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65-556: Microscopium ("the Microscope ") is a minor constellation in the southern celestial hemisphere , one of twelve created in the 18th century by French astronomer Nicolas-Louis de Lacaille and one of several depicting scientific instruments. The name is a Latinised form of the Greek word for microscope . Its stars are faint and hardly visible from most of the non-tropical Northern Hemisphere . The constellation's brightest star

130-656: A Type II Supernova in NGC 6925, was discovered by Stu Parker in New Zealand in July 2011. NGC 6923 lies nearby and is a magnitude fainter still. The Microscopium Void is a roughly rectangular region of relatively empty space, bounded by incomplete sheets of galaxies from other voids. The Microscopium Supercluster is an overdensity of galaxy clusters that was first noticed in the early 1990s. The component Abell clusters 3695 and 3696 are likely to be gravitationally bound, while

195-461: A debris disk . AU Microscopii and the binary red dwarf system AT Microscopii are probably a wide triple system and members of the Beta Pictoris moving group . Nicknamed "Speedy Mic", BO Microscopii is a star with an extremely fast rotation period of 9 hours, 7 minutes. Microscopium is a small constellation bordered by Capricornus to the north, Piscis Austrinus and Grus to

260-469: A torus -shaped inner Oort cloud with a radius of 2,000–20,000 AU (0.03–0.32 ly). The inner Oort cloud is sometimes known as the Hills cloud, named for Jack G. Hills , who proposed its existence in 1981. Models predict the inner cloud to be the much denser of the two, having tens or hundreds of times as many cometary nuclei as the outer cloud. The Hills cloud is thought to be necessary to explain

325-475: A blue-white main sequence star, it has swollen and cooled to become a yellow giant of spectral type G6III, with a diameter ten times that of the Sun. Measurement of its parallax yields a distance of 223 ± 8 light years from Earth. It likely passed within 1.14 and 3.45 light-years of the Sun some 3.9 million years ago, at around 2.5 times the mass of the Sun, it is possibly massive enough and close enough to disturb

390-571: A large number of Oort cloud objects are the product of an exchange of materials between the Sun and its sibling stars as they formed and drifted apart and it is suggested that many—possibly the majority—of Oort cloud objects did not form in close proximity to the Sun. Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800 million years after formation, as

455-462: A low metallicity . Combined with its high galactic latitude, this indicates that the star system has its origin in the galactic halo of the Milky Way . HD 205739 is a yellow-white main sequence star of spectral type F7V that is around 1.22 times as massive and 2.3 times as luminous as the Sun. It has a Jupiter-sized planet with an orbital period of 280 days that was discovered by

520-410: A probable planet orbiting between 86 and 158 AU from the star. Describing Microscopium as "totally unremarkable", astronomer Patrick Moore concluded there was nothing of interest for amateur observers. NGC 6925 is a barred spiral galaxy of apparent magnitude 11.3 which is lens-shaped, as it lies almost edge-on to observers on Earth, 3.7 degrees west-northwest of Alpha Microscopii. SN 2011ei ,

585-401: A quarter are ejected on hyperbolic orbits. The scattered disc might still be supplying the Oort cloud with material. A third of the scattered disc's population is likely to end up in the Oort cloud after 2.5 billion years. Computer models suggest that collisions of cometary debris during the formation period play a far greater role than was previously thought. According to these models,

650-450: A typical dynamically old comet with an origin in the Oort cloud could be C/2018 F4. Most of the comets seen close to the Sun seem to have reached their current positions through gravitational perturbation of the Oort cloud by the tidal force exerted by the Milky Way . Just as the Moon 's tidal force deforms Earth's oceans, causing the tides to rise and fall, the galactic tide also distorts

715-486: Is Gamma Microscopii of apparent magnitude 4.68, a yellow giant 2.5 times the Sun's mass located 223 ± 8 light-years distant. It passed within 1.14 and 3.45 light-years of the Sun some 3.9 million years ago, possibly disturbing the outer Solar System. Three star systems— WASP-7 , AU Microscopii and HD 205739 —have been determined to have planets , while other star —the Sun-like star HD 202628 — has

