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This Month in the History of Astronomy - September

Birthdays || Discoveries

Sep 1, 1877 - Francis Aston, British physical chemist who started under J.J. Thompson at Cambridge in 1910 and would win the 1922 Nobel Prize in Chemistry for his invention of the mass spectrograph, with which he was able to show that elements are often mixtures of isotopes of different, nearly whole number masses.
For example, neon has a mass number of 20.2 in the periodic table. Aston was able to show that this results from a 9:1 mixture of Ne-20 and Ne-22. Eventually he'd identify 212 naturally occurring isotopes. His later masses were accurate to almost a part in 100,000, so he was easily able to show that hydrogen had a mass of 1.008 (in atomic units), not exactly 1 as it had previously been taken to be. He was among the first to recognize that the slight deviations from exact whole number masses which isotopes had was the key to the liberation of nuclear energy.
Aston even experimented with gaseous diffusion methods using clay pipe to try and separate the two neon isotopes: since the atoms of the heavier isotope move 10% slower, their concentration in the gas should increase as the atoms of the lighter, faster isotope diffuse through the walls of the pipe more rapidly. Such technologies would become important two decades later during the development of the atomic bomb; the one dropped on Hiroshima was made from Uranium-235 laboriously separated out of natural uranium, which is mostly (99.3%) U-238.
Because Aston used photographic emulsions as the detector in his mass spectrographs, he was a photo expert and participated in total solar eclipse expeditions to Sumatra in 1926 (Jan 14 at Benkoeben, using a 19-foot focal length coronagraph with a direct vision prism in front of the lens at second and third contact for spectra of the flash), to Canada in 1932 (Aug 31, at Memphri Magoy), and to Japan in 1936 where he was clouded out; he had hoped to study the direction of sky polarization near the eclipsed sun, the object being to detect any changes in the direction from which scattered light entered from outside the shadow during the eclipse and also to find evidence for polarized sky light scattered with the coronal beam by the earth’s atmosphere, as had been found by Hugh Newall (Professor of Astrophysics at Cambridge) at Guelma, Algeria in 1905.
Sep 6, 1899 - Founding of the Astronomical and Astrophysical Society of America, now the American Astronomical Society (AAS).
Sep 7, 1914 - James Van Allen, U.S. physicist at the University of Iowa who discovered the earth's magnetosphere, a region of charged particles trapped in the earth's magnetic field. Even though they acquired the name "Van Allen Belts", they are actually more in the shape of donuts (toroids).
Van Allen was an expert in instrumentation miniaturization who used captured German V-2 rockets after WWII, as well as Aerobee and high altitude balloon launched rockets ("rockoons"), to study radiation in the upper atmosphere. Explorer 4, launched on July 26, 1958, took Geiger counters up into unexplored regions, in preparation for the first U.S. orbital satellite launch, and was the first to discover the high levels of radiation there.
Sep 10, 1857 - James E. Keeler, pioneer American spectroscopist and astrophysicist. In 1895, using the 13-inch Fitz-Clark telescope at Allegheny Observatory, Keeler showed that different parts of Saturn's rings rotate at different velocities, which demonstrated that the rings are not solid bodies but instead are a collection of small objects in independent orbits, an idea first proposed by James Clerk Maxwell.
Along with George Ellery Hale, Keeler also in 1895 founded and then helped edit the Astrophysical Journal until his untimely death five years later.
Sep 11, 1877 - Sir James Jeans, English astronomical theoretician. In the first decade of this century Jeans worked out the fundamentals of gravitational collapse processes, which are of relevance to the formation of solar systems, stars, galaxies, and clusters of galaxies.
After the age of thirty-five (1912) Jeans was an independent researcher and writer/popularizer who held no university or professorial post, though he was a research associate at Mount Wilson from 1923 to 1944. He believed in the continuous creation of matter (1928), the forerunner of the later steady state cosmological theory alternative to big bang models.
In his early, university associated years (at Princeton and Cambridge), he worked on the foundations of the kinetic theory of gases (1904). He next (1905) turned to the problem of the equipartition of energy as it applied to specific heat capacities and blackbody radiation. Finding a numerical error in the derivation of the energy distribution with wavelength as a function of temperature for blackbody radiation, this improved relationship is now known as the Rayleigh-Jeans law.
