Sagitta is the third smallest constellation (onlyPonyandSouthern crossSmaller than it).This is one of the 48 constellations of ancient Ptolemy.At that time, it was smaller than it is now, accounting for only 4 square degrees.The brightest star is Leftflag Five (Gamma Arrow).The complete constellation of Arrowhead can be seen in the vast area north of 69 degrees north latitude, while it can not be seen in the area south of 74 degrees south latitude.On the night of July 16 every year, the center of the constellation Sagittarius passes byShangzhongtianThe best observation month is August.
Sagitta belongs toBeitianSmall constellation, located inCygnusIn the Milky Way to the south and north of the constellation Aquila.It is adjacent to Fox.This constellation is located incelestial equatorNot far to the north, so it can be seen anywhere on the earth except in the Antarctic region.
Sagittarius is surrounded by the following constellations, clockwise from the north: FoxHercules, Aquila andDolphin。Several stars in the constellation Sagittarius are arranged in the shape of a flying arrow. The arrow body is similar to that of the constellation AquilaNiulang Sanxing(also calledShoulder pole star）The direction is exactly vertical, so it is easy to identify.fromAlpha AquilaMove the field of vision about 10 ° to Beta Cygnus (third class star), and Sagittarius enters the field of vision.
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Sagittarius[1]
In the past, this sky area was called "Sham", but now the name "Sham" is only a bright star in the constellation Sagittarius.Sagittarius isBayer designation When naming stars according to their luminosity, for example, the brightest star is wrongly named Gamma Arrowhead.Another similar example can be found inSagittariusFound.
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M71
Globular clusterM71: It is located between left flag five (Arrow gamma) and left flag three (Arrow delta).Classification is controversial, and some astronomers believe thatM71It is a very loose globular cluster, but some think it is a compactOpen cluster, current research tends to believe thatM71Is aGlobular cluster。13000 from the earthLight year，Apparent magnitude8.3。French astronomer in 1746Sisu(Philippe Loys de Ch é seaux) found the cluster.
According to the myth, Prometheus stole the sky fire and came to the world, and used it to benefit mankind, so he was respected by people.Later, he was unjustly punished by the god Zeus and nailed to thecaucasus mountains On the top cliff, Zeus also sent a vulture to torture him every day.One day, great heroHeraclesCame to the foot of the Caucasus Mountains, saw that Prometheus was nailed to the cliff and tortured by vultures, determined to rescue him.Heracles bent his bow to shoot the vulture to death, saved Prometheus, and made him climb againOlympus Holy Mountain。Later, in order to praise Hercules for this achievement, the gods took his arrow to kill the vulture to the sky, which is the origin of the constellation Sagittarius.
Cupid Arrow
Sagittarius
There is also a legend that this arrow is the golden arrow that Eros, the little god of love, shoots at his lover.Eros is the god of warAresHe was born by combining with Aphrodite, the god of beauty. He has a pair of lovely wings and holds a bow and arrow in his hand.It is said that Eros has two kinds of love arrows: gold arrow and silver arrow.When being shot by his golden arrow, love will come into being and make people fall in love;If he is shot by his silver arrow, he will refuse love,
It turns lovers against each other.
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Observation mode
Sagittarius is located inCygnusandAquilaBetween the Milky Way.It is one of the smallest constellations in the sky. There is no bright star in it, so it is difficult to identify.Its four brightest 4m stars constitute a short arrow, which is perpendicular to the "pole" of the constellation Aquila.Through this method, you may be able to barely find this constellation.
The brightest star
Gamma Sagittarius is the brightest star in the constellation, middle nameLeft Flag Five, the apparent magnitude is 3.47, 190 light-years away.Sagittarius alpha middle nameLeft Banner One, apparent magnitude 4.37, distance 610 light-years;Beta Sagittarius is named Zuoqi II, making the brightness 4.37, 640 light-years away. The above three stars are giant stars.The third left flag in Sagittarius δ is irregularVariable starThe apparent magnitude varies between 3.75 and 3.83 degrees, 570 light-years away from us.
Other bright stars
The stars of Sagittarius
Alpha Sagittarius: special name Sham, Chinese star Zuoqi I, is a yellow giant star, spectral type G1 II, apparent magnitude 4.37, 610 light-years away from the Earth.Together with Beta sagittarius (left flag 2), which is also 4.37, they form arrow feathers.
Sagittarius δ: Chinese star Zuoqisan is suspected to be a pair of double star systems, with spectral types of M2 II and A0 V respectively (it may also be a composite spectrum in a single image), and apparent star magnitude of 3.82.
Epsilon Sagittarius: spectral type 8 III, apparent magnitude 5.66, a total of four members, including a group of physical triads (A, C, D) and a dense near star (B).
Arrowhead η: spectral type K2 III, apparent magnitude 5.1, belonging to one of the Hyades.
