OCT - This Month's Astronomy History

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This Month in the History of Astronomy - October

Birthdays || Discoveries

Oct 1, 1958 - NASA was established by an act of Congress.
Oct 2, 1852 - William C. Ramsay, British chemist involved in the first identification of helium on earth.
Ramsay became chair of Chemistry at University College London in 1887. At a lecture on Apr 19, 1894, by Lord Rayleigh, Ramsay was encouraged to investigate the curious fact that nitrogen made chemically had a slightly lower density than nitrogen made from air, after other known components had been removed. Ramsay was able to isolate a new, inert gas, measure its atomic weight, named it argon, and thus established the existence of an eighth column in the periodic table. An unreactive gas was suspected to be a component of air as early as 1785 by Henry Cavendish. Ramsay would go on to also ID neon, krypton, xenon, and radon, receiving the 1904 Nobel Prize in Chemistry.
Radioactivity was discovered about the time argon was discovered, and another curious fact was that uranium ore, when heated, seemed to give off an inert gas. Ramsay prepared the samples (1895) used by the chemists/minerologists/spectroscopists Per Teodor Cleve and Nils Abraham Langlet, who showed the heated gas gave off the same spectral lines as those first seen in the sun's corona during a total solar eclipse in 1868.
Oct 2, 1886 - Robert Trumpler, Swiss born and educated astronomer who spent most his career in the U.S. studying galactic star clusters (open clusters), discovered the interstellar absorption of starlight by dust grains mixed in with the tenuous gas (independently of Boris Vorontsov-Vel'laminov in Russia) in 1930, was involved in an early test of Einstein's general theory of relativity (with Campbell at Lick Observatory), and made observations of Mars which seriously challenged Schiaparelli's claims about there being canals there; Trumpler's proposal that the features may be volcanic faults found support 50 years later with the Mariner 9 mission's return of the first relatively close-up photos of the surface of the planet.
Oct 5, 1882 - Robert Goddard, American rocketry pioneer.
Oct 6, 1893 - Meghnad Saha, Indian astrophysicist, who worked out the widely used Saha equation, relating the ionization state of a gas to its temperature and pressure. An understanding of thermal ionization in gases was crucial for the early work on stellar spectra and using relative absorption line strengths for the determination of the temperature in the atmospheres of stars.
Some discrepancies with the predictions of his equation led, in the 1920s, to the realization that the pressure in stellar atmospheres was more like 10^-4 or 10^-5, rather that the 0.1 to 1 atmospheres (relative to earth's surface) which he and others, lacking any other information, had initially assumed.
Saha was very active in building up Indian science, creating, among other institutions, the Institute of Nuclear Physics in Calcutta. He became a member of the Indian Parliament in 1952, four years before his death.

Scientists are often accused of living in the "Ivory Tower" and not troubling their mind with realities, and apart from my association with political movements in my juvenile years, I had lived in an ivory tower up to 1930. But science and technology are as important for administration nowadays as law and order. I have gradually glided into politics because I wanted to be of some use to the country in my own humble way.
Oct 7, 1885 - Niels Bohr, Danish pioneer atomic physicist.
Oct 8, 1873 - Ejnar Hertzsprung, Danish astronomer who first proved the existence of giant and dwarf stars around 1910.
Oct 9, 1873 - Karl Schwarzschild. Schwarzschild was the first to solve Einstein's new general relativity field equations -- while serving in the German army in WW I in 1915, coming up with the "Schwarzschild radius", the size of (the event horizon of) a black hole. He died the next year of the autoimmune disease pemphigus, which he contracted during the war. He's the father of equally famous astrophysicist Martin Schwarzschild (see May 31).
Oct 11, 1758 - Heinrich Olbers, German astronomer and mathematician. Though chiefly remembered now for Olber's Paradox in cosmology, he made important contributions at the time on comets, asteroids, and the determination of their orbits.
At sixteen, Olbers calculated the time of a solar eclipse. Five years later (1779) he determined an orbit for Bode's Comet using a process first devised by Euclid. Before he was forty he discovered a new comet (1796) and developed a new method to determine its orbit. Laplace had also recently made advances in this area of celestial mechanics, and Olbers extended the work; "Olber's method" achieved wide exposure when it was used to re-determine the orbit of the 1779 comet, and was in use throughout the nineteenth century.
