This Month in the History of Astronomy - August
- Aug 1, 1818 - Maria Mitchell, the first woman elected
as an astronomer to the American Academy of Arts and Sciences and
the American Association for the Advancement of Science. Mitchell
achieved worldwide fame for her discovery of a bright comet in
1847 (Oct 1), and publishing her calculated orbit for it in Feb
1848. This subsequently brought her in contact with such luminaries
as Ralph Waldo Emerson, Herman Melville, Elizabeth Cady Stanton,
Frederick Douglass, and Sojourner Truth; when she travelled in
Europe she met, among others, famed naturalist Alexander von
Humboldt and William Whewell (--polymath who coined terms like
scientist, physicist, linguistics, consilience, catastrophism,
uniformitarianism, and astigmatism; and suggested to Faraday
the terms electrode, ion, dielectric, anode, and cathode).
Both Mitchell's parents were Quakers, and her father was a public
school teacher who pursued an interest in mathematics and astronomy,
so all his children were brought up being educated in astronomy.
Her first observations were made (c.1840) after her father's
school closed and he got a job making astronomical observations
and geographical calculations for the U.S. Coast Survey, using
a 4" telescope.
Photo at right taken at the Vassar College Observatory refractor
sometime between 1865, when she became professor of astronomy and
observatory director there, and probably about a decade later.
Mitchell and her students began photographing sunspots daily
starting in 1873, the first regular photographs of the sun.
During Mitchell's 20+ year tenure Vassar had more mathematics
and astronomy students than Harvard, two dozen of which made
it into Who's Who In America?.
- Aug 5, 1930 - Neil Armstrong, first human to walk
on the moon.
- Aug 9, 1911 - William ("Willy") Fowler, American nuclear
physicist and astrophysicist who shared the 1983 Nobel Prize in
Physics with Indian astrophysicist Subrahmanyan Chandrasekhar.
Fowler was a life-long Cal Tech-ian, earning his Ph.D. there in 1936,
under Charles Lauritsen (who had done his own Ph.D. there under the
famed Robert Millikan, and was first director of the "Rad-Lab"),
then becoming a research fellow, assistant professor (1939), and
full professor (1946). He directed the W.K. Kellogg Radiation
Laboratory at Cal Tech (1962 to ~1976), where the first
accelerator-produced artificial radioactivity had been made (in
1934) and where it was discoverd a carbon nucleus could capture a
proton, becoming a nitrogen nucleus and releasing a gamma ray in the
process; this radiative capture process was of particular significance
in the field of nuclear astrophysics, leading to his work with Fred
Hoyle and Margaret and Geoff Burbidge on the synthesis of the elements
beyond hydrogen and helium in the cores of stars.
Besides the Nobel Prize, the list of awards Fowler received is
staggering: the Medal for Merit (1948, by President Truman), the Henry
Norris Russell award, the American Astronomical Society's highest
(1963), the National Medal of Science (1974), and the Eddington Medal
(1978) -- just to name a few.
[Photo at right shows him with the Burbidges on the left and Hoyle
at right, being presented a gift of a model of a steam engine for
his sixtieth birthday. He had grown up near the Pennsylvania Railroad
and had a life-long interest in locomotives, particularly steam
engines. For more details on this, see a brief, partial autobiography
in the 1992 Annual Reviews of Astronomy & Astrophysics,
edited by Geoff Burbidge.]
- Aug 12, 1897 - Otto Struve, Russian born astronomer from
a distinguished Baltic German family of five generations of astronomers,
who spent his career in the U.S. after escaping the Bolsheviks, starting
as a stellar spectroscopy assistant at the Yerkes Observatory in 1921.
He would go on to publish 900+ papers, articles, and books. His main
research interests centered on stellar spectroscopy -- pulsating stars,
binary stars, rotating stars, as well as the interstellar medium. By
1932 he'd become director of the Yerkes Observatory, a position he'd
hold for 15 years. From 1939 to 1950 he acted as a founding director
of the McDonald Observatory in Texas -- at the time the 82" telescope
was the world's biggest, after the Mount Wilso 100" -- and would also
be the first director of the National Radio Astronomy Observatory at
Green Bank, West Virginia (1952 to 1962).