Jeans later took the theory of compressible and incompressible gases and fluids to a deeper level than had Henri Poincaré previously, and applied these findings to a variety of astronomical problems, from the fissioning of a collapsing and spinning gas cloud into double stars, to the formation of spiral galaxies and planetary systems. He pointed out the error in Pierre Laplace's theory of the formation of the solar system, favoring instead the now out-of-favor idea that gravitational tidal interactions with a star passing close by the Sun had drawn the planetary material out of it. The slow rotation of the Sun stood as a formidable objection to the nebular hypothesis of Kant and Laplace, which proposed that planetary systems formed out of the same condensing cloud that produced the primary star. An initial rotation rapid enough to produce the Sun's planets should have produced a Sun spinning a thousand times faster. The resolution of this conundrum came by coupling the protostar with the protoplanetary disk through a magnetic field, which transfered angular momentum outward so it doesn't end up in the star.
[Hubble (left) and Jeans, at the Cassegrain focus of the 100" telescope, 1931. The primary mirror did not have a hole drilled in its center, so a diagonal flat mirror was used a little more than 50" in front of it to direct the converging beam from the secondary out to a focus at the base of the tube assembly.]
Sep 12, 1725 - Guillaume Le Gentil, French astronomer who first discovered the objects later catalogued by Messier as M32, M36 and M38, as well as the nebulosity in M8.
He's probably most famous for his observing-run-from-hell, originally to India, for the transit of Venus in 1761. This had been predicted by Edmund Halley, and by having measures from widely separated places on the earth it was hoped the AU (Astronomical Unit = earth-sun distance) could be calibrated and the scale of the solar system determined, by simple surveying trigonometry techniques. Le Gentil took the assignment to go to India.
Long story short, 1761 was a bust (he was lost at sea for five weeks, the Seven Years War had broken out between France and England so his destination was in enemy hands when he got there, etc.), so he decided to stay on that side of the globe for the June 4, 1769, transit. (Venus transits occur in pairs 8 years apart which are themselves separated by either 105 or 121 years.) After getting run out of the Phillipines by the Spanish, he returned to Pondicherry, India, a treaty having put it back in French hands, built a small observatory and surrounding support village, and then waited for the day. After a month of clear mornings -- you guessed it -- he was clouded out. His voyage back was as eventful (or more) as his trip there had been, so it was October, 1771, before he made it back to Paris, eleven years after his departure -- only to find that none of his mail had gotten through, that his wife (who had re-married) and family had had him declared dead, and had "enthusiastically plundered his estate", and then, as a kicker, that he had also been replaced in the Royal Academy of Sciences. It eventually took the intervention of the King to sort everything out.
The presumed loss of Le Gentil on the expedition was part of the rationale for the first of the famous Captain Cook's three voyages, which were funded by Britain's Royal Society, and which also led to the colonization of Australia, since the 1769 transit could only be seen from the South Pacific. The observations were deemed that valuable.
Sep 12, 1851 - Arthur Schuster, German-born British physicist, who worked in spectroscopy and periodicity analysis, particularly with regard to earthquakes and sunspot activity.
During five years at the Cavendish Laboratory of the University of Cambridge (1876-81) he worked with both James Clerk Maxwell and Lord Rayleigh before establishing a laboratory at the University of Manchester, where Ernest Rutherford ("the father of nuclear physics") worked from 1907-19.
In 1898 Schuster coined the term antimatter in two letters to the journal Nature — "Potential Matter — A Holiday Dream" — some thirty years before Paul Dirac would put the idea on a mathematical basis, four years before its discovery in cosmic rays by Carl Anderson.
Schuster was also an early investigator (1883) of self-gravitating stellar systems, like globular star clusters.
Sep 12, 1962 - President Kennedy delivers his famous lines at a speech at Rice University saying the US will put a man on the moon by 1970, the birth of the Apollo program. This was actually a reiteration of a May 25th speech, but in the interim Congress had actually authorized funding for the "the large Moon rocket" project, part of which involved the Manned Spacecraft Center in Houston, on land donated through Rice. Almost all the NASA facilities for Apollo were in the South because powerful Southern senators wouldn't vote for the $$'s unless lots of them were to be spent in their states.
