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Home , Cetus (mythology), Durchmusterung

AST 101

Lecture 4

Figures in the Sky Analemma

The position of the Sun at civil noon (standard time). This demonstrates: •The inclination of the •The equation of time •The non-circularity of Earth’s orbit Constellations

• There are about 6000 stars visible to the naked eye under good conditions • About 2000 are visible at any one time • Far fewer are visible from urban locales Orion

(images from http://www.astro.uiuc.edu/~kaler/sow/const.html) Scorpius Patterns in the Sky Many societies have identified constellations Sumer (4000 BCE): 6 constellations: •Bull (Taurus) •Crab (Cancer) •Maiden (Virgo) •Scorpion (Scorpius) •Sea Goat (Capricorn) •Fishes (Pisces) Rest of the Western Zodiac codified in Babylon (2350 BCE)

Also: Chinese, Koreans, the Mayans, American Indians, and various African tribes Greek Constellations

•366 BCE: Eudoxos publishes "Phaenomena", describing 45 Egyptian constellations. •240 BCE: Eratosthenes records 42 constellations. •150 CE: Hipparchus catalogs 1080 stars in 49 constellations. •~150 CE: Ptolmey records 48 constellations in the "Almagest" Modern Constellations

• 88 recognized by the IAU • 48 classical constellations (mythological) e.g., Camelopardalis, Scutum, Hercules, Canes Venaticorum • Southern constellations named in 17th and 18th centuries (animals, machines) e.g., Tucana, Horologium, Fornax, Musca, Doradus Zodiac

• 12 (13) constellations containing the ecliptic • Western zodiac: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpius, Sagittarius, Capricorn, Aquarius, and Pisces • Sun spends 18 days in Ophiuchus; only 7 in Scorpius. • Planets also pass through , Corvus, Crater, Hydra, Orion, Pegasus, Scutum, and Sextans • Chinese zodiac: Tiger, Horse, , Rat, Hare, Ram, Serpent, Ape, Cock, Dog, Boar, and Ox Significance of the Constellations None - except as mnemonic devices, or as position indicators. Stars in constellations: • are not physically related • are at different distances Stories in the Sky Orion and the Scorpion

J. Flamsteed Coelestis (1753) The Bears

Hevelius Uranographia (1690) : A Greek Soap Opera • King Acrisius of Argos • Danae • Zeus • Perseus • Dictys • King Polydectes • • Hermes • Athena • the Graeae • The Gorgons Doppelmayr's Atlas coelestis (1742) •Pegasus •Cepheus •Cassiopeia •Cetus • •The

Hevelius Uranographia (1690) Bayer Uranometria (1603) Cetus: Hevelius Uranographia (1690) Cassiopeia Hevelius Uranographia (1690) Today

• Perseus, Andromeda, Pegasus, Cetus, Cepheus, and Cassiopeia are all to be found in the fall evening sky. • Perseus holds the head of Medusa (the variable star Algol - the Ghoul - is her eye). • As punishment for her vanity, Queen Cassiopeia, as a circumpolar constellation, is condemned to hang upside down half the year, a most undignified position! Names of the Stars

Few stars have proper names Most are of Arabic origin

•: The Follower (rises after the Pleiades) •Algol: The Ghoul (the demon star) •: Rival of Ares (Mars) •: Armpit of the central one (Orion) •: Mouth of the Southern Fish •: left leg (of Orion) Numbers of the Stars Classic catalogs: Ptolmey’s Almagest (~150 CE) •The Bayer catalog. Stars named alphabetically (in Greek) e.g., α Orionis (Betelgeuse) β Orionis (Rigel), γ Orionis () •The Flamsteed Catalog. Stars listed numerically from west to east by constellation e.g., 1 Tauri, 2 Tauri, 3 Tauri •The Bonner Durchmusterung (1855). Stars listed numerically in latitude bands around sky. e.g., BD+48o 3456. Stars to about 9th magnitude. •Yale Catalog of Bright Stars HR 1 - HR 9110. •The Henry Draper catalog. HD 1 - HD 229000. Aliases of Betelgeuse

α Orionis 58 Orionis BD +07 1055 HR 2061 HD 39801 GC 7451 AG +07 681 GSC 00129-01287 HIP 27989 PPM 149642 SAO 113271 GCRV 3679 FK5 224 ADS 4506 AP IRAS 05524+0723 The Age of Aquarius? Precession of the

Period of precession: 26,000 years Physics of Precession

• Precession is caused by asymmetric forces. • Earth is not perfectly spherical – The equatorial radius is about 22km larger than the polar radius (0.3% departure from sphericity) • The gravitational force of the Moon and Sun, acting on the Earth’s equatorial bulge, drives the precession. Due to precession, , the intersection between the ecliptic and the equator, moves completely around the sky in 26,000 years. Why is  called the “first point of Aries”?