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Astronomy Stuff: 

Astronomy Stuff Some Selected Topics

How Big is the Universe?: 

How Big is the Universe? REALLY BIG!

Our Position and Motion in the Heavens: 

Our Position and Motion in the Heavens

Are we ever sitting still? : 

Are we ever sitting still? Earth rotates on axis: andgt; 1,000 km/hr Earth orbits Sun: andgt; 100,000 km/hr Solar system moves among stars: ~ 70,000 km/hr Milky Way rotates: ~ 800,000 km/hr Milky Way moves in Local Group Universe expands

Planets in Order and To Scale: 

Planets in Order and To Scale Build a scale model of solar system http://www.exploratorium.edu/ronh/solar_system/

Basic Properties of the Sun: 

Basic Properties of the Sun Radius is 100 times that of the Earth. 30,000 Earth’s would cover the surface. 1 million Earths would fit inside! It is a million times more massive than Earth 99.9% of mass of solar system Luminosity is 400 trillion trillion Watts.

The Milky Way Galaxy: 

The Milky Way Galaxy diameter of disk = 100,000 l.y. (30,000 pc) number of stars = 200 billion thickness of disk = 1,000 l.y. (300 pc) Sun is in disk, 28,000 l.y. out from center

Slide8: 

Planets all orbit in same direction and nearly in same plane Planetary Motion

Johannes Kepler (1571-1630): 

Johannes Kepler (1571-1630) Trained as a mathematician and theorist. Needed accurate data to make mathematical model of the solar system

What are Kepler’s three laws of planetary motion?: 

What are Kepler’s three laws of planetary motion?

Kepler’s First Law: 

Kepler’s First Law Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.

Slide12: 

An ellipse looks like an elongated circle What is an ellipse?

Eccentricity of an Ellipse: 

Eccentricity of an Ellipse

Kepler’s Second Law: 

Kepler’s Second Law A planet moves along its orbit with a speed that changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time.

Kepler’s Third Law: 

Kepler’s Third Law The ratio of the cube of a planet’s average distance (a) from the Sun to the square of its orbital period (P) is the same for each planet. a3 / P2 = 1 a3 = P2

So what is with the Zodiac Signs?: 

So what is with the Zodiac Signs? Intro to the Sun Signs

Annual Motion: 

Annual Motion

What is the cause of the seasons on Earth?: 

What is the cause of the seasons on Earth?

The Cause of the Seasons : 

The Cause of the Seasons Note apparent change in altitude of Sun.

Direct light causes more heating. : 

Direct light causes more heating.

The “altitude” of the Sun impacts both how much energy is received on Earth and the duration of daylight.: 

The 'altitude' of the Sun impacts both how much energy is received on Earth and the duration of daylight.

Axis tilt causes uneven heating by sunlight throughout the year. : 

Axis tilt causes uneven heating by sunlight throughout the year. Seasons Clip

Sun’s Motion Across the Sky: 

Sun’s Motion Across the Sky

Why are the warmest days typically a month after the beginning of summer?: 

Why are the warmest days typically a month after the beginning of summer?

Typically…: 

Typically… It takes a while for the Earth’s surface to cool or to warm up. The hottest days of summer are about a month or two after the summer solstice. Likewise, the coldest days are about a month or so after the winter solstice.

What would seasons be like if…: 

What would seasons be like if… The Earth had no tilt? The Earth’s axis lay on the ecliptic plane?

What is the Earth’s cycle of precession?: 

What is the Earth’s cycle of precession?

Precession of the Earth: 

Precession of the Earth Earth’s axis precesses like the axis of a spinning top once very 26,000 years.

Changes in Axis Tilt: 

Changes in Axis Tilt Small gravitational tugs from other bodies in solar system cause Earth’s axis tilt to vary between 22° and 25° Cycles every 41,000 years

What do you notice going on here?: 

What do you notice going on here? The Moon

What is a constellation?: 

What is a constellation?

A Constellation is…: 

A Constellation is… A region in the sky.

Thought QuestionThe brightest stars in a constellation…: 

Thought Question The brightest stars in a constellation… All belong to the same star cluster. All lie at about the same distance from Earth. May actually be quite far away from each other.

The brightest stars in a constellation…: 

The brightest stars in a constellation… All belong to the same star cluster. All lie at about the same distance from Earth. May actually be quite far away from each other.

Constellations: 

Constellations Constellation stars need not be close together in space.

Why do we see phases of the Moon?: 

Why do we see phases of the Moon?

Why do we see phases?: 

Why do we see phases? Phase Clip

What are the different Moon phases?: 

What are the different Moon phases?

Phases of the Moon: 

Phases of the Moon

The Sun & Milky Way: 

The Sun andamp; Milky Way

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