"English days of the week were inherited from gods of the old Germanic Norse culture — Wednesday is ""Wōden""’s-day (""Wōden"" or ""Wettin"" eqv. Mercury), Thursday is ""Thor""’s-day (Thor eqv. Jupiter), Friday is ""Frige""-day (Frig eqv. Venus). It can be correlated that the Norse gods were attributed to each Roman planet and its god, probably due to Roman influence rather than coincidentally by the naming of the planets. In alchemy, each classical planet (Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn) was associated with one of the seven metals known to the classical world (silver, mercury/quicksilver, copper, gold, iron, tin and"
"a minute longer than a solar year.) The sidereal year of 365.25636 days is only valid for stars on the ecliptic (the apparent path of the Sun across the sky), whereas Sirius's displacement ~40˚ below the ecliptic, its proper motion, and the wobbling of the celestial equator cause the period between its heliacal risings to be almost exactly 365.25 days long instead. This steady loss of one relative day every four years over the course of the 365-day calendar meant that the ""wandering"" day would return to its original place relative to the solar and Sothic year after precisely 1461"
"giant Jupiter's sidereal day is only 9 hours and 56 minutes. However, it is not just the sidereal rotation period which determines the length of a planet's day-night cycle but the length of its orbital period as well - Venus has a rotation period of 224.7 days, but a day-night cycle just 116.75 days long due to its retrograde rotation and orbital motion around the Sun. Mercury has the longest day-night cycle as a result of its 3:2 resonance between its orbital period and rotation period - this resonance gives it a day-night cycle 176 days long. A planet may"
"Earth's year of 365 days. Its orbital radius is at 0.0875 AU, or 8.75% the distance between Earth and the Sun. While this is quite close, the star LHS 1140 is so dim that the planet only get 0.41 times the incident flux of Earth at this distance. With an albedo of 0, LHS 1140 b has an equilibrium temperature of , compared to Earth's at . If LHS 1140 b has an albedo similar to that of Earth, the equilibrium temperature would be even lower, at . However, with a greenhouse effect at least as strong as Earth's LHS"
"slowest rotation period of any known object in the Solar System. A Venusian sidereal day thus lasts more than a Venusian year (243 versus 224.7 Earth days). However, the length of a solar day on Venus is significantly shorter than the sidereal day; to an observer on the surface of Venus, the time from one sunrise to the next would be 116.75 days. Therefore, the slow Venerian rotation rate would result in extremely long days and nights, similar to the day-night cycles in the polar regions of earth, only shorter. The slow rotation might also account for the lack of"
"Gliese 581. Just as Earth's Moon always presents the same face to the Earth, the length of Gliese 581g's sidereal day would then precisely match the length of its year, meaning it would be permanently light on one half and permanently dark on the other half of its surface. An atmosphere that is dense will circulate heat, potentially allowing a wide area on the surface to be habitable. For example, Venus has a solar rotation rate approximately 117 times slower than Earth's, producing prolonged days and nights. Despite the uneven distribution of sunlight over time intervals shorter than several months,"
"precessions are in opposite directions, and therefore add, to make the precession cycle between the tropical and anomalistic years 21,000 years on Earth and 56,600 years on Mars. As on Earth, the period of rotation of Mars (the length of its day) is slowing down. However, this effect is three orders of magnitude smaller than on Earth because the gravitational effect of Phobos is negligible and the effect is mainly due to the Sun. On Earth, the gravitational influence of the Moon has a much greater effect. Eventually, in the far future, the length of a day on Earth will"
"because the Sun's daily path is nearly perpendicular to the horizon for most of the year. The length of daylight (sunrise to sunset) is almost constant throughout the year; it is about 14 minutes longer than nighttime due to atmospheric refraction and the fact that sunrise begins (or sunset ends) as the upper limb, not the center, of the Sun's disk contacts the horizon. Earth bulges slightly at the Equator; the ""average"" diameter of Earth is , but the diameter at the Equator is about greater than at the poles. Sites near the Equator, such as the Guiana Space Centre"