Sep 13, 1912 - Horace W. Babcock, American astronomer who, in 1946-7, first discovered magnetic fields in stars other than the Sun, based on his earlier work on magnetic fields in sunspots. The particular star observed was 78 Virginis (alternately CW Virginis or ο Virginis, aka omicron), which is a type A star which has very narrow spectral lines, indicative of no rotation; however, in several other regards its spectrum was peculiar and was more typical of stars with rapid rotation. Babcock reasoned that its rotation axis might be pointed nearly directly at us, and he then detected its polarized light, due to the Zeeman effect, indicative of the strong magnetic fields (1,500 gauss - now thought to be more than 2x that) expected from a star rotating at 60 km/sec at its equator, which causes the spectral lines in polarized light to split.
Babcock was Director of the Palomar Observatory from 1964 until his retirement in 1978, and was the first to study and propose a viable method for correcting for atmospheric turbulence (star twinkling) via adaptive optics (1953), which was not realized technically for routine use until three or more decades later.
His study of the rotation curve of the Andromeda Galaxy in 1939 found an increasing mass-to-light ratio with increasing distance from the center, but he attributed this to interstellar extinction (absorption of starlight) or some dynamical effect rather than "missing mass" (aka dark matter).
[ 1977 American Institute of Physics interview ]
Sep 16, 2016 - The 500 meter Aperture Spherical Telescope (FAST) in Dawodang, China, now the world's largest radio dish, sees first "light" by observing the quasar 3C 409. The next day it observed the pulsar J1921+2153 and needed only 1 minute integration time to achieve a signal-to-noise ratio of S/N=5,000. The telescope can cover frequencies from 70 MHz up to 1.8 GHz, and is partially deformable into a parabolical surface by 2226 cable actuators which can pull on the 4450 triangular panels comprising the reflecting surface from below.
Sep 19, 1819 - (Jean Bernard) Léon Foucault, French applied and experimental physicist who first accurately measured the speed of light (1850-62), and also invented both the gyroscope (1852) and Foucault pendulum (1851) to demonstrate the rotation of the Earth. In 1845, along with Armand Fizeau, he made the first detailed photographs of the Sun's surface -- practical photography having been invented in only the last decade. Ten years later he got on at the Paris Observatory and developed improved new methods for silvering and testing mirrors and lenses (1857-58).
Sep 23, 1882 - James Joy, noted expert in astronomical spectroscopy at the Yerkes and Mount Wilson observatories, who perfected the technique of "spectroscopic parallax" -- determining the distances to stars using spectral type classification, which gives the star's absolute magnitude (M) and thus its distance modulus, m-M, once the apparent brightness (m) is measured. Joy, working along with colleagues Adams and Humason over a two decade long period, measured over 5,000 stars this way, in the process better calibrating the H-R Diagram and discovering many spectroscopic and eclipsing binares.
Working also with radial velocities, Joy used 130 Cepheid variable stars to determine the distance and direction to the galactic center, with the goal of finding the circular velocity of a star at the Sun's distance from the center, and thus the rotation period of the galaxy.
With spectra of the famous variable Mira at minimum brightness, in 1918, he was able to deduce the presence of its faint white dwarf companion star (Mira B). The system is a slow binary (roughly a 500 year period) and a very close visual one, first split by Robert Aitken 5 years later, at a separation of less than an arc-second -- ~100 AU's at an uncertain distance of ~90 parsecs. In 2007, a protoplanetary disk was discovered around Mira B.
In addition, Joy was the first to group a diverse collection of unusual variable stars with differing spectra into what are now called T Tauri stars (after the prototype). He was president of the American Astronomical Society in 1949, a few years after being its V.P., and a few years before retiring at age seventy.
Sep 24, 1925 - Geoff Burbidge, English born theoretical physicist/astrophysicist, in what he called "an accidental career" (due to his astronomer wife, Margaret, who he married in 1948 and co-authored many papers with, as well as an early, 1965 book on quasars), spent most of it, starting in 1956-7, in the U.S., mostly at the Yerkes Observatory (and the associated University of Chicago, which then ran the McDonald Observatory in Texas), and, from 1962 onwards, at the University of California at San Diego.
He was director of the Kitt Peak National Observatory from 1978 to 1984, edited The Annual Reviews of Astronomy and Astrophysics (ARAA) from 1974 to 2004, and earned the Gold Medal of the Royal Astronomical Society with his wife in 2005.
