AstronomyAstronomyPart 1Part 1

General Science ISpring ‘09

History of the UniverseHistory of the Universe

Earth = 1 of 9 planetsSun= 1 of 100 billion stars in the Milky

Way, 1 of infinite numbers in our universe

Ancient AstronomyAncient Astronomy

Golden Age= 600 BC-150 AD in GreeceBeliefs relied on philosophy (ideas) and

observations.

Geocentric ViewGeocentric View

At first, many believed the Earth was the center of the universe

A geocentric view Geo=Earth -centric=center

Heliocentric viewHeliocentric view

Eventually, this belief was formed into a heliocentric view.

We realized the SUN was the center of our galaxy.

Modern AstronomyModern Astronomy

Ideas based more on observation

Nicholas Copernicus (1473-1543, Poland)– Earth rotates– Said Earth is a planet

(only 5 known at this point: Mercury, Venus, Mars, Jupiter, Saturn)

Tycho Brahe (1546-1601), Holland

Argued that if the Earth orbited the sun, then stars should appear to move over a period of 6 months.

Called this the stellar parallax (the shift of an object against a background caused by a change in observer position; hard to see)

Kepler was his apprentice

Johannes Kepler (1571-1630)Johannes Kepler (1571-1630)

Laws of Planetary Motion– The path of each planet

is an ellipse– Each planet travels at

its own speed– Astronomical Unit

(AU) = 150 million kilometers

Galileo Galilei (1564-1642)Galileo Galilei (1564-1642)

Around at the same time as Kepler

Favored the heliocentric viewpoint

Created the telescope (which later made him go blind after

looking at the sun through it) Discovered the four

moons of Jupiter Saw craters on the moon

Sir Isaac Newton (1643-1727, Sir Isaac Newton (1643-1727, England)England)

Law of Gravity! Proved Kepler’s idea

that planets orbit in an ellipse.

What is a star?What is a star?

Simply put… a big ball of gasA light year?

- how far light travels in a year

-300,000 km/s (kilometers a second)!

MagnitudeMagnitude

The brightness of a starApparent magnitude

– How bright the start appears to be from Earth

Absolute magnitude– How bright the star really is

Measuring MagnitudeMeasuring Magnitude

Think oppositesThe brightest stars have the lowest numberThe dimmest stars have the highest number

Hertzsprung – Russell Hertzsprung – Russell Diagram (H-R Diagram)Diagram (H-R Diagram)

Came up with a way of classifying the starsUses temperature and absolute magnitude to

determine plot point on the diagram

Trip through our UniverseTrip through our Universe

A star is a big ball of gas. Light year= how far light

travels in one year– 9.46 x 1015 meters

Speed of light= 186,000 miles per second! (300,000 km/second!)

Billions and billions of stars

Carl Sagan 11/9/34-10/20/96

Binary Stars

Half of the stars in the sky have a companion star (a buddy)

Most rotate around one another= binary star

Hubble image of the Sirius (brightest star in the sky) binary system, in which Sirius B can be clearly distinguished (lower left).

ConstellationsConstellations

Star groups that form patterns as seen from Earth

Big dipper (ursa major)

Little dipper (ursa minor)

Orion

Nebula(e)Nebula(e)

A huge massive cloud of gas and dust.

Where new stars form

How Nebulae formHow Nebulae form

Gravitational forcesGravity from the sun causes gases to get

closer togetherAs the distance decreases, gravitational

forces increaseForms a “protostar.” The first stage in a

star’s life.

NovaNova

When a star suddenly increases in brightness (100x) in a few hrs/days, then dims back to original state.

Gases from one binary star strike the other causing nuclear explosions which we see as light.

Can occur several times

NovasNovas

SupernovaSupernova

Occur in stars 10-100x the size of our sunExplosions 1000x brighter than novasTemperature increasesThe iron core condenses and collapses from

gravitational forces

Neutron StarsNeutron Stars

Occur after a supernova explosionThe only thing there is neutrons. All the

protons and electrons have exploded offA spoonful weighs 100 million tons on

Earth!

Star Life- Cycle

Nebula Protostar

Main SequenceRed Giant

White Dwarf Nova

Super Giant

Super Nova Neutron Star

Black Hole

Star Birth

Life of a Star

Death of a Star

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