 1 '.
Saturn has a southern polar star, δ Octantis, with a brightness value of 4.3 m. He is so much weaker than the polar star of the earth ( α Ursae minoris ).
The sky of Saturn's moons
Since the inner moons of Saturn are all in a bound rotation to the planet, this is to be seen except for certain variations always in the same place in the sky. Therefore viewer on the side facing away from Saturn sides of these satellites get the planet never to face.
The Saturn is a very dominant object in the sky view of the inner moons. Seen from Pan has made the Saturn, for example, an apparent diameter of about 50 °. It thus appears 104 times larger than our moon and takes 11 % of the sky of a Pan. Since the orbit of Pan along the Encke division and thus within the rings of Saturn passes, they can be seen from anywhere in pan, on the side facing away from Saturn page.
Seen the rings of Saturn's moons from
In the sky the most moons, the rings of Saturn make hardly constitutes a striking appearance The reason is that the rings are indeed wide but not very thick and the orbits of most of the moons almost exactly (within 1.5 ° deviation) in the ring plane of the planets run. So you can see from the inner moons only to the edges of the rings, which keeps them virtually invisible. From the outer moons in turn, starting with Iapetus, one has an oblique view of the rings, Saturn appears much smaller because of the greater distance to them. On the surface of Phoebe, the largest of the outer moons of Saturn, the planet therefore only reaches the size of the full moon in Earth's night sky. A calculation of the distances and angles of the different moons of Saturn is difficult with the available values , but the results show that can be expected of the best views of the rings from the inner moon Mimas, whose orbit nearly 1.5 ° from the equatorial plane of Saturn differs, where it is located in relative proximity to the rings. At the point reached on the Mimas its greatest deviation in the equatorial plane of the planet can be used to determine an apparent distance of 2.7 degrees between the outer edge of the ring B and the inner edge of the ring A. The two also located in orbit moons Epimetheus and Janus offer, with maximum spacing angles of 1.5 ° to 2.9 ° from the surface of the moon as an impressive sight. The next best view is then expected to Tethys, who appears with almost half a degree at Mimashimmel. Iapetus has an angular diameter of 0.20 °, which is more than can be achieved by one of the outer moons.
Titanium
Titan is the only moon in our solar system, which is surrounded by a dense atmosphere. Images of the Huygens probe show that the titanium sky is bathed in an orange light. However, to be noticed on the surface of titanium only a hazy, brownish / dark orange color, because titanium only 1/3000 of the sunlight our Earth receives. Due to the dense atmosphere, and the much greater distance to the sun during the day, it is just as bright as the dim light of the earth on Titan. It seems likely that the Saturn permanently behind the orange smog remains invisible and even the sun is just a bright spot in the haze, which can hardly illuminate the surface of the ice-covered lakes and methane celestial body. In the upper atmosphere the sky, however, appears likely to blue and from here it is possible to take a look at Saturn.
Enceladus
In the sky of Enceladus Saturn has a visible diameter of nearly 30 °, and is thus about 60 times larger than the moon in our night sky. Moreover, since the intrinsic rotation of Enceladus is synchronous with its orbital motion around the planet, he turns the Saturn always to the same page. The planet therefore moves across the sky of Enceladus as well as not, except for slight variations arising from the eccentricity of its orbit. In contrast, the Planet of the Saturn opposite side is never seen.
The rings of Saturn can be seen at an angle of up to 0.019 °, which means that they are almost invisible. Only their shadows stand out clearly on the surface of Saturn. Like the Earth's Moon of Saturn shows regular phases, which vary from one "full Saturn", a part shade to a " Neusaturn ". The sun has seen Enceladus from a diameter of only 3.5 arcmin, about one-ninth of the diameter, it occupies on the Earth's skies.
If there is an observer on Enceladus, he can see from there, as Mimas, the largest satellite in the orbit of Enceladus, passes by on average every 72 hours before Saturn. Its apparent size is at best 26 minutes of arc, which he has about the same size as the moon in our sky. Pallene and Methoni appear with a maximum of 30 seconds of arc, however, almost star-like manner. Tethys in turn is only visible from the side facing away from Saturn's Enceladus and reached here a maximum apparent size of about 64 arc minutes, which is about twice the value of the Moon in our sky view.
Uranus
Judging by the color of the atmosphere can be assumed that the sky of Uranus appears likely in a bright blue or more cyan. It is likely that the rings of the planet from the surface can not be seen because they are very thin and dark. Uranus has a north polar star, Sabik ( η Ophiuchi ), with a magnitude of 2.4 m high and as a southern polar star, 15 Orionis, with an apparent magnitude of 4.8 m. Both are thus weaker than the polar star of the earth, Sabik but only slightly.
Uranus is unusual in that the skewness of its ecliptic, ie the angle of the axis tilt to his Bahnebenenlot whole is 97.77 °. As a result of this tendency in the northern hemisphere and once the southern hemisphere of the Sun facing after each half turn once. On 17 December 2007, the sun happened forth the celestial equator of Uranus from the north and in the 2029 North Pole will eventually be aligned almost exactly with the sun.
See the Uranus moons of the planet's surface from not very large. Next, the angular diameter of the five major moons are listed. ( By comparison, the Earth's moon, he is 31 '): Miranda, 11-15 '; Ariel, 18-22 '; Umbriel, 14-16 '; Titania, 11-13 '; Oberon, 8-9 '. The small inner moons appear as star-like points, while the outer irregular moons are not visible to the naked eye.
Neptune
Judging from the color of the atmosphere, the sky of Neptune shines likely in an azure blue or light blue color, similar to that of Uranus. It can be assumed that the rings of the planet from the surface can not be seen because they are very thin and dark.
