Edmond Halley

HalleyEdmund HalleyE. Halley
It is reasonable to assume Halley possessed and had read this book given that the Gregorian design was the principal telescope design used in astronomy in Halley's day. It is not to Halley's credit that he failed to acknowledge Gregory's priority in this matter. In 1718 he discovered the proper motion of the "fixed" stars by comparing his astrometric measurements with those given in Ptolemy's Almagest. Arcturus and Sirius were two noted to have moved significantly, the latter having progressed 30 arc minutes (about the diameter of the moon) southwards in 1800 years.


Antares Bα Scorpionisα
Antares, like the similarly-sized red supergiant Betelgeuse in the constellation Orion, will almost certainly explode as a supernova, probably within the next ten thousand years. For a few months, the Antares supernova could be as bright as the full moon and be visible in daytime. The magnitude 5.5 companion star Antares B changed from an angular separation (from its primary, Antares) of 3.3 arcseconds in 1854 to 2.67" ± 0.02" in 2006. It was first observed by Scottish astronomer James William Grant FRSE while in India on 23 July 1844.

Thomas Henderson (astronomer)

Thomas HendersonHenderson, ThomasProfessor Thomas Henderson
Henderson did not immediately publish his results, however (there had been previous, discredited attempts to claim a measurement of stellar parallax), and eventually he was beaten to the punch by Friedrich Wilhelm Bessel, who published a parallax of 10.3 light years (9.6% too small) for 61 Cygni in 1838. Henderson published his results in 1839, but was relegated to second place because of his lack of confidence. He later published confirming observations by Thomas Maclear. Alpha Centauri remained the nearest known star until the discovery of Proxima Centauri in 1915 by Robert T. A. Innes.

Latinisation of names

Latinisation or Latinization is the practice of rendering a non-Latin name (or word) in a Latin style. It is commonly found with historical personal names, with toponyms, and in the standard binomial nomenclature of the life sciences. It goes further than romanisation, which is the transliteration of a word to the Latin alphabet from another script (e.g. Cyrillic).


HIPTYCHipparcos satellite
Hipparcos and Tycho Catalogues at the CASU Astronomical Data Centre, Institute of Astronomy, University of Cambridge. Hipparcos Main Catalogue and Tycho-1 Catalogue at the CDS in Strasbourg.


Claudius PtolemyPtolemaicPtol.
Later Arabic astronomers, geographers and physicists referred to him by his name in بَطْلُمْيوس Baṭlumyus. Ptolemy's Almagest is the only surviving comprehensive ancient treatise on astronomy. Babylonian astronomers had developed arithmetical techniques for calculating astronomical phenomena; Greek astronomers such as Hipparchus had produced geometric models for calculating celestial motions. Ptolemy, however, claimed to have derived his geometrical models from selected astronomical observations by his predecessors spanning more than 800 years, though astronomers have for centuries suspected that his models' parameters were adopted independently of observations.


ultraviolet lightUVultraviolet radiation
Technology for VUV instrumentation was largely driven by solar astronomy for many decades. While optics can be used to remove unwanted visible light that contaminates the VUV, in general, detectors can be limited by their response to non-VUV radiation, and the development of "solar-blind" devices has been an important area of research. Wide-gap solid-state devices or vacuum devices with high-cutoff photocathodes can be attractive compared to silicon diodes. Extreme UV (EUV or sometimes XUV) is characterized by a transition in the physics of interaction with matter.

Northern Hemisphere

The dates vary each year due to the difference between the calendar year and the astronomical year. Its surface is 60.7% water, compared with 80.9% water in the case of the Southern Hemisphere, and it contains 67.3% of Earth's land. The Arctic is the region north of the Arctic Circle. Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in the form of snow. The Arctic experiences some days in summer when the Sun never sets, and some days during the winter when it never rises. The duration of these phases varies from one day for locations right on the Arctic Circle to several months near the North Pole, which is the middle of the Northern Hemisphere.

