Asterism (astronomy)

In observational astronomy, an asterism is a popularly-known pattern or group of stars that can be seen in the night sky. This colloquial definition[a] makes it appear quite similar to a constellation,[1] but they differ mostly in that a constellation is an officially recognized area of the sky, while an asterism is a visually obvious collection of stars and the lines used to mentally connect them; as such, asterisms do not have officially determined boundaries and are therefore a more general concept which may refer to any identified pattern of stars. This distinction between terms remains somewhat inconsistent, varying among published sources. An asterism may be understood as an informal group of stars within the area of an official or defunct former constellation.[2] Some include stars from more than one constellation.

Asterisms range from simple shapes of just few stars to more complex collections of many bright stars. They are useful for people who are familiarizing themselves with the night sky. For example, the asterisms known as The Plough (Charles' Wain, the Big Dipper, etc.) comprises the seven brightest stars in the International Astronomical Union (IAU) recognised constellation Ursa Major. Another is the asterism of the Southern Cross, whose recognised constellation is Crux (crux is an area of the night sky in which the Southern Cross is located).

Collinder 399
This picture of Brocchi's Cluster (the Coathanger), an asterism in the constellation Vulpecula, was taken through binoculars

Background of asterisms and constellations

In many early civilizations, it was already common to associate groups of stars in connect-the-dots stick-figure patterns; some of the earliest records are those of the Babylonians. This process was essentially arbitrary, and different cultures have identified different constellations, although a few of the more obvious patterns tend to appear in the constellations of multiple cultures, such as those of Orion and Scorpius. As anyone could arrange and name a grouping of stars there was no distinct difference between a constellation and an asterism. e.g. Pliny the Elder (23–79 AD) in his book Naturalis Historia refers and mentions 72 asterisms.[3]

A general list containing 48 constellations likely began to develop with the astronomer Hipparchus (c. 190 – c. 120 BC ), and was mostly accepted as standard in Europe for 1,800 years. As constellations were considered to be composed only of the stars that constituted the figure, it was always possible to use any leftover stars to create and squeeze in a new grouping among the established constellations.

Furthermore, exploration by Europeans to other parts of the globe exposed them to stars unknown to them. Two astronomers particularly known for greatly expanding the number of southern constellations were Johann Bayer (1572–1625) and Nicolas Louis de Lacaille (1713–1762). Bayer had listed twelve figures made out of stars that were too far south for Ptolemy to have seen; Lacaille created 14 new groups, mostly for the area surrounding South Celestial Pole. Many of these proposed constellations have been formally accepted, but the rest have historically remained as asterisms.

In 1928, the International Astronomical Union (IAU) precisely divided the sky into 88 official constellations following geometric boundaries encompassing all of the stars within them. Any additional new selected groupings of stars or former constellations are often considered as asterisms. However, depending on the particular literature source, any technical distinctions between the terms 'constellation' and 'asterism' often remain somewhat ambiguous. e.g. Both the open clusters The Pleiades or Seven Sisters and The Hyades in Taurus are sometimes considered as an asterisms, but this depends on the source.

Large or bright asterisms

Component stars of asterisms are bright and mark out simple geometric shapes.

