The planet orbits a (K-type) star named Kepler-61. The star has a mass of 0.63 and a radius of 0.62. It has a temperature of 4017 K and is about 1 billion years old. In comparison, the Sun 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 15. Therefore, it is too dim to be seen with the naked eye. Kepler-61b orbits its host star with about 8% of the Sun's luminosity with an orbital period of 59.877 days and an orbital radius of about 0.28 times that of Earth's (compared to Mercury from the Sun, which is about 0.38 AU). It has an eccentricity of near 0.25, meaning its orbit is mildly elliptical.

Alpha Herculis

α HerRasalgethiα Herculis
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.

Crater (constellation)

The system is 85.6 ± 0.8 light-years away from the Sun. Epsilon and Zeta Crateris mark the Cup's rim. The largest naked eye star in the constellation, Epsilon Crateris is an evolved K-type giant star with a stellar classification of K5 III. It has about the same mass as the Sun, but has expanded to 44.7 times the Sun's radius. The star is radiating 391 times the solar luminosity. It is 366 ± 8 light-years distant from the Sun. Zeta Crateris is a binary star system. The primary, component A, is a magnitude 4.95 evolved giant star with a stellar classification of G8 III. It is a red clump star that is generating energy through the fusion of helium at its core.

Gliese 667 Cc

Gliese 667 Cc (also known as GJ 667Cc, HR 6426Cc, or HD 156384Cc) is an exoplanet orbiting within the habitable zone of the red dwarf star Gliese 667 C, which is a member of the Gliese 667 triple star system, approximately 23.62 light-years (6.8 parsecs, or about 217,000,000,000,000 km) away in the constellation of Scorpius. 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. Gliese 667 Cc is a super-Earth, an exoplanet with a mass and radius greater than that of Earth, but smaller than that of the giant planets Uranus and Neptune.


CirCircinus (constellation)Circinus constellation
Circinus is a faint constellation, with only one star brighter than fourth magnitude. Alpha Circini, a white main sequence star with an apparent magnitude of 3.19, is 54 light-years away and 4° south of Alpha Centauri. Not only the brightest star in the constellation, it is also the brightest example of a rapidly oscillating Ap (RoAp) star in the night sky. It has the unusual spectral type A7 Vp SrCrE, showing increased emissions of strontium, chromium and europium. Stars of this type have oddly localised magnetic fields and are slightly variable.

HD 28375

44 Eri
HD 28375 is a star in the zodiac constellation of Taurus. Its apparent magnitude is 5.53. Based on parallax estimates made by the Hipparcos spacecraft, the star is located fairly close, about 380 light-years (117 parsecs) away. HD 28375 has a spectrum matching that of a B-type main-sequence star. Its effective temperature is about 13,000 K. An infrared excess has been detected, indicating the presence of a circumstellar disk. The dust would have a temperature of about 119 K, located about 67 astronomical units away from the star. HD 28375 is also known as 44 Eridani, although the name has fallen out of use because constellations were redrawn, placing the star out of Eridanus and into Taurus.


Kepler-1520 bb
The planet orbits a (K-type) star named Kepler-1520. The star has a mass of 0.76 and a radius of 0.71. It has a temperature of 4677 K and is 4.47 billion years old. In comparison, the Sun is 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 16.7. Therefore, it is too dim to be seen with the naked eye. Kepler-1520b orbits its host star with about 14% of the Sun's luminosity with an orbital period of slightly over 12 hours and an orbital radius of about 0.01 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).

W Hydrae

W Hydrae is a Mira-type variable star in the constellation Hydra. The star is nearly located within the Solar neighborhood, between 75 and 120 parsecs, likely at 375 light years from the Sun. It has a visual apparent magnitude range of 5.6 to 10. In the near-infrared J band it has a magnitude of -1.7, is the 7th brightest star in the night sky, and is even brighter than Sirius. The star also shows signs of intense water emissions, indicative of the presence of a wide disk of dust and water vapour.


The star's apparent magnitude, or how bright it appears from Earth's perspective, is 13. 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 67 days at a distance of 0.37 AU (close to the orbital distance of Mercury from the Sun, which is 0.38 AU). It has a highly eccentric orbit, with an eccentricity of 0.833. In 2009, NASA's Kepler spacecraft was completing observing stars on its photometer, the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time.


