Right ascension? 03? :? 47.0 (hours: minutes)?
Declination? +24? :? 07 (degrees: minutes)?
Distance? 0.38 (thousand light years)?
Brightness? 1.6 (order of magnitude)?
See the size? 1 10.0 (cents)
Pleiades (Pleiades, M45, Chinese Pinyin: m40? xěng？ Tuán) is one of the open clusters, which is a large and bright open cluster in the western part of the northern hemisphere, located in Taurus, and can be seen with naked eyes in the clear night sky. Its bright star lies in the Pleiades, hence its name. What's the catalog number of messier? M45 usually has six or seven bright stars, which is often called Seven Sisters Cluster. It is one of the brightest open clusters recently. The Pleiades cluster contains more than 3000? A star with a width of about 13 light years, a distance of 128 parsec (4 17 light years) and a diameter of about 4 parsec.
In ancient China, bright stars were listed as Pleiades. There are many legends and myths about it, also known as "Seven Sisters Group". Generally, you can see six stars with the naked eye, because the star you can't see in this cluster has low visibility and is a lower star. There are not seven stars in this cluster, but nearly 300 stars, but they are all very dark. You don't have to worry about your eyes, because it is difficult for most people (even in a clear night sky) to tell the star apart. ?
The cleverest of them? The star name, photoelectric visual magnitude and MK spectral classification of the six stars are as follows from west to east:
Taurus 17 (Pleiades I), 3.7 1, B6 III;
Taurus 19 (Pleiades II), 4.3 1, B6 IV;
Taurus 20 (often 4), 3.88, Ⅲ ⅲSn；;
Taurus 23 (Pleiades V), 4. 18, B6V；;
Taurus η (Pleiades), 2.87, B7 Ⅲ;
Taurus 27 (Pleiades VII), 3.64, B8 Ⅲ.
These stars are spinning fast. The effective surface temperature of Pleiades in blue giant is about 13500K, and the total radiant brightness is about 2200 times and the radius is about 8 times that of the sun, but the equator rotates for less than 3 days. Pleiades VII is a spectral binary star with an orbital period of several years. 7% of Pleiades have orbital periods less than? 100 day binary star. The famous gas shell star Taurus 28 (that is, Taurus BU) is located in the Pleiades cluster. More than 460 Yao stars have been found in the direction of the Pleiades. There are no red giants in this cluster. The nebula near the bright stars of the Pleiades cluster seen in the photo is called NGC 1432, which is a reflection nebula formed by the reflection of interstellar dust particles and scattered starlight. This may be a star left over from the formation of the Pleiades, but it is more likely to be a substance encountered by the Pleiades during its movement.
[Edit this paragraph] Cluster age
The Pleiades cluster is 400 light-years away from the sun, and it is young in astronomical time scale because it contains early B-type stars. It is estimated that it takes about 265,438+0 million years for a B-type star with a mass of 9 suns to shrink to the main sequence, exhaust the hydrogen in its core and start to expand into a red giant. Therefore, this value should be the age of the open cluster. However, only the color-luminosity diagram of the Pleiades clearly shows that those stars with only 0.2 solar mass have passed the initial contraction stage and are basically in the zero-age main sequence. According to the recent theory of stellar evolution, it takes time for a star with a solar mass of 0.2 to shrink to a zero-age main sequence. About 600 million years. So, how old is the Pleiades? Is it 2 1 billion years or 600 million years?
In fact, the contradiction is not as sharp as it seems. Herbig believes that before the formation of massive stars, small-mass stars have been formed by nebula matter. If the late-type main sequence stars are formed first, they will reach the zero-age main sequence stars while the early-type stars shrink to the main sequence stars, and then burn the hydrogen in their nuclei. And began to expand to the red giant stage. This theory seems to be supported by observation. Another evidence of the early formation of low-mass stars is the Taurus-Auriga dark nebula, which contains a large number of dark red stars, but no bright blue stars. ?
All this shows that the Pleiades cluster with about 300 stars began to form 600 million years ago and continued to form B-type stars. These very bright stars radiate extremely rich ultraviolet rays. They have ionized the gas and completely blown it away, leaving only traces of gas in the Milky Way. As the gas leaves, the process of star formation tends to stop. It is interesting to think of the Rose Nebula, which has a group of very bright stars in its center. This nebula may be formed by this process of blowing gas outward from the center. This idea may explain this extremely interesting ring structure of gas and star aggregates.
