... the mighty Orion and the Bear, which men also call b

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AncientAstronomy.ppt
Historical Development of Astronomy
Reference The Astronomy Timeline link in the
PHY250 website
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Constellations Intended to identify stars in the
sky conveniently
First identification of constellations found in
cuneiform texts and artifacts dating back roughly
6000 years Remnants found in the valley of the
Euphrates River, suggest that the ancients
observing the heavens saw the lion, the bull, and
the scorpion in the stars.
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Constellations The earliest references to the
mythological significance of the Greek
constellations may be found in the works of
Homer, which probably date to the 7th century
B.C. In the Iliad, for instance, Homer describes
the creation of Achilleus's shield by the
craftsman god Hephaistos On it he made the
earth, and sky, and sea, the weariless sun and
the moon waxing full, and all the constellations
that crown the heavens, Pleiades and Hyades, the
mighty Orion and the Bear, which men also call by
the name of Wain she wheels round in the same
place and watches for Orion, and is the only one
not to bathe in Ocean (Iliad XVIII 486-490). At
the time of Homer, however, most of the
constellations were not associated with any
particular myth, hero, or god. They were instead
known simply as the objects or animals which they
represented--the Lyre, for instance, or the Ram.
By the 5th century B.C., however, most of the
constellations had come to be associated with
myths, and the Catasterismi of Eratosthenes
completed the mythologization of the stars. "At
this stage, the fusion between astronomy and
mythology is so complete that no further
distinction is made between them"--the stars were
no longer merely identified with certain gods or
heroes, but actually were perceived as divine
(Seznec, 37-40). Despite the many mentions of the
stars in Greek and early Roman texts, by far the
most thorough star catalogue from ancient times
belongs to the Roman Ptolemy of Alexandria, who
grouped 1022 stars into 48 constellations during
the 2nd century A.D. Although Ptolemy's Almagest
does not include the constellations which may
only be seen from the southern hemisphere, it
forms the basis for the modern list of 88
constellations officially designated by the
International Astronomical Union (Pasachoff,
134-135). The influence of both the Greek and
Roman cultures may be plainly seen the myths
behind the constellations date back to ancient
Greece, but we use their Latin names.
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The Big Dipper North America
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The Plough - England
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The Celestial Bureaucrat - China
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Charles Wain Medieval Europe
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Ursa Major (the Bear) Greeks and Native
Americans
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The Celestial Sphere From the perspective of the
earth, the stars rotate around the earth once
every 24 hours (approximately). The Celestial
Sphere fixes the locations of the stars with
respect to each other.
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The Celestial Sphere Celestial Equator
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The Celestial Sphere From the perspective of the
earth, the projection of the earths equator on
the celestial sphere is called the Celestial
Equator.
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The Celestial Sphere Ecliptic
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The Celestial Sphere From the perspective of the
earth, the suns position in the sky changes over
the course of the year. The apparent path of
the sun during the year with respect to the fixed
starts on the celestial sphere is called the
Ecliptic.
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The Celestial Sphere Equinox
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The Celestial Sphere From the perspective of the
earth, the location of the intersection of the
Ecliptic with the Celestial Equator is called the
Equinox. There are two of these intersections,
and each occurs when line connecting the earth to
the sun is perpendicular to the earths axis of
rotation.
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The Celestial Sphere Autumnal Equinox Vernal
Equinox
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The Celestial Sphere The Autumnal Equinox occurs
when the sun passes from the earths Northern
Hemisphere to the Southern Hemisphere. Fall
begins at the Autumnal Equinox. The Vernal
Equinox occurs when the sun passes from the
Earths Southern Hemisphere to the Northern
hemisphere. Spring begins at the Vernal Equinox.
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The Celestial Sphere Summer solstice
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The Celestial Sphere The point on the Ecliptic
where the Sun is at its Northernmost point above
the Celestial Equator (ie, it is highest in the
sky in the Northern hemisphere) is called the
summer solstice. Summer begins at the summer
solstice, and the length of daylight is the
greatest in the Northern Hemisphere.
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The Celestial Sphere Winter solstice
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The Celestial Sphere The point on the Ecliptic
where the Sun is at its Southernmost point below
the Celestial Equator (ie, it is lowest in the
sky in the Northern hemisphere) is called the
winter solstice. Winter begins at the summer
soltice, and the length of daylight is the
smallest in the Northern Hemisphere.
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The Celestial Sphere The location of an object
measured in hours along the Celestial Equator is
called the Right Ascension of the object.
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The Celestial Sphere One circulation around the
Celestial Equator takes 360o. Rather than using
degrees, the Celestial Sphere is divided in 24
hours with corresponding minutes, and seconds.
Since 360/24 15o, each hour corresponds to 15o
along the Celestial Equator. The hour 0 h is
defined by a line connecting the North Celestial
Pole and the Vernal Equinox. The location of an
object measured in hours along the Celestial
Equator is called the Right Ascension of the
object.
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The Celestial Sphere The location of an object
measured degrees is called the declination of the
object.
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The Celestial Sphere The location of an object
measured degrees is called the declination of the
object. Star catalogs quote the location of
celestial object on the basis of the objects
right ascension (r.a.) and declination (dec.)
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The Zodiac The constellations that lie along the
ecliptic are collectively called the Zodiac.
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The Zodiac The constellations that lie along the
ecliptic are collectively called the Zodiac. The
constellations of the Zodiac are Cancer, Leo,
Virgo, Libra, Scorpio, Sagittarius, Capricornus,
Aquarius, Pisces, Aries, Taurus, Gemini. From the
perspective of the Earth, The sun would be in
different constellations of the Zodiac at
different times of the year (if you could see the
stars in daylight). Whats your sign?
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Footnote This is a good time to review the
Stellar Magnitudes and the Sky Maps link in the
PHY250 website.
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Newgrange Tomb (3200 BC)
Megalithic structures at Carnac (4500 BC)
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Stonehenge (3000 BC)
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Why?
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Why? Agriculture and Hunting Summer and Winter
Solstice Vernal Equinox
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Why? Agriculture and Hunting Summer and Winter
Solstice Vernal Equinox Different
constellations at different times of the
year More accurate (?) sun rises over specific
rocks at solstice, equinox
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Why? Agriculture and Hunting Summer and Winter
Solstice Vernal Equinox Different
constellations at different times of the
year More accurate (?) sun rises over specific
rocks at solstice, equinox Could be used to
identify planting and harvesting schedules and
predict the coming of the seasons Could be used
to predict the return of migrating animals
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Why? Navigation Stars at fixed locations
(celestial sphere)
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Why? Navigation Stars at fixed locations
(celestial sphere) Stars at fixed locations
could be used to locate position on the earth The
octant and sextant
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Why? Navigation Stars at fixed locations
(celestial sphere) Stars at fixed locations
could be used to locate position on the earth The
octant and sextant
Astrolabe (400) Octant (1731)
Sextant (1759)