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deep space

term in astronomy

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Deep space objects are a term commonly used in amateur astronomy. Generally speaking, deep space objects refer to celestial objects celestial bodies (Planets comet , asteroids) and fixed star Other celestial bodies. Most of these objects are invisible to the naked eye, only the brighter ones (such as M31 Andromeda Galaxy And M42 Orion nebula ）It can be seen by the naked eye, but it is rare. More than 100 deep space objects can be used Binoculars See, for example, most of the Messier Nebula Cluster Catalogue compiled by French astronomer Messier in the 18th century celestial bodies 。 If there is an astronomical telescope, the number of deep space objects that can be seen will increase significantly. A considerable number of deep space objects can be photographed through astronomical photography.

Chinese name: deep space
Foreign name: Deep sky object
Abbreviation: DSO

Category: Astronomical name
Discipline: astronomy
Classification: cluster 、 Nebula 、 Galaxy etc.

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Aligned Messier 87 （ M87 ）This is a huge star in the spring night Elliptical galaxy , 55 million people away Light year 。 In the eyepiece, you will see a small, shapeless, very weak gray smoke spot emerging in the light spots of several stars. Although finding it successfully will also bring an exciting sense of achievement, many novices will be disappointed by this scene. "Are all galaxies like this? This is not like the picture in the book at all!" Proved the fact that human eyes are not suitable for working in the dark. This is totally different from the operation of the camera in low brightness. People are diurnal animals evolved from sunlight; People's eyes are not specially designed for night. The galaxies you see with the naked eye can never be as spectacular as the pictures everywhere in the book. But that's more challenging. Many deep space objects can indeed show a large number of surprising details under long-term and appropriate observation - even our inborn imperfect eyes can see them.

telescope The effect on deep space objects is completely different from that on the moon, planets and ground scenery. For the latter, its main function is to magnify remote details. For deep space objects, the main function of telescopes is to collect more light for your insensitive eyes. The main reason for not seeing deep space objects is not that they are too small, but that they are too dark.

Therefore, deep space celestial body observation has its unique skills. All techniques are designed to help the eye see something that is almost completely dark. Here are some key points that every observer should know.

Sky brightness

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One of the most important factors affecting the observation of deep space objects is light pollution 。 Of all the objects we can list, it has the greatest impact on dim surface objects. The influence of dark sky even exceeds that of telescope aperture; A small telescope can be seen in the countryside Dark nebula And the number of galaxies Large telescope A lot more.

Some people say that even if you live in an area with serious light pollution, you can still see deep space objects through the sky light, and thus enjoy yourself. Jenny Worsnopp, an observer in New York Manhattan Almost all of them were found on the roof of Messier object ； Massachusetts ， Cambridge Tony Flanders, an amateur astronomer of City Park We have achieved this goal. Just remember, don't blame yourself or your telescope for seemingly mediocre results. Better still, remember to take your telescope to the country villa.

Dark fitness

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The human eye needs some time to adapt to the darkness. As long as you walk into a dark environment, the pupil of your eye can expand to the maximum extent in just a few seconds. But the most important part of dark adaptation is related to chemical changes on the retina, which usually takes a long time.

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After spending 15 minutes in total darkness, you may think your eyes have fully adapted to night vision. But in fact, your eyes' sensitivity to starlight can increase by 2 magnitudes in the next 15 minutes - the brightness difference is 6 times. After 90 minutes, or even longer, the dark adaptation is still increasing very slowly. So don't expect to be able to see the dim objects well in the first half hour or even less of the observation. In fact, complete darkness is impossible to achieve. Even without considering light pollution You still need some light to see what you are doing. Astronomers have long used the dim red color Flashlight Because red light does the least damage to night vision ability. In the near dark environment, you use retina On Rod-shaped cell Look at things, these cells are almost invisible visible light The red part of the band. You can see the red light, which is in the retina Cone cell At work; Cone cells can help you distinguish different colors during the day. (You have three kinds Cone cell ——Red, green and blue - but only one Rod-shaped cell , insensitive to red light.) You can use red cone cells to read star map And operating equipment to protect your rod cells from being sensitive to seeing things in the eyeglass.