Olber's expertise also came into play when the first asteroid (Ceres) was discovered in the "gap" between Mars and Jupiter, then quickly went behind the sun (superior conjunction), and was lost, since there was no way to determine an orbit without making assumptions about its eccentricity. Working with a young Karl Gauss, Olbers recovered the object on the other side of the sun close to where Gauss had calculated it to be. Olbers then went on to discover the second asteroid, Pallas (1802), as well as Vesta (1807), the fourth (and the second largest both by radius and mass, after Ceres).
In spite of these achievements Olber's main interest was in comets, and he found four more, including one (1815) with a period close to that of Halley's Comet, 72 vs. 76 years. He determined the orbits of eighteen comets in all, and also came up with an early, simple model for them consisting of a small, starlike nucleus surrounded by matter expelled from it and repelled by the sun.
Oct 13, 1933 - Founding of the British Interplanetary Society.
Oct 14, 1788 - Edward Sabine, British geophysicist and astronomer who made extensive early investigations of earth's magnetism and was the first, in 1851, to see the connection between it and Samuel Schwabe's (see below) mass of data on solar activity, linking magnetic storms on earth with the 10-11 year sunspot cycle. Sabine was also the official astronomer on Sir John Ross's 1818 expedition to find the Northwest Passage; the next year he went with William Parry to the Arctic. He administered the King's Observatory at Kew from 1849-71.
Oct 15, 1829 - Asaph Hall, early U.S. astronomer who discovered the two moons of Mars, first measured the rotation rate of Saturn, and became known as "the caretaker of the (planets') satellites". He also worked on Uranus and Neptune, stellar parallax measurements and double stars, as well as the Pleiades star cluster.
Hall started out at the Harvard observatory in 1856 and quickly showed his expertise in both observing and orbit calculation. His skill in computing numbers for astronomical almanacs earned him a transfer promotion (1862) to become an assistant astronomer at the U.S. Naval Observatory under Simon Newcomb, where he was promoted to a professorship a year later, a post he held until retirement thirty years later, though he stayed on as a volunteer observer until 1898. He then spent five years back at Harvard teaching celestial mechanics, was president of the American Association for the Advancement of Science (1902), and an associate editor for the then new Astronomical Journal from 1897 until his death ten years later.
In 1875 Hall was put in charge of the USNO's new (1873) 26" Clark refractor, the largest and probably best telescope in the world for at least the next decade. His first discovery came quickly as a result of the superior technology, and was of a white spot on Saturn, which he used to determine Saturn's rotation rate.
Two years later Mars was at a close opposition and his discovery of Deimos came on Aug 11. After six days (4+ orbital periods) he was convinced it was a Martian moon, and on this same night (the 17th) he discovered Phobos -- which is ~1¼ magnitudes brighter but very close to the planet. He had previously done the calculations to show that Mars could have satellites only if they were close to the planet, so he knew where to look (and where not to). Phobos is at magnitude 11.6 and orbits at only 9,375 km from the center of Mars (itself 3400 km in radius) in less than 8 hours. Deimos is 2½x further out. The moons allowed Mars's mass and density to be calculated rather than guesstimated for the first time.
In 1884 he showed Saturn's moon Hyperion had an orbit that was retrograding -- the whole orbit was rotating in space "backwards" -- at the rate of 20° per year.
Oct 15, 1909 - Jesse Greenstein, U.S. astronomer probably most remembered for his involvement in the discovery of quasars.
Greenstein did his Ph.D. thesis an interstellar dust at Harvard (1937) and spent about a decade at the Yerkes Observatory before moving to Cal Tech and the Mount Wilson & Palomar Observatories in 1948, which he (formally) retired from in 1980.
His early work, motivated by unusual stellar spectra, was on stellar atmospheres and abundances. This led to his development of theories of stellar interiors which required neutron-producing nuclear reactions to be present in red giant stars, to account for the creation of the heavier elements observed.