"to Minbari warcruisers and fighters. In the Babylon 5 universe, Minbar is a planet in the system of Chi Draconis — a binary star system just over 26 light years from Earth. It is the seventh planet in orbit around the local suns and has two moons. Its day is shorter than Earth's, at 20 hours and 47 minutes, and its year is about 1.5 Earth years. Like Earth, Minbar has an oxygen—nitrogen atmosphere. The polar caps are larger than those on Earth; the northern cap covers 23% of the planet's surface and, on the whole, Minbar's climate is colder"
"eventually leading to confusion about when to undertake activities dependent on weather, ecology, or hours of daylight. A solar year is actually slightly shorter than 365 days and 6 hours (365.25 days), which had been known since the 2nd century BC when Hipparchus stated that it lasted 365 + − days, but this was ignored by Julius Caesar and his astronomical adviser Sosigenes. The Gregorian calendar corrected this by adopting the length of the tropical year stated in three medieval sources, the Alfonsine tables, De Revolutionibus, and the Prutenic Tables, truncated to two sexagesimal places, 365 days or 365 +"
"24.5 s longer than the mean tropical year at J2000.0 (365.242189 days). Before the discovery of the precession of the equinoxes by Hipparchus in the Hellenistic period, the difference between sidereal and tropical year was unknown. For naked-eye observation, the shift of the constellations relative to the equinoxes only becomes apparent over centuries or ""ages"", and pre-modern calendars such as Hesiod's ""Works and Days"" would give the times of the year for sowing, harvest, and so on by reference to the first visibility of stars, effectively using the sidereal year. Sidereal year A sidereal year (from Latin ""sidus"" ""asterism, star"")"
"day is, therefore, nearly 4 minutes longer than a sidereal day. The stars are so far away that Earth's movement along its orbit makes nearly no difference to their apparent direction (see, however, parallax), and so they return to their highest point in a sidereal day. Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around Earth once per year. Therefore, there is one fewer solar day per year than there are sidereal days. This makes a sidereal day approximately times the length of the 24-hour solar day, giving approximately"
"heliacal risings of a star. It differs from the sidereal year for stars away from the ecliptic due mainly to the precession of the equinoxes. The Sothic year is the interval between heliacal risings of the star Sirius. It is currently less than the sidereal year and its duration is very close to the Julian year of 365.25 days. The Gaussian year is the sidereal year for a planet of negligible mass (relative to the Sun) and unperturbed by other planets that is governed by the Gaussian gravitational constant. Such a planet would be slightly closer to the Sun than"
"point on Earth. However, there are physical and astronomical effects that change that picture. Namely, atmospheric refraction allows the Sun to be still visible even when it physically sets below the horizon. For that reason, average daytime (disregarding cloud effects) is longest in polar areas, where the apparent Sun spends the most time around the horizon. Places on the Arctic Circle have the longest total annual daytime, 4,647 hours, while the North Pole receives 4,575. Because of elliptic nature of the Earth's orbit, the Southern Hemisphere is not symmetrical: the Antarctic Circle, with 4,530 hours of daylight, receives five days"
"in the eccentricity and inclination of Earth's orbit. Both vary over thousands of years, so the annual variation of the true solar day also varies. Generally, it is longer than the mean solar day during two periods of the year and shorter during another two. The true solar day tends to be longer near perihelion when the Sun apparently moves along the ecliptic through a greater angle than usual, taking about longer to do so. Conversely, it is about shorter near aphelion. It is about longer near a solstice when the projection of the Sun's apparent motion along the ecliptic"
"355 days. The lunar year is about 11 days shorter than the calendar year, which is either 365 or 366 days long. These days by which the solar year exceeds the lunar year are called epacts (). It is necessary to add them to the day of the solar year to obtain the correct day in the lunar year. Whenever the epact reaches or exceeds 30, an extra intercalary month (or embolismic month) of 30 days must be inserted into the lunar calendar: then 30 must be subtracted from the epact. The Rev. C. Wheatly provides the detail: Thus the"