Tie a piece of red paper in front of the flashlight with a rubber band, so that you can get dim and diffuse light. You can also replace a two battery flashlight with a bulb suitable for three to four battery flashlights to get darker and redder light. However, more than these Traditional techniques Better choice is red LED（ LED ） Flashlight 。 Its high-purity, dark red light can more effectively distinguish the range of action of rod and cone cells. LED flashlight 。

Another secret to protecting dark fitness is to observe with one eye and read the star map with the other eye. When there is no observation, close the observation eye, or find an eye mask to cover it.

Beagle Of Spiral galaxy (M51), on the left is an 8-inch machine used by veteran observer Roger N. Clark Cassegrain telescope On the right side of the sketch made in the perfect dark sky is the picture taken by the 0.9 meter (36 inch) telescope equipped with CCD on Mount Kitt, Arizona. This is the first observation with eyes Vortex structure Of“ Spiral nebula ”。 Provided by Roger Clark and NOAO respectively.

Main categories

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cluster

Open cluster

Pleiades

Globular cluster

Nebula

Supernova wreckage

Galaxy

a quasar

note appended:

A total of 110 such objects have been catalogued messier Nebula cluster Table;

and New catalog of nebulae and clusters (New General Catalog; NGC) includes nearly 8000 deep space objects.

see Index catalogue 、 Uppsala Uppsala General Catalog (UGC).

Self compiled by various astronomical research institutions Catalogue .

Discovery history

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deep space ^[1]

Long ago, as long as it was not cloudy, people could see stars in the night sky. In prehistoric times, most parts of the earth had almost no light pollution Our ancestors can see very dark starlight, some of which are classified as deep space objects by people today. In this way, some of these celestial bodies are as old as our human history. Of these "celestial bodies", the most prominent is of course a galaxy, our own Milky Way; However, we will not count it in. Similarly, we will not consider the most significant "movement" cluster ， ursa major Star cluster, this star cluster is composed of“ Big Dipper ”Most of the stars in the constellation Ursa Major form the most prominent part. First of all, most modern people do not regard them as "deep space objects". Second, their essence, such as the Milky Way is a galaxy, and the stars in the constellation Ursa Major are a physical cluster, which is gradually clear until modern times. Therefore, this kind of neglect is appropriate.

Some bright star clusters must have been known for a long time, even earlier than the recorded history. Of course, it includes Taurus In Pleiades (M45) and Bistar cluster They are also very prominent in the naked eye and have been recorded very early (for example, the earliest accurate record of the Pleiades cluster is Hesiod from about 1000 to 700 BC（ Hesiod ）Left). In the Southern Hemisphere, two Magellan Cloud （LMC -- Large Magellanic Cloud , and SMC -- Mai Zhe Lunyun) were also discovered long ago, but few ancient records have been preserved in the southern hemisphere.

Likely Aristotle （ Aristotle ）About 325 BC Open cluster M41 made ancient observation records; This makes the cluster the darkest object in ancient observational records. According to Burnham, according to P A copy of J E. Gore wrote a statement that Aristotle may also have observed the Cygnus M39 , describing it as a "cometary object". Hipparchus, a famous Greek astronomer, observed in Rhodes from 146 to 127 BC. He was the first to write Catalogue Astronomers; In 134 B.C., he observed a scorpio It may be that this event prompted him to compile this catalog. His catalog includes two "cloud like objects", Praesepe (M44) and Perseus Binary cluster The latter is now called Perseus h+chi (NGC 869+884, not in the Messier catalog).

Ptolemy（ Ptolemy ）, in the Great Syntaxas (commonly known as Astronomy (Almagest), listed 7 celestial bodies, of which 3 are general constellations, not physical ones, and 2 are inherited from Hipparchus (M44 and Perseus binary cluster ）And two new ones: one is the nebula behind the Scorpio Stinger, which is now certified as remarkable Open cluster M7 , which was proposed by some modern authors as“ Ptolemys Cluster (Ptolemy's Cluster) ", and the other is a later star cluster, which is now classified as Melotte 111 (but not in the Messier catalog).

