Lacaille charted and designated 11 stars in the constellation, giving them the Bayer designations Alpha (α Hor) through Lambda Horologii (λ Hor) in 1756. Horologium has one star brighter than apparent magnitude 4, and 41 stars brighter than or equal to magnitude 6.5. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 02 h 12.8 m and 04 h 20.3 m, while the declination coordinates are between −39.64° and −67.04°. The official constellation boundaries are defined by a twenty-two-sided polygon ( illustrated in infobox). The three letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Hor". Horologium is bordered by five constellations: Eridanus (the Po river or Nile river), Caelum (the chisel), Reticulum (the reticle), Dorado (the dolphin/ swordfish), and Hydrus (the male water snake). Its position in the southern celestial hemisphere means the whole constellation is visible to observers south of 23°N. Horologium constellation: showing the tangent line, or viewer's horizon, at latitude approx 23 N, which is parallel to the line of -67.04 declension, the lower declination boundary of the constellation.Ĭovering a total of 248.9 square degrees or 0.603% of the sky, Horologium ranks 58th in area out of the 88 modern constellations. Four star systems in the constellation are known to have exoplanets at least one- Gliese 1061-contains an exoplanet in its habitable zone. The long-period variable-brightness star, R Horologii (4.7 to 14.3), has one of the largest variations in brightness among all stars in the night sky visible to the unaided eye. The constellation's brightest star-and the only one brighter than an apparent magnitude of 4-is Alpha Horologii (at 3.85), an aging orange giant star that has swollen to around 11 times the diameter of the Sun. Horologium's associated region is wholly visible to observers south of 23°N. In 1922 the constellation was redefined by the International Astronomical Union (IAU) as a region of the celestial sphere containing Lacaille's stars, and has since been an IAU designated constellation. It was first described by the French astronomer Nicolas-Louis de Lacaille in 1756 and visualized by him as a clock with a pendulum and a second hand. 'an instrument for telling the hour') is a constellation of six stars faintly visible in the southern celestial hemisphere. Horologium (Latin hōrologium, the pendulum clock, from Greek ὡρολόγιον, lit. Visible at latitudes between + 30° and − 90°.īest visible at 21:00 (9 p.m.) during the month of December. Genitive / ˌ h ɒr ə ˈ l oʊ dʒ i ˌ aɪ, - ˈ l ɒ-/
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