  • The Great Diamond consisting of Arcturus, Spica, Denebola, and Cor Caroli.[4] An East-West line from Arcturus to Denebola forms an equilateral triangle with Cor Caroli to the North, and another with Spica to the South. The Arcturus, Regulus, Spica triangle is sometimes given the name Spring Triangle.[5] Together these two triangles form the Diamond. Formally, the stars of the Diamond are in the constellations Boötes, Virgo, Leo, and Canes Venatici.
  • The Summer Triangle of Deneb, Altair, and Vega — α Cygni, α Aquilae, and α Lyrae — is easily recognized in the northern hemisphere summer skies, as its three stars are all of the 1st magnitude.[6] The stars of the Triangle are in the band of the Milky Way which marks the galactic equator, and are in the direction of the galactic center.
  • The Great Square of Pegasus is the quadrilateral formed by the stars Markab, Scheat, Algenib, and Alpheratz, representing the body of the winged horse.[7] The asterism was recognized as the constellation ASH.IKU "The Field" on the MUL.APIN cuneiform tablets from about 1100 to 700 BC.[8]
  • One-third of the 1st-magnitude stars visible in the sky (seven of twenty-one) are in the so-called Winter Hexagon with Capella, Aldebaran, Rigel, Sirius, Procyon, and Pollux with 2nd-magnitude Castor, on the periphery, and Betelgeuse off-center.[6] Although somewhat flattened, and thus more elliptical than circular, the figure is so large that it cannot be taken in all at once, thus making the lack of true circularity less noticeable. (The projection in the chart exaggerates the stretching.) Some prefer to regard it as a Heavenly 'G'.[9]
  • The Winter Triangle visible in the northern sky's winter and comprise the first magnitude stars Procyon, Betelgeuse and Sirius.

Constellation based asterisms

Plough big dipper
The Big Dipper asterism
  • A familiar asterism is the Big Dipper, Plough or Charles's Wain, which is composed of the seven brightest stars in Ursa Major.[9] These stars delineate the Bear's hindquarters and exaggerated tail, or alternatively, the "handle" forming the upper outline of the bear's head and neck. With its longer tail, Ursa Minor hardly appears bearlike at all, and is widely known by its pseudonym, the Little Dipper.
  • The Northern Cross in Cygnus.[6] The upright runs from Deneb (α Cyg) in the Swan's tail to Albireo (β Cyg) in the beak. The transverse runs from Aljanah (ε Cyg) in one wing to Fawaris (δ Cyg) in the other.
  • The Fish Hook is the traditional Hawaiian name for Scorpius. The image will be even more obvious if the chart's lines from Antares (α Sco) to Graffias (β Sco) and Fang (π Sco) are replaced with a line from Graffias through Dschubba (δ Sco) to Pi forming a large capped "J."
  • The Southern Cross is an asterism by name, but the whole area is now recognised as the constellation Crux. The main stars are Acrux, Mimosa, Gacrux, Imai, and arguably also, Ginan. Earlier, Crux was deemed an asterism when Bayer created it in Uranometria (1603) from the stars in the hind legs of Centaurus, decreasing the size of Centaur. These same stars were probably identified by Pliny the Elder in his Naturalis Historia as the asterism 'Thronos Caesaris.'[3]
  • Adding vertical lines to connect the limbs at the left and right in the main diagram of Hercules will complete the figure of the Butterfly.[10]
  • Although hardly an ancient notion, it is easy to see why the Ice Cream Cone is sometimes applied to Boötes.[11] It is even better known as the Kite.[12]
  • The stars of Cassiopeia form a W which is often used as a nickname.[13]

Some asterisms may also be part of a constellation referring to the traditional figuring of the whole outline. For example, there are:

There are many others.[9]

Commonly recognised asterisms

Other asterisms are also composed of stars from one constellation, but do not refer to the traditional figures.

  • Four other stars (Beta — Miaplacidus, Upsilon, Theta, and Omega Carinae) form a well-shaped diamond — the Diamond Cross.[14]
  • The Saucepan or Pot, being the same stars as the Belt and Sword of Orion. The end of the handle is at Hatysa (ι Orionis), with the far rim at η Orionis.
  • The four central stars in Hercules, Epsilon (ε Her), Zeta (ζ Her), Eta (η Her), and Pi (π Her), form the well-known Keystone.[6]
  • The curve of stars at the front end of the Lion from Epsilon (ε Leo) to Regulus (α Leo), looking much like a mirror-image question mark, has long been known as the Sickle.[9]
  • The bow and arrow of the Archer also make a well-formed Teapot.[15] (There is even a bit of nebulosity near the "spout" to serve as steam).
  • Four bright stars in Delphinus (Sualocin or α Delphini, Rotanev or β Delphini, γ Delphini and δ Delphini) form Job's Coffin.[9]
  • The Terebellum is a small quadrilateral of four faint stars (Omega, 59, 60, 62) in Sagittarius' hindquarters.[16]
  • Just south of Pegasus, the western fish of Pisces is home to the Circlet formed from Gamma (γ Piscium), Kappa (κ Piscium), Lambda (λ Piscium), TX Piscium, Iota (ι Piscium), and Theta (θ Piscium).[6][9]
  • Dubhe and Merak (Alpha and Beta Ursae Majoris), the two stars at the end of the bowl of the Big Dipper are habitually called The Pointers:[17] a line from β to α and continued for a bit over five times the distance between them, arrives at the North Celestial Pole and the star Polaris (α UMi/Alpha Ursae Minoris), the North Star.
  • Rigil Kentaurus (α Centauri) and Hadar (β Centauri) are the Southern Pointers leading to the Southern Cross[18] and thus helping to distinguish Crux from the False Cross.