- Aug 12, 1919 - E. Margaret Burbidge (née Eleanor Peachey),
British born and educated astrophysicist who worked chiefly in the
U.S., at the Yerkes Observatory (six years) and briefly at Cal Tech
(when women weren't allowed to use the Mount Wilson & Palomar
telescopes), before becoming a research astronomer and then professor
of astronomy and eventually director of the Center for Astronomy and
Space Sciences at the University of California, San Diego -- as well
as in Tucson, where husband Geoff was director of the Kitt Peak
National Observatory from 1978 to 1984. In 1972-73 she herself was
director of the Royal Greenwich Observatory back in England, and was
president of the American Astronomical Society after returning to
the U.S. (and becoming a citizen). She was the first woman president
of the American Association for the Advancement of Science.
M. Burbidge is probably most thought of for being the lead author of
a famous, landmark, 108 page paper in Reviews of Modern Physics
in Oct, 1957 -- Burbidge, Burbidge, Fowler, & Hoyle, usually
referred to as B2FH -- which laid out the details of the
chained nuclear reactions for nucleosynthesis in stellar interiors,
which is the basis for our modern understanding of stellar evolution,
how the elements heavier than hydrogen and helium in the periodic
table (known collectively as "metals" in astronomy) are created, and
the processes leading up to novae and supernovae. All of these in
turn form the basis for our understanding of the chemical evolution
of galaxies, their increase in "metallicity" over time.
This work was stimulated by the discovery by Merrill five years
earlier of spectral lines for the short-lived radioactive element
technetium in the spectra of stars: since the stars are many times
older than technetium takes to decay, this showed elements were
currently being made in their interiors and then relatively quickly
transported to their surfaces (photospheres), where they were
observed. Three of the four B2FH authors were British.
Only Fowler shared in the Nobel Prize (Physics, 1983), the reasons
for which are still debated by science historians. (A possibly
relevant complication is that the prize can go to at most
three people in a given year.)
An expert in observational spectroscopy, Burbidge also contributed
to early research on quasars, co-authoring a book on them with her
husband in 1967, and at one time co-holding the world record for
having discovered the quasar (OQ 172) with the highest redshift
(z=3.53), which held for almost a decade (1974−1982). Much of this
work was done with the 3-meter telescope at Lick Observatory. She
and Geoff and Roger Lynds also made the first observations of
absorption lines in QSOs (3C 191). She'd later be involved in
the design and construction of the Faint Object Spectrograph
(FOS) for the Hubble Space Telescope.
As of 2019 Burbidge was celebrating her 100th birthday, though
she only survived another ~6 months.
- August 16, 1744 - Pierre Méchain, French astronomer and
surveyor who was luckily noticed by Jérôme Lalande at a young
age, met and befriended Charles Messier at age 30, and ended up directing
the Paris Observatory from 1799 until his death five years later from
the yellow fever he caught in Spain while trying to refine his measurement
of what's called the Dunkirk-Barcelona arc: the distance from the earth's
pole to its equator was to become the basis for the metric system's unit
of length, ten million meters. He was off by less than ¼mm per meter,
sometimes referred to as "Méchain's error". It would be nearly two
hundred years before this was noticed, by satellite measurements.
Earlier (1787) he had been involved in determining the precise distance
between the Paris Observatory and the Royal Greenwich Observatory, as
part of a veritable super-group of mathematician-scientists which included
Cassini and Legendre; they visited William Herschel while in England.
During his life Méchain discovered twenty-five of what are now called
Messier (M) objects, including the Sombrero Galaxy (M104), the Pinwheel
Galaxy (M101), and the companion galaxy (NGC 5195) to M51, the Whirlpool
Galaxy. In addition he discovered (or co-discovered) 11 comets, including
2P/Encke; his name is not now attached to any of these because their orbits
were only calculated in the decades after his death, when usable mathematical
techniques for doing so were first developed -- based on the sort of solid
observational data compiled by the likes of Méchain.
- Aug 16, 1845 - Gabriel Lippmann, French-Luxembourg physicist,
who invented the coelostat, the principle behind modern fixed solar
telescopes, and was the 1908 winner of the Nobel Prize in Physics for
his invention of an interference method of color photography (i.e., one
that did not use dyes or pigments), which he started work on almost
fifty years before Kodachrome film came on the market. Much later,
laser holography would be based on the same basic principles.