He next turned to the problem of interestellar dust again, and showed that the interstellar polarization of starlight could be explained by there being spinning grains aligned by a galactic magnetic field; elements like iron in at least some of the grains would be required to make them magnetic, while they'd have to be aspherical (longer than they are wide) in order to produce the polarization, which is rarely more than 1%. This is still a valuable basic method for mapping the galaxy's global magnetic field.
Greenstein got involved early on in the optical identification of the mysterious objects being turned up by the dozen by the 3rd Cambridge radio all-sky survey. The radio coordinates were very imprecise, but some of the objects were in the zone of sky traversed by the moon, and an occultation allowed the location to be restricted to an arc along the limb of the moon at the instant the source 'blinked' off (or on) -- a vast improvement. Spectra were then taken of the remaining candidates to try and find anything out of the ordinary. 3C 273, by Marteen Schmidt, and then Greenstein's 3C 48 were found in quick succession and determined to have extraordinary recession velocities (1964). By Hubble's Law these had to be at large distances, and were extremely luminous (100x that of a galaxy) in order to be as bright as observed at such distances. Quasars were an entirely new and unexpected class of objects. This was the first really big, astounding discovery made by the 200" telescope, and it also secured the importance of radio astronomy as an indispensible tool for exploring the universe.
Quasars having blue colors, Greenstein in the 1970's got involved in optical searches for faint blue objects. While turning up radio quiet quasars, he also found over 500 white dwarf stars. This led him back to further developments in the late stages of stellar evolution and the course a star takes from red giant to becoming a white dwarf.
Greenstein was also involved in the 1970's in the part of SETI (the Search for ExtraTerrestial Intelligence) relating to the search for extra-solar planets.
Oct 15, 1949 - Thomas Bopp, co-discoverer (within 5 minutes) with Alan Hale, of Comet C/1995 O1 on July 22, 1995, which reached magnitude -1 near its perihelion nearly two years later (April 1, 1997). One of the brightest comets of the century, Comet Hale-Bopp was said to have been seen by two-thirds of all Americans.
Oct 19, 1910 - Subrahmanyan Chandrasekhar, Indian born astrophysicist and applied mathematician who shared in the 1983 Nobel Prize in Physics for his theoretical work on the later stages of stellar evolution. He's the namesake of the upper limit for how massive a white dwarf star can be, Chandrasekhar's Limit (1.44 solar masses), first calculated in 1930; anything more and the star can no longer support itself through electron degeneracy pressure against the crush of its self-gravity, collapsing to become a neutron star, or possibly a black hole.
A Type I supernova, which shows no hydrogen lines in its spectrum, is thought to occur in a mass transfer binary star system where one of the components is a white dwarf star initially just below the Chandrasekhar Limit; matter from the other star flows down onto it and eventually puts it over the limit -- and into a supernova explosion that results in a neutron star being formed.
Though Chandrasekhar was born in present-day Pakistan, and his paternal uncle was the Indian physicist and Nobel laureate Chandrasekhara Venkata Raman, the young Chandrasekhar got into Trinity College at the University of Cambridge on a Government of India scholarship and subsequently spent the rest of his life in the West, mostly at the University of Chicago. Along the way he worked with such luminaries as Edward Milne, Max Born, Paul Dirac, Niels Bohr, Arthur Eddington (who ridiculed the notion of Chandrasekhar's Limit), Harlow Shapley, Gerard Kuiper (namesake of the Kuiper Belt, but better known then as the leading expert on white dwarf stars), Otto Struve, and Bengt Stromgren. Later he'd associate with both Enrico Fermi and J. Robert Oppenheimer. From 1952 to 1971 Chandrasekhar edited The Astrophysical Journal.
Oct 22, 1905 - Karl Jansky, American physicist and electrical engineer, who discovered the first extraterrestrial radio waves (at 20.5 MHz) in the course of investigating noise and interference in ship-to-shore communications systems for Bell Labs in 1931-32.
Using a high quality receiver and a movable aerial antenna (mounted on wheels), he was able to determine the radiation was coming from the direction of Sagittarius, which astronomers Harlow Shapley and Jan Oort had recently identified as being the direction to the center of the Milky Way Galaxy.