"sidereal day has increased by 6.5 minutes in that time span. Because of the retrograde rotation, the length of a solar day on Venus is significantly shorter than the sidereal day, at 116.75 Earth days (making the Venusian solar day shorter than Mercury's 176 Earth days). One Venusian year is about 1.92 Venusian solar days. To an observer on the surface of Venus, the Sun would rise in the west and set in the east, although Venus's opaque clouds prevent observing the Sun from the planet's surface. Venus may have formed from the solar nebula with a different rotation period"
"slightly longer than an Earth day: 24 hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. The axial tilt of Mars is 25.19 degrees relative to its orbital plane, which is similar to the axial tilt of Earth. As a result, Mars has seasons like Earth, though on Mars they are nearly twice as long because its orbital period is that much longer. In the present day epoch, the orientation of the north pole of Mars is close to the star Deneb. Mars has a relatively"
"the number of hours in a day (25, giving him an extra hour in bed and a few minutes every day adjusting his watch, a task he greatly enjoys) and the number of days in a year (about 300, so the year doesn't drag on). The planet is mostly unknown, so few space travellers ever taste the superbly made sandwiches that would be the planet's claim to fame. Magrathea is an ancient planet located in orbit around the twin suns Soulianis and Rahm in the heart of the Horsehead Nebula. Magrathea is a planet whose economy was based on the"
"than Mercury. Neptune is 30 AU from the Sun and takes 165 years to orbit, but there are exoplanets that are hundreds of AU from their star and take more than a thousand years to orbit, e.g. 1RXS1609 b. The next few space telescopes to study exoplanets are expected to be Gaia launched in December 2013, CHEOPS in 2018, TESS in 2018, and the James Webb Space Telescope in 2021. A planetary-mass object (PMO), planemo, or planetary body is a celestial object with a mass that falls within the range of the definition of a planet: massive enough to achieve"
"a period without night intervening between consecutive days, while part of winter sees a period without daytime intervening between consecutive nights. The phenomenon of day and night is due to the rotation of a celestial body about its axis, creating an illusion of the sun rising and setting. Different bodies spin at very different rates, however. Some may spin much faster than Earth, while others spin extremely slowly, leading to very long days and nights. The planet Venus rotates once every 224.7 days – by far the slowest rotation period of any of the major planets. In contrast, the gas"
"21st centuries, the date according to the Julian calendar is 13 days behind the Gregorian date, and after 2100 the disparity will widen. The Julian calendar has two types of year: ""normal"" years of 365 days and ""leap"" years of 366 days. There is a simple cycle of three ""normal"" years followed by a leap year and this pattern repeats forever without exception. The Julian year is, therefore, on average 365.25 days long. Consequently, the Julian year drifts over time with respect to the tropical (solar) year (365.24217 days). Although Greek astronomers had known, at least since Hipparchus, a century"
"365.2425 days, which matches the 4/100/400 leap year rules of the commonly used Gregorian calendar. Additional adjustments to the calendar over intervals this long are unavoidable, as the actual year is currently slightly shorter (about 365.242374 days) than assumed, the length of Earth's orbit around the Sun changes over time (tropical years are currently becoming shorter at a rate of about 0.53 seconds per century), and in any case, all of these times far exceed the likely existence of the Earth. So the year numbers should be considered approximate. Time zones and Daylight saving time can cause trouble in computer"
"revolution with respect to its apsides. The orbit of the Earth is elliptical; the extreme points, called apsides, are the perihelion, where the Earth is closest to the Sun (January 3 in 2011), and the aphelion, where the Earth is farthest from the Sun (July 4 in 2011). The anomalistic year is usually defined as the time between perihelion passages. Its average duration is days (365 d 6 h 13 min 52.6 s) (at the epoch J2011.0). The draconic year, draconitic year, eclipse year, or ecliptic year is the time taken for the Sun (as seen from the Earth) to"
"star (assumed to be fixed), is called a ""stellar day"". This period of rotation is about 4 minutes less than 24 hours (23 hours 56 minutes and 4.1 seconds) and there are about 366.2422 stellar days in one mean tropical year (one stellar day more than the number of solar days). Other planets and moons have stellar and solar days of different lengths from Earth's. A day, in the sense of daytime that is distinguished from night-time, is commonly defined as the period during which sunlight directly reaches the ground, assuming that there are no local obstacles. The length of"
