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--- courses:ast201:5 [2023/11/07 00:14] – asad
+++ courses:ast201:5 [2023/11/07 08:28] (current) – [1.2 Enters America] asad
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 ===== - Naming stars =====
+The Iranian astronomer [[wp>Abd al-Rahman al-Sufi]] (903--86) gave **proper names** in Arabic to almost a thousand stars listed within the 48 ancient constellations formalized by Ptolemy. The list was given in the famous book titled [[wp>The Book of Fixed Stars]]. Many modern English names are derived from the al-Sufi names. A very well-known example is Betelgeuse (Yad al-Jawzā). Many of these names [[uv:stars-named|can be found in this list]].
+Many of the al-Sufi names are derived from ancient Greek, and some of the modern English names also come directly from Greek without the intervention of al-Sufi. And astronomers continue to give proper names to some very prominent astronomical objects even though the professional trend is to use not the proper names but the official astronomical designations.
+Johann **Bayer**, in his //[[wp>Uranometria]]// (1603), again gave standard names of all the 777 stars found in the catalog of [[uv:brahe|Tycho Brahe]]. He followed al-Sufi for the bright stars, but many of the faint ones did not have a proper name. So Bayer invented a naming system where each star is named after its constellation preceded by a Greek letter giving its relative brightness in the constellation. So the brightest star in the Orion constellation is Alpha Orionis ($\alpha$ Ori), the second brightest one is Beta Orionis, and so on. Note that the **genitive** of the constellation is used, not the name; //Orionis//, not Orion. So the brightest star in our sky, **Sirius**, has the Bayer designation Alpha Canis Majoris which is also written, in short, as $\alpha$ CMa.
+The constellations had a long and complex history. In 1920, [[uv:iau|International Astronomical Union]] defined the boundaries of 88 standard [[uv:constellations]] thus dividing the sky into 88 countries., as shown below.
 {{https://upload.wikimedia.org/wikipedia/commons/thumb/8/89/Constellations%2C_equirectangular_plot%2C_Menzel_families.svg/1280px-Constellations%2C_equirectangular_plot%2C_Menzel_families.svg.png?nolink}}
-The Iranian astronomer [[wp>Abd al-Rahman al-Sufi]] (903--86) gave **proper names** in Arabic to almost a thousand stars listed within the 48 ancient constellations formalized by Ptolemy. The list was given in the famous book titled [[wp>The Book of Fixed Stars]]. Many modern English names are derived from the al-Sufi names. A very well-known example is Betelgeuse (Yad al-Jawzā).
+==== - After Galileo ====
+Bayer designations worked before **Galileo** because there were a limited number of naked-eye stars in each constellation not exceeding the number letters in the Greek alphabet. But only 7 years after //Uranometria//, Galileo discovered so many new 'invisible' stars with his primitive telescope that it was 'almost beyond belief'---to quote from his book //Starry Messenger// (1610).
+In order to deal with the numerous telescopic stars, the first Astronomer Royal, John **Flamsteed**, introduced a new designation in his //British Catalog//. Here, every star in a constellation is given an integer number in order of increasing RA. So Betelgeuse has the Flamsteed designation 58 Orionis.
+**Variable stars** and supernova follow a different convention. Variable stars are named using the letters from R to Z in order of discovery. So 'S And' is the second variable star discovered in Andromeda. After reaching Z, the prefix begins with a combination of two letters, e. g. RR, RS, etc. So we get 334 unique designations for each constellation. If even more variables are discovered, they are named using the letter V and an integer greater than 334 in order of discovery. So 'V341 Ori' is the 341st variable star discovered in Orion.
+The convention for **supernova** is very different. Most supernova are found in other galaxies, not in the Milky Way. Their names begin with the prefix SN after which is given the year of discovery and, then, a letter from A through Z. After reaching Z, two lowercase letters are used together, e. g. aa, ab ... az, ba, bb, etc. So the supernova 'SN 1987A' was the first supernova discovered in 1987.
+Next came the visionary catalog //Bonner Durchmusterung// (BD; Bonn, Germany) conducted by Freidrich Wilhelm **Argelander** (d. 1875) after his supervisor Freidrich Bessel (d. 1846). It listed the position and brightness of all stars brighter than $m=9.5$ and north of the declination $\delta=-2^\circ$ resulting in almost 320 thousand stars. Eduard Schoenfeld extended the catalog further to the south up to $\delta=-23^\circ$ and published //Bonner Durchmusterung Extended// (BDE) containing around 130 thousand stars. Juan Macon Thome and Charles Dillon Perrine published the //Cordoba Durchmusterung// (CD) from Argentina and, at the end of the nineteenth century David Jill and Jacobus Cornelius Kapteyn published the //Cape Photographic Durchmusterung// (CPD) from the Netherlands and South Africa using the recently invented method of photography. It contained around 610 thousand stars with $m<10.5$ and $\delta<-23^\circ$ and Kepteyn spent 10 years in Groningen for its compilation.
+The BD catalogs follow the same naming conventions containing 3 parts: first, the catalog abbreviation, next the declination band (all stars within $1^\circ$ declination falls in the same band) and, finally, the right ascension ordinal. So the star 'BD +07 1055' is in the declination band $7^\circ$ north of the celestial equator and its RA is 10 hours and 55 minutes. BD, CD and CPD designations are still widely used by astronomers. They also set the naming standard for stars; many modern catalogs similarly use the catalog abbreviation and the coordinates for identifying each object.
+But the catalogs are so numerous that it very soon becomes confusing for professional astronomers. So they remember Ptolemy's age-old advice that it is always better to give both name and position for every object.
+==== - Enters America ====
+European astronomers kept following the tradition of more and more detailed photographic and astrometric catalogs. But the end of the nineteenth century saw the emergence of the USA in the astronomy scene with a new vision different from the European one. They focused more on spectroscopy which laid the foundation of astrophysics as opposed to astronomy.
 ===== - Naming non-stellar objects =====