Even though the discovery was front-page news, until after WW II it was only followed up by amateur Grote Reber, using homemade radio equipment and a fixed, zenith pointing, backyard "dish" made of lumber yard wood.
Oct 23, 4004 B.C. - The date of Creation, as erroneously determined in about 1640 by archbishop James Ussher. Astronomers tend to use Julian Day Numbers (and decimal fractions thereof), which start Jan 1, 4713 B.C.. As no known astronomical record precedes this date, JDN's are always positive; they also 'flip over' at noon (Greenwich time), so nightime observations are not split between two days.
Oct 25, 1789 - Samuel Schwabe, German chemist and pharmicist turned astronomer who observed sunspots daily his entire life, starting in 1825, with a 2" telescope, and by 1843 had accumulated enough data to determine a periodicity in solar activity -- the sunspot cycle -- of ten years. His publication went unnoticed until 1851, when it was mentioned in a book by famed explorer and naturalist Alexander von Humboldt. This prompted several others with sunspot data to analyze it similarly, the length of the cycle was increased to 11.1 years, and not long after the connection with magnetic storms on earth was shown. Schwabe also made the first known drawing of Jupiter showing the Great Red Spot, in 1831.
Oct 25, 1877 - Henry Norris Russell, American pioneer in establishing the modern field of astrophysics. The namesake for the American Astronomical Society's highest award (for a lifetime contribution to the field), Russell is the "R" in "H-R diagram", which he first used in a 1914 paper. (Ejnar Hertzsprung, see above, is the "H".)
Oct 26, 1902 - Henrietta Swope, American astronomer known for her work on variable stars.
Swope's father was an MIT graduate in engineering who went on to become the president of General Electric (1922). After graduating from Barnard College with a degree in math and only one astronomy course (1925), Ms. Swope went to work at the Harvard College Observatory under Harlow Shapley, finding variable stars and estimating their brightnesses from photographic survery plates, and earning a Master's degree in astronomy at Radcliffe (1928).
During World War II she worked at an MIT laboratory on navigation tables, followed by five years teaching at Barnard College and the Connecticut College for Women.
In 1952 Walter Baade invited her to come to Pasadena to work with him on variable stars discovered in other galaxies using the new 200" telescope on Palomar Mountain, a post she held until her retirement in 1968. By 1964 they had found 275 Cepheid variable stars in the Andromeda galaxy, which they used to determine a distance of 710 kpc (2.3 million light-years).
Shortly after her retirement she donated a large sum to develop an observatory site in the southern hemisphere (Las Campanas, Chile), including a 40" telescope named after her and now in use for more than fifty years. She left most the rest of her estate to the observatory to support its continued operation and astronomical research.
[ 1977 American Institute of Physics interview ]
Oct, 1785 (exact date unknown) - James South, British astronomer who worked with John Herschel on double stars, publishing a prize- and award-winning catalog (with charts) on 380 of them in 1824.

Discoveries and other firsts

Oct 1, 1897 - Dedication of the University of Chicago's Yerkes Observatory with its 40" refractor, still the world's largest such telescope.
Oct 1, 1962 - The 300-foot radio telescope of the National Radio Astronomy Observatory (NRAO) goes into operation at Green Bank, West Virginia. The telescope, which collapsed suddenly on Nov. 15, 1988, was the world's 2nd largest.
Oct 4, 1957 - The USSR's Sputnik 1 becomes the first manmade object to orbit the earth.
Oct 5, 1582 - The day the Julian calendar used in Europe at the time was changed over to the currently used Gregorian calendar, by becoming Oct 15th, thus dropping the ten days since the Julian calendar had been adopted (at the Council of Nicea in 325 A.D.) by which it had slipped relative to the sun, by being 11 minutes and 14 seconds per year too long.
