This Month in the History of Astronomy - December
- Dec 1, 1811 - Benjamin (Don Benito) Wilson, namesake of
Mount Wilson, CA.
- Dec 7, 1905 - Gerard Kuiper, Dutch-born American planetary
scientist who discovered moons of both Uranus (see Feb 16) and Neptune (May 1), and Titan's
atmosphere, and studied the origins of comets and the solar system.
Even though he never proposed or discussed such a thing, for historical
reasons Kuiper is the namesake for the Kuiper Belt, which lies beyond the
orbit of Neptune (30 AU) out to ~55 AU, and is thought to contain upwards
of 100,000 mainly icy objects larger than 100 km in diameter, of which
only a thousand have been discovered (the first was in 1992). Pluto is
the largest and most massive member of the Kuiper Belt. Unlike the Oort
Cloud, which is spherical in shape and much more distant, the Kuiper Belt
is flattened, the main body of objects having orbital inclinations to the
ecliptic of ~10° or less and orbital eccentricities of ~0.1 or less.
- Dec 11, 1863 - Annie Jump Cannon, pioneer American classifier
of stellar spectra; she brought to completion the Henry Draper Catalog
(1918), which became the basis for all modern astronomical stellar
spectroscopy. It contains 225,320 stars, and HD numbers for stars
are still commonplace today.
- Dec 12, 1803 - James Challis, British astronomer, best known
for having flubbed the opportunity to have discovered Neptune.
Challis showed great promise even as a student, winning a place at
Trinity College, where he graduated with top honors (1825). In 1836 he
succeeded George Airy to the Plumian Professorship of Astronomy at
Cambridge, a post he held until his death in 1882, and while serving
as director of the observatory there until 1861.
In 1844, John Couch Adams, a young astronomer and mathematician who had
recently graduated from Cambridge, approached Challis about getting all
the data available at the observatory on the position of Uranus, going
back to 1754, with the idea of analyzing its deviations from a perfect
orbit to deduce the location of the hypothetical planet causing the
gravitational influence. A year later, in September, 1845, Adams
returned with the results of his calculations, with the object's
estimated orbital path and its coordinates for Oct 1st. Challis didn't
think so young and inexperienced an astronomer could possibly be right,
so he shelved the report. If he'd looked, he almost certainly would
have seen Neptune, less than 2° from where Adams said it would be.
Airy, then at the Greenwich Observatory, and the person who had
originally made many of the observations upon which Uranus's
perturbed orbit was based, didn't see Adams' work until almost
ten months later. He encouraged Challis to look, and he observed
Neptune twice -- but didn't recognize it due to a lack of diligence
and poor star charts.
Meanwhile, Urbain Leverrier in France had done a similar calculation to
Adams and relayed his predicted coordinates to Galle and d'Arrest, who
found Neptune immediately (See Sep 23.).
- Dec 14, 1546 - Tycho Brahe, Danish pre-telescopic astronomer
who established the first modern observatory on the island of Hveen,
about 32 km northeast of Copenhagen, in 1582. He gave Kepler his first job in the field.
- Dec 15, 1834 - Charles Young, American astronomer who
made early spectroscopic observations of the Sun, including the
first spectra of both the corona and the reversing layer in the
solar atmosphere, which can only be seen during total eclipses.
- Dec 16, 1857 - Edward Emerson (E.E.) Barnard, Amercian
observational astronomer with many discoveries to his credit:
Amalthea, the fifth moon of Jupiter; Barnard's Star, the high
proper motion star second nearest to the Sun after Alpha Centauri;
370 dark nebulae in the Milky Way; Barnard's Loop, an emission
nebula 10° across encompassing much of the constellation of
Orion and probably a 2 million year old supernova remnant; and
Barnard's Galaxy (NGC 6822), one of the closest satellite galaxies
of the Milky Way. Very early in his career, and with no formal
education, Barnard discovered five comets at a time when Hulbert
Warner offered a $200 prize for each, allowing him to build a house
for himself and his new bride. Barnard has the only honorary degree
Vanderbilt University has ever awarded.
- Dec 20, 1876 - Walter S. Adams, Mt. Wilson astronomer
who uncovered the nature of Sirius B, the first known white dwarf
star (which was first seen by the famed Alvan Clark in 1862).