One of the longstanding traditions at ARAA was for each year's issue to be led off with an autobiographical, historical retrospective by someone up in the post-retirement emeritus or hall-of-fame realm. Burbidge's own contribution in 2007 starts to get good after he and Margaret get to Pasedena.
A long, very candid and opinionated 1977 interview at the American Institute of Physics.
Sep 27, 1814 - Daniel Kirkwood: Early U.S. astronomer who first noticed the gaps in the asteroid belt (at 2.5, 2.95, and 3.3 AU's) which now bear his name in 1857. A professor of mathematics at the University of Indiana, when his work was published in 1866 it included the mechanism by which orbital resonance with Jupiter clears any object with these semi-major axes out of these zones by periodic gravitational perturbations driving them into other orbits. He used the same kind of analysis on Saturn's rings to first explain the Cassini division, Encke's division, and the gap between the B Ring and the Crêpe Ring, using Saturn's moons.
Sep 28, 1605 - Ismaël Bullialdus, French astronomer. He published Astronomia Philolaica in 1645, supporting Kepler's elliptical orbits, and assuming an inverse-square force law (for gravity) for the first time. Often credited (because of Halley) with discovering M31, but he expressedly mentioned that this "Nebula" had been observed 150 years earlier by some anonymous but expert astronomer. Considered "the most noted astronomer of his generation", Bullialdus first calculated the period of the famous variable star Mira (Omicron Ceti).
Sep, 1692 - (exact date unknown) James Bradley, the third Astronomer Royal in England, who succeeded Edmond Halley in the position (1742).
Bradley is mainly remembered for three discoveries. In 1722, using a 212 foot focal length lens, he measured the angular diameter of Venus, and thus its diameter, to a precision not attained before.
Then, in 1728, while trying to measure the parallax (distance) of the star Gamma Draconis, he instead discovered the aberration of starlight resulting from the earth's orbital motion about the sun. He was able to distinguish aberration from parallax because of the phase of the cyclical variation in the position of the star. γ Dra was chosen because it's the brightest circumpolar star, and thus could be observed throughout the year. That the effect of aberration swamped the size of the expected parallax suggested the star was many times farther away than had been supposed. From the size of the effect Bradley was able to substantially improve on Ole Rømer's value for the speed of light, calculated circa 1676-82 from the time delay or advance of Io going into Jupiter's shadow (or emerging from it), which varied by more than ten minutes depending on the relative distances of Jupiter from earth.
Finally, on Feb 14, 1748, Bradley published his results for the nutation of the earth, based on a complete 18.6 year cycle of the moon's nodes.

Discoveries and other firsts

Sep 1, 1804 - Karl Harding, working under Johann Schröter in Bremen, Germany, discovers the asteroid Juno. Though it was the third asteroid turned up, Juno is only the 12th in size, at a diameter of just 233 km. It's relatively high brightness for its size indicates a higher albedo (reflectivity) than is typical for asteroids -- 24% versus 3-10% for the most common, carbonaceous and nickel-iron asteroids -- which accounts for its relatively early discovery.
Juno has favorable oppositions every thirteen years (2005, 2018, 2031), when it is near perihelion. It was less than a month from one of these at the time of discovery. At these times it's about 1 AU from earth (and 2 AU from the sun), when it's a magnitude 7½ object easily found in binoculars and small telescopes; it stays brighter than 9th magnitude for 4-5 months then.
Juno was the first asteroid for which an occultation was observed; it passed in front of the star SAO 112328 on February 19, 1958.
Sep 1, 1859 - Solar physicist Richard Carrington observes the first solar flare ever recorded. An intense aurora followed the next day. This was one of the most active solar outbreaks ever recorded. The aurora was visible as far S as the Caribbean, and the flare was thought to have caused a 5% reduction in earth's ozone layer.
Sep 1, 1979 - Pioneer 11 makes the first ever flyby of Saturn. Afterwards it headed up and out of the plane of the ecliptic in which the planets orbit in the general direction of the constellation Aquila.
Sep 2.5, 2008 - V1309 Sco, also known as Nova Sco 2008, is the first case of direct observational evidence in which a contact binary star system is seen ending its evolution by merging into a single object.
Dubbed a “red novae” or "mergeburst", the originally 1.43 day eclipsing binary system had been monitored for over half a dozen years by the University of Warsaw's Optical Gravitational Lensing Experiment (OGLE) telescope at Las Campanas Observatory in Chile, totalling more than 1300 photometric measurements before the outburst.