Egyptian astronomy

EgyptianEgyptian astronomersastronomy
The rising of Sirius (Egyptian: Sopdet, Greek: Sothis) at the beginning of the inundation was a particularly important point to fix in the yearly calendar. One of the most important Egyptian astronomical texts was the Book of Nut, going back to the Middle Kingdom or earlier. The death of a king had a strong connection to the stars for Ancient Egyptians. They believed once a king was deceased, their soul would rise to the heavens and become a star. Translated pyramid texts describe the king ascending and becoming the Morning Star among the Imperishable Stars of past kings.

IAU Working Group on Star Names

Working Group on Star NamesIAU-approved
The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C Education, Outreach and Heritage. The IAU states that it is keen to make a distinction between the terms name and designation. To the IAU, name refers to the (usually colloquial) term used for a star in everyday speech, while designation is solely alphanumerical and used almost exclusively in official catalogues and for professional astronomy.


precessgyroscopic precessionprecessing
They are: In astronomy, precession refers to any of several gravity-induced, slow and continuous changes in an astronomical body's rotational axis or orbital path. Precession of the equinoxes, perihelion precession, changes in the tilt of Earth's axis to its orbit, and the eccentricity of its orbit over tens of thousands of years are all important parts of the astronomical theory of ice ages. (See Milankovitch cycles.) Axial precession is the movement of the rotational axis of an astronomical body, whereby the axis slowly traces out a cone. In the case of Earth, this type of precession is also known as the precession of the equinoxes, lunisolar precession, or precession of the equator.


photosphericsolar diskSun's surface
All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant. The Sun's photosphere has a temperature between 4500 and 6000 K (with an effective temperature of 5777 K) and a density somewhere around 1 to 1 kg/m 3 ; other stars may have hotter or cooler photospheres.


Alpha Tauribrightest starRohini
Past this radius, the modest outflow of the stellar wind itself declines in temperature to about 7,500 K at a distance of 1 astronomical unit (AU)−the distance of the Earth from the Sun. The wind continues to expand until it reaches the termination shock boundary with the hot, ionized interstellar medium that dominates the Local Bubble, forming a roughly spherical astrosphere with a radius of around 1,000 AU, centered on Aldebaran. Aldebaran is one of the easiest stars to find in the night sky, partly due to its brightness and partly due to its spatial relation to one of the more noticeable asterisms in the sky.


At perihelion, the Earth's center is about 0.98329 astronomical units (AU) or 147098070 km from the Sun's center. In contrast, the Earth reaches aphelion currently in early July, approximately 14 days after the June Solstice. The aphelion distance between the Earth's and Sun's centers is currently about 1.01671 AU or 152097700 km. Dates change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles. In the short term, the dates of perihelion and aphelion can vary up to 2 days from one year to another.


cometslong-period cometshort-period comet
id=mdp.39015006990892;view=1up;seq=124 From p. 110:] " … mais il faut convenir que cette suite immense de détails m'eût semblé effrayante, si Madame LEPAUTE, appliquée depuis long-temps & avec succès aux calculs Astronomiques, n'en eût partagé le travail." ( … but it must be admitted that this immense series of details would have seemed frightening to me if Madame LEPAUTE, [who has] long applied [herself] successfully to astronomical calculations, had not shared in the work.) See also: * Broughton, Peter (1985) "The first predicted return of comet Halley," Journal for the History of Astronomy, 16 : 123–132.

Convection zone

convectiveconvectionconvective zone
A convection zone, convective zone or convective region of a star is a layer which is unstable to convection. Energy is primarily or partially transported by convection in such a region. In a radiation zone, energy is transported by radiation and conduction.