Cross-border asterisms

Other asterisms that are formed from stars in more than one constellation.

  • There is another large asterism which, like the Diamond of Virgo, is composed of a pair of equilateral triangles. Sirius (α CMa), Procyon (α CMi), and Betelgeuse (α Ori) form one to the North (Winter Triangle) while Sirius, Naos (ζ Pup), and Phakt (α Col) form another to the South. Unlike the Diamond, however, these triangles meet, not base-to-base, but vertex-to-vertex, forming the Egyptian X. The name derives from both the shape and, because the stars straddle the Celestial Equator, it is more easily seen from south of the Mediterranean than in Europe.
  • The Lozenge is a small diamond formed from three stars – Eltanin, Grumium, and Rastaban (Gamma, Xi, and Beta Draconis) – in the head of Draco and one – Iota Herculis – in the foot of Hercules.
  • The diamond-shaped False Cross is composed of the four stars Alspehina (δ Velorum) and Markeb (κ Velorum) and Avior (ε Carinae) and Aspidiske (ι Carinae).[14] Although its component stars are not quite as bright as those of the Southern Cross, it is somewhat larger and better shaped than the Southern Cross, for which it sometimes mistaken, causing errors in astronavigation. Like the Southern Cross, three of its main four stars are whitish and one orange.[19]
  • From latitudes above 40 degrees north especially, a prominent upper-case Y is formed by Arcturus (α Boötis), Seginus (γ Boötis) and Izar (ε Boötis), and Alpha Coronae Borealis (Alphecca or Gemma). Alpha Coronae Borealis is far brighter than either Delta or Beta Bootis, distorting the "kite" or "ice-cream cone" shape of Bootes. From the United Kingdom in particular, where there is serious light pollution in many areas and also twilight all night for much of the time these constellations appear, this "Y" is often visible while β and δ Bootis and the other stars in Corona Borealis are not.

Telescopic asterisms

Asterisms range from the large and obvious to the small, and even telescopic.

See also

Notes

  1. ^ In usage, 'constellation' is sometimes a synonym of 'asterism', which reflects the fact that the respective words in Latin (constellatio) and Greek (ἀστερισμός, asterismos), from which the English terms are derived, are synonymous. While a terminological distinction may be present in English, such a distinction does not necessarily occur in other languages.