- Dec 20, 1904 - Founding of the Mount Wilson Solar
- Dec 21, 1898 - Ira S. Bowen, Caltech laboratory
spectroscopist who first ID'd, in 1927, the emission lines
seen in the spectra of many gaseous nebulae (like the Orion
Nebula) as being due to "forbidden" quantum energy level
transitions in common elements like O, N, Ne, and S. These
transitions are only "forbidden" in the sense that they aren't
usually observed in the laboratory, because a more rarified gas
is needed to produce them; even the best laboratory vacuum has
such a high enough density of matter that the higher energy
level state atoms or ions are collisionally de-excited
(destroyed) before the atom can transition to a lower level
by emitting radiation from these meta-stable states. In
other words, the higher energy level state is long lived enough
(milliseconds to seconds rather than microseconds or less) in a
sufficiently rarified and/or cold gas that it can radiatively
transition to a lower level. Bowen was also the first director
of the Palomar Observatory, serving from 1948 until 1964.
- Dec 25, 1642 - Isaac Newton, British "inventor" of
calculus and much of modern classical physics, including the
simple laws of motion and gravity which sufficed until
- Dec 27, 1571 - Johannes Kepler, Danish protege of
Tycho Brahe who used his extensive records
of Mars's positions to formulate the three laws of planetary
motion still in widespread use today.
- Dec 28, 1882 - Arthur S. Eddington, British theoretical
astrophysicist who was instrumental in showing why stars are the
way they are and how their interior conditions can be suitable
for the hydrogen fusion reactions which power them. He also gave
the name "expanding universe" to the mutual recession of the
- Dec 31, 1864 - Robert G. Aitken, American observer
who discovered and catalogued more than 3100 double and binary
- Dec 31, 1864 - George Willis Ritchey, expert optician
and telescope maker, and astronomer, who worked first at Yerkes
Observatory and then at Mount Wilson, where he was largely
responsible for the 60" and 100" mirrors, the largest in the
world at the time. The former went into operation in December,
1908, and Ritchey used it to take photos of the moon, star
clusters, and nebulae, the likes of which had never been seen.
They were distributed on the lecture circuit and appeared in
books on astronomy for years.
The glass disk for the 100" arrived at the shops in Pasadena
the same month, but took many years to fund, grind, figure,
and mount, and by the time it went into astronomical operation
Ritchey and Mt. Wilson director Hale had had a falling out and
Ritchey never got to observe with it.
Circa 1910, Ritchey met French mathematician, optician, and
astronomer Henri Chrétien, along with whom the Ritchey-Chrétien
design, now the standard basis for almost all large telescopes,
was worked out. This greatly enlarged the "good field" of view
(at the focus) over regular designs utilizing a parabolic primary
mirror, making wide field photography with large telescopes a
[Chrétien later developed (1927) the anamorphic lens system of
cinematography for widescreen movie projection, originally called
the Hypergonar process, but later known popularly by names such
as CinemaScope (1953), VistaVision (1954, which started the 3:2
horizontal format later adopted for 35mm film still cameras), and
Panavision (which used anamorphic prime lenses, 1957). The idea
is a lens in front of the camera lens squeezes or scrunches the
image horizontally for recording onto the film, while a complementary
lens over the film projector stretches it back out to as much as a
2¾:1 aspect ratio.]
On July 19, 1917, Ritchey discovered the new star, now known as
SN 1917A, in the galaxy NGC 6946, and from its faint magnitude
(14.6) argued that for such a nova to be so faint the galaxy
must be far outside the Milky Way not within it. He had earlier
observed the expanding nebulosity around Nova Perseii (1901) and
knew Milky Way novae were typically much brighter. It was still
to be some 15-20 years before objects like SN 1917A were
recognized as a distinct class of objects, namely supernovae.
NGC 6946 is a starburst galaxy and has had ten SNe discovered
in it in all over the century since Ritchey found the first one.
Discoveries and other firsts
- Dec 2, 1870 - Spectroscopist Jules Janssen (see
Aug 18, 1868) escapes the German
siege of Paris in a balloon in order to observe the solar eclipse
in Algeria twenty days later (see below), making it there only to
get clouded out.
- Dec 2, 1934 - The mirror blank for the 200-inch
telescope is cast in Corning, NY. (photo @ right) Also
- Dec 2, 1995 - Launch of the ESA/NASA satellite SOHO
(SOlar and Heliospheric Observatory), which led to the discovery
that coronal mass ejections occur almost daily.
- Dec 3, 1971 -- The USSR's Mars 3 becomes the first
spacecraft to make a soft landing on the red planet.
- Dec 3, 1973 - The US's Pioneer 10, the first spacecraft
to achieve escape velocity from the solar system, is the first to
flyby Jupiter. At 12:26 EST it passed the orbit of Callisto and
entered the inner Jovian system; even at 130,000 Km/Hr (81,000 mph)
it took 16 hours to complete its mission. It continued on for 29+
years before it's nuclear power source and distance from earth
(80 AU then) caused its radio transmissions to be too faint for
us to be able to detect it; contact was lost on Jan 3, 2003.
Pioneer 11 flew by Jupiter one year later.
