Big Bang

Big Bang Theorybig-bangbirth
Star formation would cease with the consumption of interstellar gas in each galaxy; stars would burn out, leaving white dwarfs, neutron stars, and black holes. Very gradually, collisions between these would result in mass accumulating into larger and larger black holes. The average temperature of the universe would asymptotically approach absolute zero—a Big Freeze. Moreover, if the proton were unstable, then baryonic matter would disappear, leaving only radiation and black holes. Eventually, black holes would evaporate by emitting Hawking radiation.

Stars and planetary systems in fiction

47 Ursae Majoris in fictionArcturus61 Cygni
Barnard's Star is a red dwarf of apparent magnitude 9 and is thus too dim to be seen with the unaided eye. However, at approximately 6 light-years away it is the second-closest stellar system to the Sun; only the Alpha Centauri system is known to be closer. Thus, even though it is suspected to be a flare star, it has attracted the attention of science fiction authors, filmmakers, and game developers.

Voyager 1

Voyager1the first spacecraft to leave the Solar System
As of September 2012, sunlight took 16.89 hours to get to Voyager 1 which was at a distance of 121 AU. The apparent magnitude of the Sun from the spacecraft was −16.3 (less than 30 times the brightness of the full moon). The spacecraft was traveling at 17.043 km/s relative to the Sun. It would need about 17,565 years at this speed to travel a light-year. To compare, Proxima Centauri, the closest star to the Sun, is about 4.2 light-years (2.65 AU) distant. Were the spacecraft traveling in the direction of that star, 73,775 years would pass before Voyager 1 reaches it.

List of exoplanets discovered using the Kepler spacecraft

1,013 confirmed exoplanets in about 440 star systemsa total of 2,321 candidatesdiscovered exoplanets
The list of exoplanets detected by the Kepler spacecraft contains bodies with a wide variety of properties, with significant ranges in orbital distances, masses, radii, composition, habitability, and host star type., the Kepler spacecraft and its follow-up observations have detected 2,300 confirmed planets, including hot Jupiters, super-Earths, circumbinary planets, and planets located in the circumstellar habitable zones of their host stars. In addition, Kepler has detected over 3,601 unconfirmed planet candidates and 2,165 eclipsing binary stars. In addition to detecting planets itself, Kepler has also uncovered the properties of three previously known extrasolar planets.

List of unusual units of measurement

football fieldfull-lengthDog year
The siriometer is a rarely used astronomical measure equal to one million astronomical units, i.e., one million times the average distance between the Sun and Earth. This distance is equal to about 15.8 light-years, 149.6 Pm or 4.8 parsecs, and is about twice the distance from Earth to the star Sirius. One barn is 10 −28 square metres, about the cross-sectional area of a uranium nucleus. The name probably derives from early neutron-deflection experiments, when the uranium nucleus was described, and the phrases "big as a barn" and "hit a barn door" were used. Additional units include the microbarn (or "outhouse") and the yoctobarn (or "shed").

HD 41742/41700

HD 41742
The wide separation of this tertiary component means that it has a separate Hipparcos entry to the primary, which confirms that the two stars lie at the same distance and are co-moving. The physical separation between the two is about 0.026 parsecs (0.084 light-years), or approximately 17200 AU. This is comparable to the ~15000 AU separation between Alpha Centauri AB and Proxima Centauri; such wide separations between components are relatively rare, at least for solar-type stars. Radial velocity observations of HD 41742 A with the HARPS spectrograph detected variations on a level of several km/s over a period of months, indicating that the star is a single-lined spectroscopic binary (SB1).

Wolf 359

star of the same name
Wolf 359 is a red dwarf star located in the constellation Leo, near the ecliptic. At a distance of approximately 7.9 light years from Earth, it has an apparent magnitude of 13.54 and can only be seen with a large telescope. Wolf 359 is one of the nearest stars to the Sun; only the Alpha Centauri system (including Proxima Centauri), Barnard's Star and the brown dwarfs Luhman 16 and WISE 0855−0714 are known to be closer. Its proximity to Earth has led to its mention in several works of fiction. Wolf 359 is one of the faintest and lowest-mass stars known.

