The Universe

The Universe
Only one exists.
Composed of space and 100 billion galaxies.
A galaxy is a grouping of millions or billions of stars kept together by gravity.
Edwin Hubble (in 1929) proposed that the Universe is expanding.
a. This is supported by a phenomenon called the Doppler shift.
1) Stars are moving away from Earth and their light
becomes dimmer. This is called the red shift. This gives support of the expanding universe.
2) If stars move toward Earth, we see a blue shift – light becomes brighter.

Theories
A. Creation theory states that the universe was created by God.

B. The Big Bang theory suggests that the universe began 10 to 20 billion years ago with a gigantic explosion.

Galaxies
Galaxies are classified according to their shape
Spiral galaxies often appear bluish because they contain many young stars
a. Young stars give off blue light when they burn
Elliptical galaxies often appear reddish because they contain many old stars
a. Old stars give off red light when they burn

Galaxies, cont.
A large cluster of galaxies is called a supercluster
Our solar system is inside the galaxy known as the Milky Way
a. The Milky Way is classified as a spiral galaxy
The Milky Way contains interstellar matter that may form new stars

Elliptical

Spiral Galaxies

Milky Way Galaxy
Top View
Side View

Stars
Distances between stars are measured in light-years - the distance that light travels in one earth year.
The closest stars to Earth are 4.3 light-years away.
Properties of stars:
a. They produce their own light.
b. They radiate (give off) these types of energy: heat, electromagnetic and light.

Their surface temperatures are estimated based on their color.
I. Hotter stars glow with light that is more intense at shorter wavelengths giving them a blue appearance.
Their apparent brightness is dependent on their temperature, distance from earth, and size.

3. Properties of stars
They produce their own light
They radiate (give off) these types of energy: heat, electromagnetic and light
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Red giant
A star that has low surface temperature and a diameter that is large relative to the Sun.

Betelgeuse Star in Orion Constellation

Stars, cont.
Held together by gravitational forces
Hydrogen combines to form helium on stars. This is called a fusion reaction and produces energy
Our sun is a typical star.

4. The life of a star:
About 90 percent of all stars are in the middle of their life cycles.
A star is born when gas and dust collapse inward.
Supergiant stars form supernovas
Most of the stars in the Milky Way, which are relatively small, will end their lives as white dwarfs.

The Solar System
Copernicus (1473-1543) first proposed that Earth and the other planets orbit the sun
The orbits of the planet were first said to be elliptical by Kepler (1571-1630)
The brightest object in our sky (besides the sun and the moon) is Venus

Nickolas Copernicus

The order of the planets are (solid and rocky inner planets) Mercury, Venus, Earth, Mars, and (outer gaseous planets) Jupiter, Saturn, Uranus, and Neptune.

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I. Mercury is closest to the sun and has very hot temperatures.
II. The inner planets and outer planets are separated by an asteroid belt.
III. The great red spot on Jupiter is believed to be a giant storm.
IV. All of the gaseous outer planets have rings.

I. Mercury is closest to the sun and has very hot temperatures.

II. The inner planets and outer planets are separated by an asteroid belt.

III. The great red spot on Jupiter is believed to be a giant storm.

IV. All of the gaseous outer planets have rings.

V. The most widely accepted model of the formation of the solar system is the nebular model where the solar system condensed out of a nebula – a huge cloud of interstellar gas and dust
- Planets may have formed out of material orbiting the early sun through the process of accretion where small particles collide and stick together to form larger masses.

V. The most widely accepted model of the formation of the solar system is the nebular model where the solar system condensed out of a nebula – a huge cloud of interstellar gas and dust
- Planets may have formed out of material orbiting the early sun through the process of accretion where small particles collide
and stick together to form larger masses.

VI. The Moon
Experiences
phases
determined by
relative positions
of Earth, sun,
and moon
(see page 599 in
the text)
VII. During a
solar eclipse the
moon blocks out
the sun