- Dec 4, 1639 - Jeremiah Horrocks and William Crabtree
are the first people to witness a transit of Venus (across the
sun), making measurements which allowed them to determine its
apparent diameter. Kepler's calculations suggested the next
transit of Venus (after the 1631 event) would
not occur until the next century, but Horrocks, a young British
amateur astronomer did his own calculations, but they were
completed only a month before the event so there was no time
to publicize them, and so he and his friend Crabtree were the
only ones to observe it.
- Dec 4, 1978 - The U.S.'s Pioneer/Venus Orbiter
becomes the first spacecraft to orbit Venus.
- Dec 5, 2020 - Japan's Hayabusa 2 spacecraft returns
to earth the first ever samples of an asteroid, 162173 Ryugu.
The capsule containing the estimated 100 milligrams of material
landed in the Woomera Prohibited Area in southern Australia as
planned. Hayabusa 1 had previously returned tiny shards from
the asteroid 25143 Itokawa on Jun 13, 2010.
- Dec 7, 1631 - French astronomer Pierre Gassendi (see
Nov 7, 1631), using Kepler's best
calculations, makes the first attempt to observe a transit of
Venus. Modern calculations show that it was not visible from
- Dec 7, 1972 - The famous Blue Marble picture of Earth
was taken by the crew of Apollo 17 from ~29,000 km (18,000 mi)
away -- hardly 7-8% of the way to the moon. Known as NASA photo
AS17-148-22727, it was the first time the trajectory made it
possible to photograph the South polar ice cap.
- Dec 8, 1845 - The fifth astroid, Astraea, is discovered.
The find is notable for several reasons:
Hencke was quite familiar with the field the object was in at
the time, but originally thought he'd found a new, variable
star, one that had brightened enough to at last be detectable.
It was the famous astronomer Johann Encke who, having read
about it in the newspaper, observed the new "star" a few days
later, and noticed its motion against the background stars,
thus confirming it as an asteroid. Two years later, Hencke
would discover the sixth asteroid (Hebe).
- It was made 38 years after the fourth asteroid (Vesta) was
discovered, the first four all having been found in a span of
just six years from 1801-07.
- The discoverer was an amateur, the German Karl Ludwig Hencke,
using a small telescope.
- Hencke had been searching for such a thing for fifteen
- Dec 10, 1974 - The launch of the first of the twin
Helios spacecraft to study the sun, the solar wind, and the
environment of the inner solar system, with Helios B (or 2)
following 13 months later (Jan 15, 1976). Both spacecraft were
sent into eccentric orbits around the sun with periods of ~190
days and perihelion distances of ~0.3 AU, closer than the orbit
of Mercury. Helios B set a spacecraft speed record of 70.22 km/sec
at its Apr 17, 1976, perihelion passage.
- Dec 12, 1971 - The launch of the first x-ray satellite,
Uhuru. It's mission ended in March, 1973, and its final catalog
consisted of 339 objects. It also gave the location for Cygnus
X-1 (which had been discovered during a rocket flight in 1964),
the first really good black hole candidate ever found.
- Dec 13, 1920 - The first stellar diameter (Betelgeuse)
is measured by Francis Pease with an interferometer at Mt. Wilson.
- Dec 14, 1962 - The U.S.'s Mariner 2 flies by Venus and
becomes the first successful interplanetry probe. Ground-based
radio astronomers, observing at 3.15 cm (9½ GHz), had only
recently (1956) measured a surface temperature on Venus of about
600°F, and Mariner 2 was able to confirm this incredibly
high value. The figure would lead to a Ph.D. thesis by Carl Sagan
and a vastly improved understanding of how the greenhouse effect
operates on planets, and how planetary atmospheres in general
evolve over time.
Mariner 2 also measured interplanetary magnetic field strengths,
as well as finding Venus's magnetic field to be at or below the
instrument's noise level of a few nanoteslas. The absence of a
strong magnetic field like earth's is thought to be a consequence
of Venus's slow spin rate.
- Dec 14, 1972 - This is actually a last: the last humans
to date to be on the moon (Apollo 17) return to earth, with Eugene
Cernan leaving the final bootprint at Taurus-Littrow and calling
it the "end of the beginning".
- Dec 14, 2013 - The unmanned Chang’e-3 lunar lander and
its Yutu (or Jade Rabbit) rover make China the third country to
land a spacecraft on the moon, Mare Imbrium to be specific.
- Dec 15, 1970 - The USSR's Venera 7 touches down on Venus
and becomes the first successful soft landing on another planet.
