The Universe, Solar System,
and Planets I
Questions:
How do we know the Big Bang happened?
How do we know the Universe is expanding?
What is the timeframe of Universe evolution?
News Flash: NASA/CNN report first stars
formed early than once thought
Edwin Hubble at Mt. Wilson
Hubble’s observations at the 100 inch during the
1920’s led him to the conclusion that the universe
is expanding, and that an object’s recession velocity
is proportional to its distance from the observer.
Hubble guiding the Hooker
100 inch telescope in 1923.
The Hooker 100 inch telescope atop Mt. Wilson
near Pasadena, CA. It was the largest telescope in
the world from 1917-1947.
Deep Hubble Space Telescope Image
A deep image of an “empty”
portion of the sky with the
Hubble Space Telescope
reveals that the universe is
filled with galaxies- many just
like our own. The light
we see from the most distant
galaxies has traveled approximately 10 billion years to
reach us.
Using the Doppler Effect to Measure Velocity
Blueshift
Redshift
Galaxy Spectroscopy

Spectra of a nearby star and a distant
galaxy
 Star is nearby, approximately at rest
 Galaxy is distant, traveling away from
us at 12,000 km/s
Stellar Spectrum
Sodium
Magnesium
Galaxy Spectrum
Calcium
Origin of the Universe Did It Begin with a Big Bang?
Discovery of the Background Radiation from initial Big Bang
-Long wavelength
-came from all directions
Penzias and Wilson, 1965
Arecibo Dish, Puerto Rico
Early History of the Universe
• Matter as we know it did not exist at the time of the Big Bang, only pure
energy. Within one second, the 4 fundamental forces were separated
– gravity - the attraction of one body toward another
– electromagnetic force - binds atoms into molecules, can be
transmitted by photons
– strong nuclear force - binds protons and neutrons together in the
nucleus
– weak nuclear force - breaks down an atom’s nucleus, producing
radioactive decay
Early History of the Universe
• After 3 minutes, photons and neutrons began
to fuse to form the nuclei of hydrogen and
helium atoms
• About 300,000 years later, temperatures were
cool enough for complete hydrogen and
helium atoms to form
• Photons escaped from matter about the same
time, and light existed for the first time
Changing Composition of the
Universe
• 200 million years later, with expansion still occurring, stars and galaxies
began forming from leftover matter - hydrogen and helium
– nuclear fusion in stars has reduced the original composition of 100%
H and He to 98%
– when a dying star explodes, the heavier elements created by fusion
are blown into space to be recycled by newly forming stars
– the overall composition of the galaxies is gradually changing to the
heavier elements
The Solar System - Its Origin
and Early Development

Our solar system,
part of the Milky
Way galaxy,
consists of the Sun,
nine planets, 64
known moons,
many asteroids,
millions of comets
and meteorites, as
well as
interplanetary dust
and gases
The Solar System - Its Origin
and Early Development
General Characteristics of the
Solar System
• Planetary orbits and rotation
– planet and satellite orbits are in a common plane
– nearly all planet and satellite orbital and spin motions are
in the same direction
– rotation axes of nearly all planets and satellites are
roughly perpendicular to the plane of the ecliptic
General Characteristics of the
Solar System
• Chemical and physical properties of the planets
– the terrestrial planets are small, have a high density, and are composed
of rock and metallic elements
– the Jovian planets are large, have a low density, and are composed of
gases and frozen compounds
• Slow rotation of the Sun
• Interplanetary material
– existence and location of asteroid
belt
– distribution of interplanetary dust
Meteorites Visitors from Outer Space
• Meteorites are believed to be pieces
of material that originated in the
formation of the Solar System about
4.6 billion years ago
– Stones - composed of iron and magnesium silicates,
about 93% of all meteorites
– Irons - composed of iron and nickel alloys
– Stony-Irons - nearly equal amounts of iron and nickel
and silicate minerals