Transcript stellarparameter1 - Physics and Astronomy

Open
cluster M45
the
Pleiades
(also
Subaru)
Globular
cluster
M13
What can we see? Stellar observables
• Stars have different colors
• Stars have different brightness
• Stars can be distributed randomly or in
groups.
What are some things we need to know?
Stellar parameters
What are some things we need to know?
Stellar parameters
•
•
•
•
•
•
•
Mass and radius
Surface temperature
Luminosity (energy emitted per second; unit watts)
Chemical composition (what stars are made of)
Age
Distance
Velocity
• We can not directly observe the stellar
parameters. We have to determine them
using our observables. We analyze the
observables and use our understanding of
physics (the study of matter and energy
and how they interact) to calculate stellar
parameters.
• Check out the stellar parameter toolbox on
the class website
How do we find out masses in astronomy?
• We use Newton’s laws of motion and
Newton’s law of gravity.
•
•
•
•
•
Stars orbiting the
Central black hole in
Our galaxy
Mass is over 1 million
Solar masses
The International Space Station (ISS)
Why are the astronauts in the ISS
weightless?
60
5
1. There is no gravity in
outer space
2. Earth is so far away that
gravity is very weak
3. There is no gravity in a
vacuum
4. They are falling
5. They are too small for
gravity to effect them
1
2
3
4
5
6
7
8
9
10
21
22
23
24
25
26
27
28
29
30
0
11
0%12
1
13
0%14
2
15 0%16
170% 18
3
4
190% 20
5
• Before answering the question:
Why are the astronauts in the ISS weightless?
Let’s look at a little physics.
What the demonstration shows
• Galileo – Objects fall at the same rate in a gravitational
field regardless of their mass.
What the demonstration shows
• Galileo – Objects fall at the same rate in a gravitational
field regardless of their mass.
• Newton’s First Law of Motion – An object at rest (or in
motion) stays at rest (or in motion) unless acted on by a
NET external force.
What the demonstration shows
• Galileo – Objects fall at the same rate in a gravitational
field regardless of their mass.
• Newton’s First Law of Motion – An object at rest (or in
motion) stays at rest (or in motion) unless acted on by a
NET external force.
• Newton’s Second Law of Motion – The force applied to
an object is equal to the mass of the object times the
object’s acceleration. F = ma
What the demonstration shows
• Galileo – Objects fall at the same rate in a gravitational
field regardless of their mass.
• Newton’s First Law of Motion – An object at rest (or in
motion) stays at rest (or in motion) unless acted on by a
NET external force.
• Newton’s Second Law of Motion – The force applied to
an object is equal to the mass of the object times the
object’s acceleration. F = ma
• Newton’s Third Law of Motion – For every force there
is an equal and opposite reactionary force. F1 = -F2
Let’s examine our answers
• There is no gravity in outer space
Let’s examine our answers
• There is no gravity in outer space
• Question: Why is the ISS going around
(orbiting) the Earth?
Let’s examine our answers
• There is no gravity in outer space
• Question: Why is the ISS going around
(orbiting) the Earth?
• Earth is so far away that gravity is very
weak
• There is no gravity in a vacuum
Let’s examine our answers
• There is no gravity in outer space
• Question: Why is the ISS going around
(orbiting) the Earth?
• Earth is so far away that gravity is very
weak
• There is no gravity in a vacuum
• Question: Why is the ISS orbiting the
Earth?
Now a little more thinking
• They (the astronauts) are too small for
gravity to effect them.
Now a little more thinking
• They (the astronauts) are too small for
gravity to effect them.
• Question: Gravity is holding the ISS in
orbit. What does Newton’s First Law tell us
should happen to the astronauts if gravity
isn’t effecting them? Would they be
weightless?
The correct answer is…
• The astronauts are falling. The ISS is
falling around the Earth and (from Galileo)
we know that the astronauts are falling at
the same rate as the ISS.
Why does the Earth orbit the Sun instead of
the Sun orbiting the Earth?
1. The Sun is more
massive so the Earth
has a larger
acceleration
2. The Sun is more
massive so it exerts a
greater force on the
Earth than the Earth
exerts on the Sun
Quiz #1
• Suppose you are on an imaginary planet called E2 that
is identical to Earth. It orbits a star that is identical to our
Sun and it is at an average distance from its sun that is
identical to Earth.
• Observables:
• E2’s rotation axis is perpendicular to its orbital plane (No
tilt).
• E2 has seasons similar to Earth but the entire planet has
summer at the same time and winter at the same time.
• PROBLEM: What must be causing the seasons?
Explain your answer using the two observables.
• How does E2’s orbit compare to Earth’s? Explain
your answer.
How light spreads out
Newton’s big realization