The name derives from Pope Gregory XIII. As much of northern Europe had turned Protestant by 1582, it stayed on the Julian calendar until a discrepancy between the two arrived, which wasn't until 1700, a leap year in one system but not the new one. Denmark, the Netherlands, and much of Germany adopted the Gregorian calendar then, but Great Britain and the colonies in America did not do so until 1752; by then eleven days were needed, so Sep 2 became Sep 13th. Riots broke out all over England because people thought they'd been made older by an act of legislation. It was not until after World War I that the Soviet Union (Russia) adopted the Gregorian calendar, though the Eastern Orthodox church still uses the Julian calendar, now 12 days off.
The new calendar is still long by about 1/8th of a day every 400 years, so around the year 5000 a currently employed leap day will have to be dropped to stay synched up with the sun.
Oct 5, 1923 - Edwin Hubble discovers the first Cepheid variable in M31, the Andromeda Galaxy, establishing that spiral nebulae are independent and external stellar systems like the Milky Way. The star, SW of the galaxy's nucleus and ranging in magnitude from 18½ to 19.8, had first been identified as a nova before additional observations showed it brightening again after dimming. The period is now taken to be 31.4 days. Hubble would eventually find several dozen more Cepheid variables in M31.
[Photo at right taken from the digitized Palomar Observatory Sky Survey. Click for larger version with a wider field of view.]
Oct 6, 2008 - Asteroid 2008 TC₃ is the first pre-detection of an earth-crossing asteroid before impact from which fragments were located.
Discovered by the Catalina Sky Survey 60" telescope, the 13 foot diameter, 80 ton rock exploded 19 hours later at an estimated 23 miles above the Nubian Desert in Sudan (the next day, local time), where ~600 meteorites weighing a total of 23 pounds were recovered months later -- many belonging to a rare type known as ureilites, which contain nanodiamonds, as well as amino acids in this case.
The fireball's "light was so intense that it lit up the sky like a full moon and an airliner 870 mi away reported seeing the bright flash," according to a newspaper report. It was recorded by a webcam 440 miles away, by a weather satellite, and an infrasound detector array in Kenya. It's estimated impacts of this size occur only 2-3 times per year.
Oct 7, 1959 - The USSR's Luna 3 returns the first photos of the Moon's far side.
Oct 10, 1846 - William Lassell discovers Neptune's moon Triton, just seventeen days after the discovery of the planet itself.
Oct 11, 1852 - The first notice is taken of the star T Tauri and the nearby nebula now known as Hind's Variable Nebula, for the English astronomer John Hind who made the observation. He suspected the star to be variable because it didn't show up on earlier star charts. But the nebula also turned out to be variable, fading and disappearing by 1868. When it returned its location had changed.
T Tauri is now the prototype for this class of irregular variables that are very young stars of roughly the same spectral type (and mass) as the sun, and most have associated nebulae. Shadowing by a dusty disk near to the star is thought to cause the variable lighting of the associated reflection nebula.
In 1981, T Tauri was first found to be a binary, with the companion star just 0.7" S of T Tauri. In 2000, T Tauri South was itself found to be a close binary system.
Oct 11, 1983 - The Infra-Red Astronomical Satellite (IRAS) discovers the ~6 km diameter asteroid 3200 Phaethon (1983 TB), which goes closer to the Sun than any other known asteroid -- just 20.9 million kilometers (0.14 A.U.). It was also the first asteroid to be discovered using images from a spacecraft. With a 1.43 year period, its high orbital eccentricity of 0.89 -- more characteristic of a comet than an asteroid -- takes it out to the inner reaches of the asteroid belt, crossing the orbits of all four terrestrial planets.
Shortly after its discovery, Fred Whipple noticed that its orbit closely matched that of the Geminid meteor stream. Phaethon was subsequently observed by NASA's STEREO spacecraft near perihelion, where its surface temperature may reach 1390°F, to be shedding dust and sporting a tail, like a comet. So it has been called both a "rock comet" and an "active asteroid". Phaethon is expected to possibly produce exceptional Geminid meteor showers from about 2020 all the way to up to about 2140.
Oct 12, 1957 - Britain's Jodrell Bank radio observatory radar detects the Russian R-7 rocket booster that put Sputnik into orbit, the final stage having gone into orbit along with its satellite payload. Only in operation for a few months (barely), Jodrell Bank was then the only facility on earth capable of doing this. Ten weeks later Moscow sent them a telegram of thanks and wishes for "every success in your work". Jodrell Bank continued to track both early earth satellites and at least one spacecraft sent to the moon, for several countries, before dedicated networks for doing this were built.
