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. Mitchell
achieved worldwide fame for her discovery of a bright comet in 1847.
- Aug 5, 1930 - Neil Armstrong, first human to walk on the moon.
- 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
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, 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 -- 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 and returned to the area. 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, after a six year stint
as a ranch foreman elsewhere in the area, he was first hired on at
the observatory when a janitor position opened up. He quickly was
promoted by George Hale to night assistant, and then to the scientific
staff (1919) just as the 100" telescope was nearing completion.
- 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, 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 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 (FeXIV). 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 still a major mystery
in solar physics.
- Aug 7, 1959 - Explorer 6 is the first satellite to return
photos of the Earth from orbit.
- 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 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 - Ernst Hartwig discovers the first ever
extragalactic supernova, in the Andromeda Galaxy. 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,
making it theoretically naked-eye visible.
[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 - Dmitry Ivanovich Mendeleev ascends to
11,500 feet in a balloon to observe an eclipse in Russia.
- 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 21-23, 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 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.
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.
- 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, 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.
- 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.
©2002-2017, 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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