Contact Information
•
Mike Skrutskie – mfs4n -
•
Room 262 – Astronomy Building
–
924-4328
Office Hours:
•
Monday 1:30 – 2:30
•
Thursday 10:30 – 12:00
Room 262 Astronomy (my office)
if those don't work contact me for arrangements
•
Course TA
–
Kim Sokal - krs9tb
•
Room 267 Astronomy Building
•
By appointment
How Do You Make Sense of it All?
Astronomy: A Search for Organization?
Stars....
Galaxies....
Astronomy: A Search for Organization?
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?


Galaxies, collections of billions of stars assembled and bound
by gravity, are a primary unit of Universal structure.
Any random deep view of the night sky shows a universe
peppered with galaxies – each containing hundreds of billions
of stars.
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?

Imagine we are able to travel to a point billions of light years
away and look back toward our galaxy...
Us?
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?
Our sun (a star) resides out toward
the edge of a thin and flat collection
of 100 billion stars – the Milky Way
Galaxy
A distant galaxy similar to our Milky Way
The Stars Near Our Sun
Associated WWW Link
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?
The Stars Near Our Sun
Associated WWW Link
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?

The Sun is embedded in the Milky Way (far from the center).
−
We have a myopic perspective.
−
The Milky Way is thin and flat, yet we see a lumpy diffuse
band across the sky because of our proximity.
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?

The Sun is embedded in the Milky Way (far from the center).
−
We have a myopic perspective.
−
The Milky Way is thin and flat, yet we see a lumpy diffuse
band across the sky because of our proximity.
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?

The Sun is embedded in the Milky Way (far from the center).
−
We have a myopic perspective.
−
The Milky Way is thin and flat, yet we see a lumpy diffuse
band across the sky because of our proximity.
Aitoff
Projection
Our Galaxy (the Milky Way) in Perspective:
How do we fit in?

Infrared light penetrates dust better than visible light.
−
An infrared view of the Milky Way reveals the real Galaxy.
Astronomy: A Search for Structure?

Hierarchical structure in the Universe leads to
an extended mailing address.....
Earth
The Solar System (in capital letters)
The Milky Way Galaxy
The Local Group
The Local Supercluster
The Universe
●
Implicit in understanding this structure
is knowing how far away things
actually are.... not an easy task!
Understanding Structure: Divining Depth
Understanding Structure: Divining Depth
Understanding Structure: Divining Depth
Still, we are focusing on
phenomenology....
Astronomy: A Search for Origins!!!

Where did all the structure and organization come from?

How did it emerge over time?

What were the starting conditions?

What physical processes were important?
−
We wish to explain, not just observe.
Astronomy: A Search for Origins!!!

Where did all the structure and organization come from?

How did it emerge over time?

What physics/physical processes were important?
Hydrogen + Helium + Gravity ⇨ Stars, Galaxies, and Humans
given about 14 billion years.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−
It happened 13.7 billion years ago.
» - a number now known to better than 1 percent!
−

Almost immediately gravity begins to form stars and
galaxies.
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” of previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time a system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

It happened 13.7 billion years ago.
a number now known to better than 1 percent!
−
Stars dieThe early Universe contained only uniformly distributed Hydrogen
and Helium.

Almost immediately gravity begins to form stars and galaxies.
−

After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” of previous generations of
stars.
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
At the same Stars
time a system of planets form from debris left in orbit
around the Sun.
form
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” of previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time a system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Five-Minute History of the Universe

The “Big Bang” brings matter, space and time into existence.
−

a number now known to better than 1 percent!
−

Stars “process” Hydrogen and Helium into heavier elements like
Iron, Calcium, and Oxygen.
After 9 billion years of cosmic recycling (4.6 billion years ago)
our Sun forms from the “ashes” for previous generations of
stars.
−

The early Universe contained only uniformly distributed Hydrogen
and Helium.
Almost immediately gravity begins to form stars and galaxies.
−

It happened 13.7 billion years ago.
At the same time system of planets form from debris left in orbit
around the Sun.
Life originates quickly on Earth.
−
but only becomes “complex” ½ billion years ago.
A Single-Year Perspective

If this history could be compressed into a single year:

The Universe starts on January 1...

The Solar System forms in early-September
A Single-Year Perspective

If this history could be compressed into a single year:

The Universe starts on January 1...

The Solar System forms in early-September

Life on Earth originates in mid-September
– - Life becomes complex in early-December
3.4 billion year old
stromatolite fossils
URL
0.3 billion year
old trilobyte
A Single-Year Perspective

If this history could be compressed into a single year:

The Universe starts on January 1...