The first real "nebula" object discovered and recorded is andromeda Galaxy (M31), observed around 905 AD, was observed in 964 AD Persia Astronomer Al Sufi recorded it in his Book of Fixed Stars. He also mentioned a "nebulous star" located at Sail base Delta The north side of the star is more than 2 degrees, which is also a very significant open star cluster IC 2391, Omicron Vela. The book also includes six objects of Ptolemy, and Foxy A new "constellation" (actually Brocchi cluster , Collinder 399, also nicknamed“ Coat hanger cluster ”）Therefore, he recorded a total of 9 celestial bodies.

Different from other deep space objects mentioned here, China and North America The ancient astronomers observed and recorded a Supernova The outbreak of; This supernova created Crab Nebula (M1), one of the most interesting deep space objects.

No new deep space objects were discovered until 1519, Magellan（ Magellan ）The report said that we saw two Magellan Cloud 。 This made the year 1609 Galileo (Galileo) Before the telescope was introduced into astronomy, the total number of deep space objects observed by people reached 11, although Al Sufi's work was not known by most people at that time. Through the telescope, Galileo find Praesepe (M44) is not a nebula, but a star cluster. Nicholas Claude Fabrici de Peiresc (1580-1637) discovered the first true nebula in 1610, Orion Nebula M42 This is also the first deep space object discovered with a telescope. Catholic Church Astronomer J- B. Cysatus (1588-1657) independently discovered M42 in 1611, but for a long time, this object was not known to the public. Shortly thereafter, in 1612, Simon Marius (1570-1624) discovered (rediscovered independently) andromeda Galaxy Andromeda Nebula ，M31）。

Giovanni Batista Hodierna (1597-1660), the court astronomer of the Duke of Montechiaro, prepared a report containing 40 entries Catalogue These were discovered by him with a simple Galilean refractor with a magnification of 20 times, including 19 real cloud like objects. This catalog was published in Palermo in 1654. However, this history was long forgotten, and was rediscovered only in the early 1980s (published by Serio, Indorato, Nastasi in the Journal of the History of Astronomy, Volume 45 (February 1985) and Volume 50 (August 1986)). This catalog includes independently rediscovered Andromeda Nebula （M31）， Orion Nebula （ M42 ）, and Brocchi cluster , first described Perseus Alpha Moving cluster It also includes at least 9 objects (probably 13, or even 15) actually discovered by him: it is confirmed that M6 is the object discovered by him, M36，M37，M38，M41， M47 ， NGC 2362，NGC 6231， And NGC 6530 (vs Lagoon Nebula M8 star clusters), and M33 is probably discovered by him, M34 NGC 752 and NGC 2451. NGC 2169 and NGC 2175 may be discovered by him.

Christiaan Huygens（ Huygens ）Independently rediscovered in 1656 Orion Nebula M42 This discovery made this celestial body widely known; He also found Orion in the nebula Quadrangle Three stars in the.

Johan Hevel or Hevelke from Dantzig (the more familiar name is Hevelius（ Herville ）, 1611-87) prepared a

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4-star Catalogue - Prodomus Astronomiae, and his star map Uranographia was published together after his death. He also summarized a list of 16 items, two of which are real celestial bodies（ andromeda Galaxy M31 and Praesepe M44）， The other 14 are constellations or do not exist at all. Derham and Messier spent a lot of time looking for these "nebulae"; Messier believes he has identified one pair of ursa major M 40 - Now we know that what he recognized is probably not the pair of stars that Hevelius saw. Havelius was the first to see M22 But it is generally believed that this person Globular cluster It was discovered by Abraham Ihle in 1665.

Published in 1712 by John Flamsteed (1646-1719) and revised in 1725 Catalogue In the "Historia Coelestis Britannica", several "nebulae" and "nebulous stars" are mentioned. Most of them were known objects at that time (later cluster Mel 111， Perseus h+chi Binary cluster ，M31， M42 ）There are also three independently discovered objects, including the rediscovered unknown Hodierna objects NGC 6530 (associated with M8) and M41, as well as an object he first discovered himself, Kylin mountain NGC 2244 (and The Rosette Nebula NGC 2237-9 is not in the Messier catalog).

Gottfried Kirch (1639-1710), an astronomical observer in Berlin, is famous for his observations of stars and comets. He discovered M11 in 1681 and M5 in 1702.

