Northern crown
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Northern Crown Constellation |
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| Latin name | Corona Borealis |
| Latin genitive | Coronae Borealis |
| Abbreviation | CrB |
| Right ascension | 15 h 16 m 04 s to 16 h 25 m 07 s |
| declination | + 25 ° 32 ′ 17 ″ to + 39 ° 42 ′ 42 ″ |
| surface | 178.710 deg² rank 73 |
| Completely visible | 90 ° N to 50.6 ° S |
| Observation time for Central Europe | spring |
| Number of stars brighter than 3 mag | 1 |
| Brightest star (size) | Gemma (2.22) |
| Meteor streams | |
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Neighboring constellations ( clockwise from north ) |
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| swell | IAU , |
 The Northern Crown constellation as seen with the naked eye |
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The Northern Crown ( Latin / Corona Borealis ) is a constellation north of the celestial equator .
description
The Northern Crown is a relatively small but distinctive constellation between Hercules and the Bear Keeper . Your stars form a semicircle. The brightest star Gemma (Latin for gemstone ) is noticeably bright at 2.22 m , the other stars only reach about the fourth magnitude.
The constellation contains two interesting variable stars , R and T Coronae Borealis , which have large fluctuations in brightness.
In the Northern Crown is the vast Abell 2065 galaxy cluster , which contains around 400 galaxies . Due to the great distance, the galaxies only reach the 16th magnitude and are therefore only visible in large telescopes or on long-exposure photographs . The rich galaxy cluster Abell 2142 , which is about 1.2 billion light years away and also does not contain a galaxy brighter than 16 mag, is an interesting research object, as the merging of two such clusters can be observed in it. It is located in the southeastern area of the constellation near ε Coronae Borealis.
history
The Northern Crown is one of the 48 constellations of ancient astronomy that were already mentioned by Claudius Ptolemy . Its counterpart in the sky is the southern crown (Corona Australis).
For the ancient Greeks, the constellation represented a crown. In other cultures it had different meanings. The Arabs saw in it a beggar's bowl, the Chinese a money chain and the Celts a fast-turning wheel or lock.
mythology
The Greek mythology of the Northern Crown was the jeweled crown of Ariadne , daughter of King Minos of Crete . With Ariadne's help, the hero Theseus defeated the Minotaur . Theseus received a thread from her with which he found the way out of the labyrinth in which the monster was held captive. After fleeing together from Crete, Theseus left her on the island of Naxos , where she was taken in by Dionysus and chosen to be his wife. Dionysus threw her crown into the sky, where it then became a constellation. This distraction of an object or a person is also called cadastre and has some equivalents in ancient poetry.
In Celtic mythology , the Northern Crown ( Caer Arianrohd ) was the wheel (or castle) of Arianrhod .
Celestial objects
Stars
| B. | F. | Names or other designations | size | Lj | Spectral class |
|---|---|---|---|---|---|
| α | 5 | Gemma , Alphekka, Gnosia, Asteroth | 2.22 m | 77 | A0 V |
| β | 3 | Nusakan | 3.7 m | 114 | F0 |
| γ | 8th | 3.81 m | 145 | B9 + A3 | |
| ε | 13 | Was true | 4.14 m | 250 | K2 III |
| θ | 4th | 4.14 m | 300 | B6 V | |
| δ | 10 | 4.59 m | 150 | G4 III | |
| τ | 16 | 4.73 m | |||
| κ | 11 | 4.79 m | |||
| ξ | 19th | 4.86 m | |||
| ι | 14th | 4.98 m | |||
| η | 2 | 4.99 m | 55 | G1 + G3 | |
| ζ | 7th | 5.07 m | |||
| μ | 6th | 5.14 m | |||
| ν | 20th | 5.20 m | |||
| σ | 17th | 5.23 m | |||
| ρ | 15th | 5.39 m | 57 | G0 V | |
| ν | 21st | 5.40 m | |||
| λ | 12 | 5.43 m |
The brightest star, α Coronae Borealis is approximately 76.5 light years from the sun away. It is a bluish-white star belonging to the spectral class A0. Every 17.36 days its brightness decreases by only 0.1 size classes. The darkening is caused by a weaker companion star that passes in front of the main star. Such stars are called eclipsed ones . The star belongs to the so-called "Bear Current", a nearby open star cluster .
