Download Unit 1: The Big Picture

Unit 1: The Big Picture
What is Astronomy?
The study of stars & anything outside
Earth
– Not astrology…no horoscope reading here!
Today we will go over
– Universe Creation (how did it all begin?)
– Universe Composition
– Universe Size (how big is it??)
Universe Creation
Big Bang Theory – universe literally explodes into
existence.
– Temperature: universe cooled from about 1023K
to about 1010K within the first second
– Temp dropped below 1 billion K after only 3
minutes, to 3000K after a million years, to 300K
today
*Water freezes at 273K and boils at 373K
– 1023= 1,000,000,000,000,000,000,000,000
A few artists’ renditions of the Big Bang
Size
Increased in size by 1030 in less than 10-30 sec.
(started out the size of an atom and grew
instantly to the size of a galaxy)
Continues to grow as galaxies are moving away
from each other…Hubble’s Law
Estimated age is 10-16 billion years
So, it’s REALLY BIG, SUPER BIG, BEYOND
COMPREHENSION
Composition
4 sec-temp too low for converting energy
into matter, too high to form atoms
3 minutes – nuclei can form
– 25% helium nuclei, 75% hydrogen nuclei w/ small
amounts of lithium and boron nuclei
300,000 years before temps cool enough
to form atoms
– 25% Helium, 75% hydrogen mix
Composition
Solar System: group of planets, moons, debris
moving around a star
Interstellar Space: space between stars filled with
dust, gas, etc.
Galaxy: systems of billions of stars
– 200 billion stars in the Milky Way
– Billions of galaxies in universe each with
potentially hundreds of solar systems
Are we alone??
Composition Continued
Intergalactic Space: the space between galaxies.
mostly nothing, can’t see it, gravitational pull
toward it exists
Galaxy Clusters: small group of galaxies
– Closest is Sagittarius galaxy 75,000 LY, Magellanic
Clouds, then Andromeda
Superclusters: groups of galaxy clusters
Cosmic Voids: space between superclusters
Milky Way Galaxy
Galaxy Cluster
Important Distances
*Astronomical Unit (AU) = distance from sun to earth
(93 million miles)
*62.25 AU = 1 light year = 6 trillion miles
*Light year = distance light travels in 1 year
Is the light we see
from stars and
other objects in
the sky
“up to date”?
Important distances to put in all in perspective
Earth’s diameter: 8,000 miles
Solar System diameter: about 8 billion miles
Distance to nearest star: 4.3 LY (Alpha Centauri)
Distance across the Milky Way: 100,000 LY
Distance to Andromeda Galaxy: 2.5 million LY
Distance across local group: 4 million LY
Distance across our supercluster: 100 million LY
**Bottom Line: There are billions of galaxies in
the universe each containing billions of
stars!
Day 2: Galaxies
Galaxy: systems of billions of stars, “island
universes”
– Thought Milky Way made up entire universe until
1920s
– Small fuzzy patches in telescopes appeared as
nebulae, Latin for clouds
– Edwin Hubble measured approximate distance
to nearby Andromeda…no way Milky Way was
that large
– 3 Types: spiral, elliptical, irregular
Spiral Galaxies (Milky Way)
Nucleus, halo, disk,
spiral arms
Gas & dust visible
Spin in direction
indicated by arms
Barred spiral: bar of
stars running through
nucleus…page 505 in
textbook for diagrams
Elliptical Galaxies
Sphere or squashed
sphere shape with
nucleus and halo
No spiral arms, little dust
or gas
Made almost entirely of
old reddish stars
Stars orbit, but not all in
the same path…don’t
rotate
Range in size from giant
to dwarf
Dwarf is the most
common type of galaxy
Irregular Galaxies
Lacking regular shapes
Large and Small
Magellanic Clouds are
among nearest neighbors
which are
– visible in the Southern
Hemisphere
– Look like clouds detached
from Milky Way
– Believed to be pulling apart
due to gravitational pull
from Milky Way
Our Home: The Milky Way
Made up of 200 billion stars, dust and gas
Gases absorb light from stars and give a
band of light in the sky
– Difficult to see stars in other spiral arms
– Scientists use radio & infrared waves to
penetrate dust
Spiral arms due to trailing of larger stars
more distant than smaller stars
Black hole center
Sun located on inner edge of Orion arm
Two types of stars:
– Population I: bright blue
stars in the spiral arms,
younger stars ( 10 BY
and younger, Sun)
– Population II: located in
the halo, bulge, and
globular clusters, older
stars (13 BY and older)
Milky Way Facts
Diameter of disk
100,000 LY
Thickness of disk
2,000 LY
Distance of Sun from Center 25,000 LY
Number of Stars
200 Billion
Time for Sun
200 Million years
to make 1 circuit