ANCIENT
KNOWLEDGE AND IDEAS
PERSPECTIVE:
In the universe of the ancients, astronomy and astrology
are synonymous. The "planets,"or
wandering bodies, include those as far out as Saturn,
plus the Sun and Moon, the most distant ones being
invisible to the naked eye. It is commonly believed
that the "evening star" (Venus) and the
"morning star" (Lucifer) are two separate
objects. The Earth is not considered a planet, nor
a celestial body of any kind for that matter, but
entirely separate from "the heavens."
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THE
STARS are observed to exhibit
a fixed pattern (firmament)
which undergoes an annual cycle.
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THE
PLANETS* — Sun, Moon, Mercury, Venus,
Mars, Jupiter, and Saturn —
are seen to move
independently of the fixed
stars and of each other.
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THE
SUN
rises
and sets daily, but its
rising and setting times, as well as its noonday
height above the horizon, vary in
an annual cycle
corresponding to the seasons.
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THE
MOON
rises
and sets daily, but almost an hour later each day. In areas bordering the sea,
its rising and setting
are noted to correspond to the tides.
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THE
PHASES OF THE MOON
are noted occur
regularly over a period of about 29.5 days, and
correspond
to the height of ocean tides.
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ECLIPSES seem to occur irregularly, and are
widely believed to be
omens of disaster.
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METEORS are believed to be atmospheric in origin (their name deriving from Meteora, the
Greek goddess of weather).
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COMETS are believed to be cosmic messengers of great joy or great peril, triumph or
defeat.
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PRE-TELESCOPIC
ERA
PERSPECTIVE:
During the early millennia of human history, the diameter
of the universe is reckoned at a few thousand
kilometers—the extent of the explored portion of the
Earth. Celestial objects are believed to be a only
few (or at most a few thousand) kilometers above Earth's
surface.
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c 2800 BCE: The original
Stonehenge is established, probably for the joint
purposes of astronomy and religious rites.
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c 2400 BCE: Sumerian scribes
develop a
calendar having twelve 30-day months (360 days
per year).
-
c 1500 BCE: Egyptian astronomers
have determined that the
Sun's annual cycle against the background of stars lasts
approximately 365 days.
-
1361 BCE: Chinese astronomers make
the first observational record of a
lunar
eclipse.
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1217 BCE: Chinese astronomers make
the first observational record of a
solar
eclipse.
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c 420 BCE:
Democritus advances a theory that all matter is
composed of minute, indivisible particles, which
he calls "atoms."
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c 400 BCE: Babylonian astronomers
can predict with precision the
daily positions of the
Sun and Moon for each day
of the lunar month.
-
c 350 BCE:
Aristotle formally states the prevailing opinion
of the day, that the Earth is fixed at the center of the
universe, and that all the
celestial bodies revolve about it in complex
patterns.
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c 300 BCE:
Euclid applies rules of logic to
mathematics and geometry.
-
c 270 BCE:
Aristarchus of Samos proposes that the
Earth circles the Sun rather than vice versa; however,
although the Greeks accept that the Earth is
spherical, the idea that it moves is generally
rejected.
-
235 BCE:
Eratosthenes calculates the
diameter of Earth and the distances to Sun and Moon. (He
is about 15% off, but remarkably close
considering he is working with the shadows cast
by sticks.)
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PERSPECTIVE:
By the beginning of the Current Era the diameter of the
Sun-Earth orbit has been calculated to be about three
hundred million kilometers. Even so, the prevailing
image of a relatively compact physical universe, with the
Earth at its center, has remained essentially unchanged
since the dawn of history. |
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128 CE:
Theon of Smyrna observes a
transit of
Venus across the Sun's disk, a phenomenon
incompatible with a geocentric universe; he
proposes that Venus and
Mercury orbit the Sun rather than the Earth.
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c 150 CE:
Hipparchus discovers the
precession of the
equinoxes and calculates the length of the solar year to within 6.5 seconds of the currently
accepted value.
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c 140 CE:
Ptolemy formulates a model of Aristotle's
geocentric universe, speculating that the stars and other
celestial objects are embedded in rotating
crystal spheres.
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c 800 CE: Incas construct an
astronomical altar which accurately measures movements of
the Sun and Moon.
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1054: Chinese astronomers observe
a brilliant "new star" (nova), visible in daylight, in the
constellation Taurus. It subsequently fades to
invisibility over a period of weeks. (The
recorded position of this star corresponds to the
location of the telescopic object known today as
the Crab Nebula
(M1), which features a rapidly rotating neutron
star at its center.)
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1066: The appearance of a
comet (later determined to be comet Halley)
is taken as an omen by both sides in the Battle
of Hastings.
