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The astronomical unit is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres or ~8 light minutes. The actual distance varies by about 3% as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once each year. The AU was originally conceived as the average of Earth's aphelion and perihelion; however, since 2012 it has been defined as exactly 149597870700 m.
61 Cygni is a binary star system in the constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitude 5.20 and 6.05, respectively, they can be seen with binoculars in city skies or with the naked eye in rural areas without photopollution.
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object.
A binary star is a star system consisting of two stars orbiting around their common barycenter. Systems of two or more stars are called multiple star systems. These systems, especially when more distant, often appear to the unaided eye as a single point of light, and are then revealed as multiple by other means.
A visual binary is a gravitationally bound binary star system that can be resolved into two stars. These stars are estimated, via Kepler's 3rd law, to have periods ranging from a few years to thousands of years. A visual binary consists of two stars, usually of a different brightness. Because of this, the brighter star is called the primary and the fainter one is called the companion. If the primary is too bright, relative to the companion, this can cause a glare making it difficult to resolve the two components. However, it is possible to resolve the system if observations of the brighter star show it to wobble about a centre of mass. In general, a visual binary can be resolved into two stars with a telescope if their centres are separated by a value greater than or equal to one arcsecond, but with modern professional telescopes, interferometry, or space-based equipment, stars can be resolved at closer distances.
Stellar parallax is the apparent shift of position of any nearby star against the background of distant objects. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at opposite sides of the Sun in its orbit, giving a baseline distance of about two astronomical units between observations. The parallax itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one astronomical unit (AU).
Epsilon Indi, Latinized from ε Indi, is a star system located at a distance of approximately 12 light-years from Earth in the southern constellation of Indus. The star has an orange hue and is faintly visible to the naked eye with an apparent visual magnitude of 4.83. It consists of a K-type main-sequence star, ε Indi A, and two brown dwarfs, ε Indi Ba and ε Indi Bb, in a wide orbit around it. The brown dwarfs were discovered in 2003. ε Indi Ba is an early T dwarf (T1) and ε Indi Bb a late T dwarf (T6) separated by 0.6 arcseconds, with a projected distance of 1460 AU from their primary star.
The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real 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.
Mu Velorum is a binary star system in the southern constellation Vela. The two stars orbit each other with a semi-major axis of 1.437 arcseconds and a period of 116.24 years. The pair have a combined apparent visual magnitude of 2.69, making the system readily visible to the naked eye. From parallax measurements, the distance to this system is estimated to be 117 light-years. The system is about 360 million years old.
Mu Cassiopeiae, Latinized from μ Cassiopeiae, is a binary star system in the constellation Cassiopeia. This system shares the name Marfak with Theta Cassiopeiae, and the name was from Al Marfik or Al Mirfaq (المرفق), meaning "the elbow". It is dimly visible to the naked eye as a point of light with an apparent visual magnitude of 5.16. The system is located at a distance of 24.6 light years from the Sun based on parallax, and is moving closer with a high radial velocity of −98 km/s. This star will move into the constellation Perseus around 5200 AD.
53 Camelopardalis is a binary star system in the northern circumpolar constellation of Camelopardalis, located 290 light years away from the Sun as determined by parallax measurements. It has the variable star designation AX Camelopardalis; 53 Camelopardalis is the Flamsteed designation. This object is dimly visible to the naked eye as a white hued star with a baseline apparent visual magnitude of +6.02. It is a single-lined spectroscopic binary system with an orbital period of 6.63 years and a high eccentricity of 0.718. The "a sin i" value of the primary is 280 Gm (1.9 AU), where a is the semimajor axis and i is the orbital inclination.
HD 59686 is a binary star system in the northern constellation of Gemini. It is visible to the naked eye as a dim point of light with an apparent visual magnitude of +5.45. The distance to this system is approximately 292 light years based on parallax, but it is drifting closer with a radial velocity of −34 km/s.