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780-464: Is a red dwarf which lies only 12.9 light-years from the Solar System . At magnitude 6.68, it is the brightest red dwarf in the sky. BO Microscopii is a rapidly rotating star that has 80% the diameter of the Sun. Nicknamed "Speedy Mic", it has a rotation period of 9 hours 7 minutes. An active star, it has prominent stellar flares that average 100 times stronger than those of

845-418: Is a curious concentration of long-period comets whose farthest retreat from the Sun (their aphelia ) cluster around 20,000 AU. This suggested a reservoir at that distance with a spherical, isotropic distribution. He also proposed that the relatively rare comets with orbits of about 10,000 AU probably went through one or more orbits into the inner Solar System and there had their orbits drawn inward by

910-443: Is a white star of apparent magnitude 4.7, and spectral type A1V. Theta and Theta Microscopii make up a wide double whose components are splittable to the naked eye. Both are white A-class magnetic spectrum variable stars with strong metallic lines, similar to Cor Caroli . They mark the constellation's specimen slide. Many notable objects are too faint to be seen with the naked eye. AX Microscopii, better known as Lacaille 8760 ,

975-486: Is hypothesized that 70,000 years ago Scholz's Star passed through the outer Oort cloud (although its low mass and high relative velocity limited its effect). During the next 10 million years the known star with the greatest possibility of perturbing the Oort cloud is Gliese 710 . This process could also scatter Oort cloud objects out of the ecliptic plane, potentially also explaining its spherical distribution. In 1984, physicist Richard A. Muller postulated that

1040-500: Is hypothesized that their ultimate origin lies in the Oort cloud, not in the scattered disc. Based on their orbits, it is suggested they were long-period comets that were captured by the gravity of the giant planets and sent into the inner Solar System. This process may have also created the present orbits of a significant fraction of the Jupiter-family comets, although the majority of such comets are thought to have originated in

1105-457: Is thought to encompass two regions: a disc-shaped inner Oort cloud aligned with the solar ecliptic (also called its Hills cloud ) and a spherical outer Oort cloud enclosing the entire Solar System . Both regions lie well beyond the heliosphere and are in interstellar space . The innermost portion of the Oort cloud is more than a thousand times as distant from the Sun as the Kuiper belt ,

1170-537: The Bayer designations Alpha through to Iota in 1756. A star in neighbouring Indus that Lacaille had labelled Nu Indi turned out to be in Microscopium, so Gould renamed it Nu Microscopii . Francis Baily considered Gamma and Epsilon Microscopii to belong to the neighbouring constellation Piscis Austrinus, but subsequent cartographers did not follow this. In his 1725 Catalogus Britannicus , John Flamsteed labelled

1235-465: The Beta Pictoris moving group , one of the nearest associations of stars that share a common motion through space. The Astronomical Society of Southern Africa in 2003 reported that observations of four of the Mira variables in Microscopium were very urgently needed as data on their light curves was incomplete. Two of them— R and S Microscopii —are challenging stars for novice amateur astronomers, and

1300-516: The Estonian astronomer Ernst Öpik proposed a reservoir of long-period comets in the form of an orbiting cloud at the outermost edge of the Solar System . Dutch astronomer Jan Oort revived this basic idea in 1950 to resolve a paradox about the origin of comets. The following facts are not easily reconcilable with the highly elliptical orbits in which long-period comets are always found: Oort reasoned that comets with orbits that closely approach

1365-406: The Kuiper cliff around 50 AU from the Sun (the orbit of Neptune averages about 30 AU and 177P/Barnard has aphelion around 48 AU). Long-period comets, on the other hand, travel in very large orbits thousands of AU from the Sun and are isotropically distributed. This means long-period comets appear from every direction in the sky, both above and below the ecliptic plane. The origin of these comets

