LIVING CORAM DEO
Monday, 11 December, 2017
The Auriga Constellation

The Auriga Constellation

The Auriga Constellation.

The Auriga ConstellationAuriga is one of the 88 modern constellations; it was among the 48 constellations listed by the 2nd-century astronomer Ptolemy. Located north of the celestial equator, its name is the Latin word for “charioteer.” In Greek mythology, Auriga is often identified as the mythological Greek hero Erichthonius of Athens, the chthonic son of Hephaestus who was raised by the goddess Athena. Erichthonius was generally credited to be the inventor of the quadriga, the four-horse chariot, which he used in the battle against the usurper Amphictyon, the event that made Erichthonius the king of Athens. His chariot was created in the image of the Sun’s chariot, the reason Zeus placed him in the heavens. Auriga is most prominent during winter evenings in the northern Hemisphere. Because of its northern declination, Auriga is only visible in its entirety as far as 34° south. A large constellation, with an area of 657 square degrees, it is half the size of the largest constellation, Hydra. The best viewing month is February at right ascension 5h 57m, and declination 42degrees 49’ at 9.00pm

Alpha Aurigae (Capella), the brightest star in Auriga, is a G8III class star (G-type giant) 43 light-years away and the sixth-brightest star in the night sky at magnitude 0.08. Capella is a spectroscopic binary with a period of 104 days; the components are both yellow giants, more specifically, the primary is a G-type star and the secondary is between a G-type and F-type star in its evolution. The secondary is formally classified as a G0III class star (G-type giant). The primary has a radius of 11.87 solar radii (R) and a mass of 2.47 solar masses (M); the secondary has a radius of 8.75 R and a mass of 2.44 M. The two components are separated by 110 million kilometres, almost 75% of the distance between the Earth and the Sun. Beta Aurigae (Menkalinan) is a bright A2IV class star (A-type subgiant). Menkalinan is 81 light-years away and has a magnitude of 1.90. Like Epsilon Aurigae, it is an eclipsing binary star that varies in magnitude by 0.1m. The two components are blue-white stars that have a period of 3.96 days. The most prominent variable star in Auriga is Epsilon Aurigae (Al Maz, Almaaz), an F0 class eclipsing binary star with an unusually long period of 27 years; its last minima occurred in 1982–1984 and 2009–2011. The distance to the system is disputed, variously cited as 4600 and 2,170 light-years. The primary is a white supergiant, and the secondary may be itself a binary star within a large dusty disk. Its maximum magnitude is 3.0, but it stays at a minimum magnitude of 3.8 for around a year; its most recent eclipse began in 2009. The primary has an absolute magnitude of −8.5 and an unusually high luminosity of 200,000 L. Epsilon Aurigae is the longest-period eclipsing binary currently known.

There are several stars with confirmed planetary systems in Auriga; there is also a white dwarf with a suspected planetary system. Discovered in 2002, HD 40979 has one planet, HD 40979 b. HD 40979 is 33.3 parsecs from Earth, a spectral class F8V star of magnitude 6.74. It is of similar size to the Sun, at 1.1 solar masses and 1.21 solar radii. The planet, with a mass of 3.83 Jupiter masses, orbits with a semi-major axis of 0.83 AU and a period of 263.1 days. HD 45350 has one planet as well, HD 45350 b, and was discovered in 2004. It has a mass of 1.79 Jupiter masses and orbits every 890.76 days at a distance of 1.92 AU.

Auriga has many open clusters and other objects because the Milky Way runs through it. The three brightest open clusters are M36, M37, and M38. Three other open clusters are NGC 2281, lying close to ψ7 Aurigae, NGC 1664, which is close to ε Aurigae, and IC 410 (surrounding NGC 1893), a cluster with nebulosity next to IC 405, the Flaming Star Nebula, found about midway between M38 and ι Aurigae. AE Aurigae, a runaway star, is a bright variable star currently located within the Flaming Star Nebula. M36 (NGC 1960) is a young galactic open cluster with approximately 60 stars, most of which are relatively bright; however, only about 40 stars are visible in most amateur instruments. It is at a distance of 3,900 light-years and has an overall magnitude of 6.0; it is 14 light-years wide. Of the three open clusters in Auriga, M36 is both the smallest and the most concentrated, though its brightest stars are approximately 9th magnitude. Most of the stars in M36 are B type stars with rapid rates of rotation. M37 (NGC 2099) is an open cluster, larger than M36 and at a distance of 4,200 light-years. It has 150 stars, making it the richest cluster in Auriga; the most prominent member is an orange star that appears at the center. M37 is approximately 25 light-years in diameter. It is the brightest open cluster in Auriga with a magnitude of 5.6. The stars of M37 are older than those of M36; they are approximately 200 million years old. Most of the constituent stars are A type stars, though there are at least 12 red giants in the cluster as well. M38 is a diffuse open cluster at a distance of 3,900 light-years, the least concentrated of the three main open clusters in Auriga. It appears as a cross-shaped or pi-shaped object and contains approximately 100 stars; its overall magnitude is 6.4. The majority of the population consists of A and B type main sequence stars, the B type stars being the oldest members, and a number of G type giant stars. One yellow-hued G type star is the brightest star in M38 at a magnitude of 7.9.

The Auriga Constellation

Auriga is home to two meteor showers. The Aurigids, named for the entire constellation and formerly called the “Alpha Aurigids,” are renowned for their intermittent outbursts, such as those in 1935, 1986, 1994, and 2007. The Aurigids are normally a placid Class II meteor shower that peaks in the early morning hours of September 1, beginning on August 28 every year. Though the maximum zenithal hourly rate is 2–5 meteors per hour, the Aurigids are fast, with an entry velocity of 67 kilometres (42 mi)/sec. The annual Aurigids have a radiant located about two degrees north of Theta Aurigae, a third-magnitude star in the center of the constellation. The Aurigids end on September 4. Some years, the maximum rate has reached 9–30 meteors per hour. The Zeta Aurigids are a weak shower with a northern and southern branch lasting from December 11 to January 21. The shower peaks on January 1 and has very slow meteors, with a maximum rate of 1–5 meteors per hour.

Credit: Go Astronomy, Wikipedia.

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