Marie Curie was one of his doctoral students at the Sorbonne; he
himself had been a doctoral student of Gustav Kirchhoff (of Kirchhoff's
Laws fame), graduating summa cum laude in 1874. Among several other
such positions, he was president of the French astronomical society
- Aug 19, 1646 - John Flamsteed. He observed the September 12,
1662, annular eclipse of the Sun from his home at age sixteen and went
on to become the first Astronomer Royal, succeeded in the position by
Edmund Halley, and he laid the foundation stone for the Royal Greenwich
Flamsteed improved on Tycho Brahe's decades old star maps, which were
based on visual observations, by a factor of fifteen in positional
accuracy. Using 20,000 observations of these ~3,000 stars, Flamsteed was
the first to determine modern, telescope based values for Greenwich's
latitude, the obliquity (slant) of the ecliptic relative to the celestial
equator, the position of the equinox (where the ecliptic crosses the
celestial equator), the distance to the sun (the value for the AU), and
the eccentricity of the earth's orbit.
When you see a star designated, say, 61 Cygni -- which was actually #85
in the 1712 edition of his catalogue, and is a very nearby (11.4 light
years) binary of two K dwarfs, and was also the first star other than
the Sun to have its distance measured -- you're using Flamsteed numbers.
- Aug 19, 1891 - Milton Humason, colleague of Edwin Hubble's
at Mount Wilson and Palomar Mountain, who was instrumental in first
measuring faint galaxy spectra, providing evidence for the expansion
of the universe.
Humason got his circuitous start in astronomy by first attending a
summer camp on Mount Wilson (1905), after which he dropped out of
high school at age 14 and returned to the area, doing a six year
stint as a ranch foreman in the area. With no further formal
education, around 1908-10 he became a mule driver on the packtrains
used to carry everything up the mountain for the construction of the
observatory there. Marrying the observatory engineer's daughter in
1911, he was first hired on at the observatory when a janitorial
position opened up. He quickly was promoted by George Hale to night
assistant to the observing astronomers, and then to the scientific
staff (1919) just as the 100" telescope was nearing completion.
By the mid-1930s he'd measured the largest redshifts (distances)
then known, z=0.131 to the Boötis I galaxy cluster and z=0.137
to the Ursa Major II galaxy cluster (1936).
After the discovery of Pluto, it was noticed that Humason had taken
four photographs of it in 1919 with the 10-inch Cooke triplet lens
refractor, but had not noticed it, the plates being made with another
purpose in mind; never-the-less, the measurements of Pluto's position
a dozen years before its discovery were a great help in quickly
pinning down its orbit early on.
- Aug 20, 1779 - Jöns Jakob Berzelius, Swedish chemist
who did no astronomy but prepared, purified, and analyzed over 2,000
compounds (1810-16), in the process establishing Dalton's atomic
theory and Proust's law of definite proportions. He's also responsible
for the introduction of the letter symbols used today in the periodic
table, and his table (1828) of atomic masses for the forty elements
then known is generally not far off from modern values. He himself
discovered four new elements: cerium (1803), selenium (1818), silicon
(1824), and thorium (1829). He's responsible for the invention of the
concepts of 'catalysts', 'radicals', 'halogens', 'organic'
(chemistry/compounds), and 'isomerism'. Berzelius also wrote a widely
used textbook (1803) and collated and edited an annual review of
chemistry research (1821-49).
- Aug 22, 1834 - Samuel Pierpont Langley, first director
of the Allegheny Observatory, a solar astronomer, inventor of the
bolometer (1878), and a famous aviation pioneer to boot. Langley
funded the observatory for fifteen years by selling an early version
of a standard time signal to cities and the then new railroads. The
bolometer made possible early observations of infrared radiation, and
in 1881 Langley ascended to the top of Mount Whitney (with James E.
