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Astronomy
Part 1
General Science I
Spring ‘09
History of the Universe

Earth = 1 of 9 planets
 Sun= 1 of 100 billion stars in the Milky
Way, 1 of infinite numbers in our universe
Ancient Astronomy

Golden Age= 600 BC-150 AD in Greece
 Beliefs relied on philosophy (ideas) and
observations.
Geocentric View

At first, many believed
the Earth was the
center of the universe
 A geocentric view
 Geo=Earth
 -centric=center
Heliocentric view

Eventually, this belief
was formed into a
heliocentric view.
 We realized the SUN
was the center of our
galaxy.
Modern 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)

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)



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,
England)

Law of Gravity!
 Proved Kepler’s idea
that planets orbit in an
ellipse.
What is a star?
Simply put… a big ball of gas
 A light year?
- how far light travels in a year
-300,000 km/s (kilometers a second)!

Magnitude

The brightness of a star
 Apparent magnitude
– How bright the start appears to be from Earth

Absolute magnitude
– How bright the star really is
Measuring Magnitude

Think opposites
 The brightest stars have the lowest number
 The dimmest stars have the highest number
Hertzsprung – Russell
Diagram (H-R Diagram)

Came up with a way of classifying the stars
 Uses temperature and absolute magnitude to
determine plot point on the diagram
Trip through our Universe
Billions and billions
of stars


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!)
Carl Sagan 11/9/3410/20/96
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).
Constellations

Star groups that form
patterns as seen from
Earth
 Big dipper (ursa
major)
 Little dipper (ursa
minor)
 Orion
Nebula(e)

A huge massive cloud
of gas and dust.
 Where new stars form
How Nebulae form

Gravitational forces
 Gravity from the sun causes gases to get
closer together
 As the distance decreases, gravitational
forces increase
 Forms a “protostar.” The first stage in a
star’s life.
Nova

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
Novas
Supernova

Occur in stars 10-100x the size of our sun
 Explosions 1000x brighter than novas
 Temperature increases
 The iron core condenses and collapses from
gravitational forces
Neutron Stars

Occur after a supernova explosion
 The only thing there is neutrons. All the
protons and electrons have exploded off
 A spoonful weighs 100 million tons on
Earth!
Star Birth
Nebula
Star Life- Cycle
Protostar
Life of a Star
Red Giant
Main Sequence
Super Giant
Death of a Star
Black Hole
White Dwarf
Nova
?
Super Nova
Neutron Star