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1178: Canterbury monks report
seeing "fire" (probably a
meteor impact) on one of the horns of the new moon.
-
1521: Ferdinand
Magellan observes the
Magellanic
Clouds during his
circumnavigation of the Earth.
-
1543: Nicolaus
Copernicus publishes his
heliocentric theory, that the Earth and other planets
follow circular orbits about the Sun (rather than
everything revolving in complicated orbits about
the Earth as had been previously believed).
-
1572:
Tycho Brahe
observes a
supernova.
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1609: Johannes
Kepler refines orbital theory,
describing planetary paths as
elliptical rather than circular and thus resolving
discrepancies with recorded observations.
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TELESCOPIC
ERA
PERSPECTIVE:
At the beginning of this era the diameter of the universe
is reckoned at a few hundred million kilometers—the
diameter of the Sun-Earth orbit, plus some margin for the
visible planets. In Europe most knowledge about the
universe is derived from the Bible and the writings of
Aristotle and Plato. Although much of this
"knowledge" is false, questioning it publicly
can be dangerous, even fatal. Astronomy and
astrology begin to diverge following Galileo's telescopic
observations.
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1609:
Galileo Galilei,
using a
telescope, discovers the
Sun's rotation, the phases of Venus,
and
Jupiter's
four largest satellites,
Callisto, Europa, Ganymede, and Io.
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1610: Nicholas
Pieresc discovers the
nebula in the constellation Orion.
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1611: Christoph
Scheiner safely observes the Sun by
projecting a telescopic
image onto a white surface.
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1611: Simon
Marius observes the
nebula in the constellation Andromeda.
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1644: Johannes
Hevelius discovers the
phases of Mercury.
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1651: In a posthumously published
book, William Gilbert has
proposed that the stars are not all the same
distance from Earth, and that the planets are
held in orbit by magnetism.
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1655: Christiaan
Huygens discovers
Titan, largest of
Saturn's satellites.
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1659:
Huygens identifies
the odd protrusions on telescopic images of
Saturn as a
ring around the planet.
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1660: Otto von
Güricke proposes that
comets return
periodically.
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1664: Giovanni
Cassini notes that the planet
Jupiter rotates once every nine hours.
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1666: Isaac
Newton develops
calculus in order
to calculate the orbit of the Moon accurately.
-
1666:
Cassini observes
polar ice caps on
Mars.
-
1672:
Cassini and Jean
Richer use parallax from two
separate locations on Earth's surface to measure
the distance of Mars from Earth.
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1675:
Cassini observes a
dark
division in Saturn's ring,
and speculates that the ring is not a single
unit, but is made up of a multitude of small
objects in orbit around the planet.
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1682:
Edmund Halley
observes the
comet which
now bears his name.
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1687:
Newton formulates
his
Law of
Universal Gravitation and
Laws of Motion.
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1705:
Halley accurately
calculates an orbital
period of approximately 76 years for the 1682
comet, using Newton's laws of motion.
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1718:
Halley discovers,
upon studying the observations of Ptolemy, that
some supposedly fixed stars have shifted position
over the centuries and therefore have "proper
motions."
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1728: James
Bradley calculates the
velocity of light.
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1759: Newton's
laws of motion are
confirmed by observations
of the return of comet Halley.
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1760: Charles
Messier begins compiling a
catalogue of nebulae, so that they can be readily
distinguished from comets.
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1781: William
Herschel discovers the
seventh planet,
Uranus.
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1784: John
Goodricke makes the first identification of a
Cepheid
variable star (Delta
Cephei).
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1801: Giuseppe
Piazzi discovers the
asteroid
Ceres (the first of thousands) between the
orbits of Mars and Jupiter.
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1840: Friedrich
Bessel deduces the existence of an
eighth planet from irregularities in the orbit of
Uranus.
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1842: Christian Johann
Doppler explains the apparent shift in
frequency of sounds emitted by objects moving
toward or away from an observer.
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1846: Johann
Galle discovers the
eighth planet,
Neptune.
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1861: Gustav
Kirchhoff uses spectrum analysis
to determine the composition of the Sun's
atmosphere.
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1864: William
Huggins demonstrates that the
Andromeda nebula (M31) consists of stars rather than gases,
and is therefore a
galaxy.
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1887: The unexpected result of an
experiment by Albert Michelson and
Edward
Morley inadvertently demonstrates the
constant velocity of
light relative to any
vantage point, moving or fixed.
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PERSPECTIVE:
By the beginning of the 20th Century CE, our solar system
is known to extend to Neptune, whose orbit has a radius
of 4,500,000,000 kilometers (30
astronomic units), triple that of
Saturn's. The distance to the stars is now known to
be far too great to be measured in terrestrial units; at
this time the Andromeda galaxy is the most distant object
known, estimated to be perhaps a few hundred thousand
light-years away. |
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1905: Percival
Lowell predicts the existence of a
ninth planet, from anomalies in the orbits of Uranus
and Neptune.
