What is the difference between Sagittarius A* and Sagittarius A star? How do you read it?

Sagittarius (commonly known as Sagittarius-translated from Japan, astronomical symbol:? ) is a constellation of the zodiac. It is aiming at Scorpio in its west with a bow, and it is adjacent to Capricorn in its east. Its bright stars are arranged in a unique teapot shape, which is not difficult to identify. Unicode code is 2650 and HTML code is 9808.

trait

Sagittarius is not difficult to identify, because its main stars are arranged like a teapot: Jisu II (δ), Jisu III (ε), Dousu VI (ζ) and Dousu III (φ) form the pot body; Bean element II (λ) is a pot cover; Jisuyi (γ) is the spout; Dousu IV (σ) and Dousu V (τ) are pot handles.

Although Tianyuan San is the alpha star of Sagittarius, its apparent magnitude is only 4.0, which is even darker than many stars in the constellation.

[Edit] Deep space objects

From the earth's point of view, the center of our galaxy lies in Sagittarius. Although the galactic center is hidden by the nebula and dust belt on Sagittarius arm, the Milky Way galaxy in Sagittarius is still very dense, with many bright clusters and nebulae in the middle.

The celestial bodies in this constellation are mainly cosmic objects in the depths of the Milky Way, including emission nebulae and dark nebulae, open clusters and globular clusters, and planetary nebulae. Sagittarius has as many as 15 messier objects-the most of all constellations. Many of them can be observed with binoculars.

Sagittarius A, which is related to the center of the Milky Way, is a complex wireless power source, and astronomers think it may contain a supermassive black hole.

Mons/8/80/ Sagittarius _ Constellation _ Map.png

Archer

Alpha Centauri (Betelgeuse), located in the south of the sky, is called Alpha Centauri in the west. Although it is difficult to distinguish with the naked eye, it is actually a three-in-one star system, in which one star is the fourth brightest star in the whole sky. However, because two of the stars are too close to be distinguished by naked eyes, its comprehensive apparent magnitude is -0.27 (more than the third brightest Nanhesan) and its absolute magnitude is 4.4. The south gate is also the outermost guide of the famous Southern Cross, because the location of the Southern Cross is too south, so most of the northern hemisphere can't see it. Legend has it that Zheng He used it to guide the way when he went to the West.

Nanmen II is the closest star system to the sun, only 4.37 light years (about 277,600 astronomical units). Proxima centauri is usually considered as a part of this star system, which is only 4.22 light years away from the sun. Because Nanmen II is relatively close to the Earth, it is regarded as the "first port of call" in the adventure novels about interstellar travel, and it is predicted that this star system will even be developed and colonized when the population explodes.

Alpha Centauri A and Alpha Centauri B.

The biggest member of Nanmen II is Alpha Centauri A, which is a G2V-shaped main sequence star, emitting yellow and white light, with brightness and volume slightly exceeding that of the sun. The second largest member of Nanmener is Alpha Centauri B, which is a main sequence star of K 1V type, emitting orange light with brightness and diameter slightly lower than that of the sun. The orbital eccentricity of these two stars is 0.52, the nearest distance is 1 1.2 astronomical unit (about the distance from the sun to Saturn), and the farthest distance is 35.6 astronomical unit (about the distance from the sun to Pluto), with a period of nearly 80 years. [6] Their total mass is a little more than twice that of the sun, and their age is about 5 to 6 billion years.

South Gate's Vision

Observing the universe from the south gate, we will see many celestial bodies seen by observers on earth, and most constellations have hardly changed, such as Orion and Ursa Major. But the brightest star in Centauri will disappear, and the sun will become a star with an apparent magnitude of 0.5 in Cassiopeia. Generally speaking, the shape of Centauri will change from \/\/to/\/,and the sun will be located at the tail end of ε star Centauri.

Bright stars near the sun, such as Sirius and Nanhe III, observed from Nanmen II, will appear in very different positions. Sirius will become a part of Orion, appearing at a distance of 2 degrees in Betelgeuse, which is slightly darker than that observed on Earth (-1.2, etc.). ). Although North Rashomon and Vega are far apart, they will be replaced. Proxima centauri will be an inconspicuous 4.5-magnitude star. Considering that it is only a quarter of a light-year away from Alpha Centauri A and Alpha Centauri B, it can be seen that proxima centauri is so dim.

If there is a planet around Alpha Centauri A or Alpha Centauri B, they will be very bright binary stars on this planet. For example, if there is a terrestrial planet at a distance of A 1.25 astronomical units (period of revolution is 1.34 years), the brightness of Alpha Centauri A is similar to that of the sun, while Alpha Centauri B will be dimmed by 5.7 to 8.6, but it will still reach? 2 1.0 and so on? 18.2 and so on. Although it is 0/90 to 2700 times darker than αA Centauri, it is still 0/70 to 2300 times darker than Full Moon. On the contrary, if there is a terrestrial planet at a distance of 0.71astronomical unit (period of revolution is 0.63), the brightness of Alpha Centauri B is similar to that of the sun for this planet, while Alpha Centauri A will be dimmed by 4.6 to 7.3, but it will still reach? 22. 1 and so on? 19.4 and so on. Although it is 70 to 840 times darker than Alpha B Centauri, it is still 520 to 6300 times darker than the full moon. For a planet orbiting one of the stars, the second sun will not adversely affect the climate or photosynthesis (approximately equal to the distance between Saturn and the sun). However, this means that for about half a year, the night sky is not dark, but dark blue, and people can walk around and even read without artificial lighting.

It is known that there are binary systems with planets around the superstars in the solar system, such as satellite systems, which shows that it is not impossible to have planets similar to Earth around these two stars. Many planetary hunter teams can't find any giant planets or brown dwarfs in this system at apparent speed. If they exist, they will tear apart any terrestrial planet in or near the habitable zone.

mons/c/C2/Position _ Alpha _ cen . png

The location of the south gate