An Etymological Dictionary of Astronomy and Astrophysics
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A faint star of 8th magnitude in a binary system with → Sirius. Called also Sirius B, it is a → white dwarf with a mass comparable to that of the Sun, but with a diameter smaller than that of the Earth. The mean distance between the stars is about 20 A.U. (angular separation 4.6 seconds of arc), and their period of revolution about 50 years. This star was discovered in 1844 by Friedrich Bessel, who noticed that Sirius had a slight wobbling motion, as if it was orbiting an unseen object. In 1863, the optician and telescope maker Alvan Clark spotted the companion. The star was later determined to be a → white dwarf.

→ companion; → Sirius.

The first rising of → Sirius at dawn shortly before → sunrise. The heliacal rising of Sirius played a significant role in ancient Egypt by heralding the annual flooding of the Nile. The event took place some 70 days after the star had been seen for the last time in the western horizon at sunset. The heliacal rising of Sirius and its association with the rebirth of the Nile was so important that it marked the start of the Egyptian calendar year. At the time, the heliacal rising occurred in early July, as seen from the ancient capital of Memphis. But due to the → precession of the equinoxes the star now reappears in early August in Egypt. The date depends on the latitude (assuming transparent skies), being later for higher latitudes. For latitude 48° it occurs on about August 19.

→ heliacal; → rising; → Sirius.

The white star in the constellation → Canis Major that is the brightest star of the sky (V = -1.46). Its other designations include HD 48915, HR 2491, and BD-16°1591. Its particular brightness is mostly due to its proximity to the Earth, being a mere 8.6 → light-years away, the fifth closest star system. Sirius is a → dwarf star of → spectral type A0 or A1 V with an → effective temperature of 9,880 K, a mass of 2.063 ± 0.023 Msun (Bond et al., 2017, ApJ 840, 70), and a → luminosity of 26 Lsun. Sirius has a radius of 1.75 solar and a minimum equatorial rotation speed of 16 km s^-1. Its → rotation period is less than 5.5 days. This star is a → visual binary (separation 4.6 arcsec, period 50 years), the companion → Sirius B being the first → white dwarf to be discovered. Sirius is a → metal-rich star, its iron content triple that of the Sun, most likely from some sort of → element diffusion.

From L. Sirius, from Gk. Seirios, literally "scorching," because of its brightness.

Tištar, from Mid.Pers. Tištar, from Av. Tištrya- "(name of the deified star) Sirius," literally "the one who belongs to the three stars," in reference to the three stars of → Orion's Belt; ultimately from PIE *tri-str-o-m- "group of three stars," then *tri-str-iia- and by dissimulation Indo-Iranian *ti-str-iia-, Av. *Tištriia- and Vedic Skt. Tisyà (A. Panaino, in Iranica, under Tištrya).

Same as → companion of Sirius.

→ Sirius; B, letter of alphabet by convention.