The progenitor of V1309 Sco, a K1-2 III star with a mass of ~1 solar masses near the beginning of the red giant branch, at a distamce of ~3 kpc and with a much smaller companion, was initially slowly increasing in brightness on a time scale of years and reached a local maximum in April 2007. Subsequently, the star faded by ~1 mag during a year. In March 2008, the main eruption started, and the star brightened by more than 5 magnitudes (x100) over the next ~6 months before the final merging of the two stars, which resulted in a very rapid brightening of another 5 magnitudes.
Sep 3, 164 BC - What many centuries later would be known as Halley's Comet makes its closest approach to earth for this apparition, forty-four days before perihelion, at only a little more than 10 million miles distance. The event was recorded on Babylonian tablets, its second earliest known appearance.
Sep 3, 1976 - The Viking 2 lander touches down on Mars, about 7 weeks after Viking 1 (see July 20).
Sep 5, 1831 - The first definitive observation of Jupiter's Great Red Spot. A spot had been observed as early as 1665, by the great Giovanni Cassini, and followed until 1713, but it's not clear that this was the same storm seen nearly 120 years later and monitored continuously ever since a close opposition of Jupiter in 1879. The spot has been shrinking in size the last several decades and in the early part of the 21st century was only about half the size longitudinally that it had been a hundred years before.
Sep 5, 1936 - "First light" for the Mount Palomar 18" Schmidt telescope. Spearheaded by Fritz Zwicky, the special design (invented only half a dozen years earlier) gives a very wide field of view, and was intended for searching for supernovae. Nineteen were found in the next 50 or so months of the survey.
Five decades later the telescope was used by Gene Shoemaker and associates to search for earth-crossing asteroids, and famously found Comet Shoemaker-Levy 9 on Mar 24, 1993, the many fragments of which crashed into Jupiter in July, 1994.
The telescope was so successful that its design was fairly quickly scaled up more than 2½x as the 48" Mount Palomar Schmidt, begun in 1939 and completed in 1948.
Sep 5, 1977 - The Voyager 1 spacecraft was launched, fifteen days after Voyager 2, but overtaking it by December on its slightly faster and more direct trajectory, and being the first to reach Jupiter and Saturn before eventually heading off into interstellar space, passing the heliopause on Aug 25, 2012. It's expected to operate until about the year 2025, when its radio-isotope thermo-electric generators will be unable to produce sufficient power to keep its instruments ON.
Sep 7, 1882 - The first astronomer, W. H. Finlay, the Chief Assistant at the Royal Observatory in Cape Town, South Africa, records observations of what would become the Great Comet of 1882 (C/1882 R1-A). It was an independent discovery, as others in the southern hemisphere saw the comet around the first of the month. Finlay said the comet was then of about the 3rd magnitude and had a tail about a degree long.
The comet was a member of the Kreutz Sungrazer family and passed perihelion on the 17th only 0.7 solar radii from the sun's surface. It was visible during daytime next to the sun, and was estimated to have reached magnitude -17. Shortly after perihelion it transited the Sun, but was only seen up until it reached the sun's limb; it was not visible silhouetted against the sun's disk.
By the end of the month, the comet's nucleus was observed to be elongated and then appeared doubled. By the middle of October it had moved north far enough for the famous E.E. Barnard to observe that it had disintegrated into (at least) five pieces, whose brightness varied from night to night. The comet was naked eye visible until February, 1883, and last seen telescopically June 1st.
Sep 8, 1966 - The TV show Star Trek premieres, inspiring a generation's interest in space, astronomy, technology, special effects, and alternative social systems.
Sep 9, 1839 - The first ever glass plate photograph was made by John Herschel (see March 7). Interestingly, the photo was of the famed 40-foot telescope of John's father, William Herschel, which had been in disuse for several decades and was shortly dismantled.
Sep 9, 1892 - Lick Observatory astronomer Edward Emerson Barnard discovers Jupiter's innermost satellite, Amalthea. It was the first moon of Jupiter to be discovered since Galileo, and was the last moon in the solar system to be discovered through visual observations.
Sep 17, 1811 - Thomas Jefferson observes an annular solar eclipse with a telescope at Monticello several years after his second term as president ends. The eclipse was unusually long, at 6 minutes and 51 seconds, something Jefferson was interested in measuring.