- Dec 19, 2013 - The European Space Agency's Gaia spacecraft
and precision astrometric observatory was launched, the successor to
the Hipparcos mission (which was operational from 1989-93) but with
100x better precision, and with the intention of measuring the
positions and motions of approximately one billion objects -- mostly
stars, but also comets, asteroids, and quasars -- brighter than
magnitude 20. Gaia will also do photometry and spectroscopy; with
the latter it is possible to measure radial velocities and thus
determine space motions from the proper motions.
Each object will be observed 70 times over five years, and the
expected accuracy in annual proper motion measurements is just
20 micro-arcseconds (µas) at 15th magnitude (200 µas at mag 20).
On Aug 30, 2014, Gaia discovered its first supernova, a Type Ia,
in a galaxy about half a billion light years away, hardly a month
after it began science operations (Jul 25). Gaia is expected to
discover about 3 SNe per day.
- Dec 21, 1947 - Don O. Hendrix and Ira S. Bowen make the
first "first light", visual observations of stars with the 200-inch
telescope. The next night photographic tests were made with a full
aperture Hartmann screen in front of the telescope to map the mirror's
figure. After an additional iteration of figuring and polishing in the
optical shop in Pasadena, the better shape led to the determination
that there was too much friction in the mirror's support structure,
designed in 1935, causing the mirror to deform as the telescope was
moved to different spots on the sky. There was also a thermal
deformation problem discovered, due to the amount of heat the
huge mass of glass retained; with different parts at different
temperatures, the differential expansion distorted the surface's
shape. With the support system re-designed and re-built, and both
insulation and cooling fans added, fixing those issues, an upturned
edge was revealed. Progress was slow because such star tests give
their greatest precision when done under conditions of the best
seeing, which typically occurs on Mount Palomar in the early Fall
(Sep and Oct). Therefore it would be almost two years later before
the mirror's figure was judged to be in tip-top shape and the
telescope went into routine, scheduled, scientific observations.
- Dec 22, 968 - A chronicler in Constantinople provides
the first clear description of the Sun's corona seen during a total
- Dec 22, 1870 - American Charles A. Young observes the
solar eclipse in Spain and shows that the chromosphere is the layer
in the sun's atmosphere where the dark lines in its normal spectrum
(discovered by Fraunhofer in 1817) are formed. The same lines are
seen in emission, as bright lines, rather than in absorption, in
the spectrum of the chromosphere.
- Dec 22-23, 1947 - Jodrell Bank first makes some of the
earliest radio wavelength observations of a meteor shower, namely
the Ursids, which it continued to do up thru 1953. (Their radiant
is in Ursa Minor, near the star β, aka Kochab, and the
responsible comet is 8P/Tuttle.) Hourly count rates derived
from radio observatories are an important suppliment to those
compiled by visual observers, who are often hampered by clouds,
which of course is not a problem at radio wavelengths.
- Dec 23, 1672 - Giovanni Cassini discovers Saturn's
- Dec 24, 1968 - The U.S.'s Apollo 8 is the first manned
spacecraft to orbit the moon.
- Dec 26, 1783 - William Herschel discovers the small nebula
associated with the star R Monocerotis, later catalogued as NGC 2261.
It became known as Hubble's Variable Nebula after his analysis of it
using early photographic material stretching from 1900-1916. The
nebula's variability had been discovered using a 6" refractor in
1861, by J.F. Julius Schmidt at the Nat'l Obs. of Greece in
It is now considered the prototypical 'cometary nebula' for its fan
shape, not for having anything to do with comets, the star being
embedded in the small end of the object. It is also of a class known
as 'cocoon nebulae', in that a dusty envelope of material surrounds
the star completely, which is typically of the T Tauri variety of
(young) variables, obscuring it from direct view. The dust both
absorbs and scatters the star's light, and clumps of denser
material moving around near to the star (proto-planets?) cast
shadows on the more distant parts of the cloud, causing the
appearance of such nebulae to change over time scales of months
(sometimes less). A few such variable nebulae have even been known
to disappear completely at optical (not IR) wavelengths.
- Dec 28, 1969 - Comet Bennett (1969 Y1) is discovered
by John Caister Bennett, an accomplished South African amateur
astronomer. The first of two bright comets in the 1970's -- the
other being Comet West in 1976 -- it reached magnitude zero or
a little brighter around the time of perihelion passage (Mar 20,
1970) and its closest approach to earth six days later.
Seen by millions, during April it sported two prominent tails
(one curved) stretching up to 20° as it headed N on its
highly inclined orbit. It was scheduled to be photographed by
Apollo 13 three days after launch (Apr 14), but on the night of
the 13th the near-disaster for which the mission was famous for
surviving scotched these plans.
©2002-2021, Chris Wetherill. All rights reserved. Display here does
NOT constitute or imply permission to copy, republish, or redistribute
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