Edmond Halley（ Harley ）(1656-1742) In 1715, on the Philosophical Transactions of the Royal Society, a paper containing six "light points and facula ”List, which includes his own discovery of globular nebulae Centaur Omega (discovered when traveling on Helena Peak in 1677) and M13 (discovered in 1714), as well as previously known celestial bodies M42 ，M31， M22 , and M11.

Jean Jacques Dortous de Mairan (1678-1771), discovered Orion nebula The nebulous matter around a star on the north side has become known to all M43 (This discovery was published in 1733.). Shortly thereafter, John Bevis (1695-1771) discovered Crab Nebula M1 。 He also created a star map He called it Britain Uranographia Britannica was completed in 1750, but due to the bankruptcy of the publisher, only one or two printed copies were produced Catalogue It has never been published. Messier must have got a copy of this star map, because he is doing some research on M1, M11，M13，M22，M31， As well as the description of M35, "English Atlas" has been mentioned many times. Strangely, Kenneth Glyn Jones attributed the discovery of M35 to de Cheseaux in 1746, although Bevis seemed to have seen it before, because it appeared in his star map.

William Derham (1657-1735) published a list of 16 cloud like objects in the Royal Society's Philosophical Transactions in 1733, of which 14 were from the list of Havelius, and the other two were from the list of Halley. Only two of them are real (M31 and M7), and the others are either nonexistent or uninteresting. These false objects confuse other astronomers (including Messier) who use this list; This list dates back to 1734 French Academy of Sciences It was published again in the Collection of Essays and included in the book Discours sur la Figure des Astres by de Maupertuis in 1742.

In about 1746, Philippe Loys de Cheseaux (1718-51) observed several cluster And "nebulous stars" Catalogue 。 According to Kenneth Glyn Jones and the Webb Society Deep Sky Observer's Handbook, Volume 3 (open and globular clusters), 8 of them are first discovered objects: IC 4665 (No. 2, uncertain), NGC 6633 (No. 3), M16 (No. 4), M25 (No. 5), M35 (No. 12, but see John Bevis' comments), M71 (No. 13), M4 (No. 19), and M17 (No. 20). In addition, he independently rediscovered M6 (No. 1), NGC 6231 (No. 9) and M22 (No. 17). De Cheseaux gave the list to Reaumur, who French Academy of Sciences However, this list has not been published in other forms. This Catalogue It was not until 1884 that more people began to know about it after investigating it in Bigourdan. In addition to observing the cloud shape in the sky facula In addition, de Cheseaux may be the first to express Aubers paradox (Olbers' paradox). Jean Dominique Maraldi (1709-88), also known as Maraldi II, discovered two globular clusters: M15 on September 7, 1746, M2 on September 11, 746. Le Gentil (full name Guillaume Joseph Hyacinthe Jean Baptiste Le Gentil de la Galaziere, 1725-92) discovered M32 on October 29, 1749, andromeda Galactic Companion galaxy 。 He also found out that year Gas nebula M8， I.e Lagoon Nebula (In this nebula cluster It has been discovered by Flamsteed before (see above), and globular cluster NGC 6712 may also be discovered. He also independently discovered the Hodierna objects M36 and M38. Abbe Nicholas Louis de la Caille (aka Lacaille, 1713-62) traveled to South Africa And observed the stars and deep space objects in the southern sky, created several southern sky constellations (most of which are still in use), and compiled a table of 42 entries of the southern sky deep space objects, 33 of which are real objects. Twenty five of them were first discovered, and at least two of them were independently rediscovered. The first objects discovered by Lacaille mainly include Ship base Eta nebula NGC 3372, globular cluster 47 Tucanae （NGC 104）， Large Magellanic Cloud In tarantula nebula NGC 2070， as well as Spiral galaxy M83 This is the first discovery Local galaxy group Other galaxies. This is Charles Messier（ messier ）(1730-1817) began to write his Catalogue The last deep space object previously discovered. In 1764, Messier discovered M3 This is the first deep space object discovered by him. Over the next decade, Charles Messier searched for star clusters and nebulous objects alone. During this period, he discovered 27 celestial bodies, 25 of which are real deep space objects (the other two are Sagittarius Nebula M24 and double star M40).