Keeler) to record the Sun's output; comparison with measurements from
nearer sea level allowed one to extrapolate to the Sun's total output
above the atmosphere, and such IR measurements over about a decade
figured prominently in the chemist Svante Arrhenius's 1896 paper on
the effect of carbon dioxide in the atmosphere, now known as the
- Aug 24, 1876 - Carl Wilhelm Wirtz, who spent his time
at both the Kiel Observatory in Germany and the Observatory of
Strasbourg, France, and is chiefly remembered now for being the
first to propose a velocity-distance relationship for the redshifts
of galaxies (1922). Wirtz relied on radial velocity measure from
Vesto Slipher, and used the angular sizes of galaxies as a proxy
for their distances, implicitly assuming all galaxies have the
same physical size.
Wirtz also thought he had data showing more massive galaxies to have
smaller redshifts than smaller galaxies, and that counter-clockwise
spiraling galaxies have smaller redshifts than clockwise spiraling
ones. He interpreted his results in terms of the de Sitter model for
the universe, which is empty of matter (zero density) but has the
interesting property that if you sprinkle test particles in it you
can see that it is in fact expanding; Wirtz thus thought that the
velocity-distance relationship was due to a higher time dilation
effect for more distant galaxies.
Discoveries and other firsts
- Aug 1, 1729 - French professor of mathematics Nicolas
Sarabat discovers the Comet of 1729, thought to be the largest
comet ever seen, based on its calculated absolute magnitude of
about -3. It might have been 100 km in diameter.
The comet was near its closest approach to earth, 3.1 AU, when
discovered, and because of this large distance it was never very
bright in apparent magnitude -- only 3-4, meaning barely naked
eye if you knew where to look. Cassini in Paris was able to
observe it until the third week of January 1730, an unusually
long time for a comet back then.
The Comet of 1729 is one of a class with an orbit assumed to
be parabolic (i.e., an eccentricity of 1.0), so it's uncertain
whether or not it will return in something like 100,000 years
or leave the solar system entirely.
- Aug 1, 1786 - Catherine Herschel discovers the first
of the eight comets she'd turn up over about the next decade.
Her older and more famous brother William was subsequently
summoned to Windsor Castle after the discovery was announced
to show Caroline's comet to the royal family. She was the
second woman to discover a comet, Maria Kirch having found
one earlier in the century.
- Aug 3, 1872 - Charles A. Young observes a flare on the
sun with a spectroscope and calls attention to its coincidence with
a magnetic storm on earth.
- Aug 5, 1864 - Giovanni Donati makes the first spectroscopic
observations of a comet (Tempel, 1864 II) and sees what are now
known as the Swan bands (3 of `em) due to molecular carbon (C2).
- Aug 6, 1181 - Chinese and Japanese observers record
a zero magnitude "guest star" in northern Cassiopeia and then
follow it as it fades over the next six months. The remnant was
only recently discovered [photo at right], by amateur Dana
Patchick in August, 2013, in archived images from NASA’s
Widefield Infrared Survey Explorer (WISE). Previously, the
best candidate was the nearby radio source 3C 58, cataloged
many decades ago, but it might be several thousand years old,
and contains a pulsar (neutron star).
The measured expansion velocity of this newly found nebula, as
well as its size and position, make it the best candidate for
the supernova 850 years ago. But there's no neutron star or
black hole at its center, only a very peculiar white dwarf,
with a temperature of 200,000°K and stellar winds of
16,000 km/sec. According to one model, SN1181 was a rare
type Iax supernova, in which two white dwarfs collide and
one somehow survives.
- Aug 6, 1996 - The head of NASA, Daniel Goldin, releases
a statement about an upcoming paper in the journal Science
on the possibility of ancient, fossilized microscopic primitive
life forms having been discovered in the Martian meteorite known
as ALH 84001, collected in 1984. A press conference the following
day at the White House with President Clinton and one of the
paper's authors (Dr. Everett Gibson) received extensive national
and international news coverage. Even though considerable doubt
was eventually cast on the paper's tentative propositions about
what had been found in the meteorite, the event and the ensuing
controversy did lead to a big increase in interest in exploring
Mars and other planets/moons where life might have arisen sometime
in the past, and gave a big boost to the nascent fields of
astrobiology and exobiology.
- Aug 7, 1869 - A widely witnessed total solar eclipse
over the U.S. (Alaska to N. Carolina) in which spectra of the
Sun's corona first revealed a mysterious green emission line.
Helium (in absorption) had only first been identified in the
sun's spectrum a year earlier (see Aug 18 below) so at first
the line was attributed to an unknown element, 'coronium'.
