Simon Marius

[Simon] MayrMarius, SimonSimon
He is also known for the first European observation of the Andromeda Galaxy. Marius was the son of Reichart Mayr, a mayor of Gunzenhausen. On the recommendation of George Frederick, Margrave of Brandenburg-Ansbach, he was admitted to the Margrave's Academy in Heilsbronn in 1586, where he studied until 1601. During this time, he published observations about a comet as well as astronomical tables, which gave him a reputation as a good astronomer and mathematician, and the Margrave appointed him as his official mathematician. Marius wanted to attend the University of Königsberg, but was unable to get a scholarship.

William Huggins

Sir William HugginsHugginsHuggins, Sir William
He was also the first to distinguish between nebulae and galaxies by showing that some (like the Orion Nebula) had pure emission spectra characteristic of gas, while others like the Andromeda Galaxy had the spectral characteristics of stars. Huggins was assisted in the analysis of spectra by his neighbour, the chemist William Allen Miller. Huggins was also the first to adopt dry plate photography in imaging astronomical objects. With observations of Sirius showing a redshift in 1868, Huggins hypothesized that a radial velocity of the star could be computed. Huggins won the Gold Medal of the Royal Astronomical Society in 1867, jointly with William Allen Miller.

Photometry (astronomy)

Most of the observational variables drop out and the differential magnitude is simply the difference between the instrument magnitude of the target object and the comparison object (∆Mag = C Mag – T Mag). This is very useful when plotting the change in magnitude over time of a target object, and is usually compiled into a light curve. For spatially extended objects such as galaxies, it is often of interest to measure the spatial distribution of brightness within the galaxy rather than simply measuring the galaxy's total brightness.

Walter Baade

W. BaadeBaadeBaade, Walter
There, during World War II, he took advantage of wartime blackout conditions (which reduced light pollution), to resolve stars in the center of the Andromeda galaxy for the first time. These observations led him to define distinct "populations" for stars (Population I and Population II). The same observations led him to discover that there are two types of Cepheid variable stars. Using this discovery he recalculated the size of the known universe, doubling the previous calculation made by Hubble in 1929. He announced this finding to considerable astonishment at the 1952 meeting of the International Astronomical Union in Rome.

Logarithmic scale

logarithmiclogarithmic unitlog
Order of magnitude. Entropy. Octave. pH. Richter magnitude scale.


physical worldthe universeuniverses
For comparison, the diameter of a typical galaxy is 30,000 light-years (9,198 parsecs), and the typical distance between two neighboring galaxies is 3 million light-years (919.8 kiloparsecs). As an example, the Milky Way is roughly 100,000–180,000 light-years in diameter, and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light-years away. Because we cannot observe space beyond the edge of the observable universe, it is unknown whether the size of the Universe in its totality is finite or infinite. Estimates for the total size of the universe, if finite, reach as high as megaparsecs, implied by one resolution of the No-Boundary Proposal.


With regard to stars, brightness is quantified as apparent magnitude and absolute magnitude. Brightness is, at least in some respects, the antonym of darkness. The United States Federal Trade Commission (FTC) has assigned an unconventional meaning to brightness when applied to lamps. When appearing on light bulb packages, brightness means luminous flux, while in other contexts it means luminance. Luminous flux is the total amount of light coming from a source, such as a lighting device. Luminance, the original meaning of brightness, is the amount of light per solid angle coming from an area, such as the sky. The table below shows the standard ways of indicating the amount of light.

Harlow Shapley

Shapley, HarlowH. ShapleyShapley
The astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy. At the time of the debate, Shapley was working at the Mount Wilson Observatory, where he had been hired by George Ellery Hale. After the debate, however, he was hired to replace the recently deceased Edward Charles Pickering as director of the Harvard College Observatory (HCO). He is also known to have incorrectly opposed Edwin Hubble's observations that there are additional galaxies in the universe other than the Milky Way. Shapley fiercely critiqued Hubble and regarded his work as junk science.

Photographic magnitude

For example, the red supergiant star KW Sagittarii has a photographic magnitude of 11.0 to 13.2 but a visual magnitude of about 8.5 to 11. It is also common for star charts to list a blue magnitude (B) such as with S Doradus and WZ Sagittae. The symbol for apparent photographic magnitude is m pg and the symbol for absolute photographic magnitude is M pg . The photographic magnitude scale is now considered obsolete. Absolute magnitude. Apparent magnitude. Magnitude (astronomy).

Phase curve (astronomy)

phase curvephase curvesphase function
The brightness usually refers the object's absolute magnitude, which, in turn, is its apparent magnitude at a distance of one astronomical unit from the Earth and Sun. The phase angle equals the arc subtended by the observer and the sun as measured at the body. The phase curve is useful for characterizing an object's regolith (soil) and atmosphere. It is also the basis for computing the geometrical albedo and the Bond albedo of the body. In ephemeris generation, the phase curve is used in conjunction with the distances from the object to the Sun and the Earth to calculate the apparent magnitude.