Pleiadian star clouds are blue, which means that they are reflection nebulae, reflecting the light of bright stars located near (or inside) them. The brightest part of these nebulae, the nebula around the Pleiades, is18591kloc-0/October 19 by Ernst? William? Leber Laichter? (William)? Temple found it with a 4-inch refractor; It is listed in the NGC catalogue, numbered NGC? 1435。 Leo. Ondra provides an online William? Temple's biography, as well as the sketch of the Pleiades five-star cloud, were included in this database with consent. The part of the nebula extending to the Pleiades was found in 1875 (i.e. NGC? 1432), the nebulae around Pleiades VI, Pleiades I, Pleiades VI and Pleiades II were found at 1880. The complexity of the complete Pleiades cluster, up to 1885 to 1888, the Henry brothers in Paris and Isaac in Britain? Roberts invented the first astronomical camera before he invented it. 1890，e.e？ Barnard found that the nebula material has a star-like gathering center very close to the Pleiades, which is listed in the IC catalogue with the number IC? 349。 19 12，Vesto？ m？ Slipher analyzed the spectra of Pleiades star clouds and revealed the properties of their reflection nebulae, because their spectra are exactly the same as those of the stars that illuminate them. ?
More information can be found in our numbered list of major stars in the Pleiades cluster and its corresponding nebula. ?
In essence, the reflection nebula is probably the dust part of the molecular cloud, which has nothing to do with the Pleiades, but passes through the Pleiades. It is not the remnants of nebulae that form clusters, which can be seen from the different radial velocities of nebulae and clusters. They cross each other at a speed of 6.8 miles per second, that is, 1 1 km per second. ?
According to the latest calculation results (G? Meynet，？ j-c？ Mermilliod？ And then what? Answer? Mede. Are you online? Astron. ? Astrophysics. ? Supplement? Jazz. ? 98,? 477-504,? 1993), the age of the Pleiades cluster is 1 100 million years. This is much older than the early published "authority", usually 6000 to 80 million years ago (such as Sky? Directory? The age given in 2000 is 78 million years). There are also calculations that the Pleiades can continue to exist in the form of clusters for about 250 million years (Kenneth? Green. Jones); After that, they will disperse into single stars (or multiple stars) along their respective orbits. ?
Hipparcos, an astronomical satellite of the European Space Agency, recently directly measured the distance of the Pleiades by parallax method. According to these measurements, the Pleiades cluster is 380 light-years away (the previous value was 408 light-years). The new distance value needs to explain the relatively dark star apparent magnitude in the Pleiades cluster.
[Edit this paragraph] Explore in depth
The Pleiades cluster of trumpler type is defined as II, 3, R type (trumpler, according to Kenneth? Green. Jones statement) or I, 3, R, N type (G&; OumlTz and Sky? Directory? 2000), which means that this cluster seems to be independent, with a high or moderate concentration towards the center, in which the brightness distribution of stars is large and there are more member stars (100 or more). ?
Some stars in the Pleiades cluster rotate at high speed, and the surface rotation speed is 150 ~ 300km/s, which is a common phenomenon in (A-B) spectral main sequence stars. Because of this rotation, they must be ellipsoids, not spheres. This rotation can be found because it makes the spectral absorption line wider and more divergent, because relative to the average radial velocity of the star, a part of the star surface on one side of the star is approaching us, while the other side is far away from us. The most prominent example of a rapidly rotating star in this cluster is the unicorn, which is also a variable star with a brightness between 4.77 and 5.50 (Kenneth? Green. Jones) .o? Struve predicted that this rotation would cause stars to throw out gas envelopes. During the period from 1938 to 1952, this phenomenon was observed by spectral analysis of Pleiades Zenger 12. ?
Cecilia. Payne-Gaposhkin mentioned that the Pleiades contains some white dwarfs (WD). This raises a special question for the evolution of stars: how did white dwarfs appear in such a young cluster? Because there is more than one white dwarf, it is quite certain that these stars are all members of the cluster, not all of them are captured field stars (in short, the capture process is not efficient in such a rather loose open cluster). [translation: field star, field? Stars refer to independent, ungrouped stars. ]? According to the theory of stellar evolution, the mass of white dwarfs cannot exceed the upper limit of about 1.4 times the mass of the sun (Chandraseka limit, the? Chandraseka? Limit), the larger white dwarf will collapse due to its own gravity. However, the evolution of such low-mass stars is very slow, and it takes billions of years to evolve to the final stage. It is obviously not enough for the Pleiades cluster to be as short as 1 100 million years. ?