HD 10180, also designated 2MASS J01375356-6030414, is a Sun-like star in the southern constellation Hydrus that is notable for its large planetary system. Since its discovery, at least seven planets, and possibly as many as nine, have been observed orbiting it, making it potentially the largest of all known planetary systems, including the Solar System. Other stars with a large known number of planets include Kepler-90, TRAPPIST-1, Kepler-11, and 55 Cancri.
A Kepler object of interest (KOI) is a star observed by the Kepler space telescope that is suspected of hosting one or more transiting planets. KOIs come from a master list of 150,000 stars, which itself is generated from the Kepler Input Catalog (KIC). A KOI shows a periodic dimming, indicative of an unseen planet passing between the star and Earth, eclipsing part of the star. However, such an observed dimming is not a guarantee of a transiting planet, because other astronomical objects—such as an eclipsing binary in the background—can mimic a transit signal. For this reason, the majority of KOIs are as yet not confirmed transiting planet systems.
Kepler-35 is a binary star system in the constellation of Cygnus. These stars, called Kepler-35A and Kepler-35B have masses of 89% and 81% solar masses respectively, and both are assumed to be of spectral class G. They are separated by 0.176 AU, and complete an eccentric orbit around a common center of mass every 20.73 days.
This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outside the atmosphere of Earth. The field of astronomy features an extensive vocabulary and a significant amount of jargon.
99 Herculis is the Flamsteed designation for a binary star system in the northern constellation of Hercules. It has the Bayer designation b Herculis, while 99 Herculis is the Flamsteed designation. This system has an apparent visual magnitude of 5.1, which, according to the Bortle scale, makes it faintly visible to the naked eye from suburban skies. Measurements made with the Hipparcos spacecraft show an annual parallax shift of 0.064″, corresponding to a physical distance of about 51.0 ly (15.6 pc) from the Sun. The system is moving further from the Earth with a heliocentric radial velocity of +1.7 km/s.
FL Lyrae is the variable star designation for an eclipsing binary star system in the northern constellation of Lyra. The combined apparent magnitude of the pair is 9.36, which means they are too faint to be seen with the naked eye. Parallax measurements from the Hipparcos spacecraft put the system at a distance of around 420 light years from the Sun. This star system was in the view field of the Kepler space telescope during 2009−2014, which allowed monitoring during that spacecraft's mission.
HD 163840 is a binary star system in the northern constellation of Hercules. It has a combined apparent visual magnitude of 6.45, which falls just below the brightness level that is visible to the naked eye for people with normal eyesight. An annual parallax shift of 35.40 mas provides a distance estimate of about 92 light years. The system is moving closer to the Sun with a radial velocity of −33 km/s. In about 769,000 years, it will make perihelion at a separation of around 27.2 ly (8.33 pc).
9 Puppis is a binary star system in the southern constellation of Puppis. It was originally designated 9 Argus, being part of the now defunct Argo Navis constellation. The system is faintly visible to the naked eye as a point of light with a combined apparent visual magnitude of 5.16. The magnitude difference between the two stars is 0.65. Parallax measurements yield a distance estimate to 9 Puppis of approximately 54 light years from the Sun, with the dynamic and trigonometric parallaxes for the system being in close agreement. It is drifting closer with a systemic radial velocity of –21 km/s. The motion of the system through space is predicted to bring it as close as 42.2 light-years in about 292,000 years.
References
- ↑ Patrick Moore (2002). Philip's Astronomy Encyclopedia (revised and expanded ed.). London: Philip's. p. 120. ISBN 0-540-07863-8.
- ↑ "dynamical parallax". Astronomy Knowledge Base. Archived from the original on 2006-07-05. Retrieved 2006-07-18.CS1 maint: discouraged parameter (link)
- ↑ The Mass–Luminosity Relation, University of Tennessee, Astronomy 162: Stars, Galaxies, and Cosmology, lecture notes. Accessed July 18, 2006.
- ↑ Mullaney, James (2005). Double and multiple stars and how to observe them . Springer. p. 27. ISBN 1-85233-751-6.