Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way.
Fornax is a constellation in the southern celestial hemisphere, partly ringed by the celestial river Eridanus. Its name is Latin for furnace. It was named by French astronomer Nicolas Louis de Lacaille in 1756. Fornax is one of the 88 modern constellations.
A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of light. The most prominent stars have been categorised into constellations and asterisms, and many of the brightest stars have proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. The observable universe contains an estimated 1022 to 1024 stars. Only about 4,000 of these stars are visible to the naked eye—all within the Milky Way galaxy.
Sirius is the brightest star in the night sky. Its name is derived from the Greek word Σείριος, meaning lit. 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated α CMa or Alpha CMa. With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star. Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.
Albireo is a double star designated Beta Cygni. The International Astronomical Union uses the name "Albireo" specifically for the brightest star in the system. Although designated 'beta', it is fainter than Gamma Cygni, Delta Cygni, and Epsilon Cygni and is the fifth-brightest point of light in the constellation of Cygnus. Appearing to the naked eye to be a single star of magnitude 3, viewing through even a low-magnification telescope resolves it into its two components. The brighter yellow star, itself a very close binary system, makes a striking colour contrast with its fainter blue companion.
Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects on the sky. This permitted the first high-precision measurements of the intrinsic brightnesses, proper motions, and parallaxes of stars, enabling better calculations of their distance and tangential velocity. When combined with radial velocity measurements from spectroscopy, astrophysicists were able to finally measure all six quantities needed to determine the motion of stars. The resulting Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Hipparcos' follow-up mission, Gaia, was launched in 2013.
Crater is a small constellation in the southern celestial hemisphere. Its name is the latinization of the Greek krater, a type of cup used to water down wine. One of the 48 constellations listed by the second-century astronomer Ptolemy, it depicts a cup that has been associated with the god Apollo and is perched on the back of Hydra the water snake.
The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A direct distance measurement of an astronomical object is possible only for those objects that are "close enough" to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances. Several methods rely on a standard candle, which is an astronomical object that has a known luminosity.
Gaia is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until 2025. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision, and the positions of exoplanets by measuring attributes about the stars they orbit such as their apparent magnitude and color. The mission aims to construct by far the largest and most precise 3D space catalog ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars, among others.
Iota Orionis is a multiple star system in the equatorial constellation of Orion the hunter. It is the eighth-brightest member of Orion with an apparent visual magnitude of 2.77 and also the brightest member of the asterism known as Orion's Sword. It is a member of the NGC 1980 open cluster. From parallax measurements, it is located at a distance of roughly 1,340 light-years from the Sun.
56 Andromedae, abbreviated 56 And, is a probable binary star system in the northern constellation of Andromeda. 56 Andromedae is the Flamsteed designation. It has a combined apparent visual magnitude of 5.69, which is just bright enough to be dimly visible to the naked eye under good seeing conditions. The distance to this system can be ascertained from its annual parallax shift, measured at 9.9 mas with the Gaia space observatory, which yields a separation of 330 light years. It is moving further from the Earth with a heliocentric radial velocity of +62 km/s and is traversing the celestial sphere at a relatively high rate of 0.183″ per year. This pair is positioned near the line of sight to the open cluster NGC 752, located 1,490 light-years away.
Sigma Orionis or Sigma Ori is a multiple star system in the constellation Orion, consisting of the brightest members of a young open cluster. It is found at the eastern end of the belt, south west of Alnitak and west of the Horsehead Nebula which it partially illuminates. The combined brightness of the component stars is magnitude 3.80.
R Centauri is a Mira variable star in the constellation Centaurus.
KW Sagittarii is a red supergiant star, located approximately 2,420 parsecs away from the Sun in the direction of the constellation Sagittarius. It is one of the largest known stars, with a diameter about 1,000 times larger than the Sun. If placed at the center of the Solar System, the star's surface would engulf Mars, coming close to Jupiter's orbit.
Delta2 Lyrae is a 4th magnitude star in the constellation Lyra, approximately 770 light years away from Earth. It is one of the M4II spectral standard stars.
RR Lyrae is a variable star in the Lyra constellation, figuring in its west near to Cygnus. As the brightest star in its class, it became the eponym for the RR Lyrae variable class of stars and it has been extensively studied by astronomers. RR Lyrae variables serve as important standard candles that are used to measure astronomical distances. The period of pulsation of an RR Lyrae variable depends on its mass, luminosity and temperature, while the difference between the measured luminosity and the actual luminosity allows its distance to be determined via the inverse-square law. Hence, understanding the period-luminosity relation for a local set of such stars allows the distance of more distant stars of this type to be determined.
The Hertzsprung–Russell diagram is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temperatures. The diagram was created independently in 1911 by Ejnar Hertzsprung and by Henry Norris Russell in 1913, and represented a major step towards an understanding of stellar evolution.
HIP 13044 is a red horizontal-branch star about 2,300 light years from Earth in the constellation Fornax. The star is part of the Helmi stream, a former dwarf galaxy that merged with the Milky Way between six and nine billion years ago. As a result, HIP 13044 circles the Galactic Center at a highly irregular orbit with respect to the galactic plane. HIP 13044 is slightly less massive than the Sun, but is approximately seven times its size. The star, which is estimated to be at least nine billion years old, has passed the red-giant phase. The relatively fast rotation of the star may be due to having engulfed one or more planets during the red-giant phase.
HD 5608 is an orange-hued star in the northern constellation of Andromeda with one known planet, HD 5608 b. It is a dim star near the lower limit of visibility to the naked eye, having an apparent visual magnitude of +5.98. The distance to HD 5608, as estimated from an annual parallax shift of 17.07 mas, is 191 light-years. It is moving closer to the Earth with a heliocentric radial velocity of −23 km/s, and is expected to make its closest approach in 1.285 million years when it comes to within 124 light-years.
BO Carinae, also known as HD 93420, is an irregular variable star in the constellation Carina.
