Antares

Antares
Diameter	(800 - 9002​ / 4 R☉)

Antares (α Scorpii, α Sco, Alpha Scorpii) is a the brightest star in the constellation of Scorpius, and is of the star type red supergiant. Antares lies ca 550 light-years from Earth.

Antares in the accient times

The name Antares comes from the Greek anti Ares (Άντάρης) and means "the rival of Ares" or "the opposite of Ares" because of its reddish color, since in the night sky it rivaled the planet Mars (Ἄρης, Ares in Greek) that it passes very close to this star every 1 year and 11 months. Its characteristic reddish color has made it an object of interest in many societies of the past.

The location of the star in the center of the constellation Scorpio explains its other name, of Arabic origin, Kalb al Akrab3 ("the heart of the scorpion"). In Egyptian astronomy it represented the goddess Serket or Selkit, announcing the dawn through her temples on the autumn equinox (3700-3500 BC); Many of the Egyptian temples are oriented in such a way that the light of Antares played an important role in the ceremonies that took place. In ancient Persia it was one of the four "Royal Stars" and probably the Guardian of Heaven referred to as Satevis; the Corasmians called it Dharind, "the grasper," and the Copts Kharthian, "the heart."

The Chinese included Al Niyat (σ Scorpii) and τ Scorpii, on either side of Antares, for their Chinese constellation Sin or Xīn, with Al Niyat being the determining star.

Features

Antares is a red M1.5Iab class supergiant located approximately 550 light years from the solar system. It is approaching us at the speed of 3.4 km / s: this value is due both to its own movement and to the movement of the Sun around the center of the Milky Way. Its luminosity in the visible spectrum is 10,000 times greater than that of the Sun. It has a surface temperature of "only" 3,600 K, so it emits a considerable fraction of its luminosity in the infrared, its bolometric luminosity being 60,000 times greater than solar luminosity. From its temperature and luminosity, its radius can be estimated at 883 solar radii, equal to 3 AU. If it were in the center of our solar system, its surface would extend between the orbits Mars and Jupiter, encompassing practically the entire main asteroid belt. And if a photon were to depart from the center of the star, traveling at the speed of light, it would take 24 minutes to reach the surface. Measuring its angular diameter results in an even larger radius of 3.4 AU. 6

Its mass is estimated between 15 and 18 solar masses. This value, together with the fact that it is in the red supergiant stage, indicates that Antares is not very far from exploding as a spectacular supernova (which could happen in the next million years), leaving a neutron star as a remnant. or a black hole. Its enormous size compared to its mass results in a very low average density, much lower than that of the Sun. It is also a pulsating semi-regular variable1 from whose surface a stellar wind blows, causing the star to be enveloped in a cloud. gas.6

Antares forms a binary system with a bluish-white star of class B2.5, Antares B, visually separated by 3 arc seconds. The separation in space between the two stars is about 550 AU and the orbital period can be about 2500 years. The companion is magnitude +5.5 and its luminosity is 1/370 that of its bright companion, even though it is 170 times brighter than our Sun. It has often been described as green or emerald in color — probably by a contrast effect — 6 and was discovered by Johann Tobias Bürg in 1819 during a lunar occultation.7

Observations

Around May 31 is the best time of year to observe Antares because that is when the star is in opposition to the Sun. At that moment Antares goes out in the twilight and hides at dawn. In that situation it is visible throughout the night, depending, of course, on where we are on Earth. For at least two or three weeks before and after November 30 the star is not visible by the dazzling Sun. This period is longer in the northern hemisphere because the decline of the star is located significantly to the south of the celestial equator. The star begins to be visible in the early hours, a few hours before dawn, during the months of February, March and April, and already in late spring can be seen at nightfall.

A few minutes of arch southwest of Antares can be seen, with binoculars, the globular cluster M4 as an cotton snowball; Through any amateur telescope can be solved in giant orange stars, whosecolor is seen in long exposure photographs.

References

]]