Gliese 667

GJ 667CcGliese 667 C
The largest star in the system, Gliese 667 A (GJ 667 A), is a K-type main-sequence star of stellar classification K3V. It has about 73% of the mass of the Sun and 76% of the Sun's radius, but is radiating only around 12-13% of the luminosity of the Sun. The concentration of elements other than hydrogen and helium, what astronomers term the star's metallicity, is much lower than in the Sun with a relative abundance of around 26% solar. The apparent visual magnitude of this star is 6.29, which, at the star's estimated distance, gives an absolute magnitude of around 7.07 (assuming negligible extinction from interstellar matter).

Alpha Herculis

α HerRasalgethiα 1 Her
Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated 64 Herculis, is a multiple star system in the constellation of Hercules. Appearing as a single point of light to the naked eye, it is resolvable into a number of components through a telescope. It has a combined apparent magnitude of 3.08, although the brightest component is variable in brightness. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 360 light-years (110 parsecs) distant from the Sun. It consists of two binary pairs in mutual orbit designated α¹ Herculis or α Herculis A (the brightest of the two) and α² Herculis or α Herculis B.

HIP 57274 d

d
HIP 57274 d is an exoplanet orbiting the K-type main sequence star HIP 57274 about 84.5 light-years (26 parsecs, or nearly 8.022 km) from Earth in the constellation Cetus. It orbits within the outer part of its star's habitable zone, at a distance of 1.01 AU. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star. HIP 57274 d is a gas giant, a planet that has a radius and mass close to that of the gas giants Jupiter and Saturn. It has a temperature of 167 K.

BD+14 4559 b

b
BD+14 4559 b is an exoplanet orbiting the K-type main sequence star BD+14 4559 about 161 light-years (49 parsecs, or nearly 1.5 km) from Earth in the constellation Pegasus. It orbits its star within the habitable zone at a distance of 0.777 AU, close to that of Venus, but its star is less energetic, thus its habitable zone is closer to it than Earth. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star. BD+14 4559 b is a gas giant, an exoplanet that has a radius and mass around that of the gas giants Jupiter and Saturn. It has a temperature of 205 K.

List of astronomy acronyms

EGGsX-Ray Flashes
ACV – (celestial object) Alpha Canes Venatici, a class of rotating variable stars with strong magnetic fields named after Alpha Canum Venaticorum (Cor Caroli), the archetype for the class. ACYG – (celestial object) Alpha CYGni, a class of rotating variable stars named after Alpha Cygni (Deneb), the archetype for the class. ADAF – (astrophysics terminology) Advection Dominated Accretion Flow, a mechanism by which matter is slowly accreted onto a black hole. ADC – (organization) Astronomical Data Center. ADEC – (organization) Astrophysics Data Centers Executive Council, an organization that provides oversight for the Astrophysics Data and Information Services.

SX Centauri

SX Cen
SX Centauri is a variable star in the constellation Centaurus. An RV Tauri variable, its light curve alternates between deep and shallow minima, varying its apparent magnitude from 9.1 to 12.4. From the period-luminosity relationship, it is estimated to be around 1.6 kpc (5200 light-years) from Earth. Gaia Data Release 2 gives a parallax of 0.2175 mas, corresponding to distance of about 4,600 pc. RV Tauri variables like SX Centauri are supergiant pulsating stars and a subtype of the population II Cepheids. They are stars that have already passed the asymptotic giant branch (AGB) and are in the last stage of their evolution before becoming a planetary nebula.

WR 147

WR 147 is a star system in the constellation of Cygnus. Its distance has been calculated to be around 2,100 ± 200 light years (630 ± 70 parsecs) away from the Earth. This puts the star in front of the OB association known as Cygnus OB2. The system is extremely reddened by interstellar extinction - that is, dust in front of the star scatters much of the blue light coming from WR 147, leaving the star appearing reddish. The distance of WR 147 has been calculated to be 630 parsecs (pc) based on infrared photometry. The extinction in the visual range was calculated to be 11.5 magnitudes and the absolute visual magnitude assumed to be −6.7.

