Currently, in astronomy, the division of the entire celestial sphere into 88 sections - constellations - with officially fixed borders is accepted. However, in the past, constellations were interpreted as sets of stars that stood out in the sky, which could be remembered according to certain outlines. At different times, they were given names associated with important concepts for people. The small southern constellation Compass is one of these kind of "monuments of the era."
How the compass appeared in the sky
In ancient times, mythological characters were transferred to heaven, in modern times, when astronomers were actively exploring the skies of the Southern Hemisphere, they tried to perpetuate the names of European monarchs or terms from the everyday life of emerging science and technology on star maps. Not all the fruits of these works survived to our days: for example, the constellation Electric Machine is now remembered only as a historical curiosity. But the star groups, identified in the middle of the 18th century by a member of the Paris Academy, professor of mathematics and astronomer N. Lacaille, were lucky, including the constellation Compass.
This constellation does not have legends dating back to antiquity, but indirectly it is nevertheless connected with one mythological image that has lived in heaven for a long time. The huge constellation Ship Argo, named after the legendary ship, appeared in the atlas of Ptolemy of the 2nd century AD. e., and a group of dim stars located where the Argo mast was sometimes depicted in atlases, in 1754 on the map of Lacaille was named the Navigator Compass (in Latin - Pyxis Nautica). Two years later, Lacaille divided the Ship of Argo into Poop, Kiel and Sails (exist today) and proposed to distinguish the constellation Mast in the place of Compass, however, the history ordered otherwise, preserving, albeit in a truncated version, the original name - Compass (Pyxis, abbreviated Pyx) .
Location and description of the constellation
The area of the sky belonging to Compass is small - only 221 square degrees. With the naked eye you can see about two and a half dozen stars in it. Only eight of them have a brightness greater than 5 m and only two are brighter than 4 m . The constellation Compass looks like an almost straight line formed by the three brightest stars - Alpha, Beta and Gamma. It is adjacent to the giant Hydra, as well as the constellations of the Sails, Pump and Stern.
In the Northern Hemisphere, Compass can not be observed everywhere. In middle latitudes, part of the constellation is visible near the horizon in the south, while full visibility is possible only south of 54 ° north latitude. The optimal time for observations falls mainly in the winter months - from January to March. In the photo, the constellation Compass appears as a scattering of rather dim stars.
Interesting stars
Alpha Compass is a hot blue giant of class B with a surface temperature of over 24,000 K, 845-880 light-years distant from us. It would be noticeably brighter if interstellar dust did not absorb part of its radiation. This star is a short-period pulsating variable like Beta Cephei. The mass of Alpha Compass is more than 10 times, and the luminosity is 10,000 times higher than that of the Sun.
The most notable star of the constellation is the double T Compass, belonging to the class of repeated novae. This system includes a white dwarf and a solar-type star. Her last outbreak was recorded in 2011. It is possible that the mass of the white dwarf is already close to critical, beyond which a supernova explosion will follow. T The compass is separated from us by several thousand light-years, and this is one of the candidates for supernovae closest to the Sun.
The constellation Compass contains several sun-like luminaries, as well as a red dwarf, near which the presence of exoplanets has been established. All these planets are gas giants, either too close to the parent star, or, conversely, too distant. Planets with a mass comparable to the earth have not yet been discovered here.
Star clusters
A portion of the sky related to this constellation includes a number of open star clusters. They can be observed in an amateur telescope. Such, for example, are the clusters NGC 2658 (located near Alpha Compass) and NGC 2627 in the area of the double star Zeta Compass.
Very spectacularly dispersed cluster NGC 2818. It is located in the southern part of the constellation, and is more than 10,000 light-years distant from us. This object is noteworthy in that it contains a fantastically shaped planetary nebula — the remainder of the gas envelope thrown into space by a star, ending its life's journey. This beautiful planetary nebula was photographed in high resolution in 2008 with the Hubble Space Telescope.
Extragalactic Attractions
Of the deep space objects in the constellation Compass, two galaxies are available for the amateur telescope (the diameter of the main mirror should be at least 200 mm): elliptical NGC 2663 and spiral NGC 2613, which is noticeably tilted by an “edge” with respect to the Earth observer. The spiral sleeves of NGC 2613 can only be allowed when shooting at high shutter speeds with a powerful telescope.
So, the modest constellation Compass - a legacy of the era of development of navigation in the southern oceans - does not shine with spectacular objects of high brightness, and in order to get the joy of independent observation of this part of the sky, the necessary conditions and the presence of a telescope are necessary. But even if the astronomy fan does not have such opportunities, he has and will still have wonderful pictures taken with the help of both powerful professional and amateur tools.