References

  1. ^ "An Etymological Dictionary of Astronomy and Astrophysics: constellation". Dictionary.obspm.fr. January 2018.
  2. ^ "An Etymological Dictionary of Astronomy and Astrophysics: asterism". Dictionary.obspm.fr. January 2018.
  3. ^ a b Allen, Richard H. (1899). Star Names: Their Lore and Meaning. Dover Publication. p. 11, p. 184–185. ISBN 978-0-486-21079-7.
  4. ^ AstronomyOnline: Image of Big Dipper, Diamond of Virgo, The Sail, Sickle, and Asses and the Manger, Astronomyonline.org
  5. ^ Spring triangle at Space.com, Accessed March 2011
  6. ^ a b c d e "Warren Rupp Observatory: Table of Asterisms". Wro.org. Retrieved 10 March 2019.
  7. ^ AstronomyOnline: Image of Cassiopeia, Square of Pegasus, The Circlet, and Y of Aquarius, Astronomyonline.org
  8. ^ Rogers, J. H. (1 February 1998). "Origins of the ancient constellations: I. The Mesopotamian traditions". Journal of the British Astronomical Association. 108: 9–28. Retrieved 10 March 2019 – via NASA ADS.
  9. ^ a b c d e f "Asterisms". Web.archive.org. 14 February 2010. Retrieved 10 March 2019.
  10. ^ Space.com: Hercules: See the Celestial Strongman Archived May 23, 2009, at the Wayback Machine
  11. ^ History of the Constellations: Bootes Archived May 12, 2011, at the Wayback Machine
  12. ^ "Astronomy Online - View Images Template". Astronomyonline.org. Retrieved 10 March 2019.
  13. ^ "Astronomy Online - View Images Template". Astronomyonline.org. Retrieved 10 March 2019.
  14. ^ a b "Starry Night Photography - Southern Cross, False Cross & Diamond Cross". Southernskyphoto.com. Retrieved 10 March 2019.
  15. ^ "Astronomy Online - View Images Template". Astronomyonline.org. Retrieved 10 March 2019.
  16. ^ "LacusCurtius • Allen's Star Names — Sagittarius". Penelope.uchicago.edu. Retrieved 10 March 2019.
  17. ^ Darling, David. "Ursa Major". Daviddarling.info. Retrieved 10 March 2019.
  18. ^ Darling, David. "Centaurus". Daviddarling.info. Retrieved 10 March 2019.
  19. ^ Moore, Patrick (2010). Patrick Moore's Astronomy: Teach Yourself. Hachette. ISBN 1444129775.
  20. ^ a b "Asterisms". Deep-sky.co.uk. Retrieved 10 March 2019.
  21. ^ "A star hop through Monoceros including M 50, The Christmas Tree Cluster (NGC 2264), Hubble's Variable Nebula (NGC 2261), NGC 2244, NGC 2301, The Rosette Nebula, 11 Beta Monocerotis, Harrington's Star 17 and Harrington's Star 18". Backyard-astro.com. Retrieved 10 March 2019.

Bibliography

  • Allen, Richard Hinckley (1969). Star Names: Their Lore and Meaning. Dover Publications Inc. (Reprint of 1899 original). ISBN 0-486-21079-0.
  • Burnham, Robert (1978). Burnham's Celestial Handbook (3 vols). Dover Publications Inc. ISBN 0-486-23567-X, ISBN 0-486-23568-8, ISBN 0-486-23673-0.
  • Michanowsky, George (1979). The Once and Future Star. Barnes and Noble Books. ISBN 0-06-464027-2.
  • Pasachoff, Jay M. (2000). A Field Guide to the Stars and Planets (4th ed.). Houghton Mifflin Co. ISBN 0-395-93431-1

External links

20s BC

This article concerns the period 29 BC – 20 BC.

== Events ==

=== 29 BC ===

==== By place ====

====== Roman Republic ======

Octavian Caesar becomes Roman Consul for the fifth time. His partner is Sextus Appuleius. He is granted the title of imperator, and for the third time in Roman history the doors of the Temple of Janus are closed, signalling peace.

Octavian celebrates in Rome three triumphs on consecutive days (August 13, August 14, and August 15) to commemorate his victories in Illyricum, Actium and Egypt.

Marcus Licinius Crassus campaigns successfully in the Balkans, killing the king of the Bastarnae with his own hand, but is denied the right to dedicate the spolia opima by Octavian.

Sofia, modern day capital of Bulgaria, is conquered by the Romans and becomes known as Ulpia Serdica.

Start of the Cantabrian Wars against Roman occupation in Hispania.

==== By topic ====

====== Literature ======

March 1 – Horace writes the ode Occidit Daci Cotisonis agmen.

Composition of Aeneid by Virgil begins.

=== 28 BC ===

==== By place ====

====== Roman Republic ======

Gaius Julius Caesar Octavian becomes Roman Consul for the sixth time. His partner Marcus Vipsanius Agrippa becomes Consul for the second time.

