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Introduction to the Night Sky and Constellations. Auriga. Orion. Comet Hale-Bopp. Taurus. The Pleiades. M33. Milky Way. Zodiacal Light. Venus. M31 (Andromeda Galaxy). Motivations for Observing the Sky. Curiosity Aesthetics Fear, religious belief.
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Auriga Orion Comet Hale-Bopp Taurus
The Pleiades M33 Milky Way Zodiacal Light Venus M31 (Andromeda Galaxy)
Motivations for Observing the Sky • Curiosity • Aesthetics • Fear, religious belief
Discovery of Astronomical Patterns & Time Cycles Practical Applications • Navigation • Time-keeping • Calendar-keeping Of immense value to all early cultures Could be critical survival technologies
Astronomical Measurements Without Telescopes • Angles • Sky to Sky • Earth to Sky • (Brightnesses) • (Colors, Shapes) • Changes in above with time
Naked Eye Instruments for Angular Measures 1580 AD 150 BC
10 degrees 5 degrees "Big Dipper" = Part of Ursa Major
The "Magnitude" System = a ranking of brightness
"Pan" of Little Dipper: a convenient magnitude template: 2,3,4,5 mag
STARS Form background "reference frame" About 2000-5000 visible to naked eye over whole sky Patterns of bright stars seem "fixed", unchanging Move "in lockstep" from East to West and return to same position in sky after 23h56m Called the “diurnal motion”
Positions of stars in night sky at given time change systematically during the year
SUN Brightest object (by far!) Scattered sunlight masks stars during day Steady brightness Slow, eastward motion against stars, 1o per day Returns to same position after 365.25days, or one year.
Lunar Phases MOON Second brightest object in sky (but much fainter than sun) Faster eastward motion against stars, 13o per day Dramatic change in (illuminated) shape or "phase" during cycle Cycle takes 29.5 days to return to same phase. 12 cycles per year Our "month" is based on lunar cycles
Planets 5 brighter starlike objects that move with respect to the stars. Mercury, Venus, Mars, Jupiter, Saturn Merc, Venus always near Sun. Others, up to 180oaway. Motion is slower than Sun, Moon. Generally eastward, but loops to west
"Retrograde Loop" in Mars Motion Eastward
Other Easily Visible Phenomena } • Meteors • Comets • Star clusters • Diffuse nebulae • Milky Way • External galaxies Transient
Sky Wheel Orientation Meridian Zenith North Pole Horizon
Constellations • Constellations are the patterns formed by brighter stars on the sky • Patterns seem fixed (i.e. don't change over years) • Recognized for millenia, by all cultures • Associated with mythological figures, animals, instruments, etc
Mesopotamian carved stone, ca. 1000 BC showing Sun, Moon, Venus, and constellations
Greek amphora, ca. 400 BC, showing Leo, Aquila, Hercules, etc
Orion, Taurus, Lepus in a classical celestial atlas.
Pattern only traces brighter stars
More modern constellations Bode, 1801