This Month in the History of Astronomy - October
- 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
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
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
- 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
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
- 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
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
- 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
[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
- 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
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
- Oct 15, 1972 - A 50 kg meteorite fall kills a cow in
- 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
- 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
- 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)
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
- 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
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).
©2002-2023, 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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