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Chapter 2: The Sky

Chapter 2: The Sky. Essential Questions. How do astronomers refer to stars? How do you compare the brightness of the stars? How does the sky move as Earth rotates? What causes the seasons? How do astronomical cycles affect Earth ’ s climate?. Constellations.

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Chapter 2: The Sky

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  1. Chapter 2: The Sky

  2. Essential Questions • How do astronomers refer to stars? • How do you compare the brightness of the stars? • How does the sky move as Earth rotates? • What causes the seasons? • How do astronomical cycles affect Earth’s climate?

  3. Constellations • Constellationsare ______ of _________that appear relatively close together. • Ancients thought the stars represented ___________, _______, and _________.

  4. What we see…

  5. Asterisms • Asterisms are ____________ we recognize in the sky. • They are only _______ of constellations or parts of ___________constellations. • Examples include: _______________in Ursa Major, the ___________________in Pegasus and Andromeda, and the ___________________in Lyra, Aquila, and Cygnus.

  6. Stellar Nomenclature(star naming) • Constellations are in ___________. • Many bright stars also have names and most names derive from ______________. • For example: _______________, the bright red star in Orion, comes from the ___________yad al-jawza, meaning “armpit of Jawza [Orion].” • We’ll learn more star names later, but astronomers have another way to identify stars…

  7. Start with Brightest and Go ____________ • Another way to identify stars is to assign ______________letters to the bright stars in a constellation in approximate order of brightness. • The brightest star would be designated by __________(α) and the next by _________(β), then ____________(γ), __________(δ), etc. • Now an example:

  8. Nomenclature Example • The brightest star in the constellation _________ _________(The Great Dog) would be called: __ ________ _____________ • This star happens to be the brightest star in the night sky and is more commonly known by its Arabic name—______________

  9. Brightness of Stars • The brightness of stars is measured on the ____________ ___________. • Invented by Greek astronomer _______________. • Ancients divided stars in ______divisions. • The brightest stars were of ___ ________________. • The dimmest stars were of ___ ______________. • Modern astronomers have extended the scale to include fainter and brighter objects.

  10. Magnitude Scale • Bright objects have a _______or _________magnitude. • ______objects have a ________and __________magnitude. • Seems backwards, doesn’t it? • _____ times for each difference • _________ ___________ _________

  11. A Model of the Sky • Ancient astronomers believed the sky was a great _________surrounding Earth with the stars stuck on the inside like _____________in a ____________. • This _______________model is not true. • Have you noticed the motions of objects in the sky?

  12. Celestial Sphere • At the _________celestial pole is a star… • _________(North Star) in the constellation _____ _________ (Little Dipper) • There is no bright star directly at the __________ celestial pole.

  13. Some definitions: • Zenith—the _________on the sky __________above your head. • Horizon—the ___________on the sky where it meets the _____________. • Celestial Equator—the __________on the “celestial sphere” _________between ________and ___________celestial poles. • Ecliptic—the _________of the _______in the sky.

  14. ____________Constellations • _______constellations are those that _________the pole star, Polaris. • They are always visible from Ohio. Just look north! • Constellations in the south are different…more on that later.

  15. Precession • The Earth spins like a __________ _______tipped at a 23.5° angle. • As ______do sometimes, the Earth _________and its north pole points at different places. This is called precession. • An entire wobble takes about ___________years!

  16. The Zodiac

  17. Zodiacal Constellations • Do you see why the zodiacal constellations are only visible during certain seasons? • I was born in June and my “zodiacal sign” is Gemini. • When is the constellation Gemini visible in the sky? • What does that mean about the zodiac under which I was born? Where was Gemini?

  18. The Seasons • Many people believe we have cool winters and warm summers because the Earth gets ___________and ____________away from the Sun over the year. • While the Earth’s orbit is _____________, and we do get about 1.7% ________/__________to the Sun than average • This is _____the _________of the seasons.

  19. Perihelion & Aphelion • In fact, the Earth is at ____________, its _________point to the Sun, around January 4th when we have winter. (~147,500,000 km) • The Earth is at _________, its ___________point from the Sun, around July 4th during our summer. (~152,500,000km)

  20. What causes the seasons then? • The _________of the Earth’s axis. • Throughout the year, the Earth’s North Pole always points ____________Polaris. • Sunlight hits the Earth at different ____________during the four seasons.

  21. The Seasons • In the summer, the Sun is _________the horizon ___________because it rises north of _________and sets north of _________. (see diagram) • The Sun also shines _________down on the ground. There is _________surface area the Sun has to heat. (think of flashlight shining ________ ______or at an _________) • Both effects cause _____________weather.

  22. Solstices • The Sun is highest in the sky on the ____________Solstice,around June 21st. On this day, the Sun rises the ____________N of E with the __________daylight hours. • The Sun is lowest in the sky on the __________Solstice, around December 21st. On this day, the Sun rises the __________S of E with the _____________daylight hours.

  23. Equinoxes • Around March 21st, the __________(Spring) Equinox occurs. The Sun rises due _________and we have ___________hours of daylight and night. • AroundSeptember 21st, the ____________(Fall) Equinox occurs. The Sun again rises due _________and we have _________hours of day and night.

  24. Direct Sunlight on Solstices and Equinoxes • During the Equinoxes, the Sun’s rays shine _________ _________on the Earth’s _________. • During the Summer Solstice, the Sun shines _______ __________on the ‘Tropic of ___________’ (23.5° North). • During the Winter Solstice, the Sun shines _________ ________on the ‘Tropic of ______________’ (23.5° South).

  25. Summer vs. Winter Solstice

  26. Astronomical Influences on Earth’s Climate • Factors affecting Earth’s climate: • _______________of Earth’s orbit around the Sun (varies over period of ~ 100,000 years) • ______________(Period of ~ 26,000 years) • ______________of Earth’s axis versus orbital plane • Milankovitch Hypothesis: Changes in all three of these aspects are responsible for ________-____________global ____________changes (ice ages).

  27. Astronomical Influences on Earth’s Climate 0 Polar regions receiving less than average energy from the sun Last glaciation Polar regions receiving more than average energy from the sun End of last glaciation

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