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1905: Albert
Einstein formulates his
Special Theory of
Relativity.
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1908:
An aerial explosion in Siberia flattens
2,000 km² of forest near the Tunguska River. Because no remains of a meteor impact
have been detected, the cause is considered to be
a cometary fragment entering Earth's atmosphere.
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1912: Henrietta
Leavitt discovers a
relationship between the
luminosity and
period of
Cepheid
variable stars.
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1913: Ejnar
Hertzsprung devises a method of determining the
distances of
Cepheid variable stars from their apparent luminosity.
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1913: Henry
Russell shows the correlation between a star's
brightness and its spectrum.
-
1913: First use of light-spectrum
Doppler shift to measure
velocities of celestial objects.
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1915:
Einstein advances
his
General
Theory of Relativity.
-
1916: Karl
Schwarzschild's solution to Einstein's gravitational
field equations predicts the existence of
black
holes.
-
1917: Harlow
Shapley determines that our
solar system is 30,000
light-years from the central plane of the Milky Way, rather than near the
center of the galaxy as previously supposed.
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1919: Einstein's
General Theory of
Relativity is confirmed by
observations during a solar eclipse.
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1920:
Michelson uses
stellar interferometry to measure the diameter of a star
(Betelgeuse).
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1920: Jan
Van Oort determines that the
Milky
Way
galaxy rotates, and calculates the
distance of our Sun from
the center of the galaxy.
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1922:
A 20-ton meteorite lands in a field in
Virginia, creating a 46 square-meter crater.
-
1924: Edwin
Hubble determines the
distance to certain
Cepheid variables and finds that they are outside the
Milky Way.
-
1927: Georges
Lemaître proposes that the universe originated
in a "primordial
atom" (precursor of
"Big Bang" theory).
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1929:
Hubble discovers
that the
universe
is expanding, as evidenced
by the Doppler red-shift of distant galaxies.
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1930: Clyde
Tombaugh discovers the
ninth planet,
Pluto, using Lowell's 1905 calculations.
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1932: Karl
Jansky detects radio-frequency noise emanating from the Milky Way,
initiating the field of
radio-astronomy.
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1943: Grote
Reber detects radio-frequency emissions from the Sun.
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1948: George
Gamow and Ralph
Alpher formulate
equations describing the universe as expanding
from a primieval explosion, dubbed the "Big Bang."
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1948: Hermann
Bondi, Thomas Gold, and Fred
Hoyle advance "Steady State" or "Continuous Creation" theories, countering the Big Bang
theory.
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1950: To explain the behavior of
long-period comets, Van Oort proposes
that a diffuse cloud of cometary bodies surrounds the solar system at a
distance of 1 - 2 light-years.
-
1951: Gerard
Kuiper proposes a
belt of cometary bodies beyond the orbit of Pluto to account
for the origin of short-period comets.
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EXPEDITIONARY
ERA
PERSPECTIVE:
By the time humans themselves venture beyond the
atmosphere of their home planet, the extent of the known
universe has expanded exponentially. It includes
not just two galaxies, but millions, perhaps billions;
the nearest, Andromeda, is 2,300,000 light-years (ly)
distant. The farthest detectable galaxies are on
the order of 15,000,000,000 ly away. And some of
the most surprising news is yet to come.
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1957:
Sputnik 1 (USSR),
first artificial
satellite launched into
earth-orbit.
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1958: James
Van Allen discovers
two belts of ionized particles above the Earth's atmosphere.
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1958:
Explorer 1 (NASA),
first scientific satellite.
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1959:
Luna 3 (USSR),
provides first photographic images of the
Moon's far side.
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1961:
Vostok 1 (USSR),
Yuri
Gagarin becomes first human to travel in space.
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1962:
Mariner 2 (NASA),
first fly-by of the planet Venus.
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1963: Maarten
Schmidt makes first discovery of a
quasar.
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1965:
Voskhod 2 (USSR),
Aleksei
Leonov becomes the
first spacewalker.
-
1965:
Mariner 4 returns
images during its fly-by of the planet Mars.
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1965: Arno
Penzias and Robert
Wilson detect
3°K background radio
emission, confirming the
Gamow-Alpher "Big Bang"
theory.
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1966:
Luna 9 returns
images after the first "soft" landing on the
Moon's surface.
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1967:
Venera 4 (USSR),
first successful exploration of the
atmosphere of Venus.
-
1967: Jocelyn
Bell and Anthony
Hewitt make the first discovery of a
pulsar (a rapidly rotating neutron star).