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1430-491: The Oort cloud . Alpha Microscopii is also an ageing yellow giant star of spectral type G7III with an apparent magnitude of 4.90. Located 400 ± 30 light-years away from Earth, it has swollen to 17.5 times the diameter of the Sun. Alpha has a 10th magnitude companion, visible in 7.5 cm telescopes, though this is a coincidental closeness rather than a true binary system. Epsilon Microscopii lies 166 ± 5 light-years away, and

1495-599: The compound microscope , the Microscope's name had been Latinised by Lacaille to Microscopium by 1763. Microscope Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.150 via cp1114 cp1114, Varnish XID 919956653 Upstream caches: cp1114 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 08:41:36 GMT Oort cloud The cloud

1560-493: The equatorial coordinate system , the right ascension coordinates of these borders lie between 20 27.3 and 21 28.4 , while the declination coordinates are between −27.45° and −45.09°. The whole constellation is visible to observers south of latitude 45°N . Given that its brightest stars are of fifth magnitude, the constellation is invisible to the naked eye in areas with light polluted skies. French astronomer Nicolas-Louis de Lacaille charted and designated ten stars with

1625-400: The gravity of the planets. The Oort cloud is thought to occupy a vast space somewhere between 2,000 and 5,000 AU (0.03 and 0.08 ly) from the Sun to as far out as 50,000 AU (0.79 ly) or even 100,000 to 200,000 AU (1.58 to 3.16 ly). The region can be subdivided into a spherical outer Oort cloud with a radius of some 20,000–50,000 AU (0.32–0.79 ly) and

1690-426: The radial velocity method. WASP-7 is a star of spectral type F5V with an apparent magnitude of 9.54, about 1.28 times as massive as the Sun. Its hot Jupiter planet— WASP-7b —was discovered by transit method and found to orbit the star every 4.95 days. HD 202628 is a sunlike star of spectral type G2V with a debris disk that ranges from 158 to 220 AU distant. Its inner edge is sharply defined, indicating

1755-436: The scattered disc and the detached objects —three nearer reservoirs of trans-Neptunian objects . The outer limit of the Oort cloud defines the cosmographic boundary of the Solar System . This area is defined by the Sun's Hill sphere , and hence lies at the interface between solar and galactic gravitational dominion. The outer Oort cloud is only loosely bound to the Solar System and its constituents are easily affected by

1820-494: The Solar System have either already stopped functioning or are predicted to stop functioning before they reach the Oort cloud. In the 1980s, there was a concept for a probe that could reach 1,000 AU in 50 years, called TAU ; among its missions would be to look for the Oort cloud. In the 2014 Announcement of Opportunity for the Discovery program , an observatory to detect the objects in the Oort cloud (and Kuiper belt) called

1885-439: The Solar System. Short-period comets (those with orbits of up to 200 years) are generally accepted to have emerged from either the Kuiper belt or the scattered disc, which are two linked flat discs of icy debris beyond Neptune's orbit at 30 AU and jointly extending out beyond 100 AU. Very long-period comets, such as C/1999 F1 (Catalina) , whose orbits last for millions of years, are thought to originate directly from

1950-466: The Sun as part of the same process that formed the planets and minor planets . After formation, strong gravitational interactions with young gas giants, such as Jupiter, scattered the objects into extremely wide elliptical or parabolic orbits that were subsequently modified by perturbations from passing stars and giant molecular clouds into long-lived orbits detached from the gas giant region. Recent research has been cited by NASA hypothesizing that

2015-399: The Sun cannot have been doing so since the condensation of the protoplanetary disc, more than 4.5 billion years ago. Hence long-period comets could not have formed in the current orbits in which they are always discovered and must have been held in an outer reservoir for nearly all of their existence. Oort also studied tables of ephemerides for long-period comets and discovered that there

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2080-510: The Sun has an as-yet undetected companion, either a brown dwarf or a red dwarf , in an elliptical orbit within the Oort cloud. This object, known as Nemesis , was hypothesized to pass through a portion of the Oort cloud approximately every 26 million years, bombarding the inner Solar System with comets. However, to date no evidence of Nemesis has been found, and many lines of evidence (such as crater counts ), have thrown its existence into doubt. Recent scientific analysis no longer supports