The Roman Senate granted Octavian Caesar the title imperium maius (supreme commander) of the Roman armed forces (Around 60 legions).

Augustus initiated a census of the Roman Republic for the first time since 69 BC.

==== By topic ====

====== Astronomy ======

May 10 – The earliest dated record of a sunspot by Chinese astronomers.

The Emilius comet is said to have crashed into modern day Pakistan.

=== 27 BC ===

==== By place ====

====== Roman Republic/Empire ======

Gaius Julius Caesar Octavian becomes Roman Consul for the seventh time. His partner Marcus Vipsanius Agrippa becomes Consul for the third time.

January 16 – Octavian formally returns full power to the Senate; they give him the titles of Princeps and Augustus. He accepts this honor, having declined the alternative title of Romulus, thus becoming first Roman emperor.

Caesar Augustus starts a new military reform. He reduces the number of legions to 26 and creates the Praetorian Guard (1,000 men).

Augustus forms the Classis Misenensis, based in the harbor of Portus Julius at Misenum.

Agrippa divides Hispania Ulterior into Baetica and Lusitania, and enlarges Hispania Citerior.

Northern statue of the Colossi of Memnon is shattered by an earthquake in Egypt (according to Strabo).

Marcus Agrippa begins the construction of the old Pantheon, Rome.

Augustus' first census of the Roman Empire (formerly the Roman Republic) reported a total of 4,063,000 citizens.

=== 26 BC ===

==== By place ====

====== Roman Empire ======

Imperator Caesar Augustus becomes Roman Consul for the eighth time. His partner Titus Statilius Taurus becomes Consul for the second time and refounds the old Contestanian Iberian capital of Ilici (Elche), known since then as "Colonia Iulia Ilici Augusta".

Cleopatra Selene marries Juba II of Numidia, and as a wedding present Augustus makes her the queen of Mauretania in her own right.

Disastrous campaign of Aelius Gallus in the Arabian Peninsula, then known as "Arabia Felix".

Tiridates II invades Parthia and issues coins dated from March and May, 26 BC.

Gavius Silo, orator, is heard by Caesar Augustus, mentioned by Seneca.

Augustus starts campaign against the Cantabrians in northern Hispania, he leads an army (8 legions) and consolidates the north-eastern region.

====== Greece ======

Dioteimus Alaieus is one of the Archons of Athens.

====== Osroene ======

Abgar III of Osroene is succeeded by Abgar IV Sumaqa.

====== Asia ======

The Andhra dynasty replaces the Kanva dynasty, and rules over the eastern part of India.

==== By topic ====

====== Astronomy ======

August 29 – Christian Cross Asterism (astronomy) at Zenith of Lima, Peru.

=== 25 BC ===

==== By place ====

====== Roman empire ======

Imperator Caesar Augustus becomes Consul for the ninth time. His partner is Marcus Junius Silanus.

The temple to Neptune on the Circus Flaminius is built.

Estimation: Rome, capital of the Roman Empire becomes the largest city of the world, taking the lead from Chang'an, capital of China.

Galatia becomes a Roman province after the death of its king. The Roman troops stationed there were relocated to Egypt.

The Roman colony of Emerita Augusta was founded, which is present-day Mérida.

====== China ======

The government gives its tributary states 20,000 rolls of silk cloth and about 20,000 pounds of silk floss.

=== 24 BC ===

==== By place ====

====== Roman Empire ======

Caesar Augustus becomes Roman Consul for the tenth time. His partner is Gaius Norbanus Flaccus.

Augustus founds the city of Nicopolis in Egypt to commemorate his final victory over Mark Antony.

=== 23 BC ===

==== By place ====

====== Roman Empire ======

Caesar Augustus becomes Roman consul for the eleventh time. His partner is Aulus Terentius Varro Murena.

Augustus relinquishes the position of consul, retains that of tribune of Rome and assumes that of Princeps, or "First Citizen." (see Roman Empire).

Augustus gets seriously ill: he gives Agrippa his signet ring and grants him the title imperium pro consule.