Sep 11, 1985 - ICE, the International Cometary Explorer, makes the first ever flyby of a comet, Comet Giacobini-Zinner.
Sep 12, 1959 - The USSR's Luna 2 becomes the first manmade object to strike the moon.
Sep 13, 1922 - The highest air temperature ever recorded at the surface of the earth was measured in Libya at 136°F. Some doubt it's reliability. Death Valley's Furnace Creek hit 134°F (56.7 °C) on July 10, 1913.
Sep 17, 1789 - William Herschel discovers Saturn's moon Mimas.
Sep 18, 2015 - The first successful detection of gravitational waves is made, at the Laser Interferometer Gravitational-Wave Observatory (LIGO). The source is thought to be a pair of merging black holes with masses roughly 20-30 times the mass of the sun, at a distance of 400 Mpc.
Sep 19, 1848 - Saturn's moon Hyperion is discovered by William Boyd.
Sep 19, 1988 - Israel launches its first satellite.
Sep 20, 1948 - The first photographic plate (#0) was taken with the 48-inch wide field Schmidt telescope at Mt. Palomar, by Hendricks -- who also ground and polished the highly aspherical corrector plate upon which the design depends. The photo was of M31, the Andromeda Galaxy, and it was a "keeper": it is reproduced at 2½x in panel #18 of the Hubble Atlas of Galaxies (1960), though there the date is given as Sep 28/29, and it is credited to Hubble. (The Sep 20 date is from Osterbrock's book "Pauper and Prince".) The telescope would eventually complete the massive and still extremely useful National Geographic / Palomar Observatory Sky Survey.
Sep 20, 1962 - Capella was first detected in X-rays, during the first of two Aerobee-Hi rocket flights, the second time on March 15, 1963. The position was confirmed by a later rocket flight on April 5, 1974, and it's X-ray luminosity measured as ~10⁴ times that of the Sun. The cause is thought to be a hot, massive corona surrounding the most massive component of the four star (two binaries) system.
Sep 23, 1846 - Johann Galle and Heinrich d'Arrest of the Berlin Observatory, using the Northumberland telescope, see and identify the planet Neptune for the first time. The discovery of Neptune was a major accomplishment in the entire edifice of celestial mechanics and mathematics built up from Newton's laws of gravity and motion over the previous 160 years.
As it turns out, the planet could have been discovered 230+ years sooner, by Galileo, who was studying his newly discovered moons of Jupiter when Neptune happened to be in close conjunction with it; he even noted the movement of the "star" from a previous night, but failed to follow up on the observation.
Sep 23, 1876 - The tight grouping of interacting galaxies now known as Stephan's Quintet (Palomar Observatory Sky Survey photo at right) is discovered by Édouard Stephan in Marseilles, France, using a 31½" Foucault reflector.
The group is famous for sporting a discrepant redshift: NGC 7320 is either a nearby foreground object, by chance seen nearly superposed on the other four galaxies (NGC's 7317, 7318 A & B, and 7319), which are some 7x farther, or it is part of the system but with a velocity which differs from the other galaxies by some 6,000 km/s. The situation is further complicated by NGC 7318B being at a recession velocity 850 to 1,000 km/sec less than its other three companions, making it difficult to understand how it could be a gravitationally bound member of the group and not just passing through its center (from the backside towards us). Off the left side of the photo, which is 7 arc-minutes across, along the arc of NGC's 7317-19 is NGC 7320C, with a velocity similar to 7318B.
Sep 23, 1962 - The TV show The Jetsons premieres, initiating a generation of cartoon-watching baby boomers into a technologically based future.
Sep 24, 1970 - First unmanned, automated return of lunar material to the earth, the Soviet's Luna 16 returns with three ounces of the moon.
Sep 25, 1957 - Stratoscope I, a balloon born telescope, headed by Martin Schwarzschild at Princeton University, flies its first scientific mission, shooting 1000 feet of 35mm film (8000 frames) of the sun over several hours before parachuting from 82,000 feet back down to the ground, providing never-before resolution of solar granulation.
Instrument and Mission details
Sep 25, 1992 - NASA's Mars Observer is launched, the first such probe to Mars in fifteen years, only to lose communication with earth three days before reaching Mars in late August 1993.
