Lecture 2 The Sky and Vocabulary

Lecture 2 – The Sky andVocabulary

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Read Chapters 1–2Let’s go over D2L a bit more.

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Why Study Astronomy?

Understand the nature of our UniverseUnderstand our place in the UniverseUnderstand how things in the UniverseEvolveUnderstand where we came fromUnderstand where we are going

Bottom line: Seek Understanding

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Confirmation Bias

Lets do a little quiz

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Clicker Question

Do you think you know the pattern?(a) Yes(b) No

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Confirmation Bias (cont’d)

When you want to test a theory, don’t justlook for examples that prove it.When you’re considering a plan, think indetail about how it might go wrong.

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The Size of the Earth

Diameter = 12,756 km

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Earth-Moon Distance

D = 384,401 km = 238,856 miles

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Earth-Sun Distance

D = 1.5 × 1013 cm ≡ 1 AU

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Solar System

Pluto average distance 39.44 AU

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Nearby Stars

D = 1,000,000 AU = 17 ly 1 ly = 63,000 AU 1 pc =3.26 ly

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The Galaxy

D=30 kpc

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The Local Group

D=5 Mpc

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Clusters of Galaxies

D=500 Mpc

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Telescope As A Time Machine

Nebraska Simulation lookback

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Angular Size

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Scientific Notation for Small NumbersCount from the position just to the left of thedecimal place always being 0.

0.00012 = 1.2 × 10−4

320 = 3.2 × 102

See the textbook for units and conversionsAU: Astronomical Unit–Mean distancebetween the earth and sun

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Units of Measurement I

speeds measured in km/s:1 km/s ≈ 2200 miles per hourlight year: about 0.3 parsecsCelestial Sphere

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Units of Measurement II

Magnitudes: measure of brightness of starsLogarithmic scale that corresponds to theway your eyes perceive variations inbrightness. First defined by Hipparchus.Change of 1 magnitude corresponds to achange in brightness by a factor of 2.512.Change of 5 magnitudes corresponds to achange in brightness by a factor of 100.The scale goes the wrong way. Brighter starshave smaller magnitudes than dimmer stars.Really bright stars have negative magnitudes.

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Apparent Magnitudes in Night Sky

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Ancient Constellations

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Modern Constellations

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Star Names

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Projection on the Sky

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3-D View

3D Big Dipper

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Outline: Where are we headed?

The earth rotates on its axis once a dayThe earth revolves around the sun once ayearThe moon revolves around the earth once amonthThe other planets revolve around the sun withvarious periodsTHE BIG QUESTION: What does all thismotion look like to us sitting in Norman, OK?

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Celestial Sphere

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View of the Sky Depends on Latitude

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60 Degrees North

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30 Degrees North

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Equator

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30 Degrees South

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Angular Distance in the Sky

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Determining Angular Size

1◦

4◦

10◦

Full Moon 0.5◦

Sun 0.5◦

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Rising and Setting

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Circumpolar Constellations

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