It was not until 1941 that the Swedish physicist Dr. Bengt Edlen
correctly identified the line as belonging to iron ionized thirteen
times (Fe XIV). This was early evidence pointing to extremely high
coronal temperatures, on the order of a million degrees Kelvin. The
atomic and electron collisions in the plasma are then violent enough
to knock so many electrons off even a big, heavy, and slow-moving
element like iron, with thirteen being half of its number of
electrons under more normal (neutral) circumstances. It was only
a few years later that the corona first started to be observed at
radio wavelengths -- though it was suspected that the radar receivers
during WW II were picking up the sun in some fashion -- which
confirmed the very high temperatures. The way in which these high
temperatures are created and maintained is not precisely understood.
- Aug 7, 1959 - Explorer 6 is the first satellite to return
photos of the Earth from orbit.
- Aug 8, 1989 - Launch of the European Space Agency's
Hipparcos precision astrometric satellite. The design objective,
utilizing only an 11" Schmidt telescope, was to provide the
positions, parallaxes, and annual proper motions for some 100,000
target stars with an unprecedented accuracy of 2 milli-arcseconds
(mas). Eventually, 118,000 stars were measured to an accuracy of
better than 1 mas. As well, two and a half million more stars down
to 11½ magnitudes had their positions measured to ~30 mas and
their brightnesses measured (at two broadband wavelengths) to an
accuracy of 0.0015 magnitudes.
- Aug 10, 2008 - The Wide Field and Planetary Camera 2 on
the Hubble Space Telescope celebrates the satellite's 100,000th orbit
around the earth by shooting a mosaic of photos of the star cluster
NGC 2074 and its surrounding ionization nebula (HII region) in the
Large Magellanic Cloud, part of the Tarantula Nebula complex.
- Aug 11, 1877 - Mars's outer satellite Deimos first seen,
by Asaph Hall of the U.S. Naval Observatory. He turned up Phobos,
the larger of Mars's two moons, six nights later.
Seventeen years later Hall would be the first to suggest that the
unexplainable advance in the perihelion of Mercury's orbit might be
due to Newton's Law of Gravity being incorrect, rather than, say,
the result of an undiscovered hypothetical planet (Vulcan). It
would be another 21 years before the issue was resolved when
Einstein announced General Relativity.
- Aug 13, 1596 - David Fabricus first notices the variability
of the long period (331.6 days) red giant star Mira, ο (omicron)
Ceti, now a prototype for this class of M spectral type star. Mira
typically lives at 9th or 10th magnitude before brightening ~250x
to 3rd or 4th magnitude, but has gotten to 2nd magnitude, and on
one known occasion was almost as bright as 1st magnitude Aldebaran.
- Aug 13, 1847 - The fourth brightest asteroid, 7 Iris,
is discovered by John Russel Hind in London. Named after the Greek
rainbow goddess, it is thought to be a low iron, LL-chondrite,
S-type of asteroid, similar in compostion to the meteor which
exploded over Chelyabinsk, Russia, on Feb 15, 2013. It has a diameter of
~135 miles and rotates once every 7.1 hours.
- Aug 14, 1959 - The first very crude photograph of the
earth from orbit is made by NASA's Explorer VI satellite, launched
a week earlier and manufactured by JPL and TRW to study trapped
radiation in the earth's magnetic field, galactic cosmic rays,
radio propagation in the upper atmosphere, and the flux of
micrometeorites (using piezoelectric crystal microphones
as sensing elements).
- Aug 16, 1968 - Paul Muller and William Sjogren at JPL
announce the discovery of lunar mascons (short for "mass
concentrations") after carefully tracking small
changes in the orbit of Lunar Orbiter 5 over 80 orbits.
The five conspicuous ones were associated with prominent maria
("seas"), suggesting these were formed by giant asteroid impacts,
with the relatively denser remnant of the asteroid buried under
the surface, causing the observed dips in the spacecraft's orbit
due to the slightly greater gravitational attraction above them.
The huge impacts would have either punched a hole in the lunar
crust down to where the moon's interior was still molten, the
magma then welling up and flooding the crater to form the mare,
or the impact also could have melted enough of the surrounding
lunar crust for it to have then flowed into and filled the
crater more from the side than from below.
