# Presentation2

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## Presentation Transcript

### 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

### 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