From then on until 1781, Messier himself also discovered 18 other cloud like objects (17 deep space objects, plus one Quadrangle M73）， The total number of objects he first discovered reached 43, and another 20 objects were discovered independently and jointly.

At the end of 1774, Johann Elert Bode (1747-1826) successfully joined in the search for new cloud like objects: he discovered M81 and M82 on the last day of the year (December 31), and later discovered three other objects (M53 in 1775, M92 in 1777, and M92 in 1779 M64 ）。 Bode compiled a deep space object with 75 entries Catalogue , published on the Astronomisches Jahrbuch in 1779 in 1777, with the title of "General List of Cloudy Stars and Clusters Discovered to Date". However, according to Kenneth Glyn Jones, this list is full of non-existent celestial bodies and constellations collected from Hevelius and others; It contains only about 50 real objects. The two objects he later discovered, M92 and M64, were published in the 1782 Jahrbuch almanac at the end of 1779. The other two objects, M48 and IC 4665, jointly discovered by Bode, were published in his star map And star catalogue - Vorstellung der Gestrine, published in 1782. About five years later, in 1779, Messier and Bode were still actively writing their Catalogue Five other astronomers also joined the "club" with their successful discovery of deep space objects: Toulouse Antoine Darquier de Pellepoix (Darquier) of Annular nebula M57， Earlier than Messier; They all found it when tracking the comet (Comet Bode in 1779). English astronomer Edward Pigott (1753-1824) discovered M64 on March 23, 1779, only 12 days earlier than Bode (April 4, 1779), and nearly a year earlier than Messier's independent discovery of it on March 1, 1780. Johann Gottfried Koehler (or Kö hler, 1745-1801), who independently discovered M81 and M82 between 1772 and 1778 (probably earlier than Bode), found M67 on April 11, 1779 at the latest in this year. When tracking Bode's comet in 1779, he found M59 and M60. When Messier found another M58 in this area, Barnabus Oriani (1752-1832) was the first to find M61. Koehler published a catalog of 20 entries in 1779. Finally, Messier's friend Pierre Mechain (1744-1804) began his career of astronomical observation and discovered M63 on June 14, 1779, which was the first celestial body discovered by him. Later, Mechain discovered about 25 objects for the first time. Because of his close cooperation with Charles Messier in observation, most of these objects were listed in Messier Catalogue in Because he did tell Messier all his discoveries, in 1947 Helen Sawyer Hogg decided to add the other three objects to the Messier catalog (M105 to M107 ）。

As an important part in the history of deep space discovery, the final version of the Messier catalog, including 103 celestial bodies, was published in France in 1784 in 1781 Astronomical almanac (Connaisance des Temps). Some personal notes of Messier and Mechain's letter to Bernoulli on May 6, 1783 mentioned that celestial bodies were expanded to Messier Catalogue The total number of celestial bodies has reached 110, all of which are real celestial bodies (although four celestial bodies have been missing for more than a century, and there are still some disputes about M102 that have not been settled yet). The catalog includes most nebulae discovered before April 1782, cluster And galaxies, of which M107 is the last discovered object in Messier (discovered by Pierre Mechain).

The Messier catalog did give the great German British astronomer Friedrich Wilhelm (William) Herschel herschel ）(1738-1822) left a deep impression when he discovered Neptune And gradually become famous. On December 7, 1781, Herschel got a copy of Messier from his friend William Watson Catalogue A copy of. At that time, he was an organ player in Bath (he didn't give up this job until May 1782), and a skilled telescope maker. On August 28, 1789, he assembled a huge telescope with a 48 inch diameter and a 40 foot focal length (he found that Saturn A new satellite of, Enceladus ）, and used this telescope to carry out a large-scale search in the visible sky area of Britain (namely the northern sky). In three steps, Herschel published a catalog of more than 2500 objects, most of which are real deep space objects. He used the best telescope at that time, so there was no competitor at all. His observation was made by his sister Caroline Lucretia Herschel（ Caroline ． herschel ）(1750-1848). She was also a passionate observer. She found Herschel Catalogue Many of cluster And nebulae (including M110 independently rediscovered, i.e. H V.18, objects discovered by Messier 10 years ago, but not included in the catalog; And independently rediscovered missing Messier Open cluster M48 H VI.22), and 8 comets were also found.