2145-449: The Sun). The effects of the galactic tide are quite complex, and depend heavily on the behaviour of individual objects within a planetary system. Cumulatively, however, the effect can be quite significant: up to 90% of all comets originating from the Oort cloud may be the result of the galactic tide. Statistical models of the observed orbits of long-period comets argue that the galactic tide is

2210-489: The Sun, and are emitting energy mainly in the X-ray and ultraviolet bands of the spectrum. It lies 218 ± 4 light-years away from the Sun. AT Microscopii is a binary star system, both members of which are flare star red dwarfs. The system lies close to and may form a very wide triple system with AU Microscopii , a young star which has a planetary system in the making with a debris disk . The three stars are candidate members of

2275-419: The Sun, in the protoplanetary disc , and was then scattered far into space through the gravitational influence of the giant planets . No direct observation of the Oort cloud is possible with present imaging technology. Nevertheless, the cloud is thought to be the source that replenishes most long-period and Halley-type comets, which are eventually consumed by their close approaches to the Sun after entering

2340-450: The Sun. The point at which the Sun's gravity concedes its influence to the galactic tide is called the tidal truncation radius. It lies at a radius of 100,000 to 200,000 au, and marks the outer boundary of the Oort cloud. Some scholars theorize that the galactic tide may have contributed to the formation of the Oort cloud by increasing the perihelia (smallest distances to the Sun) of planetesimals with large aphelia (largest distances to

2405-506: The area of the Oort cloud. Voyager 1 , the once fastest and farthest of the interplanetary space probes currently leaving the Solar System, will reach the Oort cloud in about 300 years and would take about 30,000 years to pass through it. However, around 2025, the radioisotope thermoelectric generators on Voyager 1 will no longer supply enough power to operate any of its scientific instruments, preventing any further exploration by Voyager 1. The other four probes currently escaping

2470-501: The continued existence of the Oort cloud after billions of years. Because it lies at the interface between the dominion of Solar and galactic gravitation, the objects comprising the outer Oort cloud are only weakly bound to the Sun. This in turn allows small perturbations from nearby stars or the Milky Way itself to inject long-period (and possibly Halley-type ) comets inside the orbit of Neptune . This process ought to have depleted

2535-498: The east, Sagittarius to the west, and Indus to the south, touching on Telescopium to the southwest. The recommended three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Mic". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of four segments ( illustrated in infobox ). In

2600-473: The formation of a non-volatile crust on the surface. Dynamical studies of hypothetical Oort cloud comets have estimated that their occurrence in the outer-planet region would be several times higher than in the inner-planet region. This discrepancy may be due to the gravitational attraction of Jupiter , which acts as a kind of barrier, trapping incoming comets and causing them to collide with it, just as it did with Comet Shoemaker–Levy 9 in 1994. An example of

2665-590: The galactic tide or stellar perturbations alone, and that the most likely cause would be a Jupiter -mass object in a distant orbit. This hypothetical gas giant was nicknamed Tyche . The WISE mission , an all-sky survey using parallax measurements in order to clarify local star distances, was capable of proving or disproving the Tyche hypothesis. In 2014, NASA announced that the WISE survey had ruled out any object as they had defined it. Space probes have yet to reach

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2730-404: The gravitational pulls of both passing stars and the Milky Way itself. These forces served to moderate and render more circular the highly eccentric orbits of material ejected from the inner Solar System during its early phases of development . The circular orbits of material in the Oort disc are largely thanks to this galactic gravitational torquing. By the same token, galactic interference in

2795-548: The idea that extinctions on Earth happen at regular, repeating intervals. Thus, the Nemesis hypothesis is no longer needed to explain current assumptions. A somewhat similar hypothesis was advanced by astronomer John J. Matese of the University of Louisiana at Lafayette in 2002. He contends that more comets are arriving in the inner Solar System from a particular region of the postulated Oort cloud than can be explained by