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1968:
Apollo 8 (NASA),
first manned lunar orbit.
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1969:
Apollo 11,
first manned lunar
landing; astronaut Neil
Armstrong is the first human ever to set foot on another
world.
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1970:
Venera 7, first
successful landing of a spacecraft on Venus. (It
lasts but a few minutes before succumbing to the
intense heat, pressure, and corrosive chemistry
of the
Venerian atmosphere.)
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1971:
Mariner 9, first
Mars orbiter.
-
1971: The
binary X-ray system
Cygnus X-1, possibly
containing a black hole, is discovered.
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1971: Stephen
Hawking theorizes that
mini-black-holes were generated shortly after the Big
Bang.
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1973:
Pioneer 10 (NASA),
first exploration of the planet Jupiter.
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1974:
Mariner 10, the
first fly-by of the planet Mercury.
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1975:
Venera 9, the
first craft to orbit Venus and return images of
its surface.
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1976:
Viking 1 & 2
(NASA), the first soft landings on Mars.
-
1979:
Voyager 1 & 2
(NASA) fly by Jupiter; Voyager 1 reveals
Jupiter's ring and a volcanic eruption on Jovian satellite Io.
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1979:
Pioneer 11, first
fly-by exploration of the planet Saturn.
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1979:
Pluto reaches the 20-year
"summertime" portion of its eccentric
orbit, during which it is
temporarily closer to the Sun than Neptune.
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1981:
Space Shuttle
(NASA)
maiden
voyage.
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1983: SETI (Search for
Extra-Terrestrial Intelligence)
radio-frequency
monitoring is established.
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1983:
IRAS (Infra-Red Astronomy
Satellite) is launched.
-
1983:
Venera 15 returns
the first
radar
maps of the
Venerian surface.
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1986:
Giotto space probe
(NASA) makes a close encounter with comet
Halley.
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1986:
Soyuz T15 (USSR),
first mission to space station Mir 1.
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1986:
Voyager 2 (NASA),
first fly-by exploration of the planet Uranus.
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1987: A
supernova, bright enough to be seen with the
unaided eye, occurs in the Large Magellanic
Cloud.
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1989:
Voyager 2, first
fly-by exploration of the planet Neptune.
-
1990:
HST (Hubble Space
Telescope) (NASA), first optical telescope in Earth orbit.
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1992: Charles
Bailyn, Jeffrey
McClintock, and
Ronald
Remillard identify Nova Muscae as a
black
hole approximately
18,000 light-years from Earth.
-
1993: Jane
Luu
and David
Jewitt discover four large ice objects beyond
the orbit of Pluto, confirming the existence of
the
Kuiper belt.
-
1994: HST observation of
galaxy M87
furnishes
first
convincing evidence of a black hole.
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1994: Receding from the Sun,
comet Shoemaker-Levy 9 is shattered by the tidal forces of
Jupiter's gravity, and its fragments subsequently
collide with Jupiter, affording the first visual
observation of the collision of two celestial objects.
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1994:
The asteroid Apollo passes within
100,000 km of Earth.
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1995: The first comet-sized
objects in the Kuiper belt are discovered.
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1995:
Galileo (NASA),
first Jupiter orbiter and first
Jovian atmospheric probe.
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1997:
Luu discovers a
"worldlet," possibly a new class of object,
orbiting the Sun between the Kuiper belt and the
Oort cloud.
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1998: First two
ISS
(International Space Station) modules —
Zarya (Russia) and Unity (U.S.) — launched.
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1999: Having been closer to the
Sun than Neptune since 1979,
Pluto once again takes
its place as the most distant planet for the remainder of its 248 Earth-year
orbit.
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PERSPECTIVE:
As the science of astronomy and the mysticism of
astrology had parted ways following the invention of the
telescope, a similar divergence occurs between the
science of astronomy and the technology of physical
exploration. However, in this case, the difference
is one of focus rather than of fundamental dogma, for the
sheer expense of putting humans and hardware into space
forces government to take a major role in such
efforts. Consequently, there is a reexamination of
priorities and a reallocation of resources, based more on
economics, politics, and national prestige, than on
scientific inquiry into the nature of the heavens. |
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2004:
Cassini (NASA) rendezvous
with Saturn.
-
2005:
A tenth planet, its 558-year orbit
inclined at 44 degrees to the ecliptic, is identified by
Michael Brown, Chad Trujillo, and David Rabinowitz.
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2015:
Laser Interferomer Gravitational-wave Observatory (LIGO) detects
gravitational waves generated by the collision of two black holes.
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2016:
New Horizons (NASA)
rendezvous with Pluto.
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INTERSTELLAR AND
INTERGALACTIC ERAS
PERSPECTIVE:
(To be announced...)
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