Apart from the sun be large moon Triton is the most prominent object in the sky Neptune and presents itself slightly smaller than the moon on the earth in all likelihood. With an orbital period of 5.8 days, it moves much faster than our moon around its planet. This impression is further enhanced by its retrograde movement direction with which runs counter to the direction of rotation of Neptune. The smaller moon Proteus is to be seen in contrast to Triton as a disk of about half the size of the full Moon. Neptune's small inner moons and the big outer satellite Nereid are eventually to be seen as star-like points and its outermost satellites you can not make without a telescope with certainty.
Triton
Triton, Neptune's largest moon, does have an atmosphere, but it is so thin that the sky appears almost completely black and, at best, is visible on the horizon somewhat paler haze. Since Triton has a tidally locked to Neptune, you always see the planet at the same position in his heaven. Triton's rotation axis is tilted by 157 ° to the equatorial plane of Neptune, which is relative to its orbit around the sun, in turn inclined 30 °. Therefore, the poles of Triton, similar to Uranus, Neptune twice a year aimed directly at the sun. This means that Triton's polar regions are each facing 40 years in a row the sun, before the other pole moves into the sunlight, which eventually leads to a radical change of seasons on the moon.
Neptune itself spans about 8 ° on the sky of Triton, although its maximum brightness is comparable to that of the full moon on the Earth only about because he is able to reflect per unit area of little more than 1/256 of the sunlight of full earthly moon. Because of its eccentric orbit varies Nereid significantly in brightness between the fifth and the first magnitude and the glass is much too small to see with the naked eye. Proteus is, with its just 5-6 minutes of arc, also not as good as recognizable as disc, but never appears weaker than first magnitude and can compete in its smallest distance with Canopus.
Pluto and Charon
The dwarf planet Pluto, accompanied by his largest moon Charon orbits the Sun in an orbit which is most of the time far outside the orbit of Neptune. Due to the highly eccentric orbit, however, Pluto is a period of about twenty years closer to the Sun than Neptune (The last time so far 1979-1999 ). From Pluto, the sun is still quite bright to see, since the planet still around from the 150 - to 450 -fold is achieved the moonlight. These very different values are explained by the eccentricity of the orbit of Pluto, so that a human observer in the course of the sun circumnavigation would detect a noticeable change in brightness.
Pluto and Charon have a double bonded rotation. This means that Pluto always faces the same side of Charon and Pluto 's moon also always presents the same side. Observer on the other side of the Charon never get to see the dwarf planet, get as little as observers on the other side of the Pluto Charon to face. All 124 years it is important for a number of years to a period of a mutual eclipse of the sun, if mutually take Pluto and Charon at intervals of 3.2 days the sunlight.
Comets
Unlike other celestial bodies, the sky a comet changes dramatically as soon as it approaches the Sun. During the approach of a comet, the ice on the surface starts to sublimate, that is, it passes from the solid directly into the gaseous state. This results in a tail of gas and dust from which it arises a coma around the comet body forms. An observer on the sun approaching comet can therefore see the stars only by a slightly milky appearance, which thereby generates presumably interesting halo effect around the sun and to other bright objects.
Planets outside the solar system
The constellations seen by an observer on an extrasolar planet is very different than we are used to from the Earth. Our sun is still visible to the naked human eye only up to a distance of 20-25 parsecs ( 65-80 light years). The basis for this statement is the star β Comae Berenices, the slightly more luminous than the sun just faintly appears in our firmament absolutely due to its distance of 27 light years.
Looking at the sun from the α Centauri system, the closest star system to us, contends that it appears as a bright star in the constellation Cassiopeia, being nearly as bright as the star Capella in our sky. From a hypothetical planet orbiting α Centauri A or B either, is seen as very bright second sun of each other star of the system. An Earth-like planet, for example, is 1.25 astronomical units of α Centauri A away and has an orbital period of 1.34 years, receives from its primary star a sun-like radiation, while α Centauri B from 5.7 to 8.6 magnitudes less at its sky accounts ( -21.0 m to -18.2 m). Thus, the second sun, although 190 is - to 2700 - fold less than α Centauri A, but still around the 2100 - to 150 times brighter than the full Moon. Conversely receives an Earth-like planet at a distance of 0.71 AU from α Centauri B (and an orbital period of 0.63 years ) from its primary sun the same as sun lighting the earth, but α Centauri A appears fainter 4.6 to 7.3 sizes ( -22.1 m to -19.4 m), or 70 - to 840 - times weaker than α Centauri B, but still between 5700 -. , and 470 times brighter than the full moon [B 2] In both cases, one sees the pull each secondary sun during the planetary orbit in a circular path across the sky. Starting right next to the primary sun they can be seen after half an orbital period in the sky towards her and thus represents a " midnight sun " dar. After another half period, it has the cycle then completed. On other planets, which are members of a binary system, in other similar celestial event is to be admired.
From 40 Eridani from, 16 light years away, the sun just more than an average star in the constellation of the Serpent, which has an apparent magnitude of about 3.3 m appears. At this distance, is home to most of the closest stars, including Alpha Centauri and Sirius, at positions other than in our sky.
From a planet orbiting the 65 light-years distant Aldebaran, the sun is barely seen above Antares in our constellation Scorpio. It is equipped with a light-emitting size of 6.4 m, however, hardly be seen with the naked eye. Constellations, which consist of bright, distant stars, such as the constellation Orion, the view of our planet very similar, but most of the other constellations of our night sky come in this place hardly more familiar.