2860-454: The inner Solar System. The cloud may also serve the same function for many of the centaurs and Jupiter-family comets . By the turn of the 20th century, it was understood that there were two main classes of comet: short-period comets (also called ecliptic comets) and long-period comets (also called nearly isotropic comets). Ecliptic comets have relatively small orbits aligned near the ecliptic plane and are not found much farther than

2925-426: The motion of Oort bodies occasionally dislodges comets from their orbits within the cloud, sending them into the inner Solar System . Based on their orbits, most but not all of the short-period comets appear to have come from the Oort disc. Other short-period comets may have originated from the far larger spherical cloud. Astronomers hypothesize that the material presently in the Oort cloud formed much closer to

2990-476: The nearly spherical shape of the outer Oort cloud. On the other hand, the Hills cloud , which is bound more strongly to the Sun, has not acquired a spherical shape. Recent studies have shown that the formation of the Oort cloud is broadly compatible with the hypothesis that the Solar System formed as part of an embedded cluster of 200–400 stars. These early stars likely played a role in the cloud's formation, since

3055-422: The number of close stellar passages within the cluster was much higher than today, leading to far more frequent perturbations. In June 2010 Harold F. Levison and others suggested on the basis of enhanced computer simulations that the Sun "captured comets from other stars while it was in its birth cluster ." Their results imply that "a substantial fraction of the Oort cloud comets, perhaps exceeding 90%, are from

3120-472: The number of collisions early in the Solar System's history was so great that most comets were destroyed before they reached the Oort cloud. Therefore, the current cumulative mass of the Oort cloud is far less than was once suspected. The estimated mass of the cloud is only a small part of the 50–100 Earth masses of ejected material. Gravitational interaction with nearby stars and galactic tides modified cometary orbits to make them more circular. This explains

3185-421: The orbits of bodies in the outer Solar System . In the charted regions of the Solar System, these effects are negligible compared to the gravity of the Sun, but in the outer reaches of the system, the Sun's gravity is weaker and the gradient of the Milky Way's gravitational Galactic Center compresses it along the other two axes; these small perturbations can shift orbits in the Oort cloud to bring objects close to

3250-504: The original protosolar cloud, a conclusion also supported by studies of granular size in Oort-cloud comets and by the recent impact study of Jupiter-family comet Tempel 1 . The Oort cloud is thought to have developed after the formation of planets from the primordial protoplanetary disc approximately 4.6 billion years ago. The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to

3315-428: The other two, U and RY Microscopii , are more difficult still. Another red giant, T Microscopii , is a semiregular variable that ranges between magnitudes 7.7 and 9.6 over 344 days. Of apparent magnitude 11, DD Microscopii is a symbiotic star system composed of an orange giant of spectral type K2III and white dwarf in close orbit, with the smaller star ionizing the stellar wind of the larger star. The system has

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3380-476: The outer Oort cloud. Other comets modeled to have come directly from the outer Oort cloud include C/2006 P1 (McNaught) , C/2010 X1 (Elenin) , Comet ISON , C/2013 A1 (Siding Spring) , C/2017 K2 , and C/2017 T2 (PANSTARRS) . The orbits within the Kuiper belt are relatively stable, and so very few comets are thought to originate there. The scattered disc, however, is dynamically active, and is far more likely to be

3445-489: The outer cloud are separated by a significant fraction of 1 AU, tens of millions of kilometres. The outer cloud's total mass is not known, but assuming that Halley's Comet is a suitable proxy for the nuclei composing the outer Oort cloud, their combined mass would be roughly 3 × 10 kilograms (6.6 × 10  lb), or five Earth masses. Formerly the outer cloud was thought to be more massive by two orders of magnitude, containing up to 380 Earth masses, but improved knowledge of

3510-439: The pace of accretion and collision slowed and depletion began to overtake supply. Models by Julio Ángel Fernández suggest that the scattered disc , which is the main source for periodic comets in the Solar System, might also be the primary source for Oort cloud objects. According to the models, about half of the objects scattered travel outward toward the Oort cloud, whereas a quarter are shifted inward to Jupiter's orbit, and