List of most luminous stars

most luminousmost luminous starsmost luminous stars known
Stars that are at least sometimes visible to the unaided eye have their apparent magnitude (6.5 or brighter) highlighted in blue. Note that even the most luminous stars are much less luminous than the more luminous persistent extragalactic objects, such as quasars. For example, 3C 273 has an average apparent magnitude of 12.8 (when observing with a telescope), but an absolute magnitude of −26.7. If this object were 10 parsecs away from Earth it would appear nearly as bright in the sky as the Sun (apparent magnitude −26.74).

Kepler-186f

fthe first Earth-size planet
The planet orbits a (M-type) star named Kepler-186, orbited by a total of five planets. The star has a mass of 0.54 and a radius of 0.52. It has a temperature of 3755 K and is about 4 billion years old, about 600 million years younger than the Sun, which is 4.6 billion years old and has a temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.62. Therefore, it is too dim to be seen with the naked eye. Kepler-186f orbits its star with about 5% of the Sun's luminosity with an orbital period of 129.9 days and an orbital radius of about 0.40 times that of Earth's (compared to 0.39 AU for Mercury).

Kepler-419c

c
The planet orbits an (F-type) star named Kepler-419. The star has a mass of 1.39 and a radius of 1.75. It has a surface temperature of 6430 K and is 2.8 billion years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 12. It is too dim to be seen with the naked eye. Kepler-419c orbits its host star with 270% of the Sun's luminosity (2.7 ) about every 675 days (around 1.84 years) at a distance of 1.61 AU (compared to the orbital distance of Mars, which is 1.52 AU). It has a slightly eccentric orbit, with an eccentricity of 0.184.

Pleione (star)

Pleione28 Tau28 Tau (Pleione)
In the case of Pleione, the "peculiar" emissions come from gaseous circumstellar disks formed of material being ejected from the star. There has been significant debate as to the star's actual distance from Earth. The debate revolves around the different methodologies to measure distance—parallax being the most central, but photometric and spectroscopic observations yielding valuable insights as well. Before the Hipparcos mission, the estimated distance for the Pleiades star cluster was around 135 parsecs or 440 light years.

Beta Pictoris b

bbeta Pic bβ Pictoris b
The planet orbits an (A-type) star named Beta Pictoris. The star has a mass of 1.75 and a radius of 1.8. It has a surface temperature of 8056 K and is 12 million years old. In comparison, the Sun is about 4.6 billion years old and has a surface temperature of 5778 K. It is slightly metal-rich, with a metallicity ([Fe/H]) of 0.06, or 112% of that found in the Sun. Its luminosity is 8.7 times that of the Sun. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 3. Therefore, it can be seen with the naked eye. Beta Pictoris b orbits its host star every 21 years at a distance of 9.2 AU (about the same as Saturn's distance, which is about 9.55 AU).

Kepler-62f

fKepler 62f
Kepler-62f (also known by its Kepler Object of Interest designation KOI-701.04) is a super-Earth exoplanet orbiting within the habitable zone of the star Kepler-62, the outermost of five such planets discovered around the star by NASA's Kepler spacecraft. It is located about 990 light-years (304 parsecs) from Earth in the constellation of Lyra. Kepler-62f orbits its star at a distance of 0.718 AU from its host star with an orbital period of roughly 267.3 days, has a mass at least 2.8 times that of Earth, and has a radius of around 1.41 times that of Earth.

Kepler-442b

b
The planet orbits a (K-type) star named Kepler-442. The star has a mass of 0.61 and a radius of 0.60. It has a temperature of 4402 K and is around 2.9 billion years old, with some uncertainty. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K. The star is somewhat metal-poor, with a metallicity (Fe/H) of −0.37, or 42% of the solar amount. Its luminosity is 11% that of the Sun. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.97. Therefore, it is too dim to be seen with the naked eye.

Upsilon Andromedae d

dMajriti
Upsilon Andromedae d (υ Andromedae d, abbreviated Upsilon And d, υ And d), also named Majriti, is a super-Jupiter exoplanet orbiting within the habitable zone of the Sun-like star Upsilon Andromedae A, approximately 44 light-years (13.5 parsecs, or nearly 4.163 km) away from Earth in the constellation of Andromeda. Its discovery made it the first multiplanetary system to be discovered around a main sequence star, and the first such system known in a multiple star system. The exoplanet was found by using the radial velocity method, where periodic Doppler shifts of spectral lines of the host star suggest an orbiting object.