Sep 26, 1785 - William Herschel first observes and describes the three objects along the Perseus/Pegasus border that would later (1888) be known as NGC 7619, NGC 7623, and NGC 7626 -- the brightest galaxies in what is now recognized as the Pegasus Cluster (I) of Galaxies, at a distance of about 50 megaparsecs (Mpc). Some ten months earlier (November 12, 1784) he had noted what's now known as NGC 7469 nearby; even though it is cumulatively fainter than the other three, it has a bright(er) nucleus and is now classified as a Seyfert galaxy -- one of the six in the original 1943 paper -- and so is easier to spot visually.
Sep 26, 1960 - The first quasar, 3C 48 is discovered, though its redshift would not be determined before the spectrum of a different quasar, 3C 273, was found to have a very high value.
"A direct plate [photograph] was taken [with the 200" telescope], with every expectation of finding a distant cluster of galaxies, but measurement of the plate gave the unexpected result that the only object lying within the error rectangle of the radio position [about 10 arc-seconds, obtained from previous interferometer observations] was one which appeared to be stellar. The stellar object was associated with an exceedingly faint wisp of nebulosity (surface brightness ~23 mag/arcsec² in V) and measuring 12" by 5" (N-S x E-W). The stellar object lies about 3" north of the center of the nebulosity."
- Thomas A. Matthews and Allan R. Sandage, 1963 Astrophysical Journal
Mount Wilson and Palomar were famous at this time, and for many years previously, of taking what might be called a proprietary attitude towards some objects, and thus sitting on important observations until they'd explored all possibilities and were good and ready to publish them. That was certainly the case with this photograph, which wouldn't appear in the research literature until 2½ years after it had been taken.
Sep 26th, 2022 - NASA’s Double Asteroid Redirection Test (DART) intentionally crashes into the binary asteroid 65803 Didymos, specifically the smaller component known as Dimorphos, the smallest asteroid yet visited by a spacecraft -- albeit at 14,000 mph. Using software based on anti-missile technology, DART autonomously guided itself to the collision, missing a "bull's eye" by just 17 meters (50 feet). The Italian-built minisatellite LICIAcube separated from DART fifteen days before, and observed the impact and its aftermath (photo at right), approaching within 35 miles of Dimorphos less than 3 minutes afterwards. Numerous telescopes, both ground-based and in orbit, observed the plume of dust from the intercept, as the system was less than 7 million miles from earth.
Two weeks post-impact NASA announced the preliminary result that the orbial period of Dimorphos had been reduced by 32 minutes, to 11 hrs 23 mins. A decrease of only a minute or two was the minimal expectation, so this was at the upper limit of what was thought possible. Ejected debris that might settle back onto Dimorphos in the future could reduce the reduction.
Sep 27, 2007 - NASA's Dawn spacecraft was launched, on its way to the two largest asteroids/protoplanets, Vesta (Jul 16, 2011 to Sep 4, 2012) and Ceres (Mar 6, 2015 to the mission's end on Nov 1, 2018)
Sep 28, 1969 - What would become known as the Murchison Meteorite falls near its namesake town ~100 miles north of Melbourne, Australia. The well-observed fall, and its fragmentation into three parts, is famous for totalling nearly 100 kg of carbonaceous chondrite material rich in organic compounds and water, the largest fragment being almost 7 kg.
Somewhere around 100 different amino acids have been found in the meteorite, five times the number used by life on earth, so the Murchison Meterorite often comes up in discussions of the possible seeding of future life on earth with pre-biotic compounds.
In 2020, geochemists identified bits of silicon carbide that date to 7 billion years old, meaning they were interstellar dust particles before becoming part of the original asteroid the meteorite derives from; it's also the oldest known stuff on earth.
Sep 30, 1880 - Henry Draper, using an 11" Clark refractor, makes a 50 minute exposure for the first photo of the Orion Nebula (M42).
Sep 30, 2016 - The Rosetta spacecraft ends its mission to Comet 67P/Churyumov-Gerasimenko by landing in the comet's Ma'at region before shutting off. Rosetta measured ~3x more deuterium in the comet's ice than water on earth contains, casting doubt on the long-held hypothesis that earth's water originally came from comets.

©2002-2024, Chris Wetherill. All rights reserved. Display here does NOT constitute or imply permission to copy, republish, or redistribute my work in any manner for any purpose without prior written permission.

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