- Aug 17, 1885 - French astronomer Ludovic Gully sees
the the first ever extragalactic supernova, in the Andromeda
Galaxy, during a public observing event, but dismisses it as
maybe being the result of moonlight. Three nights later, German
astronomer Ernst Hartwig is showing the Andromeda Galaxy to some
friends at the Dorpat Observatory in Estonia and sees the new
star through a 9" refractor. The observatory director, Ludwig
Schwarz, prevented Hartwig from notifying other astronomers, so
it wasn't until the last day of the month that Hartwig snuck a
Of course at that time galaxies were not recognized as exterior
to the Milky Way (the real debate over that was 30-35 years in
the future), and SNe were not recognized as exploding stars at
the endpoint of stellar evolution for another 40-45 years, so the
star was designated as the variable star "S And" -- only the 2nd
variable star found in the entire constellation of Andromeda.
Hartwig recorded its magnitude as 5.8 (5.9 by some sources),
making it theoretically naked-eye visible, and it was thought
to have peaked right around the 21st of the month. To this day
it's the only SN seen in the Andromeda Galaxy.
[Naming of variables starts with the letter R, then S, etc., and the
(abbreviation for the) name of the constellation; after Z it goes RR,
RS ... RZ, SS, ST ... SZ, all the way to ZZ before starting over with
double letters at the beginning of the alphabet (but ommiting J) up
to Q, and then using numbers starting with V335 after all the letter
combinations are used up. You can blame the 19th century Prussian
astronomer Friedrich Wilhelm August Argelander for this scheme.
(See Mar 22.)]
- Aug 17, 2017 - The first collision/merger of two neutron
stars, in the S0 galaxy NGC 4993 ~40Mpc away, is picked up by the
Laser Interferometer Gravitywave Observatory (LIGO), followed two
seconds later by its detection by NASA’s Fermi Gamma-ray Space
Telescope satellite. Despite the poor angular resolution of these
instruments, in only ~10 hours they were able to pin down the
location of the object on the sky somewhere in a 28 square degree
box in southern Virgo and eastern Hydra, where the 17th magnitude
visual object was quickly found a little NE of the galaxy at optical
wavelengths by ground-based telescopes. The event produced what is
now called a kilonova, much less luminous than supernovae but
still ~1000x brighter than a regular nova. This may solve the fifty
year mystery of the source of gamma-ray bursts, first turned up
by satellites put up during the Cold War to detect thermonuclear
explosions on earth. The first binary system composed of two
neutron stars was found in 1974 but won't merge for another 350
million years or so.
- Aug 18, 1868 - Prominences are first studied with
a spectroscope (by at least six different scientists) during
a total eclipse of the sun and are shown to be composed primarily
A 7th scientist not with the others, Norman Lockyer (see
May 17), first sees helium in the
Sun's spectrum and gives it its name. Jules Janssen also saw the
unknown line in the spectrum but didn't go out on the limb of
proposing it to be due to an unknown element.
Helium was otherwise unknown on earth until 1895, when it was
found in the uranium ore cleveite (named after one of the Swedish
chemists involved) where it is a radiogenic product, i.e., made
by the radioactive decay of the uranium.
The helium visible in the sun, by contrast, is mostly primordial,
with only a tiny fraction having been made in the core by the fusion
of hydrogen into helium (the sun's power source), there being no way
for it to get from the core up to the surface during the sun's
lifetime as a normal star; an even smaller fraction is radiogenic.
- Aug 19, 1887 - Russian chemist Dmitry Ivanovich Mendeleyev,
famous for first coming up with the periodic table of elements (1868),
ascends to 11,500 feet in a hot air balloon to observe a total solar
eclipse. In Russia at the time the date was Aug 7 because they were
still using the Julian calendar, not moving to the Gregorian calendar
until after the USSR was established.
- Aug 19, 1964 - Launch of Syncom 3, the first
geosynchronous satellite, which was used for TV broadcasts
of the 1964 Tokyo Olympic Games, and, later, by the Department
of Defense for communications during the Vietnam War.
The idea of such satellites was first brought to public attention
by science fiction writer Arthur C. Clarke in a 1945 issue of the
magazine Wireless World. Orbiting at 22,236 miles (35,785
km) above the surface of the spinning earth, such satellites have
an orbital period of exactly a sidereal day, and thus appear to
stay above a particular point.