Oct 12, 2017 - A small space rock designated 2012 TC₄ becomes the first known asteroid to pass by earth closer than the Earth-Moon distance twice. It was discovered five years earlier (Oct 4), just eight days before its first closest approach of 94,960 km. Orbital extrapolations at the time suggested it would come back around at under three Earth radii next time by. The object was picked up a second time, at the incredibly faint magnitude of 27, by the ESO's VLT (Very Large Telescope) on July 27 at a distance of 0.4 AU. The 10/12/17 pass of the 15 meter sized rock was at only 50,150 km, ~1/8th the Earth-Moon distance, and not far beyond the distance of geosynchronous satellites. The next close pass for 2012 TC₄ is now estimated to be on December 1, 2079, at a distance about 1 million km.
Oct 13, 1590 - Michael Maestlin at Heidelberg, Germany, observes the only seen occultation of Mars by Venus.
Oct 15, 1963 - The first detection of an interstellar molecule (OH), by Sander Weinreb (w/Barret, Meeks, and Henry) on the MIT Millstone Hill 84-foot dish. The detection of the hydroxyl molecule in absorption, using the radio galaxy Cas A as a background continuum source, was made possible by new correlation receiver technology and occurred at 1667.46 MHz and, shortly later, 1665.34 MHz. By the turn of the millennium, approximately 200 different molecules -- many of them organic -- had been discovered in interstellar space.
Oct 15, 1972 - A 50 kg meteorite fall kills a cow in Valero, Venezuela.
Oct 15, 1997 - Launch of the Cassini spacecraft to Saturn and its moon Titan.
Oct 12, 1892 - Famed visual observer at the Lick Observatory, E. E. Barnard, is the first to discover a comet (1892 V) by means of a photograph rather than a visual observation. (But see May 17.)
Oct 16, 1982 - Halley's Comet's approach for its 1986 apparition was first detected by U.S. astronomers David Jewitt and G. Edward Danielson using the 5.1 m Hale telescope at Mount Palomar and a CCD camera. Solid state, CCD technology was extremely new then, very expensive, and required a "CCD Doctor" (or two or three) to make and keep it working, so this was one of its first notable accomplishments.
Oct 18, 1915 - "Under exceptionally good conditions of seeing," Walter Adams at Mount Wilson Observatory succeeds in obtaining a spectrum of Sirius B, confirming it to be type A, typical of hot, blue stars (like Sirius A). This was somewhat unexpected because all intrinsically dim stars then known, with established parallaxes (distances), were cool, red dwarfs. The only other dim white or blue star then known to also be of spectral type A was 40 Eridani B.
Oct 18, 1967 - First spacecraft probe of Venus's atmosphere, by the USSR's Venera 4.
Oct 19, 1899 - A seventeen-year-old Robert H. Goddard, while climbing a cherry tree, first envisions a vehicle capable of taking humans to other planets and resolves to devote himself to the task of making it happen -- an early moment the rocket pioneer recollected and remembered the date of the rest of his life.
Oct 19, 2017 - The first object of interstellar origin, with a hyperbolic orbit of eccentricity = 1.20, is discovered by one of the Pan-STARRS telescopes in Hawaii. Subsequently named ‘Oumuamua, the object's unusual properties do not resemble any solar system object, though its spectrum and reddish-brown color are similar to type D4 asteroids.
‘Oumuamua's brightness at visible wavelengths varied by a factor of 10x over about an 8-hour period, the latter presumably being its rotation period. However, to vary so much in brightness it would have to be extremely elongated, with its length at least five to ten times larger than its projected width of maybe only 100 meters; the most elongated asteroid known has a 3:1 ratio. No telescope was able to image ‘Oumuamua as anything other than an unresolved point of light, so it's not certain whether it was cigar shaped or pancake shaped.