The Nubians, led by queen Kandake Amanirenas, take the initiative against the Roman Empire, and attack the Roman province of Egypt moving towards Elephantine.

In response to Meroë's incursions into Upper Egypt, the Roman legions move south and raze Napata. (History of Sudan).

Herod the Great builds a palace in Jerusalem and the fortress Herodian in Judaea. He also marries his third wife, named Mariamne, the daughter of high priest Simon.

Following coinage reform, the as was struck in reddish pure copper, instead of bronze. The denominations of sestertius and dupondius were introduced as large bronze coins.

====== Osroene ======

Ma'nu III Saphul becomes ruler of Osroene.

==== By topic ====

====== Architecture ======

The Roman writer, architect and engineer Vitruvius finishes writing De Architectura (known today as The Ten Books of Architecture), a treatise in Latin on architecture, and perhaps the first work about this discipline.

=== 22 BC ===

==== By place ====

====== Roman Empire ======

Lucius Arruntius and Marcus Claudius Marcellus Aeserninus are Roman Consuls.

Aemilius Lepidus Paullus and Lucius Munatius Plancus are Censors.

The Roman governor of Egypt, Gaius Petronius, marches the Nile with legions XXII Deiotariana and III Cyrenaica, and destroys the Nubian capital of Napata.

King Artaxias II returns with support of the Parthians to Armenia and claims the throne. Artavasdes I escapes to Rome, where Caesar Augustus receives him.

=== 21 BC ===

==== By place ====

====== Roman Empire ======

Marcus Vipsanius Agrippa divorces Claudia Marcella, and marries Julia the Elder, daughter of Caesar Augustus.

=== 20 BC ===

==== By place ====

====== Roman Empire ======

12 May – Peace treaty between Rome and Parthia, in which the captured eagles of Marcus Licinius Crassus and Mark Antony are returned.

Based on the scenes and the style of the work, the Portland Vase is believed to have been made in Alexandria some time between this year and AD 100.

King Herod the Great begins renovation of the Temple in Jerusalem.

Maison Carrée, Nîmes, France, is built (approximate date).

Marcus Verrius Flaccus' De verborum significatu is published. It is one of the first great dictionaries in history

====== India ======

Shakas no longer control northwest India.

26 BC

Year 26BC was either a common year starting on Tuesday or Wednesday or a leap year starting on Monday, Tuesday or Wednesday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Monday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Taurus (or, less frequently, year 728 Ab urbe condita). The denomination 26 BC for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

Argo Navis

Argo Navis (the Ship Argo), or simply Argo, was a large constellation in the southern sky that has since been divided into the three constellations of Carina, Puppis and Vela. The genitive was "Argus Navis", abbreviated "Arg". Flamsteed and other early modern astronomers called the constellation just Navis (the Ship), genitive "Navis", abbreviated "Nav".

It was identified in Greek mythology with the Argo, the ship used by Jason and the Argonauts that sailed to Colchis in search of the Golden Fleece. The original constellation is presently found near the southern horizon of the Mediterranean sky, becoming visible in springtime and sailed westward, skimming along the "river of the Milky Way." Due to precession of the equinoxes, many of the stars of Argo have been shifted farther south since Classical times, and far fewer of its stars are visible today from the latitudes of the Mediterranean. This includes its brightest 1st-magnitude star, Canopus or α Carinae. All the stars of Argo Navis are easily visible south of the equator, and pass near zenith from southern temperate latitudes.

Asterism

Asterism may refer to:

Asterism (astronomy), a pattern of stars

Asterism (gemology), an optical phenomenon in gemstones

Asterism (typography), (⁂) a moderately rare typographical symbol denoting a break in passages

Decan

The decans (; Egyptian baktiu) are 36 groups of stars (small constellations) used in the Ancient Egyptian astronomy. They rose consecutively on the horizon throughout each earth rotation. The rising of each decan marked the beginning of a new decanal "hour" (Greek hōra) of the night for the ancient Egyptians, and they were used as a sidereal star clock beginning by at least the 9th or 10th Dynasty (c. 2100 BCE).

