physics 301 astronomy review slides fall 2012. what is different about astronomy? incredible...
TRANSCRIPT
Physics 301 AstronomyReview Slides
Fall 2012
What is Different About Astronomy?
Incredible distances sizes periods of time
What is our place in the universe?
Earth orbits the Sun (revolves) once every year:
• at an average distance of 1 AU ≈ 150 million km.• with Earth’s axis tilted by 23.5º (pointing to Polaris)• and rotating in the same direction it orbits, counter-
clockwise as viewed from above the North Pole.
We can recognize solstices and equinoxes by Sun’s path across sky:
Summer solstice: Highest path, rise and set at most extreme north of due east.
Winter solstice: Lowest path, rise and set at most extreme south of due east.
Equinoxes: Sun rises precisely due east and sets precisely due west.
What determines the strength of gravity?
The Universal Law of Gravitation:1. Every mass attracts every other mass.2. Attraction is directly proportional to the product of
their masses.3. Attraction is inversely proportional to the square of
the distance between their centers.
Conservation of Energy
• Energy can be neither created nor destroyed.
• It can change form or be exchanged between objects.
• The total energy content of the Universe was determined in the Big Bang and remains the same today.
What does the solar system look like?
Properties of Waves
• Wavelength is the distance between two wave peaks• Frequency is the number of times per second that a
wave vibrates up and down
wave speed = wavelength x frequency
What is the electromagnetic spectrum?
Chemical Fingerprints
• Each type of atom has a unique spectral fingerprint
• Observing the fingerprints in a spectrum tells us which kinds of atoms are present
Lines in a star’s spectrum correspond to a spectral type that reveals its temperature
(Hottest) O B A F G K M (Coolest)
Fission
Big nucleus splits into smaller pieces
(Nuclear power plants)
Fusion
Small nuclei stick together to make a bigger one
(Sun, stars)
Sunspots
Are cooler than other parts of the Sun’s surface (4000 K)
Are regions with strong magnetic fields
The brightness of a star depends on both distance and luminosity
Inverse Square Law for Light
Luminosity passing through each
sphere is the same
Area of sphere = 4π (radius)2
Divide luminosity by area to get
apparent brightness
Brightness is inversely proportional to the square of the distance from thr observor
luminosity
Apparent brightness = --------------------------
4 π x distance 2
The relationship between apparent brightness and luminosity depends on distance:
Luminosity Brightness = 4π (distance)2
We can determine a star’s luminosity if we can measure its distance and apparent brightness:
Luminosity = 4π (distance)2 x (Brightness)
Temperature
Lum
inos
ity
H-R diagram depicts:
Luminosity
Temperature
Color
Spectral type
Radius
We see our galaxy edge-on.
Primary features: disk, bulge, halo, globular clusters
Background radiation from the Big Bang
has been freely streaming across the universe
since atoms formed
at temperature ~3000 K: visible/IR.
BIG BANG
VELOCITY
Velocity = (the speed) + (direction) of the motion of mass.
Expressed as a VECTOR QUANTITY
MAGNITUDE expressed as distance/time (10km/hr)
DIRECTION expressed in a direction (west)
30 km/hr
west
Gravity is
a force of attraction
that exists
between any two masses,
any two bodies,
any two particles.
What is Gravity?
What have we learned?• What is the Sun’s structure?
—From inside out, the layers are
• Core• Radiation zone• Convection zone• Photosphere• Chromosphere• Corona• Solar wind
Most massive stars:
100MSun
Least massive stars:
0.08MSun
(MSun is the mass of the Sun.)
What happens to a star is determined by the amount of mass a star has.
Low Mass (sun)
High mass (Betelgeuse)
Some Other Stars on and Off the Main Sequence
Hubble Classifies Galaxies
The Tuning Fork
Three Basic Types of Galaxies
Spiral
Variations exist within these three types.
Elliptical
Irregular