The planet orbits a (M-type) red dwarf star named K2-72, orbited by a total of three planets, of which K2-72e has the longest orbital period. The star has a mass of 0.21 and a radius of 0.23. It has a temperature of 3497 K and its age is unknown. In comparison, the Sun is 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 unknown. K2-72e orbits its host star with an orbital period of 24 days and an orbital radius of about 0.1 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).

38 Virginis b

The star is metal-rich, with a metallicity ([Fe/H]) of 0.16, or 117% the solar amount. Its luminosity is 3.48 times that of the Sun. The star's apparent magnitude, or how bright it appears from Earth's perspective, is 6.11. Therefore, 38 Virginis is on the edge of not being visible to the naked eye, but it can be clearly spotted with binoculars. 38 Virginis b orbits its star every 825 days at a distance of 1.82 AU (close to Mars's orbital distance from the Sun, which is 1.53 AU). It likely receives 3% more sunlight as the Earth does from the Sun, due to its effective temperature being close to that of the Earth (in fact, only 3 degrees warmer).

List of the most distant astronomical objects

most distant objectList of most distant astronomical objectsmost distant
Here, this distinction is indicated by a "p" subscript for photometric redshifts. 1 Gly (gigalight-year) = 1 billion light-years., there were about 50 possible objects z = 8 or farther, and another 100 z = 7 candidates, based on photometric redshift estimates released by the Hubble eXtreme Deep Field (XDF) project from observations made between mid-2002 and December 2012. Not everything is included here. Objects in this list were found to be the most distant object at the time of determination of their distance. This is frequently not the same as the date of their discovery.

Extraterrestrial sky

Mercurian dayanywhere elselunar sky
Uranus has a northern polar star, Sabik (η Ophiuchi), a magnitude 2.4 star. Uranus also has a southern polar star, 15 Orionis, an unremarkable magnitude 4.8 star. Both are fainter than Earth's Polaris (α Ursae Minoris), although Sabik only slightly. A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater average distance (semi-major axis) than Neptune, 30 astronomical units (AU). Pluto, accompanied by its largest moon Charon, orbits the Sun at a distance usually outside the orbit of Neptune except for a twenty-year period in each orbit.

Zeta Leporis

ζ Lepζ Leporis
Zeta Leporis, Latinized from ζ Leporis, is a star approximately 70.5 ly away in the southern constellation of Lepus. It has an apparent visual magnitude of 3.5, which is bright enough to be seen with the naked eye. In 2001, an asteroid belt was confirmed to orbit the star. Zeta Leporis has a stellar classification of A2 IV-V(n), suggesting that it is in a transitional stage between an A-type main-sequence star and a subgiant. The (n) suffix indicates that the absorption lines in the star's spectrum appear nebulous because it is spinning rapidly, causing the lines to broaden because of the Doppler effect.

X-ray astronomy

X-ray emissionX-rayX-ray source
In the Crab Nebula X-ray spectrum there are three features that differ greatly from Scorpius X-1: its spectrum is much harder, its source diameter is in light-years (ly)s, not astronomical units (AU), and its radio and optical synchrotron emission are strong. Its overall X-ray luminosity rivals the optical emission and could be that of a nonthermal plasma. However, the Crab Nebula appears as an X-ray source that is a central freely expanding ball of dilute plasma, where the energy content is 100 times the total energy content of the large visible and radio portion, obtained from the unknown source.


WASP-43 is a K-type star in the Sextans constellation that is about 80 parsecs (261 light years) away. The star has a mass of 0.58 times that of the Sun, but is more diffuse with a radius of 0.93 times that of the Sun. The star's effective temperature is 4,400 K, making the star cooler than the Sun, and is metal-poor with regards to the Sun because it has a metallicity of [Fe/H] = −0.05 (89% the amount of iron in the Sun). The star is young, and is estimated to be 598 million years old (as compared to the Sun's 4.6 billion years). Analysis of emission lines have indicated that WASP-43 is an active star. WASP-43 has one detected planet in its orbit, WASP-43b.


Kepler-90i (also known by its Kepler Object of Interest designation KOI-351 i) is a super-Earth exoplanet with a radius 1.32 that of Earth, orbiting the early G-type main sequence star Kepler-90 every 14.45 days, discovered by NASA's Kepler spacecraft. It is located about 2,545 light-years (780 parsecs, or nearly 2.4078 km) from Earth in the constellation Draco. The exoplanet is the eighth in the star's multiplanetary system. As of December 2017, Kepler-90 is the star hosting the most exoplanets found.


