Three intersecting circles with turns in steps of two, four and four. A jumbling puzzle.

• Inventor: Dmitry Andreev
• Mechanism: Intersecting circles
• Patents: Unknown
• Producer: Custom
• Year: 2022
• Original Price: $0.00 USD
• Current Price: No Data

Achernar is the brightest star in the constellation of Eridanus, and the ninth-brightest in the night sky. It has the Bayer designation Alpha Eridani, which is Latinized from α Eridani and abbreviated Alpha Eri or α Eri. The name Achernar applies to the primary component of a binary system. The two components are designated Alpha Eridani A (the primary) and B (the secondary), with the latter known informally as Achernar B. As determined by the Hipparcos astrometry satellite, this system is located at a distance of approximately 139 light-years (43 parsecs) from the Sun.

Of the ten apparent brightest stars in the night-time sky, Alpha Eridani is the hottest and bluest in color, due to Achernar being of spectral type B. Achernar has an unusually rapid rotational velocity, causing it to become oblate in shape. The secondary is smaller, of spectral type A, and orbits Achernar at a distance of roughly 12 astronomical units (AU).

The system bears the traditional name of Achernar (sometimes spelled Achenar), derived from the Arabic آخر النهر ākhir an-nahr, meaning "The End of the River". However, it seems that this name originally referred to Theta Eridani instead, which latterly was known by the similar traditional name Acamar, with the same etymology.

Properties:
Achernar is in the deep southern sky and never rises above the horizon beyond 33°N, roughly the latitude of Dallas, Texas. It is best seen from the Southern Hemisphere in November; it is circumpolar above (i.e. south of) 33°S, roughly the latitude of Santiago. On this latitude, e.g. the south coast of South Africa (Cape Town to Port Elizabeth) when in lower culmination it is barely visible to the naked eye as it is only 1 degree above the horizon, but still circumpolar. Further south, it is well visible at all times during night.
Achernar is a bright, blue star with about seven times the mass of the Sun.

It is a main-sequence star with a stellar classification of B6 Vep, but is about 3,000 times more luminous than the Sun. Infrared observations of the star using an adaptive optics system on the Very Large Telescope show that it has a companion star in a close orbit. This appears to be an A-type star in the stellar classification range A0V–A3V, which suggests a stellar mass of about double that of the Sun. The separation of the two stars is roughly 12.3 AU and their orbital period is at least 14–15 years.

As of 2003, Achernar is the least spherical star in the Milky Way studied to date.
It spins so rapidly that it has assumed the shape of an oblate spheroid with an equatorial diameter 35% greater than its polar diameter. The polar axis is inclined about 60.6° to the line of sight from the Earth.
Since it is actually a binary star, its highly distorted shape may cause non-negligible departures of the companion's orbital trajectory with respect to a Keplerian ellipse. A similar situation occurs for the star Regulus.

Because of the distorted shape of this star, there is a significant temperature variation by latitude. At the pole, the temperature is 17,124 K, while the equator is at 12,673 K. The average temperature of the star is about 15,000 K. The high polar temperatures are generating a fast polar wind that is ejecting matter from the star, creating a polar envelope of hot gas and plasma. The entire star is surrounded by an extended envelope that can be detected by its excess infrared emission, or by its polarization.
The presence of a circumstellar disk of ionized gas is a common feature of Be stars such as this.
The disk is not stable and periodically decretes back into the star. The maximum polarization for Achernar's disk was observed in September 2014, and it is now decreasing.

Historical visibility
Due to precession, Achernar lay much farther south in ancient times than at present, being 7.5 degrees off the south pole around 3400 BCE (decl −82º 40') and still lying at declination −76º by around 1500 BCE. Hence the Ancient Egyptians could not have known it. Even in 100 CE its declination was around −67º, meaning Ptolemy could not possibly have seen it from Alexandria—whereas Theta Eridani was visible as far north as Crete. So, Ptolemy's "End of the River" was certainly Theta Eridani. Alpha Eridani was not visible from Alexandria until about

Until about March 2000, Achernar and Fomalhaut were the two first-magnitude stars farthest from any other, their nearest neighbors being each other. Antares is now the most isolated first-magnitude star, although Antares is located in a constellation (Scorpius) with many bright second-magnitude stars, whereas the stars surrounding Alpha Eridani and Fomalhaut are considerably fainter.

Size: 145x157 mm
Weight: 130 grams

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