The only possible explanation is that these white dwarfs used to be massive stars, so they can evolve rapidly, but some reasons (such as strong stellar wind, mass accretion of neighboring stars or rapid rotation) make them lose most of their mass. Therefore, they may throw most of their mass into space and form planetary nebulae. In a word, the mass of the last remaining star (i.e. the original star core) must be lower than the Chandraseka limit, so that it can evolve into a stable white dwarf and be observed by us. ?
The latest observation of the Pleiades star cluster since 1995 has found several candidates for abnormal stars or star-like objects, namely the so-called Brown dwarfs (brown? Dwarf). This celestial body, which is still only a hypothesis, is considered to be between a giant planet (such as Jupiter) and a small star (the theory of star structure points out that the smallest star, that is, a celestial body that can generate energy through nuclear fusion in its life stage, should not be less than 6% to 7% of the mass of the sun, that is, 60 to 70 times the mass of Jupiter). Therefore, the mass of brown dwarfs should be about 10 to 60 times that of Jupiter. Theoretically, they can be observed in the infrared band, the diameter is equal to or smaller than Jupiter (65,438+043,000 km), and the density is 65,438+00 to 65,438+000 times that of Jupiter, because much stronger gravity will press them more tightly. ?
Even with the naked eye, in general, the Pleiades cluster is quite easy to find, located in the bright red giant Aldebaran (Taurus α, star 87, 0.9, etc. , spectrum K5? III) Northwest direction/near 10/0 degree. Hyades, another equally famous open cluster, is obviously surrounded by Biru V. Now we know that Biju is not a member of Biju cluster, but a foreground star (68 light-years away from us, while the distance of Biju cluster is 150 light-years). ?
In binoculars or wide-angle lens, this cluster is a spectacular celestial body, at 1? More than 100 stars can be displayed in the diameter range of15 degrees. For a telescope, even at the lowest magnification, this cluster is too big to see the whole picture in one field of view. There are many binary stars and multiple stars in the cluster. Pleiades five-star cloud NGC? 1435 needs a dark sky to see, and the observation effect is best under a wide-angle mirror (Tempel found it with a 4-inch telescope). ?
Because the Pleiades star cluster is close to the ecliptic (only 4 degrees away), the phenomenon that the star cluster is blocked by the moon often happens: this is a very attractive spectacle, especially for those who only have cheap equipment (in fact, you can observe it with the naked eye, but even the smallest binoculars or telescopes will increase the interest in observation-the Pleiades star cluster eclipse in March 1972 is the author. This phenomenon can vividly illustrate the relative size of the moon and this cluster: burnham pointed out that the moon can be "stuffed into a quadrilateral composed of Pleiades VI, Pleiades I, Pleiades V and Pleiades II" (in this case, Pleiades IV and even Pleiades III will be blocked by the moon). Similarly, planets will also run near the Pleiades (Venus, Mars, Mercury and even occasionally pass by), presenting a magnificent scene.
There are 600 trillion planets and tens of millions of galaxies in the universe. The galaxy where our earth is located is called the Milky Way? Way? Galaxy, the solar system is located on the spiral arm of Orion next to the Milky Way. The earth revolves around the sun, the whole solar system revolves around the Pleiades cluster, and the Pleiades cluster revolves around the center of the Milky Way. Every 240,000 years, the solar system will complete a revolution.
In ancient China, the Pleiades was one of the 28 Pleiades, which were called Pleiades VII (Atlas), Pleiades XII (One-horned Fairy), Pleiades IV (Maya), Pleiades I (Electra) and Pleiades XVI (Serrano).
The cluster of seven fairies is the embodiment of seven fairies in Greek mythology. They are Atlas and his wife Puleo's seven beautiful daughters-Maya, Electra, Serrano, Taikhta, Merope, Alcyone and Stroh Pei.
In ancient Japan, the Pleiades cluster was regarded as a beautiful jewel with special emotional connection. There are Japanese pop songs with its theme, such as the representative works of singer gu cun Shinji (namely Guan's Cantonese song "Star" and Tan's "Horn") and An 8.
Related Myth: In ancient times, you could really see seven fairies, just like seven fairies, wearing blue and white gauze clothes, walking and dancing in the clouds. Later, I don't know in which year, a star suddenly darkened and disappeared. While people were surprised, they began to spread such a beautiful legend-"Seven little sisters got married". Huangmei opera "The Fairy Couple" is their story.