KOI 10
Kepler-8 is situated some 1050 pc (or 1050 pc light years) from Earth. With a mass of 1.213 M sun and a radius of 1.486 R sun, Kepler-8 is more massive than the Sun by about a fifth of the Sun's mass, and is nearly three halves its size. The star is predicted to be 3.84 (± 1.5) billion years old, compared to the Sun's age at 4.6 billion years. Kepler-8 has a metallicity of [Fe/H] = -0.055 (± 0.03), making it 12% less metal-rich than the metal-rich Sun; metallicity is important in stars because stars richer in metal are more likely to harbor planets.

Epsilon Draconis

ε Draε Dra63/ε Dra
In 2007, Floor van Leeuwen and his team calibrated the star's apparent magnitude at 3.9974 with an updated parallax of 22.04 ± 0.37 milliarcseconds, yielding a distance of 45.4 parsecs or approximately 148 light years from Earth. Given a surface temperature of 5,068 Kelvin, theoretical calculations would yield a total luminosity for the star of about 60 times the solar luminosity. Epsilon Draconis is resolvable as a double star in telescopes of 10 centimeters aperture or larger. The companion has an apparent brightness of 7.3 at an angular distance of 3.2 arcseconds. It is a giant of spectral class F5, orbiting the yellow giant at about 130 astronomical units.


cataloghis book on astronomyMagna Syntaxis
The brightest stars were marked first magnitude (m = 1), while the faintest visible to the naked eye were sixth magnitude (m = 6). Each numerical magnitude was considered twice the brightness of the following one, which is a logarithmic scale. (The ratio was subjective as no photodetectors existed.) This system is believed to have originated with Hipparchus. The stellar positions too are of Hipparchan origin, despite Ptolemy's claim to the contrary. Ptolemy identified 48 constellations: The 12 of the zodiac, 21 to the north of the zodiac, and 15 to the south. Book IX addresses general issues associated with creating models for the five naked eye planets, and the motion of Mercury.


red shiftzred-shift
Doppler correctly predicted that the phenomenon should apply to all waves, and in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth. Before this was verified, however, it was found that stellar colors were primarily due to a star's temperature, not motion. Only later was Doppler vindicated by verified redshift observations. The first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is sometimes called the "Doppler–Fizeau effect".


quasarsquasi-stellar objectQSO
It has an average apparent magnitude of 12.8 (bright enough to be seen through a medium-size amateur telescope), but it has an absolute magnitude of −26.7. From a distance of about 33 light-years, this object would shine in the sky about as brightly as our sun. This quasar's luminosity is, therefore, about 4 trillion (4 × 10 12 ) times that of the Sun, or about 100 times that of the total light of giant galaxies like the Milky Way. This assumes the quasar is radiating energy in all directions, but the active galactic nucleus is believed to be radiating preferentially in the direction of its jet.

Black hole

black holesblack-holeblack hole physics
Since 1995, astronomers have tracked the motions of 90 stars orbiting an invisible object coincident with the radio source Sagittarius A*. By fitting their motions to Keplerian orbits, the astronomers were able to infer, in 1998, that a 2.6 million object must be contained in a volume with a radius of 0.02 light-years to cause the motions of those stars. Since then, one of the stars—called S2—has completed a full orbit. From the orbital data, astronomers were able to refine the calculations of the mass to 4.3 million and a radius of less than 0.002 light years for the object causing the orbital motion of those stars.

Astronomical constant

astronomical constantsIAU (1976) System of Astronomical Constants
The IAU also recommends values in SI units, which are the values which would be measured (in proper length and proper time) by an observer at the barycentre of the Solar System: these are obtained by the following transformations: : The astronomical unit of time is a time interval of one day (D) of 86400 seconds. The astronomical unit of mass is the mass of the Sun (S). The astronomical unit of length is that length (A) for which the Gaussian gravitational constant (k) takes the value 0.017 202 098 95 when the units of measurement are the astronomical units of length, mass and time.

Kuiper belt

Kuiper belt objectKuiper belt objectsKuiper cliff
It is too dim (magnitude 35) to be seen by Hubble directly, but it was detected by Hubble's star tracking system when it occulted a star. The scattered disc is a sparsely populated region, overlapping with the Kuiper belt but extending to beyond 100 AU. Scattered disc objects (SDOs) have very elliptical orbits, often also very inclined to the ecliptic. Most models of Solar System formation show both KBOs and SDOs first forming in a primordial belt, with later gravitational interactions, particularly with Neptune, sending the objects outward, some into stable orbits (the KBOs) and some into unstable orbits, the scattered disc.