Because a new decan also appears heliacally every ten days (that is, every ten days, a new decanic star group reappears in the eastern sky at dawn right before the Sun rises, after a period of being obscured by the Sun's light), the ancient Greeks called them dekanoi (δεκανοί; pl. of δεκανός dekanos) or "tenths" (The word is of Proto-Indo-European origin and derived from drekkana in Sanskrit. Ancient Indian Sage Parashara uses drekkana in his system of Astrology which corresponds to the modern idea of decan.)

Decans continued to be used throughout the Renaissance in astrology and in magic, but modern astrologers almost entirely ignore them.

Great Diamond

The Great Diamond is an asterism. Astronomy popularizer Hans A. Rey called it the Virgin's Diamond. It is composed of the following stars:

Cor Caroli (α CVn), in Canes Venatici

Denebola (β Leo), the tail of Leo

Spica (α Vir), the wheat of Virgo

Arcturus (α Boo), the brightest star in BoötesThe Great Diamond is somewhat larger than the Big Dipper. The three southernmost stars are sometimes regarded as being their own asterism, the Spring Triangle.

Lying within the Great Diamond is the set of stars traditionally assigned to Coma Berenices. Many nearby galaxies, including galaxies in the Virgo Cluster, are within this asterism, and some of these galaxies can easily be observed with amateur telescopes.

Index of optics articles

Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.

Lists of constellations

The following lists of constellations are available:

Modern constellations - a list of the current constellations.

Former constellations - a list of former constellations.

Chinese constellations - traditional Chinese astronomy constellations.

List of Nakshatras - sectors along the moon's ecliptic.

Lynx (constellation)

Lynx is a constellation named after the animal, usually observed in the Northern Celestial Hemisphere. The constellation was introduced in the late 17th century by Johannes Hevelius. It is a faint constellation, with its brightest stars forming a zigzag line. The orange giant Alpha Lyncis is the brightest star in the constellation, and the semiregular variable star Y Lyncis is a target for amateur astronomers. Six star systems have been found to contain planets. Those of 6 Lyncis and HD 75898 were discovered by the Doppler method; those of XO-2, XO-4, XO-5 and WASP-13 were observed as they passed in front of the host star.

Within the constellation's borders lie NGC 2419, an unusually remote globular cluster; the galaxy NGC 2770, which has hosted three recent Type Ib supernovae; the distant quasar APM 08279+5255, whose light is magnified and split into multiple images by the gravitational lensing effect of a foreground galaxy; and the Lynx Supercluster, which was the most distant supercluster known at the time of its discovery in 1999

Night sky

The term night sky, usually associated with astronomy from Earth, refers to the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.

Natural light sources in a night sky include moonlight, starlight, and airglow, depending on location and timing. Aurorae light up the skies above the polar circles. Occasionally, a large coronal mass ejection from the Sun or simply high levels of solar wind may extend the phenomenon toward the Equator.The night sky and studies of it have a historical place in both ancient and modern cultures. In the past, for instance, farmers have used the status of the night sky as a calendar to determine when to plant crops. Many cultures have drawn constellations between stars in the sky, using them in association with legends and mythology about their deities.

The anciently developed belief of astrology is generally based on the belief that relationships between heavenly bodies influence or convey information about events on Earth. The scientific study of celestial objects visible at night takes place in the science of observational astronomy.

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

Stellar Group

Stellar Group or stellar group may refer to:

CompaniesStellar Group (construction company), of Jacksonville, Florida

a sports management company co-founded by Jonathan BarnettAstronomya grouping of stars

moving group or stellar group, a group of co-moving stars

stellar association

star cluster, a group of gravitationally bound stars

open cluster

galactic cluster

globular cluster

super star cluster

star cloud, a visually defined patch of stars

asterism (astronomy), a group of stars forming a pattern

traditional constellation

multiple star, a set of stars forming a close visual grouping

star system, a gravitationally bound system of stars

Bound
Unbound
Visual grouping

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