Spectroscopic binary
There is a star calledSpectroscopic binaryThe spectroscopic binary refers to the binary stars that can be judged through the observation and analysis of the position change of the spectral line of a celestial body. Because the distance between the two sub stars of such binary stars is very close and the rotation period is very short (most of them are less than 10 days), their two sub stars can not be distinguished by naked eyes or photographic methods through telescopes.According to the Doppler effect, when the star moves close to us, its spectral line moves to the purple end, and when the star moves far away from us, its spectral line moves to the red end. With the rotation of the two sub stars, the spectral line of the star's spectrum moves regularly, according to which, we can find binary stars.If one of the two sub stars is bright and the other is dark, the spectral line of one bright star can be seen to shift periodically, and the spectral line of the other dark star can not be seen, so the binary star can also be found.The binaries discovered by these methods are called spectroscopic binaries
Bispectral spectroscopic binary
Sagittarius astrogram
fromChild starA binary star judged by the change of apparent velocity.The measured spectral lines of two sub stars are calledBispectral spectroscopic binary(also known as double line spectroscopic binary star). It is calledMonospectral spectroscopic binary(Also known as single line spectroscopic binary star).The former can generally be represented by the abbreviated symbol SB2, while the latter can be represented by SB1.The curve drawn with the orbital phase as the abscissa and the apparent velocity as the ordinate is called the apparent velocity curve.Solve the orbital elements P (period), e of the separable optical binary on the radial velocity curve（Eccentricity）, T (time of passing the near star point), (longitude of the near star point calculated from the ascending intersection point), K (half amplitude of the radial velocity of sub star 1), K (half amplitude of the radial velocity of sub star 2), (radial velocity of the common center of mass), Msin and Msin (M and M are the masses of sub stars 1 and 2, and are orbital inclination angles), asin and asin (a is the true length of the semi major axis of the orbit around the common center of mass of sub star 1),A is the corresponding quantity of sub star 2), which is the case of SB2.For SB1, track elements P, e, T, K, mass functionF (M, M) is and asin, where subscript 1 represents measured spectral line sub star, and subscript 2 represents unmeasured spectral line sub star.The orbital elements of SB2 can be combined with the values obtained by other methods (such as eclipsed binary photometric solution, visual or interference binary orbital solution, polarization method, etc.) to obtain the respective mass values of the two sub stars, which is one of the most reliable and basic methods for calculating the mass of stars.The true radius of the two sub stars can also be obtained by combining the SB2 orbital elements with the photometric solution of the eclipsed binary star.The above orbital elements of a spectroscopic binary are collectively referred to as spectroscopic orbital solutionsSpectrophotolysis。
With the development of research, the original SB1 may be changed into SB2, such as the Great Tomb Five and the Arrow U, etc.The number of spectroscopic binaries discovered is about 5000, published in 1978Orbital Elements of Spectrometric Binary StarsThe seventh table lists 978 spectroscopic binaries.The orbital period of spectroscopic binary stars can be as short as 82 minutes (Sagittarius WZ) and as long as about 88 years (Ophiuchus 70).In telescopes, it is generally impossible to directly distinguish the two sub stars of a spectroscopic binary (called visual binary).useInterferometryAnd occultation observation methods can distinguish more and more sub stars of spectral binaries.Generally, spectroscopic binary stars are regarded asClose binary。Some close binary stars containX-ray pulsar, double star orbital motionDoppler effectMake the pulse frequency increase and decrease regularly. By analyzing the X-ray data, we can obtain the spectral decomposition of the X-ray band corresponding to SB1, for exampleCentaurX-3 In the absence of optical observation data, only the spectral decomposition obtained from the X-ray data can determine that the lower limit of the unmeasured mass of the sub star in the X-ray band is 15.6 solar mass from the mass function.containRadio pulsarThe situation of the close binary PSR1913+16 is also very similar. The radio band spectral decomposition corresponding to SB1 can be analyzed from the change of radio pulse frequency.Therefore, in a sense, the binary can be regarded as a spectral binary in the radio band.
Double star meaning
Sagittarius
Spectral binaries, especially bispectral binaries, are fundamental to the calculation of star mass, radius, etcparameterExtremely important.Monospectral binary stars can also provide constraints on the basic parameters of stars.There are many kinds of stars in spectroscopic binaries, involving a wide range of physical and evolutionary problems.At present, there are still a large number of spectroscopic binaries to be foundObject end prismA class of new technologies are engaged in detection with high efficiency.There are still a large number of spectroscopic binaries that have not been found yet.Visible light andPhotographic wavebandFor example, spectroscopic binaries reflecting orbital motion by radio spectral line displacement, X-ray spectral line displacement, atmospheric ultraviolet spectral line displacement, etc. are basically new areas to be explored.Although already inLarge Magellanic CloudBispectral spectroscopic binaries have been found in, while the discovery and research of extragalactic spectroscopic binaries are still in the initial stage.