Ernst Öpik

E. J. OpikE. J. ÖpikErnst
In 1922, Ernst Öpik published a paper in which he estimated the distance of the Andromeda Galaxy. He determined the distance using a novel astrophysical method based on the observed rotational velocities of the galaxy, which depends on the total mass around which stars are rotating, and on the assumption that the luminosity per unit mass was the same as that of our galaxy. He concluded that the distance was 450 kpc. His result was in good accordance with other estimates of these days (100 to 1000 kpc) and were closer to recent estimates (778 kpc) than Hubble's result (275 kpc). His method is still widely used.


R136 is located approximately 157,000 light-years away from Earth in the Large Magellanic Cloud, positioned on the south-east corner of the galaxy at the centre of the Tarantula Nebula, also known as 30 Doradus. R136 itself is just the central condensation of the much larger NGC 2070 open cluster. For such a distant star, R136a1 is relatively unobscured by interstellar dust. The reddening causes the visual brightness to be reduced by about 1.8 magnitudes, but only around 0.22 magnitudes in the near infrared. The distance to R136a1 cannot be determined directly, but is assumed to be at the same distance as the Large Magellanic Cloud at around 50 kiloparsecs.

Jodrell Bank Observatory

Jodrell BankJodrell Bank Discovery CentreJodrell Bank Observatory (JBO)
It discovered radio noise from the Great Nebula in Andromeda—the first definite detection of an extragalactic radio source—and the remains of Tycho's Supernova in the radio frequency; at the time it had not been discovered by optical astronomy. The "Mark I" telescope, now known as the Lovell Telescope, was the world's largest steerable dish radio telescope, 76.2 m in diameter, when it was constructed in 1957; it is now the third largest, after the Green Bank telescope in West Virginia and the Effelsberg telescope in Germany. Part of the gun turret mechanisms from the battleships HMS Revenge and HMS Royal Sovereign were reused in the telescope's motor system.

Elliptical galaxy

elliptical galaxiesellipticalellipticals
Galaxy color–magnitude diagram. Galaxy morphological classification. Hubble sequence. Lenticular galaxy. M–sigma relation. Osipkov–Merritt model. Sersic profile. Elliptical Galaxies, SEDS Messier pages. Elliptical Galaxies.

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.

Star system

multiple star systemmultiple systemstriple star
Sirius, a binary consisting of a main-sequence type A star and a white dwarf. Procyon, which is similar to Sirius. Mira, a variable consisting of a red giant and a white dwarf. Delta Cephei, a Cepheid variable. Epsilon Aurigae, an eclipsing binary. Spica. Alpha Centauri is a triple star composed of a main binary yellow dwarf pair (Alpha Centauri A and Alpha Centauri B), and an outlying red dwarf, Proxima Centauri. Both A and B form a physical binary star, designated as Alpha Centauri AB, α Cen AB, or RHD 1 AB, where the AB denotes this is a binary system. The moderately eccentric orbit of the binary can make the components be as close as 11 AU or as far away as 36 AU.

Edwin Hubble

HubbleEdwin P. HubbleEdwin Powell Hubble
Hubble's results for Andromeda were not formally published in a peer-reviewed scientific journal until 1929. Hubble's findings fundamentally changed the scientific view of the universe. Supporters state that Hubble's discovery of nebulae outside of our galaxy helped pave the way for future astronomers. Although some of his more renowned colleagues simply scoffed at his results, Hubble ended up publishing his findings on nebulae. This published work earned him an award titled the American Association Prize and five hundred dollars from Burton E. Livingston of the Committee on Awards.

Robert T. A. Innes

Robert InnesRobert Thorburn Ayton InnesDr Robert T A Innes
In 1915, he found a faint star fairly close to and sharing the same large proper motion with Alpha Centauri, which until then was believed to be the closest star system to the Sun. Innes believed, on rather slim evidence, that it was closer than Alpha and in 1917 named it Proxima. He was not able to measure its distance accurately with his 9-inch refractor or the short focus Franklin-Adams astrograph. The definitive distance was measured by Harold Lee Alden at the Yale observatory station in Johannesburg which was equipped with a long focus camera designed for stellar parallax work. Alden’s more precise measurements confirmed Proxima to be the closest star to the sun.

SN 1006

supernova of 1006supernova that occurred in 1006 CEthe 1006 supernova
SN 1006 was a supernova that is likely the brightest observed stellar event in recorded history, reaching an estimated −7.5 visual magnitude, and exceeding roughly sixteen times the brightness of Venus. Appearing between April 30 and May 1, 1006 AD in the constellation of Lupus, this "guest star" was described by observers across China, Japan, Iraq, Egypt, and Europe, and possibly recorded in North American petroglyphs. Some reports state it was clearly visible in the daytime. Modern astronomers now consider its distance from us to be about 7,200 light-years.