Earth
---12,742 km in
diameter
---Mass = 6 billion
trillion tons
---Yet is but a spec of
dust in the universe
•Traveling at about 65 mph in a car it
would take one whole month without
stopping to travel the Earth once.
What is the Universe?
•Everything that exists
today, in the past & in the
future
•Mostly space, but made up
of bodies floating in space,
planets & their moons, stars
& galaxies
How is Distance in Space
Measured?
•Objects in space are SOOOOOO
far apart that measuring in miles or
kilometers is silly
•Measured in light years instead
Light Year
•Isn’t a measurement of time, it measures
distance
•Amount of distance light travels in a year
•6 trillion miles which is about 186,000 miles a
SECOND
Light Year Conversion Table
Kilometres
9,460,528,404,846
Miles
5,878,499,812,499
Light Year
•Distance to the nearest star is 25 trillion
miles away or 4.3 light years
•Our sun is only 8 light minutes from us
•Light travels so fast that it can go all the way
around Earth 7 ½ times in just 1 second
Galaxies
Universe organized into millions of galaxies
•Galaxy: large groups of stars held together
by gravity
•Galaxies are put into clusters & then
super clusters to identify them by names
•Every Galaxy is unique like a fingerprint or a
snowflake
•But all galaxies share some characteristics &
are grouped by their shape into one of four
categories.
4 types of galaxies
Spiral
Barred Spiral
Elliptical
Irregular
Spiral Galaxies
•Giant, flat pinwheels with many
arms that spin around a central
core.
Examples: Milky Way,
Andromeda
•it has three main
components: a disk, in
which the solar system
resides, a central bulge
at the core, and an all
encompassing halo.
Milky Way
•Our galaxy
•100,000 light years across & 6000 light
years thick
•Seems huge, but if the universe was the
size of a football stadium, the Milky Way
wouldn’t even be as big as a pinhead
•Named because of the band of milky light
we see across the sky on a clear, dark night
Spiral Galaxies
NGC 4586
NGC 1232
NGC 4501
Spiral Galaxies
Andromeda
Andromeda
These pictures are exposed using only the X-rays that are
given off from Andromeda
Barred Spiral
•Large bar running down middle
• Arms trail from the bar like water from a sprinkler
•Occurs in about 1/3 of spiral galaxies
Elliptical Galaxies
• Vary in shape from nearly flat disks to spherical (egg
shaped) to nearly circular to flat disks
•Home to only older stars
•Most galaxies are elliptical
Elliptical Galaxies
Irregular
Galaxies
• No definite shape
• Formed when galaxies collide or come close
and their gravitational forces interact.
•Another source may be very young galaxies that
have not yet reached a symmetrical state.
Irregular Galaxies
Large Magellanic Cloud,
Small Magellanic Cloud
163,000light years away
200,000 light years away
Local Group
• Family of galaxies including Milky
way & its neighbors,
• Local groups only take up a tiny
amount of space in the universe
•There are tens of billions of other
galaxies