Astronomy Picture of the Day

1
Astronomy Picture of the Day
2
Review Kepler's Laws
1. Planets travel aound the sun in elliptical
orbits with the sun at one focus of the
ellipse. 2. A line connecting the Sun and a
planet sweeps out equal areas in equal times. 3.
The square of a planet's orbital period is
proportional to the cube of its semi-major axis.
(P2 a a3)?
3
Review Newton's Laws of Motion
1. Every object continues in a state of rest or
a state of uniform motion in a straight line
unless acted on by a force. (Inertia)? 2. F
ma 3. For every action there is an equal and
opposite reaction.
G m1 m2 R2
Newton's Law of Gravity F
4
Orbit of Earth around Sun
5
Gravity and Orbits

• Throwing an object fast enough will put the
  object into orbit! (Neglecting air resistance)?
• Moon is continually falling towards the Earth
  in its orbit (Gravity vs. inertia)?

6
Correction to Keplers Third Law

• Earth and sun actually rotate about their common
  center of mass
• Corresponds to a point inside sun
• Used to detect extrasolar planets

7
Question

• The force of gravity between two objects
  decreases rapidly with the
• A) product of the two masses.
• B) elipticity of the orbit.
• C) separation distance.
• D) orbital velocity.

8
Question

• The acceleration experienced by a falling
  object due to Earth's gravity _____ the mass of
  the object.
• A) increases with
• B) decreases with
• C) is independent of

9
That one was complicated, because we need to
remember
G m mE R2

• Fg

AND
Fg m
a
G m mE m R2
G mE R2
So, a

10
Chapter 2 EM Waves

• What is a wave?
• What are the main properties of waves?
• What two things do all waves transport?

11
Waves are a type of disturbance that can
propagate or travel. Waves carry information and
energy.
Properties of a wave
wavelength (?)?
crest
Equilibrium position
amplitude (A)?
trough
velocity (v)?
? is a distance, so its units are m, cm, or mm,
etc. Period (T) time between crest (or trough)
passages Frequency (f) rate of passage of
crests (or troughs), f???
v ????f?
1 T
(units Hertz or cycles/sec)?
12
Refraction
Waves bend when they pass through material
of different densities.
air
water
swimming pool
prism
glass
air
air
13
All radiation (including visible light) travels
as Electromagnetic waves.
That is, waves of electric and magnetic fields
travelling together.
What are some examples of objects with magnetic
fields
What are some examples of objects with electric
fields
14
(No Transcript)
15

• Electric Force - opposites attract, likes repel
• Oscillating charges radiate
• All objects have temperatures greater than
  absolute zero - random thermal motion
• All objects radiate!
• Why dont we see the radiation coming from many
  ordinary objects?
• Dog whistle analogy

16
Electromagnetic Radiation
(How we get information about the cosmos)?
What are some examples of electromagnetic
radiation and what are the different ways in
which we might experience them or make use of
them?
17
Electromagnetic Radiation
(How we get information about the cosmos)?
What are some examples of electromagnetic
radiation and what are the different ways in
which we might experience them or make use of
them?
Light (see)? Infrared (heat)? Ultraviolet (
sunburn)? Microwaves (cooking,
communication)? AM radio (communication)? FM
radio (communication)? TV signals (communicati
on)? Cell phone signals (communication)? X-rays
(medical applications)?