3575-511: The place of origin for comets. Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs . These centaurs are then sent farther inward to become the short-period comets. There are two main varieties of short-period comets: Jupiter-family comets (those with semi-major axes of less than 5 AU) and Halley-family comets. Halley-family comets, named for their prototype, Halley's Comet , are unusual in that although they are short-period comets, it

3640-466: The principal means by which their orbits are perturbed toward the inner Solar System. Besides the galactic tide , the main trigger for sending comets into the inner Solar System is thought to be interaction between the Sun's Oort cloud and the gravitational fields of nearby stars or giant molecular clouds . The orbit of the Sun through the plane of the Milky Way sometimes brings it in relatively close proximity to other stellar systems . For example, it

3705-477: The protoplanetary discs of other stars." In July 2020 Amir Siraj and Avi Loeb found that a captured origin for the Oort Cloud in the Sun's birth cluster could address the theoretical tension in explaining the observed ratio of outer Oort cloud to scattered disc objects, and in addition could increase the chances of a captured Planet Nine . Comets are thought to have two separate points of origin in

3770-467: The relations of Abell clusters 3693 and 3705 in the same field are unclear. The Microscopids are a minor meteor shower that appear from June to mid-July. Microscopium lies in a region where Ptolemy had listed six 'unformed' stars behind the tail of Piscis Austrinus. Al-Sufi did not include these stars in his revision of the Almagest , presumably because he could not identify them. Microscopium

3835-449: The scattered disc. Oort noted that the number of returning comets was far less than his model predicted, and this issue, known as "cometary fading", has yet to be resolved. No dynamical process is known to explain the smaller number of observed comets than Oort estimated. Hypotheses for this discrepancy include the destruction of comets due to tidal stresses, impact or heating; the loss of all volatiles , rendering some comets invisible, or

3900-425: The size distribution of long-period comets has led to lower estimates. No estimates of the mass of the inner Oort cloud have been published as of 2023. If analyses of comets are representative of the whole, the vast majority of Oort-cloud objects consist of ices such as water , methane , ethane , carbon monoxide and hydrogen cyanide . However, the discovery of the object 1996 PW , an object whose appearance

3965-598: The sparser, outer cloud and yet long-period comets with orbits well above or below the ecliptic continue to be observed. The Hills cloud is thought to be a secondary reservoir of cometary nuclei and the source of replenishment for the tenuous outer cloud as the latter's numbers are gradually depleted through losses to the inner Solar System. The outer Oort cloud may have trillions of objects larger than 1 km (0.6 mi), and billions with diameters of 20-kilometre (12 mi). This corresponds to an absolute magnitude of more than 11. On this analysis, "neighboring" objects in

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4030-440: The stars 1, 2, 3 and 4 Piscis Austrini, which became Gamma Microscopii, HR 8076 , HR 8110 and Epsilon Microscopii respectively. Within the constellation's borders, there are 43 stars brighter than or equal to apparent magnitude  6.5. Depicting the eyepiece of the microscope is Gamma Microscopii , which—at magnitude of 4.68—is the brightest star in the constellation. Having spent much of its 620-million-year lifespan as

4095-455: Was consistent with a D-type asteroid in an orbit typical of a long-period comet, prompted theoretical research that suggests that the Oort cloud population consists of roughly one to two percent asteroids. Analysis of the carbon and nitrogen isotope ratios in both the long-period and Jupiter-family comets shows little difference between the two, despite their presumably vastly separate regions of origin. This suggests that both originated from

4160-634: Was introduced in 1751–52 by Lacaille with the French name le Microscope , after he had observed and catalogued 10,000 southern stars during a two-year stay at the Cape of Good Hope . He devised fourteen new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. All but one honoured instruments that symbolised the Age of Enlightenment . Commemorating

4225-537: Was not well understood, and many long-period comets were initially assumed to be on parabolic trajectories, making them one-time visitors to the Sun from interstellar space. In 1907, Armin Otto Leuschner suggested that many of the comets then thought to have parabolic orbits in fact moved along extremely large elliptical orbits that would return them to the inner Solar System after long intervals during which they were invisible to Earth-based astronomy. In 1932,

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