Open cluster

open star clusterstar clusteropen clusters
Other open clusters were noted by early astronomers as unresolved fuzzy patches of light. The Roman astronomer Ptolemy mentions the Praesepe, the Double Cluster in Perseus, and the Ptolemy Cluster, while the Persian astronomer Al-Sufi wrote of the Omicron Velorum cluster. However, it would require the invention of the telescope to resolve these nebulae into their constituent stars. Indeed, in 1603 Johann Bayer gave three of these clusters designations as if they were single stars. The first person to use a telescope to observe the night sky and record his observations was the Italian scientist Galileo Galilei in 1609.

Molecular cloud

giant molecular cloudmolecular cloudsmolecular gas
Molecular clouds, and especially GMCs, are often the home of astronomical masers. • Accretion (astrophysics) • Astrochemistry • Atomic and molecular astrophysics • Cosmic dust • Cosmochemistry • Evaporating gaseous globule • Interstellar ice • List of interstellar and circumstellar molecules • Nebula • Orion Molecular Cloud Complex • Formation and evolution of the Solar System


Astronomers observe objects in the infrared portion of the electromagnetic spectrum using optical components, including mirrors, lenses and solid state digital detectors. For this reason it is classified as part of optical astronomy. To form an image, the components of an infrared telescope need to be carefully shielded from heat sources, and the detectors are chilled using liquid helium. The sensitivity of Earth-based infrared telescopes is significantly limited by water vapor in the atmosphere, which absorbs a portion of the infrared radiation arriving from space outside of selected atmospheric windows.


chromosphericchromospheric activitychromospherically
Plage (astronomy). Orders of magnitude (density). Moreton wave. Animated explanation of the Chromosphere (and Transition Region) (University of South Wales). Animated explanation of the temperature of the Chromosphere (and Transition Region) (University of South Wales).

Gaia (spacecraft)

GaiaGaia spacecraftGaia'' spacecraft
The first data release, Gaia DR1, based on 14 months of observations made through September 2015, took place on 14 September 2016 and is described in a series of articles published in Astronomy and Astrophysics. The data release includes "positions and … magnitudes for 1.1 billion stars using only Gaia data; positions, parallaxes and proper motions for more than 2 million stars" based on a combination of Gaia and Tycho-2 data for those objects in both catalogues; "light curves and characteristics for about 3000 variable stars; and positions and magnitudes for more than 2000 … extragalactic sources used to define the celestial reference frame".

Neutron star

neutron starsdying starneutron star formation
In October 2018, astronomers reported that GRB 150101B, a gamma-ray burst event detected in 2015, may be directly related to the historic GW170817 and associated with the merger of two neutron stars. The similarities between the two events, in terms of gamma ray, optical and x-ray emissions, as well as to the nature of the associated host galaxies, are "striking", suggesting the two separate events may both be the result of the merger of neutron stars, and both may be a kilonova, which may be more common in the universe than previously understood, according to the researchers.


Saturn's atmosphereExploration of Saturnhome planet
Saturn appears to the naked eye in the night sky as a bright, yellowish point of light. The mean apparent magnitude of Saturn is 0.46 with a standard deviation of 0.34. Most of the magnitude variation is due to the inclination of the ring system relative to the Sun and Earth. The brightest magnitude, -0.55, occurs near in time to when the plane of the rings is inclined most highly, and the faintest magnitude, 1.17, occurs around the time when they are least inclined. It takes approximately 29.5 years for the planet to complete an entire circuit of the ecliptic against the background constellations of the zodiac.


AlhaiotAlpha Aurigaealpha Aurigae (Capella)
In Inuit astronomy, Capella, along with Menkalinan (Beta Aurigae), Pollux (Beta Geminorum) and Castor (Alpha Geminorum), formed a constellation Quturjuuk, "collar-bones", the two pairs of stars denoting a bone each. Used for navigation and time-keeping at night, the constellation was recognised from Alaska to western Greenland. The Gwich'in saw Capella and Menkalinan has forming shreets'ą įį vidzee, the right ear of the large circumpolar constellation Yahdii, which covered much of the night sky, and whose orientation facilitated navigation and timekeeping.

Black hole

black holesblack-holeblackhole
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.