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Bit of Administration ….
• Lab 2
– New observation dates: March 22 - April 5
• No need to duplicate observations in hand!
– New due date: April 9 at my office
• Homework
• Reading
– BSNV pp. 153 - 168
• No office hours today
– Feel free to e-mail for later in week
Astronautics
• Interplanetary Travel
• The Central Concept …
The paths of interplanetary spacecraft are
simply orbits around the Sun …
And the spacecraft obey the same physical laws
as do planets.
Astronautics
• Transfer Orbit = Minimum Launch Energy
• Launch in the direction of motion of the launch platform.
• Arrive at destination at aphelion ( for outer target) or
perihelion (for inner target) of spacecraft orbit.
(Aphelion - point of orbit most distant from Sun
Perihelion - point of orbit closest to Sun)
Transfer Orbit for the Moon
Astronautics
• Transfer Orbit = Minimum Launch Energy
• Launch in the direction of motion of the launch platform.
• Arrive at destination at aphelion ( for outer target) or
perihelion (for inner target) of spacecraft orbit.
(Aphelion - point of orbit most distant from Sun
Perihelion - point of orbit closest to Sun)
•Advantages - Fuel efficiency
•Disadvantages - Long travel time
Astronautics
• Gravity Boosts
• Gain in energy due to gravitational “slingshot” around
a more massive body.
• Note: More massive body loses energy, but in case of
planet and spacecraft this is not a problem!
Astronautics
• Gravity Boosts
In frame of Jupiter
but Jupiter is moving …
In frame of Solar System
Astronautics
• Gravity Boosts - NASA missions
The Physics of Light
• Light as a Wave = Electromagnetic Radiation
• Wavelength (l) has units of length
• Frequency (n) - number of crests passing per second
- has units of cycles per second, or Hertz
• Speed - for light, c = 3x105 km/sec
3 x 105 km/sec
Wavelength
The Physics of Light
• Light as a Wave = Electromagnetic Radiation
• Wavelength (l) has units of length
• Frequency (n) - number of crests per second
• Speed - for light, c = 3x105 km/sec
Small wavelength
Large frequency
Large wavelength
Small frequency
The Physics of Light
• Light as a Wave = Electromagnetic Radiation
• Wavelength (l) has units of length
• Frequency (n) - number of crests passing per second
- has units of cycles per second, or Hertz
• Speed - for light, c = 3x105 km/sec
n
c
l
The Physics of Light
• Electromagnetic
Spectrum
1 km = 1000 m
1m
1 mm = 0.001 m = 10-3 m
1 mm = 10-6 m (“micron”)
1 nm = 10-9 m (nanometer)
The Physics of Light
• Electromagnetic Radiation
• Light acts as an electric force
- - - - - - - - - - - - - • Light acts as a magnetic force
N
N
N
S
S
S
S
S
N
N
S
S
S
S
N
N
N
N
S
S
S
N
N
N
The Physics of Light
• Electromagnetic Radiation
Antenna
The Physics of Light
• Doppler Shift
The Physics of Light
• Doppler Shift
• Source moving toward observer or
observer moving toward light source
Shorter Wavelength
Higher Frequency
Blueshift
• Light source moving away from observer or
observer moving away from light source
Longer Wavelength
Lower Frequency
Redshift
The Physics of Light
• Doppler Shift
• Source across observer’s line of sight
Same Wavelength as emitted
Same Frequency as emitted
No Shift
The Physics of Light
• Doppler Shift
l
lrest
v

c
v = velocity of light source or observer (+ => toward each other)
l = rest 
wavelength
l = change (shift) in wavelength
c = 3 x 105 km/sec