The object also appeared to accelerate, by 0.1%, on its way away from perihelion, relative to a strictly inertial course, during the only 11 days it was possible to observe it, being too faint after that. Such behavior in comets is due to their outgassing of material, but none could be detected coming from ‘Oumuamua. The object also emitted no radio radiation at the several wavelengths for which this was checked. It was similarly undetectable in the infrared, which was surprising since post-perihelion it should have been plenty warmed up by the sun. There were indications that its surface was unusually reflective, like metal rather than rock.
The object will take decades to leave the solar system, but current chemical rockets are insufficient to allow a spacecraft to catch up with it.
Oct 20, 2014 - Comet Bernardinelli–Bernstein (C/2014 UN₂₇₁) is first imaged at magnitude 22 by the Dark Energy Survey (DES) at the Cerro Tololo Observatory, at a distance of 29 AU (almost as far as Neptune), the most distant ever for a comet to be discovered. DES was searching for trans-Neptunian objects and the find was not announced until Jun 19, 2021, after new, improved search algorithms were applied to the old data, which were numerous enough to ID the comet as coming in from the Oort Cloud on a parabolic orbit. Pre-discovery images were quickly found in the Paranal Observatory's VISTA survey images taken on Nov 15, 2010, when the object was 34.1 AU from the sun. Subsequent observations have shown outbursts brightening the comet by a magnitude and showing a coma.
In order to be visible even at these faint levels at such great distances the comet must have a diameter of ≥100 kilometers (and perhaps as large as ~100 miles), making it the largest Oort Cloud comet yet discovered. It will reach perihelion in January 2031 outside the orbit of Saturn.
Oct 20, 2020 - NASA's Osiris Rex mission spacecraft "touches down" on the asteroid 101955 Bennu to collect a sample for return to earth three years later. Expected to leave a small scar about a foot across on a presumably relatively hard and solid, dust strewn surface, instead a crater some 25 feet wide is shown in images taken as the spacecraft retreated from the sampling operation. Mission specialists describe what happened as being like hitting quicksand or a pond, though the extremely loose material made for a sample collection of some 4x the amount which the mission was designed for and hoping to get. Estimates put the amount of the asteroid kicked up by the short blast of compressed gas to make material available for the collection device at 6 tons. This seems to confirm that Bennu is a "rubble pile" with virtually no internal cohesion beyond the tiny amount of gravity holding it together (micro g's), which was suggested beforehand by its very low density (only 1.2 gm/cm³) despite appearing to be made of rock, and was one of the reasons it was the mission's target in the first place.
Oct 22, 2136 B.C. - The first recorded solar eclipse is witnessed by Chinese astronomers. Eclipse prediction was probably already a fairly well developed science at this time because royal astronomers Hsi and Ho were executed by an unhappy emperor for their failure to predict the eclipse.
Oct 22, 1975 - The USSR's Venera 9 spacecraft sends back the first photos from Venus's surface.
Oct 24, 1851 - William Lassell discovers Uranus's moons Ariel and Umbriel.
Oct 24, 1931 - The first mention in the scientific literature of using radio waves for interstellar communication with civilizations on other planets, by E.W. (Ernest William) Barnes.
Speaking of these other possible planetary systems, "...If even one such system were found, the present theory of planetary origins would collapse [see below]. Failing any such invention of a super-telescope, there remains the possibility of wireless communication. As I have already indicated, I have no doubt that there are many other inhabited worlds, and that on some of them beings exist who are immeasurably beyond out mental level. We should be rash to deny that they can use radiation so penetrating as to convey messages to earth. Probably such messages now come. When they are first made intelligible a new era in the history of humanity will begin. At the beginning of the era the opposition between those who welcome the new knowledge and those who deem it dangerously subversive will doubtless lead to world war."
(Nature, vol 128, pgs 722-24)
Since there are already enough reasons for world war, I suppose this explains why the status quo, the Establishment, Dave Barry's "The Committee That Really Runs America", or whatever you call it, has pretty effectively scotched SETI without being too overt by the outright banning of it.