The Solar System forms in early-September

Life originates in mid-September

– - Life becomes complex in early-December
–
Dinosaurs roamed the Earth for two weeks between
December 10 and December 25

Humanity (intelligence?) arose at 10 p.m. on December 31

Recorded history began around 11:59:45 on December 31
Overcoming Human Biases

Location, Wavelength, and Time to name a few
Lecture Notes: Human Biases in Astronomy
Human Biases

Time
−
A human lifetime is a blink of the eye relative to the
timescale of cosmic events.
• - Going back to that cosmic year, a human lifetime is about 2
one-hundredths of a second.
»
−
Stars and galaxies change incredibly slowly by comparison.
−
Astronomers must reconstruct the workings of the Universe
from this “snapshot” view.
Lecture Notes: Lookback time
Lecture Notes: Lookback time
Human Biases

Time
−
A human lifetime is a blink of the eye relative to the
timescale of cosmic events.
• - Going back to that cosmic year, a human lifetime is about 2
one-hundredths of a second.
»

−
Stars and galaxies change incredibly slowly by comparison.
−
Astronomers must reconstruct the workings of the Universe
from this “snapshot” view.
The Astronomer's task is similar to asking an alien
anthropologist to reconstruct the intricacies of human
relationships and politics from a snapshot of the events
happening on Earth at one instant.
Lecture Notes: Lookback time
Human Biases

Time
−
A human lifetime is a blink of the eye relative to the
timescale of cosmic events.
−
Astronomers must reconstruct the workings of the Universe
from this “snapshot” view.


This task is similar to reconstructing the intricacies of
human relationships and politics from a snapshot of the
events happening on Earth at one instant.
Astronomers have two powerful tools to address this
shortcoming
−
Light travels “slowly”. A stale view of the universe permits
Astronomers to look back in time.
Lecture Notes: Lookback time
“Lookback” Time

Light takes time to get from one place to another.
Light travels at a speed of 300,000 km/s
−


The travel time is instantaneous for most everyday
experience where distances are small.
Travel time becomes important for more distant objects


Light takes just over a second to get to the Moon
(400,000 kilometers away).
In a year light traverses a distance of a light-year.
“Lookback” Time

We get a “stale” view of the
Universe, seeing more distant
object as they were in the more
distant past.
– We see the Sun as it was 8.3
minutes ago because the
light took 8.3 minutes to
traverse the distance from
the Sun to the Earth (150
million kilometers).

For extremely distant objects,
billions of light-years, the light
takes billions of years to get
here, bringing a view that is
billions of years out of date.
“Lookback” Time


We see the Sun as it was 8.3 minutes ago because the light
took 8.3 minutes to traverse the distance from the Sun to the
Earth (150 million kilometers).
For extremely distant objects, billions of light years, the light
takes billions of years to get here, bringing a view that is
billions of years out of date.
−
We see the distant universe as it was in the distant past.
Human Biases

Time
−
A human lifetime is a blink of the eye relative to the timescale
of cosmic events.
−
Astronomers must reconstruct the workings of the Universe
from this “snapshot” view.


This task is similar to reconstructing the intricacies of
human relationships and politics from a snapshot of the
events happening on Earth at one instant.
Astronomers have two powerful tools to address this
shortcoming
−
Light travels “slowly”. A stale view of the universe permits
Astronomers to look back in time.
−
Computer simulation can permit scientist to watch events
play out over millions or billions of years.

Insert the laws of physics and turn the crank...
Lecture Notes: Lookback time
Simulation
Real
Some computer animations:
Collision between Galaxies
Formation of Structure in the Universe
Simulation
Real
Some computer animations:
Collision between Galaxies
Formation of Structure in the Universe
Tour the Millenium Simulation
Human Biases

Location
Human Biases

Location
Human Biases

Location

Location
−
−
Human Biases
High density of matter compared with intergalactic space.

1019 atoms per cubic centimeter in air.

1 atom per cubic “stadium” in intergalactic space.
High temperature compared with intergalactic space
• 300 Kelvins room temperature vs. 3 Kelvins elsewhere.
−
Dominance by elements other than hydrogen and helium.
Human Biases

Location
Human Biases

Wavelength
Human Biases

Wavelength
−
The universe looks quite different when we look outside
the tiny slice of the spectrum accessible to the human eye.
Human Biases

Wavelength
Human Biases

Comprehending large numbers
It's easy to visualize 5, 10, or even 100 things.
−


What's the difference between a million, a billion, or a
trillion (from a visualization standpoint)?
How do we make large numbers conceptually
meaningful?
Human Biases

Comprehending large numbers
It's easy to visualize 5, 10, or even 100 things.
−


What's the difference between a million, a billion, or a
trillion (from a visualization standpoint)???
How do we make large numbers conceptually
meaningful?
−
The mass of the Sun is
2,000,000,000,000,000,000,000,000,000,000 kg
−
Using scientific notation makes the above number
manageable, but not necessarily comprehensible.
= 2 x 1030 kg
Human Biases

Scale models can put these numbers in a relative context.
Human Biases

Scale models can put these numbers in a relative context.
NO!