Science

1. Galaxies
Spiral
Elliptical
Irregular
Astronomers
Ptolemy – believed the Earth was at the center of the universe
Copernicus – the Sun is at the center of the universe.
Galileo Galilei: first to use a telescope to observe celestial bodies.
Isaac Newton:explained that gravity is the force that keeps planets orbiting the sun and moons orbiting
planets.
What is it?
Astronomy is the study of all physical subjects beyond Earth.
Light-year: a unit of length equal to the distance that light travels through space in 1 year.
The speed of light is approximately 300,000 kilometers per second (about 186,000 miles per second)
Telescopes
A telescope is an instrument that collects electromagnetic radiation from the sky and concentrates it for
better observation.
Types
Refracting: a curved objective lens bends light and focuses the light to be magnified by the eyepiece.
Reflecting: light enters the telescope and is reflected from a large, curved mirror to a focal point above the
mirror.
Telescopes
Hubble Space Telescope: an optical telescope that is in space.
Provided clearer images in space than any ground based telescope.
Chandra X-ray telescope is the most powerful X-ray telescope ever built.
Launched in 1999.
Inner Planets - all are terrestrial
Mercury- terrestrial
Closest to the Sun
Can be as hot as 427° C
Its year is only 88 Earth days long!
Venus – terrestrial
About the same size, mass, and density as Earth.
Rotates in the opposite direction than Earth.
It's day (243 Earth days) is longer than it's year (about 225 Earth days).
Hottest planet: Averages 464 ° C because there is so much greenhouse gas.
Planets – inner
Earth – terrestrial
Just the right distance from the Sun.

2. Allowed water to develop which is the key to life.
Mars – terrestrial
The Red Planet
Cold planet, thin atmosphere, very low pressure
There is ice found on Mars.
Outer Planets - all gas giants
Jupiter- gaseous
Largest planet. Has the Great Red Spot (a spinning storm)
Made of primarily hydrogen and helium.
Takes almost 12 years to revolve!
Saturn- gaseous
Second largest planet
Similar composition to Jupiter.
Rings are made of icy particles.
Uranus- gaseous
Bluish-green color.
Made of mostly hydrogen and methane.
Very dense and it’s axis is titled almost 90 ° !
Planets - outer
Neptune- gaseous
Bluish color
Temperature is -225 °C
The atmosphere has belts of clouds
Pluto – like a terrestrialplanet
Farthest from the Sun. Has a moon called Charon
Now considered a dwarf planet.
It is more like an asteroid.
Half the size of Mercury
Made of rock and ice. Atmosphere is mostly methane.
Asteroids
Asteroids are large rocky bodies in orbit around the sun.
Irregularly shaped.
Most orbit in a region between Mars and Jupiter called the asteroid belt.
Meteors
A meteoroid is a small, rocky body orbiting the sun.
They are smaller than an asteroid.
A meteorite is when a meteoroid enters the Earth’s atmosphere and strikes the ground.
A meteor is the bright streak of light caused by a meteoroid or comet dust burning up in the atmosphere.
Stars
A star is a hot, brilliant ball of gas.
Stars go through a life cycle.
Absolute magnitude is the actual brightness of a star.
The H-R (Hertzsprung-Russell) diagram is a graph showing the relationship between a star’s surface
temperature and it’s absolute magnitude.

3. Our sun is an average star (dwarf star).
HR Diagram
HR Diagram
Our Sun
Our sun is an average star (dwarf star).
The energy from the sun is produced by fusion.
Sun spot- cool, dark spots on the sun
Solar flare- giant storm on the surface of the sun.
Can affect satellites
Solar Flare
Old Stars
Supernovas: death of a large star by explosion.
Produces silver, gold, and lead.
Neutron Stars: a star formed from the left over materials a supernova. Extremely dense.
Particles inside the star become neutrons.
Pulsars: a spinning neutron star.
Nebulae: a cloud of gas and dust that is created by the energy of the supernova explosion. New stars can
be born here. (stellar nurseries)
Black Holes: an object that is so dense (in other words, has enough mass in a small enough volume) that
its gravity is strong enough to prevent light or anything else from escaping.
Astronomers theorized that these are created after a supernova and when the universe began.
Galaxies
A galaxy is a large grouping of stars in space (1 million to 1 trillion stars)
Types:
Spiral- bulge at the center and spiral
Most galaxies are this type.
The Milky Way is thought to be this type
Elliptical- bright centers and very little dust and gas.-
Contain only old stars.
Irregular
No definite shape
Constellations
Constellations are sections of the sky that contain recognizable star patterns.
Different cultures named the constellations after their gods or objects in their daily lives.
The constellations change from season to season because of Earth’s revolution.
Comets
Comet: a small body of ice, rock and cosmic dust loosely packed together.
“Dirty snowballs”
Comet tails: gas and dust that the comet gives off when solar radiation heats it.
They orbit in an elliptical shape.

4. Scientists believe comets come from outside our solar system (Oort Cloud)
Astronomy
Astronomy
Our Place in the Universe
The Universe - 93 billion light years in diameter
Virgo Supercluster: 110 million light years in diameter. This is a group of about 100 galaxy groups.
The Local Group - 10 million light years in diameter. This is a group of over 50 galaxies.
The Milky Way Galaxy - 100,000 light years in diameter
Our Solar System - the Sun's gravity extends out to around 2 light years. So it is about 4 light years in
diameter.