The now out-dated and mostly forgotten theory of planetary origins mentioned relied on a catastrophe, where the gravity of a star passing very close by the sun drew out material from either (or both) stars which subsequently condensed into the solar system. In the life of the galaxy out where the sun orbits, the statistical expectation would be that such near-collisions only ever happen once or twice (or not at all) in the roughly ten billion years since the galaxy formed. This would make the origin of the solar system a virtually singular event, though the observational data to calculate the total galaxy lifetime stellar collision cross-section didn't exist back then. So they didn't know stars don't ever collide (or even almost collide), and no examples have yet been turned up. This is fundamentally because the stars in the disk all orbit the galaxy in near-circular orbits with random velocity deviations on the order of only ~5% or less: maybe ±10 km/sec, compared to an orbital velocity 225-250 km/sec. Even if the 'impact parameter' was ideal it's still no certainty a solar system would result.
The article finishes... "But the survivors, when they extricate themselves from the economic consequences of the peace treaty, will begin what we may correctly term a strenuous correspondence course. I should like to be living then. We might get a true understanding of the evolution of the universe."
It is true that Marconi would tantalize New York newspaper reporters with sensational quips about the possibility of interstellar communication with alien civilizations via radio a dozen or fifteen years before Barnes wrote the above, but Marconi never appeared to have done any calculations on how or whether it could really be done, and he never submitted anything on the subject to a scientific journal.
Oct 24, 1946 - The first camera is launched into space, aboard a captured V-2 rocket (numbered #13), from the White Sands Missile Range in New Mexico. It reached a height of 65 miles and took a picture every 1½ seconds, the film being successfully recovered from its steel container after the rocket crashed backed down into the desert. Subsequent flights would take the first UV pictures of the Sun and other astronomical objects.
Oct 25, 1671 - Giovanni Cassini discovers Saturn's moon Iapetus.
Oct 25, 2017 - Japanese astronomer Tadashi Kojima becomes the first amateur to discover an exo-planet. While hunting for novae in Taurus, Kojima found a star whose brightening fit the pattern expected for a gravitational microlensing event, where two stars are almost perfectly in line with earth and the gravity of the nearer one lenses (or magnifies) the light of the more distant star. The presence of the planet, ~20% more massive than Neptune and roughly 1 AU from its host star, could be deduced from its varying effect on the brightening of the background star, as the planet's orbital motion causes its small contribution to the lensing gravity to vary with time.
Oct 26, 2004 - The Cassini spacecraft makes its first close approach to and flyby of Saturn's moon Titan.
Oct 27, 1577 - The date of perihelion passage of the Great Comet of 1577 (aka C/1577 V1). The first recorded observation was Nov 1, in Peru, and the first European observation, in Italy, came Nov 7.
Tycho Brahe first observed the comet on Nov 13th, and observed it until Jan 26, 1578. By comparing his position for the comet on the sky with other's positions, especially those of Thadaeus Hagecius in Prague, Brahe was able to use parallax to show that the comet was further away than the moon -- maybe 3x further -- i.e., it was not an atmospheric phenomenon.
Twenty-two years later, after being exiled from Denmark to Prague, Brahe employed Kepler as his assistant, and after Brahe died 3-4 years later Kepler inherited his observations and was eventually able to determine the comet's orbit. That it had traversed the orbit of Venus, a proposal made earlier by the distance estimates of Michael Maestlin (Kepler's former teacher), before Brahe had died, seemed to be the death knell for the idea of celestial spheres, transparent crystalline spheres made of an unknown material ("quintessence") hypothesized to exist for the sole purpose of carrying the planets around on their orbits, because the comet would have had to crash right through them according to the observations. Nevertheless, the idea held on until later in the seventeenth century, when Newton developed his principles of gravity and motion, from which Kepler's three empirical laws of planetary orbital motion could be derived.
Oct 28, 1971 - Great Britain launches its 1st satellite.
Oct 29, 1749 - M32, a satellite galaxy of the Andromeda Galaxy (M31), is the first such dwarf galaxy discovered, by the French astronomer Le Gentil using an 18 ft focal length telescope. He described it as a "nebula about one minute [of arc] in diameter which appeared to throw out two small rays; one to the right and the other to the left". It would be almost another 175 years before M31 and M32 were recognized by Hubble as galaxies (see Oct 5th above).

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