The Clarke Belt, as it's now called, currently has more than 500
active satellites as well as a large number of dead ones -- like
Syncom 3, which was deactivated in 1969.
- Aug 19 & 20, 2020 - California wildfires come within
meters of the domes at the Lick Observatory on Mount Hamilton, but
do no substantive damage, though the historic residence of E.E.
Barnard (photo at right) was destroyed.
- Aug 20, 1977 - The Voyager 2 spacecraft was launched, on
its way to conducting a grand tour of the four outer planets. This
was 15 days before Voyager 1, but the latter was on a slightly faster
and more direct trajectory, so it overtook Voyager 2 in several months
(December) and was the first to flyby both Jupiter and Saturn (see
below) before heading up and out of the plane of the ecliptic towards
- Aug 21, 1914 - A total solar eclipe and the second attempt
to verify the general relativity theory of Albert Einstein, which even
though it wasn't published yet already was predicting that starlight
passing close to the limb of the sun would be deflected by twice the
amount predicted using Newton's law of gravity.
Unfortunately, World War I broke out and Erwin Finlay-Freundlich of
the Berlin-Babelsberg Observatory, Germany, and his equipment were
interned at their intended observation site in Russia as war spies.
Clouds obscured the eclipse there in any event, as there were two
other groups planning on making observations also.
This total solar eclipse occurred on the same calendar date as the
one widely seen in the U.S. in 2017, but at the opposite node of
the moon's orbit. It lasted a similar length, of 2 minutes 14
- Aug 21, 1972 - OAO-3, the fourth Orbiting Astronomical
Observatory, and the second to function properly, is launched.
Renamed Copernicus once in operation, to commemorate his
birth 500 years earlier (1473), the satellite observed in both
the ultraviolet and x-ray regions until 1981.
- Aug 21-23, 1924 - Mars was at opposition and closer to
Earth than at any time in the century before, or the next 80 years.
In the U.S., a "National Radio Silence Day" was promoted during a
36-hour period, with all radios quiet for five minutes on the
hour, every hour, so that any possible radio signals from Mars
might be detected. At the Naval Observatory a receiver was lifted
3 kms (10,000 ft) above the ground in a dirigible to get the best
- Aug 22, 1888 - One of the few recorded and reasonably
verifiable instances of a human death (and a serious injury of
another man) caused by a meteorite -- a meteoritic airburst in
this case -- in present-day Iraq.
- Aug 24, 2016 - The European Southern Observatory announces
the discovery of an earth-like planet in the nearest star system,
Proxima Centauri, only 4¼ light years away. Proxima Centauri
b orbits in the habitable zone at a distance of but 0.05 AU from
Proxima Centauri, and has a period of 11.2 days; its mass is 1.3x
earth. The planet was found using the radial velocity method, and
causes a motion in Proxima Centauri of only 2 meters per second,
about the limit set by granulation and other motions related to
convection in the star's atmosphere.
Announced 4½ months earlier, Project Starshot has the objective
of sending a fleet of ~1000 light sail nano-spacecraft (each weighing
a few grams) to Proxima Centauri b at 15-20% the speed of light in a
travel time of 20-30 years, starting in 2036.
- Aug 25-26, 1764 - Charles Messier independently discovers
M33, the Triangulum galaxy, the third major member of the Local Group
(of galaxies) after us (the Milky Way) and Andromeda (M31). The
object had first been noted at least 110 years earlier by
Giovanni Battista Hodierna.
Twenty years later, William Herschel, who was generally careful to
avoid Messier's objects when compiling his own catalog of nebulae,
recorded it as H V-17 on Sep 11, 1784. Herschel also recorded
separately the bright H II region NE of the galaxy's core as
H III.150, now known as NGC 604, one of the largest such star
forming regions yet found, with a diameter of nearly half a
kiloparsec (~450 pc). Three other H II regions in the galaxy
were large and bright enough to also get NGC numbers: 588, 592,
- Aug 25, 1981 - Voyager 1 flies by Saturn, the first ever
spacecraft to do so.