William Herschel classified cloud like objects into eight categories: Bright nebula Dark nebula Extremely dark nebula Planetary nebula A very dense cluster of rich stars composed of large (i.e., bright and dark) stars compact cluster The loose and sparse star clusters composed of stars were not clear about the nature of these objects at that time, so this classification has more historical significance today.

William (and Caroline) Herschel actually discovered almost all the celestial bodies in the northern sky around 1800. However, the southern hemisphere is still waiting for people to explore. James Dunlop (1795-1848) made the first large-scale observation in the southern hemisphere after Lacaille. He and Sir Thomas Makdougall Brisbane Brisbane The owner of the Observatory (1823-1827) came to Australia together in 1821 new south wales , where he wrote a star map（ Brisbane Catalogue (Brisbane Catalog), including more than 7000 stars in the southern sky. He compiled the deep space objects discovered at that time into a Catalogue of Southern Nebula Clusters Observed in New South Wales with 629 entries. This catalog was given to William herschel His son, John Herschel herschel ）And was published by him in the Royal Society in 1827. For this work, Dunlop won the gold medal of the Royal Astronomical Society, and French Academy of Sciences Lalander Award. However, these awards could not cover up a large number of "non-existent" objects in his catalog, as well as the poor description of objects, so that it was almost impossible to verify them accurately later: only about half of the entries could be associated with real objects.

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John Frederick William (John) Herschel (1792-1871) inherited his father's work, published in 1833 Catalogue 525 new entries (Northern Celestial Objects) have been added to. But John Herschel also wanted to write a catalogue of the southern sky. On November 13, 1883, he and his family went on a journey Cape of Good Hope, South Africa The passenger ship arrived at the destination on March 4, 1834. In the following days, he focused on studying the southern sky. He compiled a catalog of 1713 entries of the cloud like objects observed in the southern sky, which was published in 1847. Apparently, he compiled the discoveries of him and his father, as well as the deep space objects discovered by others, into his total of more than 5000 items Catalogue (General Catalog). Herschel's work ultimately gave cluster ）The great discovery era of. However, it will take a long time to reveal the nature of different deep space objects, and new research methods (especially photography and spectral analysis Art): The cloud and fog essence of "real" nebula was revealed by William Huggins (1824-1910), a British amateur astronomer and pioneer of spectral analysis, in the 1860s. It was not until the 1920s that Edwin Hubble (1889-1953) really revealed that the essence of galaxies was actually related to ours Galaxy The same independent "island universe".

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The Big Dipper and Deep Space Objects

The Big Dipper is a famous constellation easily recognized in the northern sky, and many people regard it as a plow or a carriage. Along its familiar lines, there are many famous bright nebulae, which stand out in this carefully constructed starry sky scene. They all come from Messier catalog On the left are two spiral galaxies M101 and M51, which are far away from the Milky Way. They are cosmic windmills and eddies, respectively. On the right is M108, a distant spiral galaxy facing us, and a planetary nebula M97, which is close to us and looks like an owl's face. This image was taken on January 16, and the wonderful thing is that it also contains an additional object passing by temporarily, that is, Comet Katarina (C/2013US10) visible along the handle.^[1]

Comet Lemmon and Deep Space Objects

Comet Lemmon has swept over the ecliptic plane, headed for the outer solar system, and disappeared in the night sky of the Earth. At this position about 16 light minutes (2 astronomical units) away from the sun, it is still waving its greenish comet head. It is located on the right in the 4-degree telescope image taken last Saturday. At the same time, many deep sky clusters and nebulae in Cassiopeia can be seen. In fact, this rich background sky is typical in the crowded star field of the Milky Way. Near the center of the image is the open star cluster M52, about 5000 light-years away. About 11000 light-years away, the red glowing nebula NGC 7635 at the lower left of M52 is named Bubble Nebula because of its appearance. The fading Comet Lemmon is not the only object in the foreground. The dim track on the right is a satellite, which passes through this field of view during a long exposure period. It shines in the sunlight, but disappears when it passes the shadow of the earth.^[2]

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