"situation is quite different for Mercury and Venus. Mercury's sidereal day is about two-thirds of its orbital period, so by the prograde formula its solar day lasts for two revolutions around the Sun— three times as long as its sidereal day. Venus rotates retrograde with a sidereal day lasting about 243.0 Earth days, or about 1.08 times its orbital period of 224.7 Earth days; hence by the retrograde formula its solar day is about 116.8 Earth days, and it has about 1.9 solar days per orbital period. By convention, rotation periods of planets are given in sidereal terms unless otherwise"
"Earth's angular velocity and ""ω"" the planet's angular velocity. Then where ""T"" and ""T"" are Earth's and the planet's years (i.e. periods of revolution around the Sun, called sidereal periods). For example, Venus's year (sidereal period) is 225 days, and Earth's is 365 days. Thus Venus's synodic period, which gives the time between two subsequent eastern (or western) greatest elongations, is 584 days. These values are approximate, because (as mentioned above) the planets do not have perfectly circular, coplanar orbits. When a planet is closer to the Sun it moves faster than when it is further away, so exact determination"
"potential ""rogue planets"" are excluded. In the Solar System, all the planets orbit the Sun in the same direction as the Sun rotates (counter-clockwise as seen from above the Sun's north pole). At least one extrasolar planet, WASP-17b, has been found to orbit in the opposite direction to its star's rotation. The period of one revolution of a planet's orbit is known as its sidereal period or ""year"". A planet's year depends on its distance from its star; the farther a planet is from its star, not only the longer the distance it must travel, but also the slower its"
"the year, which together have 360 days and 360 nights). The most famous example of this type is the Riddle of the Sphinx. This Estonian example shows the pattern: The riddle describes a crawling baby, a standing person, and an old person with a walking stick. This type includes riddles along the lines of this German example: The conceit here is that Two-legs is a person, Three-legs is a three-legged stool, Four-legs is a dog, and One-leg is a walking stick. An example of this type is given here in thirteenth-century Icelandic form: The cow has four udders, four legs,"
"fall and winter are slightly shorter than spring and summer—but in global terms this is balanced with them being longer below the equator. In 2006, the northern hemisphere summer was 4.66 days longer than winter, and spring was 2.9 days longer than fall due to the Milankovitch cycles. Apsidal precession also slowly changes the place in the Earth's orbit where the solstices and equinoxes occur. Note that this is a slow change in the ""orbit"" of the Earth, not the axis of rotation, which is referred to as axial precession (see ). Over the next 10,000 years, the northern hemisphere"
"Uranus, however, have retrograde rotation. For prograde rotation, the formula relating the lengths of the sidereal and solar days is or equivalently On the other hand, the formula in the case of retrograde rotation is or equivalently All the solar planets more distant from the Sun than Earth are similar to Earth in that, since they experience many rotations per revolution around the Sun, there is only a small difference between the length of the sidereal day and that of the solar day—the ratio of the former to the latter never being less than Earth's ratio of 0.997. But the"
"but the second was 21.1060. If a certain interval ""I"" is measured in both mean solar time (UT1) and sidereal time, the numerical value will be greater in sidereal time than in UT1, because sidereal days are shorter than UT1 days. The ratio is formula_4 where ""t"" represents the number of Julian centuries elapsed since noon 1 January 2000 Terrestrial Time. Of the eight solar planets, all but Venus and Uranus have prograde rotation—that is, they rotate more than once per year in the same direction as they orbit the Sun, so the Sun rises in the east. Venus and"
"Venus Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. It has the longest rotation period (243 days) of any planet in the Solar System and rotates in the opposite direction to most other planets (meaning the Sun would rise in the west and set in the east). It does not have any natural satellites. It is named after the Roman goddess of love and beauty. It is the second-brightest natural object in the night sky after the Moon, reaching an apparent magnitude of −4.6 – bright enough to cast shadows at night and, rarely,"