- Aug 25, 1989 - Voyager 2 flies by Neptune. ditto
- Aug 25, 2003 - NASA's Space Infrared Telescope Facility
(SIRTF), renamed the Spitzer Space Telescope a few months later
after its proponent, Princeton professor Lyman Spitzer, is launched.
The 33" f/12 telescope, made of beryllium, was cooled to just
5.5°K by a supply of liquid helium designed to last only
a few years. After it ran out in 2009, observations at the two
shortest wavelengths (3.6 and 4.5 microns) continued until 2020,
the instruments having warmed up to only 30°K.
- Aug 25, 2012 - Voyager 1, heading in the direction of
the constellation Camelopardalis, reaches interstellar space by
going through the heliopause.
- Aug 27, 1962 - Mariner 2 is launched aboard an
Atlas-Agena B rocket on its way to a Dec 14th fly-by of Venus, the first interplanetary
- Aug 27, 2016 - The Juno spacecraft makes the first
of its planned three dozen orbits close to Jupiter (perijove),
reaching only 2600 miles above the cloudtops. Juno also returned
the first photos of Jupiter's north pole, as well as aurorae at
its south pole.
- Aug 28, 1789 - William Herschel discovers Saturn's
- Aug 29, 1993 - The Galileo spacecraft flies by the
asteroid Ida on its way to Jupiter.
- Aug 30, 1992 - The first Kuiper Belt object, 15760
Albion (aka 1992 QB1), is discovered by David Jewitt
and Jane Luu with the University of Hawaii's 2.2m telescope.
[Discovery images at right; the streak below 1992 QB1
in the first twp frames is a fast moving nearby asteroid.]
- Aug 30, 2019 - The discovery of the first true
interstellar comet, Comet Borisov = C/2019 Q4 = 2I, by the
Russian Gennady Borisov -- the eighth comet he's discovered.
The earliest photo of the object was subsequently found to
have been made on Dec 13, 2018.
With an orbital eccentricity of e=3.36 this was the second
interstellar object to enter the solar system on a hyperbolic,
unbound (e > 1) "orbit", but the first to look and behave like
the local comets we're already familiar with. Jewitt and Luu
(see previous entry) estimated from its coma that the comet
was producing 2 kg/sec of dust and 60 kg/sec of water shortly
after it was found.
The discovery was at about the 18th magnitude and was made in
the relatively empty zone of the sky north of Cancer and Gemini
and below Lynx (about 08h26m, +33°39'). It's perihelion
occurred at ~2 AU on Dec 8 and it was only expected to reach
~15th magnitude, because the odds favor it having a small
nucleus (and mass) for it to have been tossed out of its parent
solar system's (presumed) Oort Cloud.
- Aug 31, 1846 -- Urbain-Jean-Joseph Le Verrier announces
the result of his analysis of the perturbations in Uranus's orbit
and the celestial coordinates of the hypothetical planet which
must be causing them. Neptune was discovered ~3 weeks later
(Sep 23) at the Berlin Observatory by Johann Galle.
The same technique, when applied to the orbit of Mercury,
eventually led in a roundabout way to the development of
Einstein's General Relativity 70 years later, after decades
of inconclusive searches for a hypothetical planet Vulcan. It
was Le Verrier, analyzing timing data from transits of Mercury
spanning decades, who first measured the advance in the
perihelion of its orbit, at the tiny amount of less than
half an arc-second per year. At the time this could only
be explained by the gravity of an undiscovered perturbing
object, like an unknown planet, but in curved spacetime the
orbit is not closed by a small amount.
- Aug 31, 1932 - G.G. Cillié and Donald Menzel
(who got on at Harvard the same year, and 22 years later would
become director of the Harvard Observatory) use eclipse spectra
to show that the sun's corona has a higher temperature than the
This eclipse was also important in the very early history of
radio astronomy: Karl Jansky, studying the possible sources of
noise in transatlantic phone systems (which used radio
transmission) for Bell Laboratories in Holmdel, NJ, with a
100-foot antenna used it to eliminate the sun as the cause.
Within 6-8 months (see TM_May.htm#D5) he was able to locate
the main cause not due to thunderstorms as emanating from the
center of the Milky Way.
- Aug 31, 1991 - Japan's Yohkoh solar observing
spacecraft is launched. Over years of observation it would
show that magnetic reconnection is responsible for flares
and coronal mass ejections.
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