α Coronae Borealis is also called Gemma (Latin for “precious stone”) or Alphekka. The latter name is of ancient Arabic origin and could be derived from al-fakkah (the broken one). This refers to a “broken ring” of stars (the Northern Crown constellation).
ρ Coronae Borealis is a sun-like yellow dwarf star of the spectral class G0 V at a distance of 55 light years. It is somewhat more luminous than our sun and, at around 10 billion years, around twice as old. In 1997 an exoplanet and a circumstellar disk similar to the Kuiper belt were discovered near the star .
Double stars
| system | Sizes | distance |
|---|---|---|
| β | 3.7 m | 0.2 " |
| η | 5.6 m / 5.9 m | 0.7 to 0.4 " |
| γ | 4.1 m / 5.5 m | 0.7 " |
| ζ | 5.0 m / 6.0 m | 6.3 " |
| σ | 5.6 m / 6.6 m | 7 " |
The system η Coronae Borealis is 59 light years away. Its double star nature was recognized by Wilhelm Herschel in 1784 . The two yellowish glowing main sequence stars of the system of the spectral classes G1 and G3 move around a common center of gravity in only 41.6 years. Seen from Earth, the stars are 0.7 (year 2000) to 0.4 (year 2020) arc seconds apart . To separate them, you need a medium-sized telescope with an opening of 15 cm or more.
Friedrich Georg Wilhelm Struve first discovered that γ Coronae Borealis is also a double star in 1826. The system, about 145 light years away, consists of two bluish-white stars of the spectral classes B9 and A3, which orbit each other in 93 years.
The ζ Coronae Borealis system is 450 light-years away and consists of two roughly equally bright stars of spectral class A2.
Due to the larger angular distance of 6.3 or 7 arc seconds, both systems can also be resolved into single stars with a smaller telescope.
Variable stars
| object | size | period | Type |
|---|---|---|---|
| α | 2.22 to 2.3 m | Eclipsing star | |
| R. | 5.7 m -14.8 m | irregularly variable | |
| S. | 5.8 m -14.1 m | 360, 26 days | Mira star |
| T | 2.0 m - 10.8 m | recurring nova | |
| U | 7.7 m - 8.9 m | 3.45 days | Algolstern |
R Coronae Borealis is the namesake of a group of variable stars that change their brightness irregularly. A rapid decrease in brightness can be observed in stars of this type. After a period of time that cannot be determined in advance, the brightness slowly increases again. When examining the spectrum of these stars, it was found that their surface contains a relatively large amount of helium and carbon . It is assumed that the stars repel parts of their outer gas envelope at irregular intervals. Thereby condense the carbon molecules to opaque soot particles out. The cloud of soot evaporates over time and the star appears brighter again.
R Coronae Borealis has a maximum brightness of 5.7 m and can barely be seen with the naked eye. At the minimum, the brightness drops to 14.8 m and the star can only be observed in a larger telescope.
S Coronae Borealis is a reddish Mira star of the spectral class M7e, which is also just visible to the naked eye in the phase of its maximum brightness of 5.8 m , while it only reaches 14.1 m at a minimum . The period of the brightness fluctuations is 360 days. The discovery of the variability of this star, which is about 1400 light years away, was made in 1860 by Henke.
T Coronae Borealis is a variable star of the recurring nova type . With a brightness of 10.8 m it is only very faint, but became noticeably bright with eruptions in 1866 and 1946 with up to 2.0 m .
U Coronae Borealis was recognized by Winnecke as changeable in 1863 . It is an eclipse variable star of the Algol type , the apparent magnitude of which fluctuates between 7.66 m and 8.79 m with a period of 3.45 days . The components of this double star are a blue and white main sequence star of the spectral type B6 and a yellow and white subgiant of the spectral type F8.
Messier and NGC objects
The Northern Crown does not contain any brighter star clusters , gas nebulae, or galaxies that have been included in the Messier Catalog or NGC .
See also
Web links
Remarks
- ↑ Ovid 's Metamorphoses 8.169 to 182
- ↑ In-The-Sky: Alphecca. Accessed January 11, 2018 .
- ↑ Jum Kaler, Stars , Eta Coronae Borealis
- ↑ Jum Kaler, Stars , Gamma Coronae Borealis
- ↑ The International Variable Star Index : S CrB on the American Association of Variable Stars (AAVSO) website
- ↑ The International Variable Star Index : U CrB , on the American Association of Variable Stars (AAVSO) website